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ahicks · 06-25-2013, 09:56 AM

Quote:

Originally Posted by DGBPokes

All good comments, and I have taken the exact route you described. With my class A and toad, and the biggest pass is La Veta and it is not a bad one, more long and gradual than steep.

However, Some of the comments regarding braking prompt me to ask a question. I have a Workhorse W22 , with Bosch Brakes and have had decent issues before, so I am very sensitive to steep down grades. When descending these steep grades, I ALWAYS use the tranny as much as possible. But at the same time worry about over revving the engine. I would appreciate readers comments regarding over revving; comments like how much over rev, for how long, shifting and anything else.

P.S. I have a Allison tranny.....reportedly a rock solid tranny.

Yes, that's what I was talking about. When you start to worry about over rev, drop another gear by slowing to the point you can do that safely. This will give the the available engine braking a better advantage over what is required to keep you from speeding up. Eventually you will get to the point where you find a gear that will hold the coach in a safe rpm range. Remember that gear, and the percentage of grade you're going down, and your downhill battles are over? The next time you get to a similar grade, you'll know what gear it must be in (and the corresponding speed you must be at to get there) to get down it comfortably?

Steeper grade = lower gear = lower speed.

For example - My 6 speed DP will run down a 4% OK in 5th gear with the exhaust brake on. Like this, it will hold the speed in the 70's. But when we get to a 6% downgrade, I'll slow down to 50 or so, and go to 4th gear and that will hold us. If that 6% hill gets steeper towards the bottom maybe, and the rpms start climbing into the danger zone even though I'm in 4th gear, I'll get on the brakes hard enough to slow us to 40 or so where I can safely shift to 3rd gear to give that a try? I'm only going to be going 40 mph or so like that, but I'll be doing that at an rpm the engine is comfortable with - without using the brakes? Nothing exact here. Just something I played with a little and found it works fairly well. Betting by time you get back you'll have a system down pat as well. -Al

JacknKay · 06-25-2013, 11:22 AM

I just drove down New Priest Grade, (CA Hiway 120) that goes to Yosemite NP. This grade is 6% for several miles with a lot of switchbacks. I put the tranny in Tow/Haul and touched the brakes lightly during the decent. The engine did all the work and yes it did get up to about 4500 RPM, but it ran well all the time down.
This was not my first climb/decent on the trip. We drove HiWay 49 from Oakhurst, Ca north to HiWay 120 to Groveland. That was a true white-knuckler. This is a narrow two lane HiWay with switchbacks up and down. Luckily there was no traffic so I could take my half the road from the middle. There were several cliffs sticking out that you could see some rigs or trucks had kissed the rocks.
I am a true believer in the Tow/Haul mode, especially when towing. Use it to save your brakes and sanity.
Jack