Does anyone have a real life comparison driving comparable weight vehicles with 3208 CAT engines, one with an exhaust brake and one without it?? It is my understanding that the 3208 cannot tolerate a great deal of backpressure (25psi) compared to later model engines (in the 55psi range). A lot of heavy Barths run the 3208 with no exhaust brake. Opinions anyone?
Thanks

The Allison AT542 and the AT545 transmissions without a torque converter lockup are not compatible with an engine exhaust brake. Before you go and try to hunt this down look at the info for the transmission.

If you put an exhaust brake on one of those you’re wasting good money. For the exhaust brake to work properly your torque converter needs to lock and hold to slow you down. You will also overheat the transmission on top of making your wallet empty.

The exhaust brake that came on the Roadway Express City units a few years back worked fairly well. Those were 3208T with I think a 5 speed stick. I have never driven an Automatic Transmission W/ the 3208 CAT so I can not comment on that.

I heard the same about backpressure as you did. The 3208 CAT could not handle as much pressure.

Bill N.Y.

Thanks for your insight Bill,
Barth_user1

Bill N.Y. any idea if the Allison MD3060 has this torque converter lockup feature? Doesn't seem to work with my pacbrake (factory installed) so I've never been real pleased with the braking performance of my 3116 Cat. Manual doesn't give much info.

Honestly... there's a lot that can go wrong with these.

Read this pdf file for procedures on what to check. Pac brake PDF file

The 3060 is a 6 speed automatic. I believe yours is a lockup style converter. If the PacBrake is an add on then it might not be equipped with the correct style lockup converter.

Below are several torque converters for your transmission.
Torque ..... Stall
Conver ..... Torque
Number ..... Ratio
________________
TC-411 >>> 2.71
TC-413 >>> 2.44
TC-415 >>> 2.35
TC-417 >>> 2.20
TC-418 >>> 1.98
TC-419 >>> 2.02
TC-421 >>> 1.77

Check to see if there's anything wrong with the PacBrake first. You'll want to check for a sticking or seized actuator or butterfly shaft. If it's electric or air check to see if it activates and moves to a closed (90 degree) position. Even if all looks right externally the inside of the PacBrake could hide a broken off butterfly or the inside shaft could be bent.

If the PacBrake seem right schedule an appointment with a certified Allison transmission shop to have the locup converter checked and the interface for the exhaust brake inspected and checked out. If it's been awhile since your last transmission service have that done too.

Bill, my Regency has 250 hp 3208T cat with an allison MT643 4 speed auto with a william exhaust brake. When the exhaust brake is on, and the air brake is used, the tranmisson shifts down. Does this transmission have tc lockup? sky

quote:

Originally posted by sky:
Bill, my Regency has 250 hp 3208T cat with an allison MT643 4 speed auto with a william exhaust brake. When the exhaust brake is on, and the air brake is used, the tranmisson shifts down. Does this transmission have tc lockup? sky

It sure sounds like it. The exhaust brake interfaces with the transmission control and downshifts at the same time as lockup.

The max RPM of the engine should not go above 300 RPM of max no load. If you floor the engine in neutral and the max no load is 2,100 then the exhaust brake interface should not allow you to go past 2,400 rpm while downshiffting and TC lockup.

Bill N.Y.