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So I wanted to tie this topic off.
My exhaust brake hasn't worked since I bought the coach - well it kinda did but was operating backwards to what it should. Now, my TCM is very old - like pre '95 - and I called John at transmissioninstruments.com and talked to him on what I'd done to diagnose the problem (for like the last 2 years) - the guy is VERY smart on the Allison TCM/ECM (he told me he's repaired over 2700 TCMs himself) and after talking to him I cut a wire on the TCM harness and wired in a LED to positive and "watched" what the pacbrake control wire was doing. It was operating opposite to everything I read.
I called him back, talked to him some more, reported what I saw with the LED and finally sent my TCM (push button tranny control and TCM combined) to him for repair. He emailed me and said it was operating correctly for it's mfg date. Seems around '95 they changed the operation of the TCM and my TCM operation was not how the VIM was wired - every doc I found showed it wired the wrong way. He attached a "wiring supplement" that I hadn't seen (attached) that said on this particular TCM, move a wire in the harness from D2 to E3. We did this today and FINALLY the exhaust brake works as designed - YAY!! So move one wire and done (+2 years...).
Best I can tell, my TCM was replaced sometime in the coach's life with an older one than was original and now the wiring was wrong on the VIM. I guess after they replaced the TCM they couldn't figure out why it wasn't working and gave up, using the exhaust brake manually or not at all.
I hope this helps someone else that has the same problem I did - plus you have John's website for help.
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Rick and Larrie Dee
1997 40' Newmar London Aire DP CTA 8.3 (Mechanical) 325 Spartan MM
Bringing her back to her glory.
'08 Jeep GC Overland.
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