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Old 03-22-2021, 03:20 AM   #1
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Join Date: Jun 2020
Location: Long Beach, CA
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Year: 1998
Coachwork: Blue Bird
Chassis: TC2000, 40' MPV
Engine: 5.9 Cummins/B300 trans
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Exhaust brake question

My bus ('98 5.9 12v) came with a professionally installed Pacbrake system, https://pacbrake.com/product-lines/exhaust-brakes/. It doesn't work any more (yet). I've downloaded and read the manual and found that the main valve may be stuck open due to lack of use/maintenance. This whole idea of blocking the exhaust to slow the bus seems as though it could cause engine damage or head gasket issues. I know diesels run a fairly high compression rate but are these systems safe to use? Is this worth pursuing or should I just move on?
Thanks for your help


https://www.dropbox.com/s/e0u3dwmktb...brake.jpg?dl=0

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Old 03-22-2021, 04:38 AM   #2
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They are safe in the respect that I've never heard of an exhaust brake causing engine damage. They're also safe if you know how to use them correctly but incorrect usage can be dangerous in terms of vehicle stability and handling. All it really does is use the engine compression against itself which created drag instead of torque so you're forcing your drive wheels to slow down without taxing your brakes. This is why they're so common on big trucks so long as they're used appropriately they're a great benefit.
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Old 03-22-2021, 10:57 AM   #3
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Year: 1991
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Check with Cummins. Some engines require stiffer valve springs to work properly (mine was one of them) and must have a way to lock the converter. In the end I decided to just replace the Allison with a retarder model.
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Old 03-22-2021, 11:03 AM   #4
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The Isuzu NPR chassis I chose to power my Skoolie came with an exhaust brake. It allows me to select brake or no brake. I've found it very helpful in slowing the bus from road speed --especially when towing the Toad. When engaged, the braking effect automatically shuts down at 30 mph which relieves the exhaust back pressure and keeps the engine from stalling which could cause safety issues because a stalled engine won't provide power steering or vacuum generation for braking.
Jack
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Old 03-22-2021, 11:13 AM   #5
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Year: 1991
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I’ll concur with ol trunt. I have a 74 Dodge powerwagon with a NPR 3.9 engine with the exhaust brake and it is helpful to a point. The higher the RPM the better it works. It is a lot better than nothing. That said it is not a Jake brake or Allison retarder.
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Old 03-22-2021, 11:45 AM   #6
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Join Date: Jun 2020
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Year: 1998
Coachwork: Blue Bird
Chassis: TC2000, 40' MPV
Engine: 5.9 Cummins/B300 trans
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Thanks all
I guess I'll get after fixing it. I can pop a valve cover and check the springs. I have every reason to believe that they were installed with the unit. The original owner spared no expense on this bus. I have the 5.9 12v in question and they emphatically state the exhaust springs need to be changed and they come with the kit. This pneumatic flap valve on the other hand is tough to get to, I can't see the top of it from above or below. I may have to take it in to be serviced.
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