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Lloyd T · 05-29-2023, 08:05 AM

Roadmaster R2900 Engine Cummins ISC 315 8.3L Engine CPL# 2092 Engine Ser # 45856593 ECU 007NM Cal # 29529429 Allison Transmission ID from tag on LH side of Transmission Model MD3060 E002578 S/N 6510209330 99F02 TID2

PacBrake cyl broke supports ends. I wired it open to drive 2000 miles. Replaced cyl new. Now when driving in 6 gear, turn eng brake sw on. Coast, down shift from 6 to 4. and not feeling any exhaust restriction. Before I felt eng braking in any gear and no down shift. What went wrong. Thanks for your help. Lloyd

wolfe10 · 05-29-2023, 08:13 AM

OK, before this happened, when you engaged the exhaust brake, what did the Allison shift pad window do (change to 6th to XXX OR stayed in 6th)?

Common for transmission ECU to be programmed for a downshift to/toward a lower gear with 4th and 2nd being common choices, though any gear can be programmed in.

Have you manually verifed that the butterfly valve will open/close? Yes, the "return to open" spring is strong, but you should be able to move it with a vice grip, etc.

You can also tie a string around the arm that activate the butterfly valve in the exhaust brake to see if the valve is closing.

jacwjames · 05-29-2023, 09:33 AM

Were you lubricating the PacBrake on a regular basis prior to the cylinder braking??
You said you had to tie the PacBrake back to finish your trip, unless I'm mistaken there is a spring the forces the butterfly valve open, the air cylinder actually closes it.

I would check the butterfly valve on the PacBrake and make sure it is free, they sometimes hang. You should be able to take a large vice grips and clamp in onto the end where the cylinder attaches and move the butterfly valve.

I lubricate mine a couple time of year by using the high temp lube sold by PacBrake. Every couple years while I'm lubricating mine I detach the cylinder and fully move the butterfly valve and it moves free.

Lloyd T · 05-30-2023, 08:34 PM

I don't think the trans pad did anything last year. I do know that at 60 mph I turned sw on and let off fuel pedal I could feel engine breaking and no down shift to any lower gear. The anchor end of cyl broke. So exhaust pushed to valve completely closed. Stuck closed. No power 800 rpm max. Wired it open to get home. The spring is inside cyl. The valve works freely. No tension. Yes I'v lube the valve shaft.

Lloyd T · 05-30-2023, 08:38 PM

Who and how do they program the transmission ECM to change or eliminate down shifts? What could I have done to make that change? I store inside with batteries disconnected during winter. I keep a battery maintainer on the batteries.

Lloyd T · 05-30-2023, 08:40 PM

Is there a computer program that I can use to do the down shift eliminate?

Thanks for all the help. This is a great source of good useful help. Thanks so very much to all. Lloyd

jacwjames · 05-31-2023, 06:11 AM

I'm not sure if it is an Allison TCM or Cummins ECM software change. Each has a special computer software system to access the programming.

Only advice I can give is to call an Allison shop and ask them and find out the price. If they can't do it call a Cummins shop and get a price.

wolfe10 · 05-31-2023, 06:15 AM

Quote:

Originally Posted by Lloyd T

Is there a computer program that I can use to do the down shift eliminate?

Thanks for all the help. This is a great source of good useful help. Thanks so very much to all. Lloyd

Yes, an Allison dealer or someone else with the Allison "programmer" (sorry, don't know their name for their device) can reprogram the exhaust brake pre-select gear to anything you choose. I had mine changed to 5th.

I guess, with an electrical diagram of the exhaust brake electrical circuit, a knowledgeable electrical tech could bypass the Allison ECU-- past my pay grade.

Lloyd T · 05-31-2023, 07:22 AM

Thanks I’ll look up the wiring diagram and study it. 5 gear programmed sounds much better. I can always touch the down arrow on trans pad.

RoadTrip2084 · 05-31-2023, 08:16 AM

Quote:

Originally Posted by Lloyd T

Thanks I’ll look up the wiring diagram and study it. 5 gear programmed sounds much better. I can always touch the down arrow on trans pad.

Keep in the mind the PAC brake is most effective at higher engine RPMs, hence the default to 4th gear to kick the RPMs up to the high side.

Cav 6 · 06-07-2023, 03:16 AM

Is this conversation about engine brake or Jake brake? My 2003 Dynasty has a Jake brake that requires the use of a foot pedal to activate.

Happycarz · 06-09-2023, 07:58 PM

Exhaust brake

Lloyd T · 06-11-2023, 05:48 PM

still working on problem. I hope to stop by and talk to a Cummings Tech next week. Thanks for help.
Lloyd

DaveLamar · 06-16-2023, 11:04 AM

I am a cummins tech and have a similar motorhome with the same engine.
Your exhaust brake butterfly must be seized. I know mine is. when air is apply to it it close the butterfly in the exhaust stream. Since your cylinder broke I am assuming the butterfly is seized. you will most likely have to replace the whole thing.