Foretravel Motorhome Forums => Foretravel Tech Talk => Topic started by: Paul Smith on August 24, 2012, 04:14:59 pm
Title: Retarder 101
Post by: Paul Smith on August 24, 2012, 04:14:59 pm
Hello!
I've driven 2 different Foretravels since 2005, in lots of mountains, and I've recently run into retarder issues I've not run into before.
For example, today I'm coasting down a 6% grade in 6th gear. As I reach 70mph I don't want to go any faster and I apply the retarder, and the transmission promptly drops to 5th gear. I'm thinking if I stay at 70mph in 5th that will heat up the transmission more than if I was able to stay in 6th. I'm also thinking if I can stay in 6th and retard to 70mph the retarder will heat up instead of the transmission.
Is the transmission working correctly? If so, what is its objective in dropping to 5th?
What am I missing here? There are other scenarios I'll go into later.
best, paul
Title: Re: Retarder 101
Post by: wolfe10 on August 24, 2012, 04:18:07 pm
For a given amount of braking HP, it will heat the transmission fluid less to have it in a lower gear/less retarder than higher gear/more retarder.
The lower gear/less retarder both generates less heat AND because the engine water pump is turning faster, gets rid of the heat faster.
Brett
Title: Re: Retarder 101
Post by: Paul Smith on August 24, 2012, 04:56:52 pm
Quote
For a given amount of braking HP, it will heat the fluid less to have it in a lower gear/less retarder than higher gear/more retarder.
The lower gear/less retarder both generates less heat AND because the engine water pump is turning faster, gets rid of the heat faster.
Thanks, Brett!
That's quite clear and concise.
I was not aware the engine was a major heat sink for the transmission/retarder. I thot they had their own heat exchangers.
It still bothers me that my retarder does not seem to be pulling its weight (because it rarely heats up much ;o)
best, paul
Title: Re: Retarder 101
Post by: amos.harrison on August 24, 2012, 08:11:12 pm
Paul,
Remember that retarder effectiveness is proportional to engine rpm. If you stay in 6th and apply retarder you will get less braking. I would have manually downshifted first to get rpm up to 2000, then start applying the retarder.
Title: Re: Retarder 101
Post by: gam on August 24, 2012, 08:41:04 pm
Brett isn't it a lower gear for engine breaking[back pressure on the exhaust becouse of the turbo ] and the retarder is a separate system in the transmission with it's own heat exchanger ? Gam
Title: Re: Retarder 101
Post by: wolfe10 on August 24, 2012, 08:50:12 pm
Well, I am one of the "Bretts".
NO, a diesel has close to zero braking, as there is no throttle plate. The only exception is some of the smaller, newer diesels with VGT's. None were ever used in Foretravels.
Said another way, a non-VGT turbo will not generate any back pressure, so virtually no engine braking.
That is why the choices for engine braking on a diesel are:
Exhaust brake (basically a "potato stuck in the tail pipe").
Engine brake/compression brake (opens the exhaust valve at TDC to release the stored energy from compressing 17:1or so).
Transmission retarder.
Title: Re: Retarder 101
Post by: J. D. Stevens on August 24, 2012, 09:43:07 pm
Remember that retarder effectiveness is proportional to engine rpm. If you stay in 6th and apply retarder you will get less braking. I would have manually downshifted first to get rpm up to 2000, then start applying the retarder.
Brett H,
My recollection of the diagrams of the retarder show that it is on the output shaft of the transmission, i.e., on the drive shaft. It seems that the effectiveness of the retarder would not be dependent on engine rpm, except for the more effective cooling of the fluid at higher engine rpm. The retarder effectiveness would be proportional to drive shaft rpm. Do I have this wrong?
... NO, a diesel has close to zero braking, as there is no throttle plate. ...
Brett W,
My experience has been that a diesel engine provides significant braking even without a retarder. One can control speed on a downhill run by selecting an appropriate combination of gear and speed, even without an exhaust brake or retarder. I learned from my father, an OTR trucker, that you should descend a steep hill in the gear you would use to climb it. With the proper gear selection, you would probably not need to use brakes. To the best of my knowledge, his early trucks has no exhaust brakes or compression brakes. What am I missing?
Title: Re: Retarder 101
Post by: George Hatfield on August 24, 2012, 09:58:46 pm
Keep in mind that the transmission temperature is not showing the temp of the fluid in the retarder, which is usually much higher when the retarder is engaged. I reported on this previously, but while coming down the long hill to the west of Durango, CO, at a speed of maybe 55-60 mph, my retarder hit 300 degrees. Don't recall the trans temp, but it was much lower. The second it hit 300 degrees, the trans automatically shifted down, I think from 6th to 4th. This caused an immediate decrease in the retarder temp due, I guess, to better cooling of the the retarder fluid. I now monitor the retarder temp on any long hill and keep it below about 280 by slowing down. Normally run about 40-45 mph on long steep hills. I really think going faster puts too much energy into the retarder and this causes it to to get excessively hot.
Title: Re: Retarder 101
Post by: J. D. Stevens on August 24, 2012, 10:07:56 pm
Per Allison document about retarder operation:
"They generate the greatest braking at high drive shaft RPM and work independent of engine speed or gear ratio."
Title: Re: Retarder 101
Post by: Paul Smith on August 24, 2012, 10:09:26 pm
Quote
Keep in mind that the transmission temperature is not showing the temp of the fluid in the retarder, which is usually much higher when the retarder is engaged. I reported on this previously, but while coming down the long hill to the west of Durango, CO, at a speed of maybe 55-60 mph, my retarder hit 300 degrees. Don't recall the trans temp, but it was much lower.
That's not been my experience. My VMS 240 CL shows me retarder and transmission temperatures. I've never seen a retarder temperature higher than my transmission temperature.
Normal base transmission temperature is 190F. I've never seen retarder temperature higher than even that.
best, paul
Title: Re: Retarder 101
Post by: George Hatfield on August 24, 2012, 10:21:02 pm
Paul... I suspect your VMS 240 CL is not reading the PID for the retarder. Mine is always higher when the retarder is on... but is the same temp as the trans when the retarder is off. The second the retarder engages, the temp jumps. Is there any way to check the PID your VMS retarder temp is reading?
We drove today through Illinois and the trans and retarder temp were about 180 most of the time since I rarely had to use the retarder. Love this flat land driving. Got 9.4 mpg with the Mode switch on. Normal average is about 8.5 mpg.
Title: Re: Retarder 101
Post by: Paul Smith on August 24, 2012, 10:21:18 pm
Quote
That's not been my experience. My VMS 240 CL shows me retarder and transmission temperatures. I've never seen a retarder temperature higher than my transmission temperature.
Even heading west out of Rocky Mountain National Park recently where my transmission temperature got very high.
best, paul
Title: Re: Retarder 101
Post by: J. D. Stevens on August 24, 2012, 10:22:18 pm
My experience has been that a diesel engine provides significant braking even without a retarder. One can control speed on a downhill run by selecting an appropriate combination of gear and speed, even without an exhaust brake or retarder. I learned from my father, an OTR trucker, that you should descend a steep hill in the gear you would use to climb it. With the proper gear selection, you would probably not need to use brakes. To the best of my knowledge, his early trucks has no exhaust brakes or compression brakes. What am I missing?
Would the braking effect I have seen from diesel engines that are not using retarder, exhaust brake, or compression brake, be the drag of air compressor, water pump, hydraulic pumps, air drag, miscellaneous friction, etc.?
Brett W's excellent response sent me searching. There is a good description of engine braking at Engine braking - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Engine_braking).
Title: Re: Retarder 101
Post by: Paul Smith on August 24, 2012, 10:27:17 pm
Quote
"They generate the greatest braking at high drive shaft RPM and work independent of engine speed or gear ratio."
So would this be basically "Greatest braking at high road speed?"
best, paul
Title: Re: Retarder 101
Post by: J. D. Stevens on August 24, 2012, 10:41:36 pm
So would this be basically "Greatest braking at high road speed?"
best, paul
That is my understanding. That statement regards the effectiveness of the retarder only, not any other components of the coach's "braking systems."
Title: Re: Retarder 101
Post by: Barry & Cindy on August 25, 2012, 01:00:44 am
RE " the retarder is a separate system in the transmission with it's own heat exchanger ?"
Retarder is not separate from Allison transmission. Retarder uses transmission fluid to 'Retard'. This transmission fluid is the same shared fluid source the transmission uses to function.
Heat is removed from transmission fluid with the same coolant that cools engine using a big round external heat exchanger.
Two large forward facing transmission fluid hoses connect to the heat exchanger.
Title: Re: Retarder 101
Post by: Michael & Jackie on August 25, 2012, 01:34:18 am
Seems like more than Retarder 101 to me! To make simple, when probably I cannot not.....as I understand you Barry, if I monitor the transmission temp I am monitoring the retarder temp, right? I recall being told by the dealer to keep trans temp below about 240, maybe a bit less. And that if I do that, then the retarder is protected, right?
Further, excepting that it would be safe anyway so long as the temp stays in these ranges, it is nonetheless best to control my downhill speed by gear selection than use of the retarder.
Do I have this summarized correctly? Seems a valuable dialogue, I want to be sure I am getting this right so I can have a simple rule of operation in these mountains. Thanks, All......Mike
Title: Re: Retarder 101
Post by: Paul Smith on August 25, 2012, 08:32:32 am
Quote
Keep in mind that the transmission temperature is not showing the temp of the fluid in the retarder, which is usually much higher when the retarder is engaged. I reported on this previously, but while coming down the long hill to the west of Durango, CO, at a speed of maybe 55-60 mph, my retarder hit 300 degrees. Don't recall the trans temp, but it was much lower. The second it hit 300 degrees, the trans automatically shifted down, I think from 6th to 4th. This caused an immediate decrease in the retarder temp due, I guess, to better cooling of the the retarder fluid. I now monitor the retarder temp on any long hill and keep it below about 280 by slowing down. Normally run about 40-45 mph on long steep hills. I really think going faster puts too much energy into the retarder and this causes it to to get excessively hot.
I'm assuming concern about fluid temp is related to insuring it has a longer useful life.
I also assume the retarder gets its fluid from its transmission.
Now I don't think folks would want transmission fluid to go to 300 or even 280 degrees. So does allowing retarder fluid go to 280 degrees effectively reduce the useful life of (at least some of the) transmission fluid?
In the above the trans shifted down from 6th to 4th and decreased the retarder temp. The downshift probably slowed the FT making the retarder less effective (according to the earlier Allison quote), in other words "worked the retarder fluid less" which, at least in part, helped cool fluid in the retarder..
I've emailed SilverLeaf asking where their VMS gets its retarder temp info.
best, paul
Title: Re: Retarder 101
Post by: jor on August 25, 2012, 09:51:33 am
Quote
It still bothers me that my retarder does not seem to be pulling its weight (because it rarely heats up much ;o)
My trans temp according to the VMS is usually higher than the engine temp. On long 6 and 7 percent grades it will climb to 214 or so. According to Silverleaf, the VMS is reporting the trans sump temp just like the dash gauge. The Allison documentation states that the maximum safe temp for my trans (4060) is 230. I'm going a lot slower than Paul so maybe that's the difference.
I need to make the VMS change that shows retarder temp as soon as I figure out how! jor
Title: Re: Retarder 101
Post by: J. D. Stevens on August 25, 2012, 09:55:40 am
Seems like more than Retarder 101 to me! To make simple, when probably I cannot not.....as I understand you Barry, if I monitor the transmission temp I am monitoring the retarder temp, right? I recall being told by the dealer to keep trans temp below about 240, maybe a bit less. And that if I do that, then the retarder is protected, right?
Further, excepting that it would be safe anyway so long as the temp stays in these ranges, it is nonetheless best to control my downhill speed by gear selection than use of the retarder.
Do I have this summarized correctly? Seems a valuable dialogue, I want to be sure I am getting this right so I can have a simple rule of operation in these mountains. Thanks, All......Mike
Mike,
Yes, indeed the fluid is shared between the retarder and transmission. My practice is to leave the retarder switch on all the time, except if the road might be slick. That couples retarder operation with operation of the service brake. I leave the joy stick in the "Off" position except to control speed on hills.
Like brakes, the retarder was designed to control the speed of the vehicle by converting kinetic energy (movement) to heat. Use the retarder to slow or control the speed of the vehicle. It is particularly useful on long, steep downhill grades. Operate at speeds that don't cause systems to overheat.
The engine is designed to control the speed of the vehicle by converting heat to kinetic energy. Operate it at speeds that don't cause systems to overheat.
Use and enjoy all the nifty systems those clever engineers have put together for us to use. They included a few temperature gauges to help us use them without abusing them by allowing them to get too hot. Don't worry! Be happy! :))
Title: Re: Retarder 101
Post by: Paul Smith on August 25, 2012, 10:06:21 am
Quote
My trans temp according to the VMS is usually higher than the engine temp. On long 6 and 7 percent grades it will climb to 214 or so. According to Silverleaf, the VMS is reporting the trans sump temp just like the dash gauge. The Allison documentation states that the maximum safe temp for my trans (4060) is 230. I'm going a lot slower than Paul so maybe that's the difference.
My transmission temperature is also normally higher than the engine temperature on going downhill.
And my VMS also agrees with my dash transmission sump temperature.
best, paul
Title: Re: Retarder 101
Post by: Barry & Cindy on August 25, 2012, 04:49:20 pm
1) Several years ago, Silverleaf told me they cannot display retarder temp because only Allison proprietary diagnostics have access to retarder temp sensor. Things may have changed.
2) For our transmission temp dash gauge, Foretravel installed a single-wire sensor located in the elbow of the hose coming from transmission cooler return. We later moved the sensor to the transmission hose going to the cooler, so we now display the actual fluid temp as it heads to the cooler, which increased the gauge temp reading.
3) Transmission fluid temps are often read from the sump where cooled fluid is mixed with a pool of fluid in the bottom of the transmission, which is where the internal transmission parts pump from.
4) Temperature readings from hot fluid going to cooler will read higher than sump. And probably fluid returning from cooler will read lower than sump.
5) Petroleum base transmission fluid probably starts to breakdown about 250 degrees, but synthetic fluid has a much higher temperature tolerance and is recommended for our retarder transmissions. Heat abuse is cumulative.
6) Allison transmission computer will automatically lower retard levels when it determines internal fluid temps are too high to keep transmission safe.
7) Transmission uses a modulated valve that allows more fluid into retard chamber at higher retard settings.
8) Initiating any retard setting, causes an external storage accumulator to quickly pump a quantity of fluid into retard chamber, ahead of the modulator doing its thing. A 12-volt valve opens to let motorhome air pressure force the fluid out of the accumulator.
9) High transmission temps will raise engine temp gauge as heat is absorbed by engine coolant.
Our transmission will usually down-shift when we activate retarder and we do not worry about relatively short burst of temps over 325. Anything to save our air disk brakes for emergency stops. We seldom touch service brake pedal going down mountains.
Since temp gauge readings may not reflect how hard the retarder is working, I would pay more attention to how well retarder is slowing down a motorhome to determine if retarder is working ok.
A few years ago, we found our retarder did not seem to slow us down, and after two days of diagnosing with a computer while driving, and replacing a few parts, a high-tech Allison repair facility could not find our problem. On day three, they found a small pin terminal connector at the computer was just touching, but not fully seated into the plug. This allowed diagnostics to think there was a good connection, but did not allow enough current to flow to fully open the modulating valve. We were happy to have our problem solved and Allison only charged us for 5 hours labor. All retarder electronic and mechanical control parts they examined were located on the outside and transmission pan did not have to be dropped.
Title: Re: Retarder 101
Post by: RRadio on August 25, 2012, 05:15:11 pm
Has anyone installed a Jake Brake in conjunction with a retarder?... How did that work out?... just curious
Scott
Title: Re: Retarder 101
Post by: J. D. Stevens on August 25, 2012, 05:49:16 pm
8- Initiating any retard setting, causes an external storage accumulator to quickly pump a quantity of fluid into retard chamber, ahead of the modulator doing its thing. A 12-volt valve opens to let motorhome air pressure force the fluid out of the accumulator.
A picture of the hydraulic accumulator is here: Big Air Leak Hydraulic Accumulator (http://www.foreforums.com/index.php?topic=15185.msg91353#msg91353) The picture was taken through the small access door on passenger side aft of the wheels. If you follow the big hose from the rear of the accumulator, it goes directly to the retarder assembly at the fore end of the transmission. The connection of the hose to the retarder is visible in the upper left corner of the picture.
Title: Re: Retarder 101
Post by: amos.harrison on August 25, 2012, 06:08:39 pm
I descend mountains using the trans gauge. I select the initial trans gear based on my experience with the % grade placard. If my trans gauge moves above 200 degrees using the retarder, I go down a gear, applying service brakes firmly if necessary to keep engine rpm below redline. I continue this process to the bottom. No fuss, no fear! Never exceeding posted truck speed limits.
Title: Re: Retarder 101
Post by: Paul Smith on August 25, 2012, 06:11:49 pm
"Our transmission will usually down-shift when we activate retarder and we do not worry about relatively short burst of temps over 325."
325 degrees for the retarder or transmission?
best, paul
Title: Re: Retarder 101
Post by: Paul Smith on August 25, 2012, 11:03:12 pm
Quote
Paul... I suspect your VMS 240 CL is not reading the PID for the retarder. Mine is always higher when the retarder is on... but is the same temp as the trans when the retarder is off. The second the retarder engages, the temp jumps. Is there any way to check the PID your VMS retarder temp is reading?
I watched the retarder temp today in a short ride. As soon as I applied the retarder its temp jumped. Not a lot. But a real jump.
So it appears clear the VMS retarder temp readout IS related to the retarder. Where, is the question.
best, paul
Title: Re: Retarder 101
Post by: Barry & Cindy on August 26, 2012, 12:24:11 am
RE: "Our transmission will usually down-shift when we activate retarder and we do not worry about relatively short burst of temps over 325. 325 degrees for the retarder or transmission? Paul"
Paul, We only have one tranny temp sensor and it measures tranny fluid from the transmission on its way to the heat exchanger to be cooled. So the answer to your question is retarder.
Our Cummins C-8.3 325 engine is not computerized so there are no engine functions for SilverLeaf to report on. We already know Allison gear-attained & output fluid temp, so I think that SilverLeaf would only be able to add sump fluid temperature for us. We never added SilverLeaf and don't know transmission sump temps.
Does anyone know if SilverLeaf can measure more than sump temps for us?
Title: Re: Retarder 101
Post by: Dave Katsuki on August 26, 2012, 09:59:19 pm
I have noticed that going down hill, when the engine is not under load and running at 180 deg, the trans takes a long time to cool down after retarder operation, and am wondering if the fact that the engine thermostat is closed (little engine heat generated) causes low coolant flow through the radiator, and hence slower trans cooling. Does the trans have a bypass somehow, and if so, how does coolant get pumped through the radiator if the engine thermostat is closed?
Do more recent coaches or different engines have a different cooling flow? (ours is a 99 ISC)?
I haven't traced the coolant pipes carefully, but it looks like the only flow through the trans heat exchanger is pumped by the engine water pump.
Title: Re: Retarder 101
Post by: Paul Smith on August 26, 2012, 11:08:02 pm
For example, today I'm coasting down a 6% grade in 6th gear. As I reach 70mph I don't want to go any faster and I apply the retarder, and the transmission promptly drops to 5th gear. I'm thinking if I stay at 70mph in 5th that will heat up the transmission more than if I was able to stay in 6th. I'm also thinking if I can stay in 6th and retard to 70mph the retarder will heat up instead of the transmission.
Is the transmission working correctly? If so, what is its objective in dropping to 5th?
As I climbed 6 or so passes today crossing Nevada East to West on US-50 I realized Brett's comment right after my original post answered my question but not explicitly.
It appears to me the transmission is programmed to downshift when the retarder is activated going downhill so as to anticipate heating from the retarder/transmission and downshifting spins the engine faster than it otherwise would thereby increasing its cooling.
Based on other comments here it appears a better approach is to downshift manually and let the engine provide what downhill resistance it can and then use the retarder (and subsequent manual downshifts to go down in the same gear I went up) to keep the engine from red lining. At a minimum that would delay heating the retarder a bit while at the same time the engine starts delivering improved cooling.
Tomorrow we'll cross Carson Pass in CA out of Minden, NV on CA-88. It's a pretty drive. And a much more relaxed way to cross the Sierras than CA-120. We'll spend Labor Day in Sonora, CA A group of families have tent camped every Memorial Day and Labor Day since '68 and in recent years we've done so in a campground outside Tuolumne, CA (unfortunately we cannot get our Foretravel into that campground but our Element does go there nicely).
We're currently in Fallon, NV at another $15/night full-hookup Casino. We'll camp in the Fairgrounds in Sonora.
best, paul
Title: Re: Retarder 101
Post by: Jerry Whiteaker on August 27, 2012, 12:15:10 am
Does anyone read the operator's manual for the Allison World Transmission? This should be a link to one dated 2002 if you don't have one. http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM2157EN.pdf (http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM2157EN.pdf) Much of the information is repeated several times according to different types of shift pads and levers and it is boring after a few paragraphs. Anyone new to this transmission and maybe some of the older folks too may not understand how it differs from a car transmission. Basically it turns the ordinary driver into a truck style driver without him knowing it. If you step on the brake it will downshift same as the truck driver would downshift to use the engine to slow his truck. Unlike the truck driver possibly could, it will not do this if doing so will overspeed the engine. Slow down enough and it will keep downshifting. It will not upshift until you step on the throttle or increased ground speed (as in going down a grade) threatens to overspeed the engine. If an upshift to prevent an engine overspeed occurs there will be a sudden loss of engine braking, and probably leave the driver wondering what happened. All this will happen whether or not the retarder is on or off. If you have preselected a lower gear range, and the engine rpm rises to an overspeed condition the transmission will upshift above the highest selected gear to protect the engine. I'm not sure the manual fully explains it that way.
When the retarder is on the brake light is on. When the brake light is on the transmission gets a signal from the brake light and downshifts if it is allowed too. I think that is why the retarder causes a downshift.
I personally don't like for the transmission temperature to go above 250 as the temperature of the fluid coming out of the retarder is a lot hotter than that. Like others have said retarder braking effect is directly related to road speed. Full retard at 10 mph has only a small effect, while 1/2 retard at 60 mph has a large effect. What works for me in mountains is to use about 3 or 4 notches of retard on the joystick and downshift enough to hold the desired speed which is usually 40 - 60 mph. I know from experience that this will usually keep the transmission temperature from going too high. Retard joystick position can be increased with slower mph as less heat will be generated. If coming down the grade at 70 mph 3 notches of retard may cause an overheat. I don't mind an occasional tap on the brakes to help control the speed. Again this requires some common sense, a tap at 70 mph heats up the brakes more than one at 40 mph. The transmission will protect itself if the fluid temperature becomes too high by reducing or turning off the retarder, but by that time the fluid is probably smoking hot.
Title: Re: Retarder 101
Post by: Barry & Cindy on August 27, 2012, 01:29:15 am
I always figured when our engine coolant gauge is reading 180 which is most of the time, that the thermostat is wide open and the coolant system is keeping us at 180.
I figured that below 180 thermostat is mostly closed and at 180 it opens.
When we heat up the transmission on a downhill retard operation, at the bottom, our transmission fluid usually cools VERY fast as if the tranny temp gauge has a spring to bring it back. Maybe, since we are measuring the absolute hottest fluid leaving the tranny, that when a bottom of downhill run, the transmission fluid leaving the tranny without the retard is much cooler, hence we see a quick drop.
I would think that after the tranny fluid heat is transferred to the engine coolant, the heated coolant would find its way back to the engine and for sure open the thermostat.
You raise a good question Dave.
Title: Re: Retarder 101
Post by: Caflashbob on August 27, 2012, 01:38:58 am
Does anyone read the operator's manual for the Allison World Transmission? This should be a link to one dated 2002 if you don't have one. http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM2157EN.pdf (http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM2157EN.pdf) Much of the information is repeated several times according to different types of shift pads and levers and it is boring after a few paragraphs. Anyone new to this transmission and maybe some of the older folks too may not understand how it differs from a car transmission. Basically it turns the ordinary driver into a truck style driver without him knowing it. If you step on the brake it will downshift same as the truck driver would downshift to use the engine to slow his truck. Unlike the truck driver possibly could, it will not do this if doing so will overspeed the engine. Slow down enough and it will keep downshifting. It will not upshift until you step on the throttle or increased ground speed (as in going down a grade) threatens to overspeed the engine. If an upshift to prevent an engine overspeed occurs there will be a sudden loss of engine braking, and probably leave the driver wondering what happened. All this will happen whether or not the retarder is on or off. If you have preselected a lower gear range, and the engine rpm rises to an overspeed condition the transmission will upshift above the highest selected gear to protect the engine. I'm not sure the manual fully explains it that way.
When the retarder is on the brake light is on. When the brake light is on the transmission gets a signal from the brake light and downshifts if it is allowed too. I think that is why the retarder causes a downshift.
I personally don't like for the transmission temperature to go above 250 as the temperature of the fluid coming out of the retarder is a lot hotter than that. Like others have said retarder braking effect is directly related to road speed. Full retard at 10 mph has only a small effect, while 1/2 retard at 60 mph has a large effect. What works for me in mountains is to use about 3 or 4 notches of retard on the joystick and downshift enough to hold the desired speed which is usually 40 - 60 mph. I know from experience that this will usually keep the transmission temperature from going too high. Retard joystick position can be increased with slower mph as less heat will be generated. If coming down the grade at 70 mph 3 notches of retard may cause an overheat. I don't mind an occasional tap on the brakes to help control the speed. Again this requires some common sense, a tap at 70 mph heats up the brakes more than one at 40 mph. The transmission will protect itself if the fluid temperature becomes too high by reducing or turning off the retarder, but by that time the fluid is probably smoking hot.
Interesting info. My 97 has the brake light relay disconnected. No downshift that i noticed and the cruise works with the retarder if in the on position and the lever off the zero position. The extra cooling and engine braking would seem to be the reasons for any downshift. Not needed in my limited usage. really enjoyable to drive in the hills
Title: Re: Retarder 101
Post by: jor on August 27, 2012, 09:24:29 am
Quote
I personally don't like for the transmission temperature to go above 250
Jerry, is that 250 on the dash gauge/VMS? My documentation states a max trans temp of 230. Thanks. jor
Title: Re: Retarder 101
Post by: Jerry Whiteaker on August 27, 2012, 09:40:24 am
Jerry, is that 250 on the dash gauge/VMS? My documentation states a max trans temp of 230. Thanks. jor
Yes, it is on the dash gauge. I don't have VMS due to mechanical engine. I don't ever remember seeing a number anywhere in my manuals. I have switched to synthetic fluid so it should be able to take a higher temp. Only rarely does it go above 230.
Title: Re: Retarder 101
Post by: J. D. Stevens on August 27, 2012, 09:57:05 am
The brake lights on our coach are not activated by the retarder when it is engaged via the joystick. MOT installed the joystick in 2010 using kits from Allison. Behavior is a bit different when the brake lights are not activated by the joystick.
Title: Re: Retarder 101
Post by: Keith and Joyce on August 27, 2012, 05:07:00 pm
J.D. Yes, there are a lot of different frictional losses in the rotating/reciprocating components of the drive line coupled with parasitic loads from the ancillary items (compressor, alternator etc.) as well as rolling resistance and wind resistance. If not one could coast forever, so says Sir Isaac Newton. If you want to test this try driving on flat tires and letting off the accelerator.
Keith
Title: Re: Retarder 101
Post by: Kent Speers on August 27, 2012, 08:01:39 pm
Two points, the old adage about going down the hill in the same gear you came up the hill is NO LONGER VALID due to the higher horsepower of the current engines you can climb a hill in a gear that is much too high for use in the decent.
The second is that Cummins told me that their 180 thermostat begins to open at 180 and is fully open at 195.
After following this thread, I'm glad I have a Jake Brake.
Title: Re: Retarder 101
Post by: J. D. Stevens on August 27, 2012, 09:57:51 pm
After following this thread, I'm glad I have a Jake Brake.
I had another brand of DP with an exhaust brake. It had a Cummins 5.9 and Allison 3000. It had drum brakes. I have driven the SOB and the FT across mountain ranges. I really like my FT with disk brakes and the retarder. The retarder coupled to the service brakes provide great stopping control for normal operation. The joystick control provides a really sweet control system in the mountains.
I observe temperature gauges and avoid temperatures that are beyond normal ranges for our equipment. I expect that the engine and drive train will outlast me if I properly lubricate it and don't overheat it.
Title: Re: Retarder 101
Post by: jor on August 27, 2012, 10:26:23 pm
Quote
I don't ever remember seeing a number anywhere in my manuals. I have switched to synthetic fluid so it should be able to take a higher temp.
I'm glad this came up. Jerry, the manual you linked to is the same one I have in hard copy. The actual not to exceed sump temp is 250, not 230. I've also got 100% (close, anyhow) Transynd. I was under the impression that synthetic doesn't actually change the overheat temp. I'm going to look into it over at rv.net. I think there was a discussion on it a while back. jor
Title: Re: Retarder 101
Post by: John S on August 27, 2012, 11:20:07 pm
Allison was at one of the grandventions and they said not to exceed 250 at te sump. Also, that Transynd takes heat better but the 250 is still the limit.
Title: Re: Retarder 101
Post by: Dan Stansel on August 27, 2012, 11:36:29 pm
Going over the Big Horn Mountains this week my temp went from 180 to 200 at the highest point. As soon as a level area came up it went back to 180. The trans never seemed to move going up or coming down and it is about 20 miles with a 5 to 6 % grade up and down. Thought this was acceptable for my 400 cummings. 3 or 4 gear going up and 4 coming down with retarder and minimun braking. Tow chev HHR has m&g brakes. tks DAN
Title: Re: Retarder 101
Post by: Dean & Dee on August 28, 2012, 10:16:32 am
I had an emegency stop siuation last Friday when a young lady in front of me decided to stop to take a left just as I had glanced in my right side mirror. I was probably going 30 mph and when I saw her it looked like it was too late. I had my left hand on the retarder joystick and instinctivly yanked it back as I stood on the service brakes.
I may have been 8" from her bumper when I finally stopped and I am sure the folks sitting outside the restaurant she was turning into could hear my expletives coming from the open drivers window. There was enough force that the recliner ended up against the back of the passengers seat.
I am not sure how much the retarder helps at lower speeds but I am pretty sure that it helped to keep me from shortening up her car a bunch. I have previosly noticed that the first couple of clicks back typically give much more retard than the last couple and wondered if the low end of the retarder was working correctly.
Dean
Title: Re: Retarder 101
Post by: jor on August 28, 2012, 10:45:26 am
Quote
I have previosly noticed that the first couple of clicks back typically give much more retard than the last couple and wondered if the low end of the retarder was working correctly.
If your retarder works like mine you shouldn't have to use the joystick in a situation like that. If the retarder is on, when you apply the service brake lightly the retarder engages 1/3, more pressure on the service brake pedal results in 2/3 and hard pressure yields 100% retarder. jor
Title: Re: Retarder 101
Post by: jor on August 28, 2012, 10:54:19 am
Quote
Allison was at one of the grandventions and they said not to exceed 250 at te sump. Also, that Transynd takes heat better but the 250 is still the limit.
Thanks, John. I've also sent a PM to Tom, the retired Allison engineer, for his opinion. There is a voluminous thread on Allison/Transynd over at rv.net but the maximum temp is only touched upon. It's interesting that among this group with similar rigs that there is so much variation in temperatures in similar driving conditions. I guess it's academic as it doesn't sound like anyone is cooking their transmissions. In my case, during a long 7% descent, using 4th and 3rd, my sump temp gets to maybe 214. Then, when back on level, it slowly recovers. Thanks. jor
Title: Re: Retarder 101
Post by: Carol Savournin on August 28, 2012, 10:57:15 am
{I may have been 8" from her bumper when I finally stopped and I am sure the folks sitting outside the restaurant she was turning into could hear my expletives coming from the open drivers window. There was enough force that the recliner ended up against the back of the passengers seat. }
Oh, My Stars. That is when I LOVE those air horns. She would be heading home to change her undergarments.
Title: Re: Retarder 101
Post by: jor on August 28, 2012, 11:08:52 am
Got a reply from Tom, the Allison guy. Just as John said, the max is 250. Transynd doesn't change that number but the transmission can take the high heat longer. Nice to know. Hope I never see 250 though. jor
Title: Re: Retarder 101
Post by: txforetravel on August 28, 2012, 11:10:46 am
Oh yes, those Air Horns are a wonderful thing! I do get a "stink eye" from my passenger when I give a little honk when passing a field of goats! I love to watch them scramble!
Title: Re: Retarder 101
Post by: Tom Lang on August 28, 2012, 11:42:45 am
I have a couple of comments.
One time, while going north on the Grapevine out of Los Angeles, a long downgrade with trucks limited to 35mph, I was cruising down the #2 lane with the retarder keeping my speed at 60-65. All of a sudden some idiot dives right in front of my front bumper and slams on the brakes. I have no choice but to do the same. The retarder was about two notches engaged, but I always pull it all the way back when hitting the brakes (maybe improving the response time). When all was said and done, I was doing 45 or so and the transmission had downshifted all on it's own. The idiot then took off, and I had to push the retarder all the way forward and tap the accelerator to allow gravity bring my speed back up. The automatic downshift did appear to multiply the retarder braking effect.
Another time, I had the misfortune of having a traffic light turn red at exactly the wrong moment while doing 60 on a should-have-been freeway-like highway with this lone traffic light out of nowhere. I simultaneously hit the retarder and brakes and came to a very fast stop. Good thing my wife was belted in, but everything I "thought" was put away ended up-front, and I managed to put a crack in the shower wall. I suspect this coach could out-stop some cars.
Title: Re: Retarder 101
Post by: Dean & Dee on August 28, 2012, 11:59:17 am
If your retarder works like mine you shouldn't have to use the joystick in a situation like that. If the retarder is on, when you apply the service brake lightly the retarder engages 1/3, more pressure on the service brake pedal results in 2/3 and hard pressure yields 100% retarder. jor
Jor, I guess I knew that but when traveling in traffic or city i always have left hand on the joystick. Like I said, it was an automatic reflex to yank it back.
Oh, My Stars. That is when I LOVE those air horns. She would be heading home to change her undergarments.
Carol I agree (and I use them often) but in an area with a ton of tourists wandering about I didn't want to take a chance on causing the elderly to fall over clutching their chest's or tramatize small children as they scream and drop their ice cream cone's causing angry parents to throw dropped ice cream at my coach. :P Besides, I was busy checking MY undergarments :o and like I said, I am sure that EVERYONE could hear my verbal displeasure with her driving skills. ;D Dean
Title: Re: Retarder 101
Post by: Dean & Dee on August 28, 2012, 12:18:55 pm
One time, while going north on the Grapevine out of Los Angeles, a long downgrade with trucks limited to 35mph, I was cruising down the #2 lane with the retarder keeping my speed at 60-65. All of a sudden some idiot dives right in front of my front bumper and slams on the brakes. I have no choice but to do the same. The retarder was about two notches engaged, but I always pull it all the way back when hitting the brakes (maybe improving the response time). When all was said and done, I was doing 45 or so and the transmission had downshifted all on it's own. The idiot then took off, and I had to push the retarder all the way forward and tap the accelerator to allow gravity bring my speed back up. The automatic downshift did appear to multiply the retarder braking effect.
Another time, I had the misfortune of having a traffic light turn red at exactly the wrong moment while doing 60 on a should-have-been freeway-like highway with this lone traffic light out of nowhere. I simultaneously hit the retarder and brakes and came to a very fast stop. Good thing my wife was belted in, but everything I "thought" was put away ended up-front, and I managed to put a crack in the shower wall. I suspect this coach could out-stop some cars.
Did a lot of demo drives with customers when the retarder trans came out. Told the customer to get on the brakes. They normally tried them out some. Then I yelled at them to "GET ON THE BRAKES". They would almost stand up in the front seats. The look on their faces was priceless. Yes I warned them about looking in the camera as unaware cars behind might be in trouble.
My lever is set so forward is on. Are yours opposite?
Title: Re: Retarder 101
Post by: Tom Lang on August 28, 2012, 01:22:09 pm
My lever is set so forward is on. Are yours opposite?
Fully forward only retards when the brakes are applied, pulling back 1-6 notches applies varying degrees of retarding whenever my foot off the accelerator pedal.
Title: Re: Retarder 101
Post by: Dean & Dee on August 28, 2012, 02:48:02 pm
Fully forward only retards when the brakes are applied, pulling back 1-6 notches applies varying degrees of retarding whenever my foot off the accelerator pedal.
Yep, mine works this way as well.
Title: Re: Retarder 101
Post by: Caflashbob on August 28, 2012, 03:41:01 pm
Wonder why mine is setup reversed? Only 97's or mine or customer preference?
The joystick in our '97 turns retarder "off" (activated by brakes if "Retarder" switch is on) in forward position. It turns the retarder "on" (activated when accelerator is released) when pulled back to positions 1-6.
The joystick was added by MOT after we bought the coach. We did not express a preference for direction of operation, so they would have made a "normal" installation. I drove another FT with a joystick and it operated by pulling back to engage.
Title: Re: Retarder 101
Post by: Caflashbob on August 28, 2012, 10:14:49 pm
The joystick in our '97 turns retarder "off" (activated by brakes if "Retarder" switch is on) in forward position. It turns the retarder "on" (activated when accelerator is released) when pulled back to positions 1-6.
The joystick was added by MOT after we bought the coach. We did not express a preference for direction of operation, so they would have made a "normal" installation. I drove another FT with a joystick and it operated by pulling back to engage.
Thanks mine is the other way. ? Wonder why MOT did it one way and either FOT or the customer did it the other way?
Title: Re: Retarder 101
Post by: Paul Smith on August 28, 2012, 11:14:37 pm
Since my VMS 240 CL claims my retarder temp is never higher than the transmission temp (contrary to the experience of others, here), and the VMS reading of retarder temp jumps as soon as I engage the retarder, I'm beginning to wonder of my VMS is reporting retarder temp in Centigrade not Fahrenheit.
best, paul
Title: Re: Retarder 101
Post by: George Hatfield on August 28, 2012, 11:30:09 pm
Paul.... One of the problems with the VMSpc retarder temp early on was the PID was not calibrated properly. Thus the readings were too low. They fixed this problem with a new version software (cited previously) which I am now using. Could you have the same problem with your setup? One way to tell is to look at the temp of the trans and retarder when you are driving down the road without the retarder engaged...both temps should be the same.
We drove from Wall, SD to an RV park outside of Custer City, SD today. It was a very hilly route. I kept an eye on the retarder temp and trans temp. The retarder temp jumps as soon as the retarder is applied and at one point was over 250 degrees F. However, the trans temp showed little change and remained around 185 or so. I try to keep the retarder temp below 250 degrees by slowing down and downshifting to improve cooling. When the engine goes from about 1400 rpm to about 1700 rpm in a lower gear the impact on the retarder temp is immediate and it drops into an acceptable range. Going slower means there is less heat generated in the retarder and with higher rpms there is better cooling. Maybe I am being too cautious with the 250 degree max, but I like being on the safe side when I can be. The trans fluid is Transyn.
Title: Re: Retarder 101
Post by: Barry & Cindy on August 29, 2012, 12:03:31 am
RE: " Wonder why mine is setup reversed? Only 97's or mine or customer preference?
I think all 97's were manufactured without a joystick. Three levels of retard was activated only with brake pedal.
When joy sticks are mounted by a coach owner or mechanic it can be mounted with zero position toward the front or rear. Installer makes the choice either on purpose or by chance. Both ways work.
Most have zero position forward. If you would like to change the way your joy stick is mounted, you can easily re-mount it the other way around.
Title: Re: Retarder 101
Post by: Gayland Baasch on August 29, 2012, 09:20:18 am
I must be the only one here that has a factory installed decal (or so it would appear, to the left of the drivers seat) that says to not run to long at 300 degrees.
Title: Re: Retarder 101
Post by: Dave M (RIP) on August 29, 2012, 10:49:14 am
Interesting decal, since everyone is aware that 250 degree is the max. So wonder what "too Long means"? Think if you hit 300, you are too late unless the location of the temp sender was mounted somewhere else insteadof in the sump pan. Dave M
Title: Re: Retarder 101
Post by: Gayland Baasch on August 29, 2012, 12:36:49 pm
I was paraphrasing the "too long", it said more like, ease up, if that doesn't help, pull over until it cools down, again I'm paraphrasing. I've never gotten it over 215 going down the I90 passes in western Montana and Idaho with an ambient temp of 90. Once over the pass the temp drops right back to normal.
Title: Re: Retarder 101
Post by: Caflashbob on August 29, 2012, 01:35:24 pm
Interesting decal, since everyone is aware that 250 degree is the max. So wonder what "too Long means"? Think if you hit 300, you are too late unless the location of the temp sender was mounted somewhere else insteadof in the sump pan. Dave M
I was told long ago by my trash truck guys and the Allison guys that one hour at 300 would burn the trans fluid. If you pull the dip stick and it was orange and smelled burned it was.
Continuous 250 no issues ever heard of.
Bob
Title: Re: Retarder 101
Post by: LBoyd on August 29, 2012, 10:47:12 pm
Today I was coming down a a very long 7% grade into Deadwood SD. The signage said that trucks were limited to 25 mph which seemed to slow for the road. I tried to hold it down to 40 mph by down shifting to 5th and moving the retarder to 3 clickes back to be cautious. I had to apply some brake. At the bottom of the long grade my trans had downshifted to 4th and I got a warning bell (first time!). A check of the trans temp (dash gauge) showed 250 which was also a first. I don't know how to check retarder temp. Bell rang for about 30 secs and stopped when the trans temp fell to about 230. The warning bell was disconserting. I'm not sure why I got such a high temp in this instance.
Title: Re: Retarder 101
Post by: John S on August 29, 2012, 11:07:29 pm
I did that grade a week ago. It was in the upper 90s. I was in third gear and hit only 235 or so. I was running 25 mph.
Title: Re: Retarder 101
Post by: J. D. Stevens on August 29, 2012, 11:36:17 pm
The signage said that trucks were limited to 25 mph which seemed to slow for the road. I tried to hold it down to 40 mph by down shifting to 5th and moving the retarder to 3 clickes back to be cautious. I had to apply some brake.
Trust the speed limit for the trucks. The low speed limit is based on the grade. Holding steady at a higher speed on a steep grade in a vehicle as heavy as yours can make a BIG difference in the amount of energy that must be dissipated. The grade is not such a big deal in a car. It is a big deal in a vehicle that weighs over 20,000#.
Title: Re: Retarder 101
Post by: Paul Smith on August 29, 2012, 11:53:57 pm
Quote
Today I was coming down a a very long 7% grade into Deadwood SD. The signage said that trucks were limited to 25 mph which seemed to slow for the road. I tried to hold it down to 40 mph by down shifting to 5th and moving the retarder to 3 clickes back to be cautious. I had to apply some brake. At the bottom of the long grade my trans had downshifted to 4th and I got a warning bell (first time!). A check of the trans temp (dash gauge) showed 250 which was also a first. I don't know how to check retarder temp. Bell rang for about 30 secs and stopped when the trans temp fell to about 230. The warning bell was disconserting. I'm not sure why I got such a high temp in this instance.
For 7% in my 1999 40ft U320 I think I would have been in 4th early on.
Then use the retarder/service brakes to keep from red lining.
best, paul
Title: Re: Retarder 101
Post by: Gary Bouland (RIP) on August 30, 2012, 02:56:48 pm
Quote
Today I was coming down a a very long 7% grade into Deadwood SD. The signage said that trucks were limited to 25 mph which seemed to slow for the road. I tried to hold it down to 40 mph by down shifting to 5th and moving the retarder to 3 clickes back to be cautious. I had to apply some brake. At the bottom of the long grade my trans had downshifted to 4th and I got a warning bell (first time!). A check of the trans temp (dash gauge) showed 250 which was also a first. I don't know how to check retarder temp. Bell rang for about 30 secs and stopped when the trans temp fell to about 230. The warning bell was disconserting. I'm not sure why I got such a high temp in this instance.
I came down that same Deadwood grade on last Sunday ( just in time to be tail end charlie in the Old Car parade , one hour to get thru Deadwood, good car show ). I never exceeded 200 tranny temp but I used truck speed as Max and geared down, If I recall I was in third at the light at the bottom. Grades are easy, gear down, slow down, use retarder, when speed and/or RPM picks up bleed speed off until down to posted then, repeat. Gary B
Title: Re: Retarder 101
Post by: wolfe10 on August 30, 2012, 03:08:56 pm
Yes, maintaining a lower speed of descent ALWAYS takes less braking HP (and therefore less heat) than going faster. A reasonable gauge is that you are faster than the loaded 18 wheelers BUT, slower than the empty ones.
Said another way, you can produce sufficient braking HP to maintain that speed WITHOUT OVERHEATING THE TRANSMISSION/RETARDER. Overheating-- slow down and gear down to where the amount of heat produced by the Allison retarder does not exceed your cooling system's ability to dissipate the heat.
Title: Re: Retarder 101
Post by: Dave M (RIP) on August 30, 2012, 04:08:28 pm
I confess to charging up mountains hard, passing all RVs, Trucks empty or loaded, some cars, but when it comes to going down, I am one of the slowest, save brakes, keep temps well under control etc. Such a nice thing to have a hot rod for a coach.
We all have seen and smelled the effects of idiots running too fast down with brakes smoking etc. They also are the ones who need brake repairs, drums, rotors, shoes, pads, etc. Very costly redoing some brakes.
They must have small engines trying to keep up with the folks with normal engines or something or are clueless to what is going on.
We all do what feels best for us. Don't we ? Dave M
Title: Re: Retarder 101
Post by: Pierce & Gaylie Stewart on August 30, 2012, 11:22:20 pm
Dave,
Everyone does what feels best. Trouble is some don't make the mental transition from their daily driver to a big, heavy motorhome. Perhaps a little overconfidence from driving in familiar areas can lead to not realizing how close to the edge of the operating envelope they are. Trips out to the National Parks in the west are a real reality check with the two lane roads having potential to be far more dangerous than the fairly mild downgrades on the interstates. Adding to the strain of steep roads are the string of cars behind just adding more pressure to make a faster decent.
The smoking brakes with a nasty smell are only a very small percent from totally loosing the brakes with another mile downhill ahead. Just have to turn off the radio and plan ahead.
I totally lost brakes following the lead vehicle at one of the big fires in the Malibu Mountains. I was already in first gear when the brake pedal didn't slow us down any longer. Terrible feeling and even worse when you push the parking/anchorlok button and nothing really happens. Had to put the right side of the rig into the ditch next to the road and drag the front I beam in the dirt to get it stopped. Not much time from when the brakes first start to fade until they are totally gone. Not really much smoke either. Five minutes later, we headed down again, still in first but slower. Auto rear slack adjusters were not working so front had to do all the work. We all had our seat belts unfastened after the first time.
Pierce
Title: Re: Retarder 101
Post by: Roland Begin on August 31, 2012, 08:59:21 am
Dave, Adding to the strain of steep roads are the string of cars behind just adding more pressure to make a faster decent. .
Pierce
One thing I keep telling my DW, "Don't worry about anything behind you. If they would have gotten up earlier this morning they'd be in front".
Roland
Title: Re: Retarder 101
Post by: John S on August 31, 2012, 11:24:21 am
On the downhill side, I always run a bit slower then the up hill side. I can stop without a problem going up hill. Going down hill s much harder so, I downshift and learned to stab te brakes and I go usually 10 mph under my speed if the target is above 25. At 25 moh I use 2 gear or third gear and the retarder depending on the length of the hill. Two miles or so third longer and i am in 2nd.
Title: Re: Retarder 101
Post by: LBoyd on September 01, 2012, 09:43:39 am
It is pretty obvious that I misread the hill-the bell was a good clue. Does overheating the trans/retarder cause deterioration of the transmssion fluid?
Title: Re: Retarder 101
Post by: Pierce & Gaylie Stewart on September 01, 2012, 10:32:38 am
High automatic transmission temperatures will shorten the life of the fluid, seals and transmission. Here is a quote from a transmission site; "The effect is also cumulative. Short term exposure to high heat levels (or even prolonged exposure to moderate heat) can break down the oil to the point where even very short episodes of overheating will lead to failure."
And the site: Transmission temperature/failure chart. (http://www.txchange.com/heatchrt.htm)