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Old 08-18-2010, 09:11 AM   #1
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Gas engine braking on a long descent

Can anyone give me any feedback on their experiences with gas engines in a class a while descending long steep mountain grades. Such as how well did the engine/transmission do in holding back the coach? Any problem with brakes overheating, What gear was used on the descent in relation to the gear you where in when you reached the top of the grade and started down. Any information in this area will be greatly apperciated.
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Old 08-18-2010, 09:19 AM   #2
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I've only descended on the eastern mountains with my gas class A. I'll turn off the over drive so that it remains in third gear and use short braking so as not to overheat the brakes. No issues with my setup.
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Old 08-18-2010, 09:24 AM   #3
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Quote:
Originally Posted by phrrent View Post
Can anyone give me any feedback on their experiences with gas engines in a class a while descending long steep mountain grades. Such as how well did the engine/transmission do in holding back the coach? Any problem with brakes overheating, What gear was used on the descent in relation to the gear you where in when you reached the top of the grade and started down. Any information in this area will be greatly apperciated.
Use the same gear going down that you used going up.
DON'T ride the brakes. I apply constant pressure to brake when I'm going down too fast , for a few seconds and then let up to cool them down. As stated previously turn off the over drive as well.
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Old 08-18-2010, 09:46 AM   #4
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I use the transmission to control my speed on all steep or long decents instead of the brakes. Mine is a Ford V10 with a four speed transmission. It does a great job of holding back the speed. When I am in a decent all I look at is how fast I am gaining speed. If it is to fast I jab the brakes to slow me down so I can drop down to a lower gear. Sometimse it is just a jab on the brakes to slow me down if I am not gaining speed to fast. I am not really concerned about what gear I am in.
I don't have a problem with overheated brakes.
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Old 08-18-2010, 09:46 AM   #5
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Engine braking on gas engines

Opposed to diesel, gasoline engines naturally have a braking effect caused by throttle position induced vacuum. The engine's braking is nearly always sufficient to avoid using the brakes like in a gasoline car.

On especially steep mountain passes it may be necessary to downshift to get sufficient engine braking to avoid using the brakes.

An Allison transmission with hill holding "on" will downshift automaticaly if you touch the brakes while going downhill (no throttle).

On my previous Ford you can down shift out of overdrive going downhill by pressing on the shift lever. Both avoid using the brakes on all but the steepest mountain passes.
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Old 08-18-2010, 10:02 AM   #6
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On my 35 foot Class A with a loaded toad ( I do not use Aux brakes). I tap the brakes once, while in the tow/haul mode. This is more than sufficient to control speed at a safe level. If I start to gain speed, one more tap is all that is necessary to bring her back to a safe speed. I do not use brakes unless a semi truck tries to pass another one on a steep grade and can't. One of my pet peeves. Talking Ford V-10 with tow/haul.
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Old 08-18-2010, 10:11 AM   #7
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We have crossed the country (round trip) nine times in our gas Class As. I always used the engine braking for decents. Usually the same gear going down as going up but.... DON'T over rev the engine. SLOW DOWN with your brakes in short hard applications and SLOW DOWN more than you think you need to. If you smell the brakes pull over ASAP and let them cool. Then drive at a slower pace because you were going too fast. If you think you are blocking traffic pull over when you can. NEVER speed up for someone else.
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Old 08-18-2010, 10:13 AM   #8
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Steepness of the hill matters. Gas engine has a really hard time slowing down a motorhome on the downgrade into Skagway,AK with 11% grade for 11 miles. Brakes will overheat on really long steep grades even when you start out slow and just tap the brake now and then. Engine revs will climb quickly on really steep grade. If you smell brakes pull over to a safe spot and look at the scenery.

If you ever kept your motorhome in cruise control and seen the revs go through the roof, using the engine to slow you does the same thing going down. At some point you must tap that brake.
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Old 08-18-2010, 10:30 AM   #9
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One factor that should be considered is, does the torque converter in the automatic transmission lock up when using the engine for braking? If not, engine braking will not be nearly as effective, and the heat generated by torque converter slippage while generating retarding horsepower on long, steep grades can lead to excessively high transmission fluid temperatures.

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Old 08-18-2010, 03:37 PM   #10
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Can't add much to the others except that on our last rig (workshorse chassis/8.1/allison) the downhills woudl get quite noisy due to the high engine rev's. We woudl do as others have said -- anticipate, gear down early, don't ride the brakes just hit them as needed to maintain speed/engine revs.

That being said, one of the big things that drove us to our current rig is the 2-stage engine breaking on the ISL. Quieter, no high revs and on the same hills we rarely have to use the brakes.

BTW, by hills I mean the GrapeVine (I5) and the Cajon Pass (I15) in So Cal.
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Old 08-19-2010, 02:32 AM   #11
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I have a 33' Pace with a Ford V10 engine and I use the tranny to slow me down going down hill..... Here is the way I do mine.
I watch my speed and my tachometer. I take the tranny out of OD and watch the tach and when it hits 3600 rpm, I tap the brakes and slow back down to 2500 rpm and down shift if necessary according to the grade of the road. I watch the tach again and when it hits 3600 rpm I tap the break again and slow to 2500 rpm. This seems to work well on most Rockie Mountain Passes. It kinda divides your braking power between your tranny and your break pads.

Like the guy said about Skagway pass going down. When I cap that one out going down, I put the coach in LOW GEAR and CRAWL DOWN THAT MOUNTAIN USING THE BRAKES TO KEEP THE TACH BELOW 3600 RPM. My toad has a breaking system on it but when I go down a 11 degree grade I unhitch and let Willa drive the toad and carry the video in case I go over the side she can submit the video to Americas Funniest Videos and make some money. (i have canceled all my insurance and when I die its gonna be a SAD DAY FOR EVERBODY)

A good rule of thumb...........NEVER GO DOWN A MOUNTAIN ANY FASTER THAN YOU THINK YOU CAN ''COME UP'' THAT SAME MOUNTAIN..... If it is a ten mile per hour ''Grinder'' going up ......... Do the same GOING DOWN and do not be ashamed to unhook your toad. (someone needs to survive to tell the tale)
Like so much of my other valuable information, if you use this valuable information you must pay me ten cents the next time you see me ....... of course, if it dont work for you..... I NEVER KNEW YOU.......
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Old 08-19-2010, 12:50 PM   #12
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Thanks everone for the input, I've been over most of the steep mountains in the west and quite a few in the east, but only in either a semi or expedite truck all with diesels engines, some with and some without engine breaks. But never in a gas powered engine, all of the info that you have given me will help in deciding which engine I will want in my motorhome. Once more, thanks very much.
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Old 08-19-2010, 02:06 PM   #13
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Quote:
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Steepness of the hill matters. Gas engine has a really hard time slowing down a motorhome on the downgrade into Skagway,AK with 11% grade for 11 miles.
I didn't have too much trouble going down into Skagway last year with our 24K pound coach plus toad. 2nd gear at about 4,200 rpm put me at 25 to 30 mph with occasional push on the brakes.

Don't be afraid of engine revs in lower gears. The Workhorse engine and Allison trans. are almost bullet proof. They will get you there and back.

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Old 08-20-2010, 07:12 AM   #14
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I did Teton Pass this summer. Victor Idaho to Jackson wyoming. 5 miles up and 5 miles down, 10% plus grades all the way. Up was 4000 rpm in first, 27 MPH. For 5 miles continuous.

Down, I used either first or second. Stabbing the brake fairly hard only when needed. Engine braking alone would not hold her back, many times I had to upshift to second because the rpm's were getting too high.

The whole run was no problem at all, except perhaps for those behind me.
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