Pontiac GTO Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
188 Posts
Discussion Starter #1
Title says the gist of it. Found a 71 3/4 truck posi rear end. And was wondering if the GM 4 and/or 5 speed transmissions can be mounted. I mean up to including early 1990s trannys and rear ends.
 

·
Former Super Moderator
Joined
·
9,919 Posts
GMC and Chevy trannys are going to mount to the engine with the wrong bolt pattern. You may be able to use an adapter plate. Rear end is going to be from a leaf spring with the truck to a coil spring and 4 link with the GTO, so unless you go with an aftermarket 4 link sub frame and links, I'd say no, they won't work without tons and tons of fabbing. Would be cheaper and easer to just get the parts that fit.
 

·
Super Moderator
Joined
·
5,789 Posts
Doesn't mean it can't be done, it's just going to be more difficult. If you want to fit soemthing badly enough, it can usually be dome somehow - it's just a question of how hard and how expensive it's going to be.

If you've got an idea you're passionate about, dont' let that stop you. :cheers

Bear
 

·
Registered
Joined
·
574 Posts
I took a rear diff out of a 89 GTA and cut all the brackets off of it and welded some spring perches on and stuck it under a v-8 s-10 blazer I used to have. Of course your idea is opposite. You would have a bunch of brackets to line up and weld on. It's possible. Just time and fabrication. As for a 4- speed Depends on the tranny. A m-21 is a m-21 doesn't matter if it's a chevy or pontiac or buick or what ever. As long as you have the correct bell housing they bolt up. Several after market tran's 5-6 speed that would bolt up with the correct pontiac bell housing too. Unfortunatly not all of it is cheap.
 

·
Registered
Joined
·
188 Posts
Discussion Starter #6
If I swapped in a newer Chevy 350 motor then I think a GM 5-speed would match up. Or is there a year cut off where Chevy 350s do not fit at all?
 

·
Registered
Joined
·
188 Posts
Discussion Starter #7
The Borg warner T5 seems the have the same four bolt pattern as Muncie. The shifter looks to be different however, is there a way to overcome that
 

·
Former Moderator
Joined
·
2,895 Posts
T5 won't last very long behind anything with enough power to drive through Mcdonalds...... And the GM 5 speed is mounted at an angle from centerline of motor (still perpendicular lol)with a specific bellhousing and boltpattern and is really just not strong enough. Why do you think GM only put them behind 305's and not the 350's? I would swap in a Muncie or a t-10 with a factory Pontiac bellhousing and all the linkage if you want a stick. A stickshift behind your 350 Pontiac with some sensible mods would make for a pretty neat little package. Back it up with a 3:55 rear axle and have some fun while you save up for that 400+ inch engine.
 

·
Registered
Joined
·
188 Posts
Discussion Starter #9
is there much difference between the Muncie M20, M21, and M22 besides the 20 being wide ratio and the 21/22 close ratio?
 

·
Former Moderator
Joined
·
2,895 Posts
All have 1 to 1 fourth gear, on the M21 and M22 the ratios are spread more evenly, the M20 has a larger 3rd to 4th gear spread.
 

·
64-67 Expert
Joined
·
8,569 Posts
The M-20 is the one to use with any gear that is 3.55 or less numerically. The M-21 has a taller first gear that is compatible with 3.90-4.33 rear gear ratios, but sluggish out of the hole with a more normal, street type ratio. I'd recommend a belhousing, but don't know what engine or vehicle you have.
 

·
Registered
Joined
·
188 Posts
Discussion Starter #14
I have a 71 lemans with a 350v8 and 350 3spd tran but I'm in the process of acquiring a 77 400 engine (auto)
 
1 - 14 of 14 Posts
Top