OVERDRIVE SWITCH

RKB'S HD · September 22, 2002

JUST READ ON THE ALLISON WEB SITE THAT THERE IS SUPPOSE TO BE A OVERDRIVE DISABLE SWITCH AVAILABLE

FOR THE ALLISON TRANS, HAS ANYONE HEARD OF THIS OR KNOWS OF A PART #?

Woody1 · September 22, 2002

GM makes it available for motorhomes only. You should read further. Says so on that same websight. Not trying to be snotty or nasty here.

bluenote · September 22, 2002

GM makes it available for motorhomes only. You should read further. Says so on that same websight. Not trying to be snotty or nasty here.

Actually, this is incorrect.

You can now install an OD lockout switch on the Allison 1000 tranny in our Chevy and GMC trucks. You need to have the latest computer updates to your tcm to allow for this switch to work, and then there are a small handful of parts you'd need to get. The dealers can do this for you, however, many people have done it themselves. Read through the following thread from The Diesel Page forums. There is an explanation of what you need to do for the OD lockout switch.

The Diesel Page

Woody1 · September 22, 2002

I stand corrected. Just read it, think i will keep mine stock for now. Question tho.....It mentions getting the latest updates done. Mine is on 2nd transmission(replaced under warrenty) . What does this update do? What does it include? Mt dealer doesnt have a clue as to what it contains. Says it has to do with "busy shifting". Thats all he knows. Have contacted local Detroit/Allison dealer to see if he knew, said he was gonna check into it and get back to me. Well, that was 2 weeks ago.

DMAX Daddy · September 22, 2002

2003's have this switch at the end of the gearshift. Hold for 2 or more seconds lockouts out OD. Tapping it momentarily still is tow/haul toggle.

bluenote · September 22, 2002

What does this update do? What does it include?

The update includes, among possibly some other things I haven't heard about...recalibration to improve shift busyness when using cruise control, recalibration to improve 2-1 harsh shifting issues, recalibration to improve engine idle surge issues, and of course, the ability to now install an OD lockout switch (which is standard on the 03's as mentioned). I had a reflash on my '01 in November of '01, and then the latest update in June of '02. There is a definite improvement, IMHO. I'm toying with the idea of installing the OD lockout, but haven't taken the plunge yet. I'd suggest that anybody driving the D/A combo, or even the 8.1/Ally combo should go over and check out the forums at The Diesel Page. There are lots of very knowledgeable people on the site, and the info shared in the forums is invaluable.