Originally Posted by Mr_D
Allison calls that change from 6th to 2nd as a "preselect", meaning the trans is told to aggressively downshift to 2nd as fast as it can without harming the engine or trans.
BTW: on both a CAT 3126 and Cummins ISC the governed RPM is different under power then exhaust braking conditions. I've verified this with both Cummins and CAT over the years. On the ISC the under power RPM is 2,200 and with the exhaust brake active (not just turned on) it's 2,400.
I have posted this elsewhere but U may have missed it for the operation of the exhaust (PAC) brake.Not sure if it will work for the jake engine brake. We have put on over 4000 miles of comfortable driving since the modification.
Here is the setup for the PAC brake, on all the time, but able to coast when letting off accelerator.
let up on pedal and coast, trans will not down shift and PAC will not operate, the dash light will
on. Press on accelerator pedal to continue. Going down hill vehicle will coast unless you wish to slow
To Slow down - Depress brake pedal and relay will make contact and activates PAC and Downshift
If ready to continue acceleration simply depress fuel pedal and PAC will release till next event.
If you were in cruise then depress fuel and pull the cruise switch to resume previous speed.
Alternative is to depress the foot switch (optional) and will return to normal PAC operations.
Normal may be preferred in some traffic conditions.
The computer will not allow your rig to have both brake and fuel at the same time.
This arrangement is for a 99 Freightliner Winnebago and may not function the same in other MH.
(created by Jerry Donofrio, 99 Chieftain, Willingboro, NJ 6093515172)
relay = simple low current single or double pole.
Foot switch= old fashion hi low beam switch
Both found in most automotive stores.
below is the diagram