Gasser HotRod Forums banner

Saginaw 4-speed rebuild help

31K views 28 replies 8 participants last post by  1937Austin 
#1 ·
Anyone have any tips on rebuilding a mid '70s GM 4-speed? I have one and want to put it in my '55 but want to go through it first. Kit's appear to be real cheap.

Are there any parts that should be replaced regardless? It looks like the input shaft is one of those. Are there any resources (books) that I can follow to do it right?

Thanks in advance,

Mike
 
#2 ·
Boy, it's been a long time since I thought about the saginaws. One thing I remember is replacing the front wave spring washer (???? can't remember the actual name of it) with a torrington bearing. Some thing about the washer breaking and causing too much play??? One other thing that I was always going to do on the 4 speed Saginaws was, find an OD unit off of the 3 speeds and put it on the 4 speed to make a 4 speed overdrive. It's a bolt on addition but there was something about an actuation pin or something that had to be modded or?? I'm sorry for the lack of info. It has been 35 years since I thought about this. There should be info out there on GM boards etc. I remember them saying that the addiditon of the torrington bearing increased the strength of the Saginaws a lot. It was a major weakness. I hope the info helps and you can figure out what to do with. Mark L
 
#4 ·
Oh great! Maybe I'll stick with the 700r4 until I can afford a TKO 500 or T56. The last thing I want to do is put it together and break it on the first run... I guess I need to do more research.

Balloon deflated... :(
 
#7 ·
Why not an M-20? Isn't it stronger than a T-10? Here's a craigslist for an M20 wide ratio. http://portland.craigslist.org/wsc/pts/2446771550.html

I thought that M20s were wide ratio, M21s were close ratio, and M22s had straighter cut gears for more torque. It seems like a decent deal for a good trans. I did some research online and couldn't find any structural differences between an M20 and M21 other that wide and close ratio. Is there a torque rating for what these trannys should take?

Mike
 
#9 ·
When picking a M20, try to get one with a 1" counter shaft. The early 7/8" counter shaft trans are the weakest ones. But if the price is right, it'll suffice till you can score a better one. Still better than a Sag or T10 in my opinion.
 
#10 ·
After doing a bunch of reading about Muncies and decided on a M20. I found that the close ratio works best with 4:56 or lower gears. I have 3.73s. The lower 1st gear 2.56 instead of 2.20 makes for quicker starts with the 3.73 gears.

I picked up a M20 - wide ratio from '64-'65 - 7/8" shaft. It came with a Competition Plus shifter and the price was right.

The guys at Garage Motorsports said that this will handle the 400 HP no problem. I got the parts to rebuild it and will decide when I'm in it if I'm going to change it to a 1" shaft. They even got me updated synchros (late style) and the collars that go over the hubs that keep the tranny from popping out of gear when decellerating.

I will go through the shifter also.

Can't wait to get into it.

Mike
 
#11 ·
Mike. If you do a rebuild, would you do a project type thread either in projects or in this transmission section so we can all see and learn about doing the rebuilds. My first car was a '55 chevy with a transplanted 348, three carbs and solid lifters. It also had the early weak 3 speed trans. I'd blow that sucker every weekend and end up rebuilding or replacing it on Mondays. My old back yard is probably still full of the needle bearings that fell out. But that was 1968 and I've not had a manual trans apart since then. Would be great to see it again. Mark L
 
#14 ·
Hey hey! One of the last pieces of the puzzle. I have a scoop coming, too! (Thanks Jeff from trifive forum) looks like this :


Soon, soon, I will be able to put it together...
 
#17 ·
Well you will finally have a good Pontiac race part on your Chevy. Now it's gunna go fast. That is an early Ford truck air scoop from their big trucks. Pontiac bought them from Ford for their Super Duty Pontiacs in the early '60's. 8^) Mark L
 
#18 ·
I think I hurt my M20 today. Pulled a couple really good holeshots and now there's nobody home where second gear should be. I won't be able to pull the side cover off till tomorrow sometime. This should be interesting.......
 
#19 ·
check the mid plate, i was street racing back in the late 70's and pulled a hard 1-2 shift, blew the bearing out of the mid plate, broke the drivers side axle, and broke two rocker arms all at the same time. the 70 mustang 351C with N2O, i was racing flat towed me home that nite !!! ( I had him till it broke).
 
#22 ·
Well, it's nowhere near what I expected. To start off, the pin that the shift fork detent "scissors" pivot on in the side cover was laying in the bottom of the case along with the detents. Plus, I managed to shatter all three of the 3-4 hub keys and split 4th gear synchro into two pieces. All in all, a relatively easy fix. While I'm in there, I'll throw a bearing and seal kit in it and upgrade the sliders to the torq-lok style.
 
#23 ·
^^^ At least you are (were) banging the gears! I can't wait.

I got a kit to rebuild my M-20 a few months ago but haven't had time to put it together. The trans had been rebuilt before - and not very well. They used the wrong synchros and the forks are shot.

So I got a new input shaft, forks, and all the bearings/seals/gaskets/and the correct synchros. Also picked up the torq-loc hubs.

My case is an early one (7/8" shaft) but I told them what I was doing with it and thye thought it would be just fine.

Any tips to for me?

Mike
 

Attachments

#24 · (Edited)
Mine is a 7/8" case also. I knew I was gonna break it sooner or later. Did you upgrade your slider hubs to the newer style, 1" narrower hubs with the thicker synchro's?

Oops! Just looked at the pic of your synchro's and answered my own question. Lol!
 
#28 ·
I had a '72 Firebird Formula 455 with the 455HO. It also had the M22. I can't tell you how many "car guys" informed me that the front bearings were going out because of the loud whine. I remember after telling one old guy (Geezz, I just remembered that now I'm older than the old guy was back then--geezzz!!!) that it was a heavy duty straight cut gear transmission and it was built that way for strength, that he called me, basically, a dumb ass because no car company would ever make a noisy transmission like that on purpose. I loved it. Mark L
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top