Allison 5sp: Goodwrench (Dumb Question)

AKlowriderZ71

New member
May 14, 2012
719
0
0
Wyoming
Mechanically, how does the 5 speed become a 6 speed by swapping the valve body & TCM? How does it not need different or more hard parts as well?

I used to work in GM dealer service depts, and I remember GM having a procedure for converting the 5 speed to a 6 speed. But nobody ever asked about it & I never looked into it back then.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,681
5,835
113
Phoenix Az
The 5 speed always had the possibility of a 6th gear, it just needed a way to apply it


Sent from my iPhone using Tapatalk
 

Mike L.

Got Sheep?
Staff member
Vendor/Sponsor
Aug 12, 2006
15,681
232
63
Fullerton CA
Reprogramming a 5 speed TCM for 6th gear and using a 6 speed valve body can be problematic because the solenoids are different. The adapts don't like working with 6 speed solenoids. Plus, there are no adapts programmed for 5-6 upshifts and 6-5,4,3...downshifts. There can be tie ups along the way.
 

mike diesel

I'm alright.
Sep 6, 2012
4,005
0
36
SLC, Utah
Mechanically, how does the 5 speed become a 6 speed by swapping the valve body & TCM? How does it not need different or more hard parts as well?

I used to work in GM dealer service depts, and I remember GM having a procedure for converting the 5 speed to a 6 speed. But nobody ever asked about it & I never looked into it back then.

The 5 speed has always been a 6 speed but only 5 gears are enabled in the tcm and valve body.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,681
5,835
113
Phoenix Az
That looks like a girls hoodie. Real tight in the waist. If I remember, james has a beer belly.:roflmao::hug::D


Wha?! Come on now, I ain't even broke 175 yet! Lol. You need another daiquiri


Sent from my iPhone using Tapatalk
 

sickdiesel

New member
Apr 22, 2010
1,019
0
0
I used to hear that but never have seen it for myself. Without the valve body change im not sure how that could be. Unless they built 6 speeds with only 5 spds available?

ya, we have done a few of those with success. Makes it nice to be able to do that quickly in the tuning and not have so swap out any hard parts.