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Old 09-30-2016, 10:08 AM   #1
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PAC brake problem

I have a 2002 38' with 400 isl motor. My PAC brake has started to work intermittently. After it stops working you can pull over and shut down for a few minutes and then everything is working fine. After it is working and you are on road it continues to work until you shut down then when you start running again it might be working or not. Any ideas.
Thanks Jack
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Old 09-30-2016, 10:58 AM   #2
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Jack,

First, let's confirm that you DO have an exhaust brake and not an engine compression brake. They are VERY different! The ISL is the only engine that could be ordered with either. Our 2003 had a two stage engine compression brake.

When it doesn't work, how far into the "process" does it go? Does the Allison shift pad change from "6" to you pre-select gear-- likely 4th or 2nd?
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Old 09-30-2016, 11:19 AM   #3
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It is a PAC brake not a jake brake but I think both are compression brakes. I have not looked a shift pad when working and when not working so not sure. I know when it is not working the rpm goes down to about 800 but if I turn the PAC brake off the rpm goes to about 1200 when letting off throttle. I talked to John at Cummings Yakima yesterday,he was involved in original set up with Alpine,and he disentangle have an answer
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Old 09-30-2016, 12:11 PM   #4
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Brett
It is an engin brake.
Thanks Jack
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Old 09-30-2016, 12:40 PM   #5
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First step is to verify that the Allison shift pad does change the indicated "go to" gear.

If not, the problem is in the "dash area" not the engine.
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Old 09-30-2016, 12:51 PM   #6
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There are two types of diesel engine brakes.
1. The Compression Release brake is a set of valves, one in each cylinder, that opens when the engine is at or near the top of the compression stroke to release the compressed air to atmosphere, causing a vacuum to develop during the unpowered power stroke. This vacuum causes the engine braking effect, and a tremendous amount of noise. This setup is commonly called a Jake Brake or an engine brake.
2. An Exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle.


Pacbrake is a manufacturer of emission valves, engine brakes and exhaust brakes serving the diesel engine industry. It is not a type of brake, as they make both and more. Jacobs Vehicle Systems, maker of the original Jake Brake, also makes exhaust brakes, and more.
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Old 09-30-2016, 01:14 PM   #7
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I will try to take it for a drive and look at the shift pad to see if it changes to a lower number. I know you can manually shift down but driving an Alpine for more than 14 years I have never done so.
Thanks Jack
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Old 10-03-2016, 12:33 PM   #8
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I had trouble with my engine brake on the ISL not working. It would downshift to 4 but really was not doing anything to slow me down. I found the rear wire was not connected and hooked that up - now have 1/2 of the brake working - there is no difference in braking between the low and high setting. I did wedge myself in there this last weekend and get a hand on the front wire - wiggled it and made sure it was connected. The short test drive back to storage seemed to indicate it's still only giving me half function.

It's really hard to even lay a finger on these connections, much less do any troubleshooting. The original owners of our coach had a pacific queen installed so removing the floor panel is very difficult. If you can remove that panel then access to the front connection would not be difficult.
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Old 10-03-2016, 03:34 PM   #9
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Brett
The shift pad changes to 4 when working and does not when not working. Took it for a drive today to see if the pad changed and it did wnen working. When I started the brake was not working so i manually shifted down on the shifting pad. After a couple times of manually shifting down without the brake working it started working magically so still a mystery. And it is a PAC brake not a jake brake. Thanks Jack
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Old 10-03-2016, 03:38 PM   #10
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Interesting--a PAC manifold exhaust brake on an ISL 400??????
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Old 10-03-2016, 04:06 PM   #11
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It is a 2002 38' with 400hp isl motor and a PAC brake 1 speed.
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Old 10-03-2016, 04:13 PM   #12
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The PAC brake was standard in 2002 the jake brake was an option.
Jack and Vivian
Graham Washington
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Old 10-03-2016, 05:10 PM   #13
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OK--mine is a very early 2003 [built Feb02] and looks very much like an 02. However, my 03 came with an ISL 400 and has a 1-stage Jake.......Another WRV mod.....I guess.
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Old 10-03-2016, 06:29 PM   #14
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My guess is you have loose connections on the dash switch.
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