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Old 06-04-2008, 07:26 AM   #57
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I recognize that our setup is a little different than the Workhorse chassis generally discussed but would like to relate a specific story.

We went to Palo Duro Canyon State Park in Tx in September, 06. For those of you who don't know about it, the entrance road is about 2 miles of 10% grade with at least 4 hairpin turns. The worst part is a straight run of 10%, followed by a wicked hairpin boardered by a stone wall.

Coming around the turn at the top of this part of the decent, I brought us completely to a stop to survey the situation. I locked the transmission (Allison 1000) into the lowest gear on the lever and proceeded very slowly. Though I stabbed at the brakes a couple of times, we started to pick up speed rapidly. In the middle of the run, the transmission upshifted, I assume because it was unable to hold us back any more. Since I had no gear options that I could get to, I stood on the brake pedal hard several times, trying to balance how long I was on it with not depleting the air in the tanks. I was fortunate to slow us down enough to be able to make the hairpin turn. Apparently, I didn't jeapordize the brakes because there was no smell from them immediately after that experience.

I've since learned that the exhaust brake isn't very effective in the lower gears in spite of the fact that the RPMs were in a range that it should have been. As a result, I'm all but paranoid about any grade steeper than 9%. I'll run down 6% and even 7% grades all day long (I64 in Maryland for example - 13 miles of 6%). Last year, we took Route 321 from West Jefferson toward I-77 and had to go down a couple of miles of 10% on that road. Fortunately, the turns were far more gradual than the hairpins at Palo Duro. Since the road could tolerate a bit faster speed, the engine seemed happy with holding us in 2nd gear and there were no upshifts.


I have no idea about what I could have done differently at Palo Duro other than disconnecting the toad before tackling the decent (we do have a good, proportional toad brake). I've bought and study the East and West versions of the Mountain Directory, trying desperately to avoid putting myself in the same kind of situation as the driver in the referenced story where I try to drive our RV someplace that I shouldn't.
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Old 06-04-2008, 07:43 AM   #58
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There's every chance that your transmission upshifted because the engine RPMs hit their upper limit in the lower gear, so the transmission upshifted to protect the engine. If that's the case, to keep the transmission in the lower gear, I'd suggest monitoring the tachometer and using stab braking to keep the RPMs below the point at which an upshift will occur.

Out of curiosity, is the torque converter of the Allison 1000 locked in 1st gear when the exhaust brake is in use? If not, then the exhaust brake would not feel very effective.

Rusty
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Old 06-04-2008, 08:12 AM   #59
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Yes it sounds like a torque converter not locked up. While desending grades you must watch the tach as much as you watch the speed. I wonder when the manufactures of motorhomes will go to auto shift instead of automatic transmissions. A lot of trucks now have that as an option. The difference between the 2 is an auto shift is a manual transmission shifted by a computer which also controls the clutch.There is no clutch pedal, just throttle and brake. Drives just like automatic but can be held in any gear with no slip.
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Old 06-04-2008, 01:35 PM   #60
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I suspect that you are right about torque converter not locking up in 1st. I was afraid to get into the brakes too hard too soon in that long part of the decent. It was my first experience with anything that steep and I was hoping that if I started slow enough,I'd be OK. I was so engrossed in trying to keep us on the narrow road that I didn't watch the tach. I'm still concerned at how often I could stab brake and keep air pressure up. On and off the pedal can really take it down pretty quickly. No way would I want the parking brake trying to come on due to low air pressure in the middle of a run like that.
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Old 06-04-2008, 03:59 PM   #61
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Air brake systems should give you warning that they are running low on air without looking at the gauge, an alarm should go off at 60 psi which is still enough to release the brakes. Also I don't know if you have an application gauge. It tells you how much pressure is going to the brakes, if you have drum brakes as most trucks do it will require more pressure as the brakes heat up and expand the drums. Also a very important item overlooked by most drivers of air brake systems (Trucks and RV's) is draining the air tanks on a daily basis. If water has accumulated in the tank there is less room for air and if you've ever had a brake line freeze in the winter you will know what I'm talking about. It all comes down to knowing your vehicle and it's systems.
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Old 06-04-2008, 04:25 PM   #62
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Old 06-04-2008, 07:03 PM   #63
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Rick, I believe that I do know my air brake system, maintain it properly including checking the tanks for water (have not found any in 4 years.) I have a good checklist for the system checkout including verifying that the alarm comes on. And yes, mine are drum brakes.

None of that is my point, however. If I'm coming down a steep slope and my low air warning buzzer goes off, I figure that I'm in a heap of trouble. What it means is that I haven't managed that slope very well. I just don't want to be there. I suspect the driver in the article that lead to this discussion was exactly there (not having managed the slope well) but for different reasons that I mentioned.

That management means that I need to put myself in a position not to use up my resources (air) faster than they can be replenished. It takes the compressor some time to bring the air pressure back up to operating range. While it is doing that, I assume that I'm charging down the hill, potentially out of control because the drive train isn't providing me enough slowing power or I wouldn't have needed to brake so hard in the first place.

Personally, I see no difference in making the same statement about a normal hydraulic brake system. If the brakes are "used up" (overheated) it means that the driver didn't manage the slope correctly.
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Old 06-06-2008, 05:24 PM   #64
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Not sure I would have slept much leaving my wife in that position unsupervised!
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BEBOP:
Here is a rather humorous anecdote regardig proper descent off the mountain. This was in the 30 foot Georgie boy (1984) with the 454 and three speed, on Good Friday
My wife (the blonde) is driving. I told her when she got to the top of the grade to put the tranny in 2nd gear hold 35 mph, and keep it there until she got to the bottom of Cuesta Grade at San Louis Obispo in Central Calif. I took a nap but......I woke up hearing an engine doing about 8000 RPM. I asked her what gear and she said 2nd. I go look, she is in first and doing about 45 MPH.
I hear the rear main let loose at that point. She got it slowed down and we limped at 20 mph for the next 15 miles on the freeway into the RV park. We sat it out over the Easter weekend, started up Monday morning and banging loudly to a shop two towns away. We got to their driveway and the engine froze up. They pulled the MH in with the fork truck. We rode the Greyhound home 200 miles with about 4 bags of "stuff". NO Toad in those days. 2 months and $5000.00 later we retrieved the motorhome.
She doesn't drive this motorhome
Bebop </div></BLOCKQUOTE>
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Old 06-06-2008, 05:31 PM   #65
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Hugely bad idea!!

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Rocket Heart:
Stoopid question time .....does the emegency brake offer any help in those situations?? </div></BLOCKQUOTE>
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