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Old 01-18-2015, 10:06 PM   #1
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Engine braking

I'am a newbee to a 39' 2001 Tradewinds with a 3126 Cat engine and a 6 speed Allison transmission and I need some help in Useing the engine brake system. When you start to deceind a grade which is approximately 6 per cent in fifth gear and you apply the engine brake system in which the coach starts to slow a little is it also suppose to change the transmission gearing to a lower number or is everything suppose to remain the same in fifth gear?? Not being familiar with this type of braking system its a little confusing Also does anyone know what are the allowable engine speeds are for the 6 speed Allison before needing to down / up shifting?? Any help in this matter would be greatly appreciated
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Old 01-18-2015, 10:26 PM   #2
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Leave the engine brake on, descend and let the brake do it's work, if it slows you too much apply a little accelerator and let it keep the speed you want. Too fast? Back off and let it work. Don't try to outsmart it.
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Old 01-18-2015, 10:45 PM   #3
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Our current coach downshifts, our previous one did not. One had to use the transmission control pad to manually downshift to the appropriate gear on the previous coach.

On both coaches, the exhaust brake alone was not enough to slow the coach. We had to use the service brake, though A LOT LESS than without the exhaust brake. Our first coach was on an Isuzu truck chassis and the exhaust brake was amazing! It would slow the coach to walking speed on every decline we found.

I have read that the Allison will protect itself from over-revving and lugging, though I try to keep an eye on it as well.

Your exhaust brake may be malfunctioning, you may have not asked enough of it yet, or it may be functioning properly but by design or intention not interfaced with the transmission. Was it original to the coach? Do you have any paperwork for the exhaust brake?

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Old 01-18-2015, 11:03 PM   #4
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Usually they are set to preselect 2nd gear, both our Dutch Stars were that way, one with a CAT 3126 and our present ISC 350. I did have the CAT engined one reprogrammed to only preselect 4th and hated it. Traded it off before I had a chance to have it reset.
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Old 01-19-2015, 09:52 AM   #5
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Engine Braking

Thank you everyone, this a awesome way to get answers from fellow RVers who have the experience that I don't have yet. That's exactly what my M/H was doing shifting down to 2nd when I was deceinding on its own with the engine brake on I had never had that happen before, when I drove a gas coach I did it manually and had to watch the engine speeds. I have all so notice that gear 6 is more of a overdrive and 5 is more of a city type or standard drive gear, is that right? Also does anyone know what are the best speeds to down shift at and what are the RPM's / speeds to maintain when descending??
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Old 01-19-2015, 10:08 AM   #6
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Quote:
Originally Posted by Always-Going View Post
I'am a newbee to a 39' 2001 Tradewinds with a 3126 Cat engine and a 6 speed Allison transmission and I need some help in Useing the engine brake system. When you start to deceind a grade which is approximately 6 per cent in fifth gear and you apply the engine brake system in which the coach starts to slow a little is it also suppose to change the transmission gearing to a lower number or is everything suppose to remain the same in fifth gear?? Not being familiar with this type of braking system its a little confusing Also does anyone know what are the allowable engine speeds are for the 6 speed Allison before needing to down / up shifting?? Any help in this matter would be greatly appreciated
Always-Going
This video my be helpful:


And this info:http://pacbrake.com/exhaust-brakes-h...do-they-bring/

BTW, you don't have worry about the Allison...(it's "smart" enough automatically protect itself and your engine).
See this Allison information:
http://www.rvtechlibrary.com/transmissions/keypad.php
Mel
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Old 01-19-2015, 10:29 AM   #7
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You may need to Lube the Pac Break. Mine is just behind the left rear tires in the engine compartment. Here is a Doc on Lube Points. There is special oil for this but I'm not sure you need it.

Pacbrake Exhaust Brake Maintenance with Superlube

Dick
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Old 01-19-2015, 11:04 AM   #8
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Originally Posted by Always-Going View Post

Also does anyone know what are the best speeds to down shift at and what are the RPM's / speeds to maintain when descending??
There are two types of Engine Braking. One is called Compression Engine Brake and the other is called Exhaust Brake.

Not sure which one you are referring to so it's best not to confuse the two.

Here is a great article which describes how each one works.

Allison transmissions will not let you manually downshift until it has attained a safe speed to do so. You can manually select a lower gear BUT that doesn't mean the Allison will go there. The Allison's are smarter than their operators.

When the indicator pad states 2nd gear when using your Engine Brake, that is only an AIM point for the Allison. Once the coach slows to a lower speed the Allison will downshift automatically to the next lower gear until it reaches 2nd. If your speed increases it's up to you to reduce it with the service brakes.

It pays to know what your specific UP-SHIFT points are for your coach. When controlling descent speed with an Exhaust Brake it's best to keep the Allison in a lower gear such as 3rd or 4th. Once you hit 5th your coach will take off like there is no tomorrow.

When I am descending medium grades I keep the Allison in 4th gear until it reaches 52-53 mph. At 54 I know it will up-shift to 5th so I tromp on the brakes to reduce the speed 5-8 mph. For really steep grades I reduce my speed BEFORE the grade such that I am in 3rd gear doing 30-35 mph and have my emergency flashes on in the right lane.

Bottom-line, slower is better plus you will have more control of your rig and less shorts to clean up once you get to the bottom of the grade.

Dr4Film ----- Richard
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Old 01-19-2015, 11:23 AM   #9
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The allison will keep the engine rpm at of below 2600 RPM on a Cat engine if it is working correctly.
As stated above the allison will down shift working towards 2 gear when ever it determines it will not over speed the engine. Also as stated to lower your speed
brake hard a few times to get your speed down but DO NOT ride the brakes.
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