Foretravel Motorhome Forums => Foretravel Tech Talk => Topic started by: Tom Lang on November 07, 2014, 12:29:15 am
Title: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Tom Lang on November 07, 2014, 12:29:15 am
I'm the one that usually starts the coach. And you're right. With the '96, you turned the key to the first click position, waited for the "Wait to Start" light to go out, turned the key the rest of the way, and the coach roared to life.
The '03, there is no "Wait to Start", you just start it but it takes a long time as it checks to make sure it thinks everything is ok and then the start seems a lot harder.
But, once the '03 is started, you better be ready because it wants to GO! I find that sort of disconcerting. The '96 seemed much more "patient".
Sounds like the idle speed is too fast.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Neal Pillsbury on November 07, 2014, 01:07:39 am
Tom, The point of the observation is that the idle torque difference between the small block ISC or 8.3 and the big block ISM is something for the uninitiated to be aware of. If you are not alert, you will be creeping and doing modifications to your bodywork with the parking brake full on! My idle is at 700 RPM (spec is 600 to 800) and it over rides the parking brake. When you slow for a stop light, the "push" is remarkably different also (stronger than that from a small block), and don't become lackadaisical about your service brake pressure while waiting for the light to change or the idle torque will collect you a Smartcar front cap ornament!
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Caflashbob on November 07, 2014, 02:42:30 am
Tom, The point of the observation is that the idle torque difference between the small block ISC or 8.3 and the big block ISM is something for the uninitiated to be aware of. If you are not alert, you will be creeping and doing modifications to your bodywork with the parking brake full on! My idle is at 700 RPM (spec is 600 to 800) and it over rides the parking brake. When you slow for a stop light, the "push" is remarkably different also (stronger than that from a small block), and don't become lackadaisical about your service brake pressure while waiting for the light to change or the idle torque will collect you a Smartcar front cap ornament!
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: John S on November 07, 2014, 07:27:02 am
mine was at 600 and cummins said it should be 700 so that is where i set it. It does press a bit but the park brake will hold still. It is a torque machine, that is for sure.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Michelle on November 07, 2014, 09:10:12 am
If you are not alert, you will be creeping and doing modifications to your bodywork with the parking brake full on! My idle is at 700 RPM (spec is 600 to 800) and it over rides the parking brake.
OK Neal, I'm confused by this part of the discussion (happens a lot). It reads like you're saying you've got the coach in gear, not neutral, with the parking brake on. Am I misinterpreting what you're saying? Figured I'd ask because if I'm confused maybe someone else is.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Caflashbob on November 07, 2014, 10:44:42 am
mine was at 600 and cummins said it should be 700 so that is where i set it. It does press a bit but the park brake will hold still. It is a torque machine, that is for sure.
Both my tech gurus seperately turned my idle down to 550 versus overrun the brakes at idle. Makes something in the dash rattle once in a while although unless I add Lucas to the tank which smoothes the idle quite a bit
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Neal Pillsbury on November 07, 2014, 11:41:02 am
............It reads like you're saying you've got the coach in gear, not neutral, with the parking brake on.........
You are not confused, Michelle. We are talking about differences between the two coaches. I think that in the spirit of making a comparison, the difference in idle torque between the small block and the large block Cummins requires a paradigm shift in thinking for most owners of 8.3 L Cummins: Although poor SOP (Standard Operating Procedure), there is generally "No Harm, No Foul" if an 8.3L operator forgets to select neutral while momentarily engaged in some other activity, as long as you are keeping your maintenance up and the parking brake is set. With the ISM-450, it is imperative that you not rely upon the parking brake to hold the coach in place while the coach is in gear. Not saying this happened, but consider the scenario where on a test drive of an ISM-450, two experienced 8.3 owners pull over in a safe location to exchange drivers. Pull in, stop, shift to neutral, set the parking brake, unbelt and get up to change drivers.......What the? The coach is creeping ahead! This is the first time this has happened in over 150,000 miles of FT travel! Focused better, it becomes apparent that the "drive to neutral" shift wasn't paid enough attention to and did not occur. The coach is still in drive! PARADIGM SHIFT! It is not safe to rely upon the parking brake in an ISM-450, when the coach is running and in gear, at least until you do everything that Dave has suggested. If you do, there may be harm and there will be a foul! I too thought that the idle was perhaps too high. FOT says the RPM is set properly and the brakes are adjusted properly. Neal
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Michelle on November 07, 2014, 12:44:40 pm
Not saying this happened, but consider the scenario where on a test drive of an ISM-450, two experienced 8.3 owners pull over in a safe location to exchange drivers. Pull in, stop, shift to neutral, set the parking brake, unbelt and get up to change drivers.......What the? The coach is creeping ahead!
Ah - what you were commenting on makes sense now that I understand the hypothetical situation. At least it's not like someone driving away while still plugged in at a friends' house :-X
maybe it would be a good time for a little experience, since my background is more with the MCI bus, can mention that with the S Cam brakes, when a driver starts engine, dials D and step on throttle without releasing the parking brake
That's apples and kumquats, Dave ;) . Different brakes, and we're not talking about actually stepping on the throttle. But good to know if one were to drive a machine with S Cam brakes (I'll have to go Google those now to see what they are).
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Peter & Beth on November 07, 2014, 01:05:51 pm
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: Andy 2 on November 07, 2014, 01:10:08 pm
In a nut shell Michelle (drumb Brakes)
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320 )
Post by: littledubz on November 07, 2014, 01:36:43 pm
I have a CDL in NJ with an air brake endorsement, and the among the many tests you are "supposed" to do on air brakes for you pre trip inspection is the parking brake test. This is where the parking brake is applied and the truck put into gear. and given some throttle. The truck is not supposed to creep, and creeping would indicate that the parking brake needs attention. If you cannot put your coach in drive with parking brake applied and have it stay still, I would think that is a problem, and although not earth shattering, is not the way your parking brake is supposed to work. I have more experience in trucks than with buses or motorhomes, but that is the way CDL drivers are trained, at least in New Jersey. BTW, since you are not driving commercial vehicles, you are not required to be trained on air brakes, but there are also other tests that you should know how to do.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: John S on November 07, 2014, 04:08:23 pm
Mine does not move forward but it did and I had to back the idle off to 700 to prevent it. The park brake is adjusted properly too. It is just not as strong as it needs to be for the big coach. On the level it is fine but you really have to watch it if you are heading down hill and leave it in gear. I do not think it will move but a bit of throttle and it will.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Pierce & Gaylie Stewart on November 07, 2014, 04:26:11 pm
Even with the parking brake adjusted, big torque at a slightly fast idle speed will move the coach if headed downhill. Normal idle will still move the coach if pointed down grade. Meritor disk brakes work much better if warm than dead cold. Use chocks like emergency services, public utilities.
Some coaches may have less vibration with a higher idle speed but will pay for it as the parking brake will be less effective.
Pierce
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Caflashbob on November 07, 2014, 08:29:15 pm
Turn down the idle speed. If parked more than a short stop in nuetral use the low rpm fast idle.
Cummins might be recommending the 700 rpm for oil pressure or smog issues or cooling fan speeds?
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: kb0zke on November 07, 2014, 09:34:30 pm
When we first got our coach it hadn't been used much in the previous couple of years, and I noticed that sometimes it didn't seem to want to stop completely while in gear. Shifting to neutral resulted in a pretty quick stop with the same brake pressure. Now that the coach has been driven more I don't notice that anymore. Maybe I'm just more used to how much pressure is needed, or maybe driving the coach has helped the brakes. We were told that the rear brakes were new when we got the coach, so maybe it is just that they are now broken in.
No matter what, I would be concerned about any coach that didn't want to stop properly.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Caflashbob on November 07, 2014, 09:42:43 pm
When we first got our coach it hadn't been used much in the previous couple of years, and I noticed that sometimes it didn't seem to want to stop completely while in gear. Shifting to neutral resulted in a pretty quick stop with the same brake pressure. Now that the coach has been driven more I don't notice that anymore. Maybe I'm just more used to how much pressure is needed, or maybe driving the coach has helped the brakes. We were told that the rear brakes were new when we got the coach, so maybe it is just that they are now broken in.
No matter what, I would be concerned about any coach that didn't want to stop properly.
Use of the retarder allows some glazing of the pads. But turning off the retarder requires a fair amount of concentration of whats going on around you. Regular heating of the brakes results in stronger stopping in my experience.
Glazed brakes symptom can be the parking brake issue mentioned.
Lower idle and deglazed brake seems to work well.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: krush on November 07, 2014, 09:45:26 pm
Torque has nothing to do with it at idle. A shaft spinning at 700rpm is a shaft spinning at 700rpm. It might be the torque converter on the HD4060R transmits more torque through at the same RPM. The 4060 has a slightly lower 1st gear ratio (according to specs), but the u360 has a higher ratio rear end--so this should be offset.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Pierce & Gaylie Stewart on November 07, 2014, 10:56:02 pm
With a 2 stroke, we can idle as smooth as glass at 600 RPM but with cold brakes, I have to shift into neutral going down our driveway or I can't stop with the service brakes . When warmed up, I can lock up all six on a flat road.
Bigger cans on the rear might be OK at very low speeds as the engine is fighting the rear brakes but at any other time, the engine/transmission/retarder/Jake are helping the rear cans/brakes slow the coach. Bigger cans on the rear can mean rear lockup in ice or snow or even in a panic stop. If the rear comes loose going downhill in the snow, no one is going to catch it except another vehicle or guard rail.
Pierce
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Tom Lang on November 07, 2014, 10:57:09 pm
Here's a mostly off topic question for the FT brain trust.
Why is it, that my 1987 Mercedes 300D acts like this: No creep at idle when I take my foot off the brake, and no backwards slip when aimed uphill unless the hill is really steep. As long as it has traction, it will go up just about any hill with only modest application of throttle. The engine is diesel, so I know torque is higher than similar gas cars. None of my gas automatics have ever behaved like this, no matter how powerful the engine.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Pierce & Gaylie Stewart on November 07, 2014, 11:07:52 pm
It's called "stall speed." Here is Bank's page that describes it better than I can. Banks Power | Understanding Stall Speed (http://www.bankspower.com/techarticles/show/10-understanding-stall-speed)
Tom, you are lucky. Mercedes are about the only automatic transmissions that you can pull start or coast down a hill and do a 30 mph "bump start". All diesel and gasoline.
Pierce
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Tom Lang on November 07, 2014, 11:48:18 pm
It's called "stall speed." Here is Bank's page that describes it better than I can. Banks Power | Understanding Stall Speed (http://www.bankspower.com/techarticles/show/10-understanding-stall-speed)
Cool. So, if I always parked the Benz on the top of a hill, it could be fully drivable with the battery and every electrical component and wire removed. As long as I can keep the tank filled.
Tom, you are lucky. Mercedes are about the only automatic transmissions that you can pull start or coast down a hill and do a 30 mph "bump start". All diesel and gasoline.
Pierce
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Pierce & Gaylie Stewart on November 08, 2014, 12:31:59 am
Yes. The warmer the transmission is, the faster you have to pull it or coast it. I have done this on all years and models except for the newer ECU diesels that need a little juice. One time with a gas V8, the battery 99% died miles from town up by some old gold diggings. The engine lights would barely glow. It was a three speed auto so I just coasted it and it started. The shorted battery gave the alternator bad advice and the engine barely ran once it started. I was worried I might not be able to get back to town but tried turning on the headlights and the engine ran great.
Some of the Mercedes diesels did not have a priming pump either on top of the secondary fuel filter or down on the side of the injection pump so when you changed filters, you either had to wear out the starter motor or pull start it. I always pull started.
So, you attach a tow strap, have someone pull you to to about 30 mph while in neutral with the key in the run position. At about that speed, you pull the lever back into low and in a few seconds, the engine spins and starts. The mechanical Mercedes diesels don't use a fuel solenoid like most other diesels do to turn on the fuel. They use a vacuum actuator to turn OFF the fuel so it will keep running until it runs out of fuel without any electrical system. That's why your door locks, trunk, gas filler all operate off of the engine mounted vacuum pump. You do have to have the transmission fluid between the high and low marks on the dip stick for towing to work.
Old Hydra-Matics or Power-Glides that GM put into their cars would do the same thing along with Dodge Fluid Drive automatics. Daimler Benz may put in an extra pump but you can't tow four down as the owner's manual gives the number of miles possible to tow.
Pierce
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Tom Lang on November 08, 2014, 12:43:27 am
Wow.
Thanks, Pierce. That was a lot more than I bargained for.
I've known all along that old Benz is a keeper.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: littledubz on November 08, 2014, 09:12:13 am
Regarding creep, I think what Pierce said is relevant and logical (imagine that!).
I have never driven a truck that has disc brakes. I think the drum brakes that you tend to find on trucks have a lot of disadvantages. Drum brakes are more likely to lock up than disc brakes. When you're idling they are probably more likely to stay locked and not allow creep than disc brakes, even more so when they haven't been used or are cold.
I would think that ALL truck drivers would have the same opinion on creep (i.e. there should be none). But these are not trucks, they don't have truck brakes. So the horror a truck driver would feel at the thought of creep is not relevant to a motor coach driver.
All that being said, putting your coach in to neutral is something simple that you should always do when you're not sitting in the drivers seat.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Gary Bouland (RIP) on November 08, 2014, 09:57:07 am
From experience with trucks..... If your service OR Park brake will not hold vehicle in drive at idle you have a MAJOR problem. You should drive CAREFULLY to a shop that can inspect and adjust brakes , in the case of Disc's the calipers , and slack adjusters . A DOT inspection that found that the vehicle would creep in drive would put you out of service and just common sense a MH driver should use the same air brake criteria as a trucker. On second thought please DON'T drive it, tow it.
Gary B
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: pocketchange on November 08, 2014, 10:09:48 am
Regarding creep, I think what Pierce said is relevant and logical (imagine that!).
I have never driven a truck that has disc brakes. I think the drum brakes that you tend to find on trucks have a lot of disadvantages. Drum brakes are more likely to lock up than disc brakes. When you're idling they are probably more likely to stay locked and not allow creep than disc brakes, even more so when they haven't been used or are cold.
I would think that ALL truck drivers would have the same opinion on creep (i.e. there should be none). But these are not trucks, they don't have truck brakes. So the horror a truck driver would feel at the thought of creep is not relevant to a motor coach driver.
All that being said, putting your coach in to neutral is something simple that you should always do when you're not sitting in the drivers seat.
My turn..
NUTZ.. If this was true and it ain't, disc brakes on trucks would be the norm. It is a fact that the swept contact area of drum type brakes under all conditions makes a mockery of disc brakes.
I have had one trailer with disc brakes in over fifty years of driving OTR and could not be happier than the day I got back with good old fashioned drum brakes (thank you..)
Please note, I am not saying disc brakes are a bad idea. On a four wheeler, they are great. Just that on heavy trucks, they are less than acceptable (& I'm not real happy having disc brakes on my FT, fwiw.)
Disc brakes' major contribution is in greatly reducing unsprung weight which does improve handling and overall ride comfort, an obvious improvement over drum brakes on any MH. pc
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Don & Tys on November 08, 2014, 10:37:44 am
I have no experience or opinion as regards disc brakes vs drum on heavy duty OTR trucks, but I absolutely love the disc brakes on our coach. No squeals, very linear feel, easy to modulate and get to smooth stop. In spite of a few air horn inspired moments, never felt like I even tested the limits of the stopping power on our coach. The combination of the retarder and the air disc brakes on our coach is one of the features that sold me on Fortravels in the first place. Just curious, what makes you unhappy about the brakes on your coach, the performance of the braking system, or the idea that they are disc brakes? Don
...I'm not real happy having disc brakes on my FT, fwiw.
Disc brakes' major contribution is in greatly reducing unsprung weight which does improve handling and overall ride comfort, an obvious improvement over drum brakes on any MH. pc
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: John S on November 08, 2014, 10:46:06 am
From experience with trucks..... If your service OR Park brake will not hold vehicle in drive at idle you have a MAJOR problem. You should drive CAREFULLY to a shop that can inspect and adjust brakes , in the case of Disc's the calipers , and slack adjusters . A DOT inspection that found that the vehicle would creep in drive would put you out of service and just common sense a MH driver should use the same air brake criteria as a trucker. On second thought please DON'T drive it, tow it.
Gary B
Gary, I think he was saying at a slight throttle. I know mine will not move if i park it and put on the park brake but I do take it out of gear. I do feel though that on the M11 it is just barely holding and that is over multiple motorhomes I have been in with the M11 and have driven. If you touch the throttle it will move with the park brake on. My 8.3 did not come close to it.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: littledubz on November 08, 2014, 10:51:06 am
Pocketchange
Please help me understand. You've said two things that appears to me to be in contradiction
"I'm not real happy having disc brakes on my FT" and "Disc brakes' ...major contribution is in greatly reducing unsprung weight which does improve handling and overall ride comfort, an obvious improvement over drum brakes on any MH"
Are you saying that they are a major improvement in that one area, but they are worse in every other area and you would still not prefer to have them on your RV?
You're also saying "if this were true, and it ain't", but I don't know which one of the 9 statements I made you're disagreeing with.
My point, which may have gotten lost in all that other stuff, is a truck driver would not find creep acceptable, and is trained to identify it and have it resolved, but that may not be relevant to a motor home driver because their vehicle has disc brakes.
I would love to hear if you agree or disagree with that one point.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Pierce & Gaylie Stewart on November 08, 2014, 11:06:14 am
Before Crown and American LaFrance went to 10" drums, fire trucks had poor brakes. The big drums and putting a weaker spring in the treadle valve made smoking the tires pretty easy.
Disk brakes are much more expensive to manufacture so may be a big reason why big rigs don't have them. They are much easier to work on, and are much less likely to fade than drums. Depending on pad material, they may work better when a little warm. You will need a cherry picker to R&R drums they are so heavy.
Our U300 brakes work great even on the steepest grades. I have not experienced any fade yet with them. I have had to put the right side of an American LaFrance into a soft ditch coming down out of the Santa Monica mountains on a campaign fire. I was in first gear with the AnchorLoks on but brakes had completely faded out.
The vast majority of big rigs are manual transmissions so no worry about creep in drive.
Pierce
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Michael & Jackie on November 08, 2014, 11:25:50 am
Back to the beginning, IF you are new to the ISM....I had smaller engine before....the torque or whatever you call it, I found at a stop light, and I kept it in gear, it took goodly pressure on the brake. Unlike the other coach, it would start moving, creep I guess you would say for perhaps so slow to not catch your attention if you looked away a moment.
So.....if I was getting an ISM from some other starting point, I think it a good admonition. It may be different feel, may see some creep
As for moving with park brake on and in gear, I just think have not done. So tried....see what I think John S said (?), hold on flat surface, no throttle, 725 rpm. But if on much of an incline, I rather doubt it would hold? Still, no plans to part in gear, far as I know. Hmmm
Thanks Neal
mike
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Lon and Cheryl on November 08, 2014, 01:58:33 pm
I hold a.CDL B with air brake endorsement also. I was terrified when I first went to move.my coach in reverse cold. I had to put it in neutral to wrestle it to a halt. It would not hold in either direction with the parking brake on. Not acceptable. I replaced the rear spring chambers and.adjusted the slack adjusters front and rear as close as.I could, then monitored the discs with a remote thermometer after driving to make sure they were not rubbing. Big difference. If it won't hold with parking brake the rear springs in the chambers could be.fatigued.
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: Neal Pillsbury on November 08, 2014, 09:21:49 pm
Well, it's very interesting that this thread has more opinions and less common sense of purpose than a room full of politicians.
Back to the beginning, IF you are new to the ISM....I had smaller engine before....the torque or whatever you call it, I found at a stop light, and I kept it in gear, it took goodly pressure on the brake. Unlike the other coach, it would start moving, creep I guess you would say for perhaps so slow to not catch your attention if you looked away a moment.
So.....if I was getting an ISM from some other starting point, I think it a good admonition. It may be different feel, may see some creep
As for moving with park brake on and in gear, I just think have not done. So tried....see what I think John S said (?), hold on flat surface, no throttle, 725 rpm. But if on much of an incline, I rather doubt it would hold? Still, no plans to part in gear, far as I know. Hmmm Thanks Neal
I was making a comparison between the U270 36' and the U320 42' operating/driving characteristics.
These FACTs about the big blocks "creeping" against the strength of the parking brake spring force on the disc brakes and the additional "push" that a big block exerts, which requires additional service brake pressure at a stop light have been talked about for years on this forum. Like many others, I sort of dismissed those thoughts because the 8.3's (most of my RV experience) properly adjusted and maintained, do not come close to showing alarming or "wake up call" type characteristics. So during my comparison days, I lived and learned quickly. With the ISM-450, at least, it deserves your full attention and respect based on my "back to back" comparison.
It certainly seemed to be an appropriate topic to include in the comparison.
Look at a few of the threads from over the years:
Through various forum members (now including me, after posing the idle speed and parking brake questions last week), Foretravel (James Triana) has told us:
Properly set up and maintained, the U320 parking brakes are designed to hold the coach on level ground on up to a few degrees of grade, WITHOUT the engine and transmission engaged.
Greater than a few degrees of grade, also WITHOUT engine and transmission engaged, one needs to ensure the use of chocks to prevent the coach from overriding the parking brake spring force applied to the disc brakes.
Also, the much larger torque values of the M11's will require significantly greater service brake pressure to counteract the greater "push" of the larger block engines.
Just a few of the many earlier threads that have discussed the same topic or closely related topics to this.
Effectiveness of Emergency/Parking Brake (http://www.foreforums.com/index.php?topic=8419.msg36915#msg36915) AIR BRAKE CHAMBER (http://www.foreforums.com/index.php?topic=14571.msg85269#msg85269) New to RVing (http://www.foreforums.com/index.php?topic=20736.msg152521#msg152521) M 11 and parking brak (http://www.foreforums.com/index.php?topic=6414.msg27315#msg27315) Parking Brake Effectiveness (http://www.foreforums.com/index.php?topic=12501.msg67252#msg67252) Setting low idle (http://www.foreforums.com/index.php?topic=17021.msg111736#msg111736) Motor Mount Replacement (http://www.foreforums.com/index.php?topic=21088.msg156191#msg156191) Parking Brake (http://www.foreforums.com/index.php?topic=12298.msg64034#msg64034) M 11 and parking brak (http://www.foreforums.com/index.php?topic=6414.msg27319#msg27319) Breaks or Brakes (http://www.foreforums.com/index.php?topic=684.msg1933#msg1933) Parking Brake (http://www.foreforums.com/index.php?topic=8417.msg36899#msg36899)
The interesting diversions into discussions of "S" cam drum brakes on commercial vehicles, CDL training, individual brake system optimizations, proposed design experiments, Etc. stray quite a way from the RVIAA standards and the two primary purposes of our air brake system designs and their capacity:
Hold a non-operating vehicle in place on a level surface (Parking)
Bring a moving vehicle to a controlled stop in the case of "loss of all service air" braking capacity (Emergency)
We are not heavy duty truck designs, with 80,000 Lb. payload capacities, we are not commercial carriers of freight or people, we are not regulated by 10 CFR 49, Subtitle B, Federal Motor Carrier Safety Regulations. Many of the principles, applied within reason, are appropriate to our safe operation and our thought processes, but knowing where and how to draw the line is well beyond most RV owners, without special training. That's part of why it is a federal offense to tamper with or redesign air brake systems on any vehicle over 26,000 lb. GVWR, without proper certification.
A bit of a side issue, but WRT to CDL training, CDL licenses must usually be surrendered when obtaining a license in another state (what I was required to do long ago), until recertification in the new state is achieved. Most CDL holders prefer to surrender their CDL, if it is not being (or not planned to be) actively used, as local law enforcement and the legal system is far more strict on CDL holder infractions, and rightfully so. CDL license holders should know that logic better than most. It used to be illegal to have two types of licenses or to simultaneously hold CDL licenses in two different states. I don't know about now. All that doesn't mean that one shouldn't avail themselves of CDL training if one can come by it reasonably. I have found that the quality of instruction varies widely and good research on the internet or in the library can be much more meaningful and less costly, unless one needs the "hands-on"or personal instruction to understand the topic.
So, I stand by the premise that there are stark differences between the U270, 36' and U320, 42' operating/handling braking system characteristics........... that the uninitiated would be well served to know about. Like most of the 8.3 owners, I dismissed them for years, but no longer. Thanks, Mike, "for Getting It". Neal
Title: Re: Coach moving at idle despite parking brake (split from Re: Handling Comparison:36' U270/42' U320
Post by: sitemod on November 08, 2014, 10:03:30 pm
Topic is now locked. Too many posts that were reported to the moderators and had to be deleted due to their inflammatory nature.
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