Retarder 101

Topic: Retarder 101 (Read 3053 times) previous topic - next topic

Re: Retarder 101

Reply #25 – 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

Re: Retarder 101

Reply #26 – 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

Re: Retarder 101

Reply #27 – 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?

Re: Retarder 101

Reply #28 – 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.

Re: Retarder 101

Reply #29 – August 26, 2012, 11:08:02 pm

Quote from: Paul Smith – August 24, 2012, 04:14:59 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

Re: Retarder 101

Reply #30 – 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 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.

Re: Retarder 101

Reply #31 – 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.

Re: Retarder 101

Reply #32 – August 27, 2012, 01:38:58 am

Quote from: Jerry Whiteaker – 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 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

Re: Retarder 101

Reply #33 – 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

Re: Retarder 101

Reply #34 – August 27, 2012, 09:40:24 am

Quote from: jor – August 27, 2012, 09:24:29 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.

Re: Retarder 101

Reply #35 – August 27, 2012, 09:57:05 am

Quote from: Jerry Whiteaker – August 27, 2012, 12:15:10 am

When the retarder is on the brake light is on.

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.

Re: Retarder 101

Reply #36 – 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

Re: Retarder 101

Reply #37 – 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.

Re: Retarder 101

Reply #38 – August 27, 2012, 09:57:51 pm

Quote from: Kent Speers – August 27, 2012, 08:01:39 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.

Re: Retarder 101

Reply #39 – 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

Re: Retarder 101

Reply #40 – 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.

Re: Retarder 101

Reply #41 – 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

Re: Retarder 101

Reply #42 – 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

Re: Retarder 101

Reply #43 – 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

Re: Retarder 101

Reply #44 – 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

Re: Retarder 101

Reply #45 – 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.

Re: Retarder 101

Reply #46 – 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

Re: Retarder 101

Reply #47 – 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!

Re: Retarder 101

Reply #48 – 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.

Re: Retarder 101

Reply #49 – August 28, 2012, 11:59:17 am

Quote from: jor – August 28, 2012, 10:45:26 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.

Quote from: Carol Savournin – August 28, 2012, 10:57:15 am

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.

Besides, I was busy checking MY undergarments

and like I said, I am sure that EVERYONE could hear my verbal displeasure with her driving skills.

Dean

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