GM Tranny Bolt Patterns

[Shannen Durphey]

Steve Ochs wrote:

> Message text written by INTERNET:diy_efi at esl.eng.ohio-state.edu
> >Anybody know if the 3.8L Buick FWD engine and the 2.8L/3.1L/3.4L Chevy FWD
> > share the same bellhousing pattern? I thought so originally until I found
> > out that the Quad 4 and the 2.8L are different. So maybe the Buick is
> > different too.
> ><
>
> Boy, gone from the digest for two days and I miss a lot!!!  I wish I could
> have gotten into this discussion earlier.
>
> Here is the scoop:
>
> Rear Wheel Drive -
> There are two bolt patterns made, Chevy and BOP (Buick-Olds-Pontiac)
> Some transmissions came in both, some in Chevy only.
> The 700-R4/4L60/4L60-E came in Chevy ONLY until 1995 when the split case
> became avaialble.  All BOP applications used the THM-200-R4, THM-200,
> THM-250, or THM-350 until those trannys were discontinued (last was 200-R4
> in 1990).  That is why 3800 was not available in Camaro/Firebird until
> 1995.  In order to be more flexible including outside customers, a 2-piece
> case was designed for the 4L60-E.  The transmission housing is the same but
> the bellhousing can be replaced with different versions (like a manual
> tranny).
> All Chevy truck engines mated to the 700-R4/4L60/4L60-E (including 2.8L
> V-6, 4.3L V-6, & All V-8s) have the Chevy bolt pattern.  No adapters have
> ever been used with the 700-R4 tranny.
> <big snip>

  Sorry guys, but I have *got* to disagree.  That's one thing technicians and
engineers do. :)  I work on these things daily and I will say that 2.8 and 2.5
used in RWD does not have traditional Chev bolt pattern. I'll send photos if I
have to, but no way are they the same.  Original "Iron Duke" 151 has Chev
pattern, but not newer vers.  Trans is cast with different or dual type bolt
pattern.  Only other note that should be added is that the new rating system
for trans is broken down similar to following example.

4L80E trans:

4=# of forward gears
L= Longitudinal(RWD) (T is for Transaxle)
80 relative torque rating
E electronically shifted

Hope I didn't step on any toes.  :)
Shannen