Community Forums

ron55 · 04-27-2008, 06:33 AM

You didn't tell him that IF YOUR BRAKES DO FAIL, as your speed increases your allison tranny just keeps shifting up and you go faster and their is nothing you can do.

DriVer · 04-27-2008, 07:07 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RON55:
You didn't tell him that IF YOUR BRAKES DO FAIL, as your speed increases your allison tranny just keeps shifting up and you go faster and there is nothing you can do. </div></BLOCKQUOTE>RON55, The only reason why this "perfect storm" would happen is if you were not in the right gear to descend and the diver overheated the brakes. The pumping action on the brakes scrubs off a lot of energy. If you are in the correct gear there is little or hardly any need to scrub speed.

You are correct regarding the Allison over-speed feature however I have never reached that amount of speed during my 7 years of ownership where the transmission up-shifted on its own. I have seen tach speeds approaching 5,000 RPM without an up-shift. I have routinely seen where I can hold my speed quite well running as much as 4200 RPM however that number varies depending on the grade. Lower RPMs are preferable and are obtained by downshifting the transmission to a lower gear.

I would also like to mention that you can not manually downshift the Allison if you are going too fast, it simply will not down shift until the speed and RPM are reduced.

bruceh · 04-27-2008, 07:44 AM

[/QUOTE]RON55, The only reason why this "perfect storm" would happen is if you were not in the right gear to descend and the diver overheated the brakes. [/QUOTE]

I have been in situations where I was already in first gear on some long steep downgrades and was forced to use my brakes a LOT. Once you are in first, that's it. Had I had a brake problem I would have been in serious trouble. I know how to conserve brakes but it was still a tense descent.

Another contributing factor is that these modern, low compression engines don't offer as much engine braking as the higher compression engines of the past, especially when you are trying to slow 12 tons.

I have been down Hurricane ridge (not in a motor home) and it (in my mind) would be a first gear descent. Whether or not the deceased driver was in the correct gear in unknown to me. Many people try to drive motor homes like cars and they are at great risk.

BEBOP · 04-27-2008, 08:02 AM

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

max49 · 04-27-2008, 11:47 AM

I hope I never have to feel that helpless feeling of going down a hill, out of control, with no brake

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RON55:
You didn't tell him that IF YOUR BRAKES DO FAIL, as your speed increases your allison tranny just keeps shifting up and you go faster and their is nothing you can do. </div></BLOCKQUOTE>

I don't think, and hope it does'nt but I've had my P-32 in first or 2nd gear , going down a mtn and without me even realizing it the engine was up to 5000 RPM and it did'nt upshift.
Some of these 'safety features' are for the equipment only , not for for the occupants and other people on the road.
If our rig was 'running away' down a mountain, I think we'd all say, "to heck with the engine and transmission, if it will just help me slow down and stop before someone's killed"
I almost always take all downhills , on the interstate (7% or less) in a low enough gear that I almost never need to use the brakes.
Just today , I drove 35 or 40 extra miles, one way to avoid a 1/2 mile section of twisting 15% grade.

dieselclacker · 04-27-2008, 03:43 PM

[QUOTE]Originally posted by max49:
Just today , I drove 35 or 40 extra miles, one way to avoid a 1/2 mile section of twisting 15% grade.

15% grade, zowie, Max, I would have driven the extra 40 miles also to avoid a grade like that, going down, or up!!

Dieselclacker

JWatkins · 04-27-2008, 06:19 PM

I have hit the 4200 or so RPM coming down and I was wondering how much potential there is for damage doing that. I still needed to scrub some speed several times to keep it under 65 MPH.
Joe

DriVer · 04-28-2008, 01:05 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JWatkins:
I have hit the 4200 or so RPM coming down and I was wondering how much potential there is for damage doing that. I still needed to scrub some speed several times to keep it under 65 MPH.
Joe </div></BLOCKQUOTE>Joe, I have sustained 4200 RPM descent engine speeds with an occasional pump on the brakes to scrub off speed as required. If the motorhome continued to accelerate, I would have needed to scrub off more speed and attempt to downshift to the next lower gear.

65 MPH is a lot of speed to build up inertia wise on a long descent. In my experience a slower descent rate say 60 MPH is more easily controlled. Road conditions vary and one's approach to one condition may not be appropriate for another. Ideally I would want a slight downhill grade, sustain low RPM and a have tail wind to boot.

Getting into the correct gear before the descent is the key to whole process. You can always start in a lower gear and shift up if you are going too slow.

JWatkins · 04-28-2008, 02:10 AM

Thanks, Driver. I actually do try to keep it slower than 65, but coming down off of the"Grapevine" here in California, I have hit the 70 MPH mark even after shifting out of overdrive on my Allison 5 speed. I will attempt to make it slower starting out and see what I get. I am not opposed to being in the truck lane dogging along in order to be safer.
Joe

dieselclacker · 04-28-2008, 03:17 AM

Joe, I always use third gear comming down the Grapevine in our Allison 5 speed equipped Allegro. Try it you will be able to maintain a decent speed without going over 4000 RPM.

Dieselclacker

Pubtym · 04-28-2008, 03:25 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Fred K:
Too me, over heated brakes = operator error 90% of the time. When watching the video, I counted seven people in the motorhome. It possibly could have been overweight also. </div></BLOCKQUOTE>

Agree...can't take the bone out of the head of MH owner drivers like this...but just maybe...the brain can be tweaked...sadly...this was not a MH driver...driver was an idiot..

ron55 · 04-28-2008, 04:38 AM

I travel Colorado high mountains in July and August and have found some down hill where low 1st gear would not hold back enough and I had to ride the brakes to keep her in lst gear, then I do have some concern about all the brake failures.
I realize the Allison is operator proof, I just wish it would stay in the gear I select regardless of my speed. I rather blow her up than go over.

DriVer · 04-28-2008, 07:36 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RON55:
I travel Colorado high mountains in July and August and have found some down hill where low 1st gear would not hold back enough and I had to ride the brakes to keep her in lst gear, then I do have some concern about all the brake failures. </div></BLOCKQUOTE>I would not admit that I had to ride the brakes because that in of itself might place you outside of the warranty envelope if you damage your brakes by riding and overheating your brake components.

My strategy is to pump the brakes hard at times and then release them as to not overheat the brakes. You can scrub a lot of energy with a brief hard application of the brakes.

Ding-a-ling · 04-28-2008, 10:12 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DriVer:
You can scrub a lot of energy with a brief hard application of the brakes. </div></BLOCKQUOTE>Amen to that!

Been there, done that! Found it works well.