The Stovebolt Site Forums The Shop Area Driveline GM 4 SPEED?

Not quite sure what my Bro. brought by, but it looks to be a cast iron 4 speed that needs a little TLC etc. etc.. I did so happen to get a couple of numbers off the side cover is ( GM 6261886) Tailshaft housing is (6281884) front bearing retainer (1) bar GM (3859093) Housing on machined part # N107667. Hopefully these here numbers can tell me what this here trans came out of and what manual I will need to rebuild it. Thanks.........

Hey if it’s cast iron has a 7 bolt side cover 3 shifter shafts that’s a Saginaw, there are 4 different ones. On The input shaft there are rings ground around the shaft. It goes 0 rings 1 ring, 2 rings, 3 rings. And this will tell you what the gear ratios are. I just rebuilt one for my 55, it’s easy. You can get a rebuild kit on line for under $100. You find info on the numbers online, I was looking then figured it really doesn’t matter. Thanks keep on truckin

A picture would help. You didn’t state if it has shifter sticking out the top or on the side, which would be what Paul, above, mentioned. GM used SM-420 and SM-465 4 speeds with the shifter sticking out the top, both good, both have parts available. 465’s come with long and short input shafts for 13, 14” clutches and 11 and 12” clutches.

Ed

Well the trans. is a side mounted shifter. Basically it has 2 rings on the input shaft and has the 7 bolt holes in the side cover. I just need to know where did you get your rebuild kit and manual or book you went by to tear it down and back together, It is a 4 speed, I had forgot to metion.. Thanks for all the help.....

You have a Saginaw 4 speed. It was used in late 1970's and 80's GM pony cars like the Chevy Vega, the OHC six Pontiac Firebird, and a few other mid-size GM factory hotrods with 4 and 6 cylinder engines. Any factory pony car service manual from that era should have repair instructions, and there are a bunch of them available at reasonable prices on Ebay. It's a weak sister compared to the earlier Muncie trans, even though the Muncie had an aluminum case. A former GM research engineer I worked with in the Tennessee state trade school system was on a team that tried to beef up the heat treating of the gears to work behind high horsepower V8's, and they didn't have a great deal of success.
Jerry

I had good luck with the folks at "The Gear Box" they are located in South Carolina. They carry many hard to find parts for GM 4 speeds, Muncie and Saginaw. They supply parts for many other brands as well, they also have literature available.

https://www.thegearbox.org/saginaw-3--4-spd.html

Ok now that we have determined the trans. that my brother brought by seems to be a little week for his 1/2 69' chevy pickup with the 350' in it, what 4 speed with the side mounted shifter would be recommended? We don't want a 3 speed and don't want a 4 speed with the shifter on top with the granny low. I am not sure what his rear gear ratio is? Thanks...

If he doesn't hotrod it, the Saginaw will work. It's got a direct drive 4th. gear, which will work best with a rear end ratio somewhere in the 3.40 to 3.70 range. A 3.55 would be just about ideal, unless he's planning to do something stupid like run extremely tall (or short) tires. Just don't do any kamikaze launches like revving up the engine and side-stepping the clutch. I've seen people get away with using a T-5 overdrive transmission behind some pretty healthy V8's but that's really pushing the envelope!
Jerry

Hmmm. Surprised no one mentioned a m20 or m21 mucie 4speed? About as good as it gets for hotrodding and abuse. Opps just read through again. Hotrod lincoln touched on it....

Those were good transmissions- - - -40 years ago or so. We ran them in 1/4 mile dirt trackers behind some high-revving small blocks and abused them terribly. A 1.88:1 2nd. gear against a 4.56 rear end gave an 8-something final drive ratio, and the box got hammered with full throttle several times a lap. The problem now is finding one that hasn't been blown up and rebuilt several times. About the only tougher transmission was the MOPAR "rock crusher" 4 speed that was used behind their high HP big block engines. Those boxes are even harder to find these days than the Muncie.
Jerry

Muncie's are out there if you look and parts are available from a number of suppliers. The price is driven up because of the collector car market and everyone wanting to be numbers matching. If your just wanting a good 4 speed the Saginaw will hold up very well as long as you do as Jerry says and not abuse it too much. I had a friend in school with a very nasty 67' C10 with a 327 backed by a Saginaw, a lot of folks lost money to that truck.

It is a 1/2 ton with a 6 ft. bed hopefully with a full load of firewood back and forth through the hills should not be a problem with the Saginaw? He does cut a lot of firewood.

Maybe a ¾ton or bigger might ba better option if wood hauling is his main goal. Bigger brakes and suspension to boot....

I wore out a clutch once a year on a late 60's Ford F-150 1/2 ton with a 302 V8 and a 3 speed. Fortunately it had a "lifetime warranty". I think it cost Auto Zone 3 of 4 clutches before they started refusing to replace them! Just because I had the bed full of wood and a 16 foot trailer piled high- - - - -why did the clutch keep burning out?
Jerry

I have to share this...... I have been hearing every older guy tell me how weak saginaws were and how they tore up 10 before they put a super T10 in or a auto. When i built my turbo LS drift car on a budget I scored a cheap/free saginaw 4 speed with a shifter and bellhousing. The car made 535/540 tq for a full 2 seasons and never broke with that setup and let me tell you I was shifting that car sideways off the rev limiter every day. I pushed the car farther with a built 6.0 LS and the trans finally exploded at 643hp 713 ft lbs. I then got ANOTHER free one and ran it for about 3 months and it then exploded again so I ended up putting a T56 in the car.

Moral of the story is they are way stronger that everyone says. I feel like everyone online has “heard” of them breaking from someone else that “heard” it online somewhere. My buddy has one behind a 5.3 LS in a 2wd c10 with no issues for years and he hammers it around town pretty good. So dont be scared.

Thanks for the replys, there Bolters, need to get me a service manual for it now? I looked on line and didn,t see one, I'll keep looking....

The Saginaw four speed is plenty strong as long as you are not doing big giant holeshots, slicks, clutch dumps, dry burn outs. Here is the thing. They are a nice simple trans to rebuild. Yes you can get a rebuild kit for under a hundred, but spring for the better kits with the forged syncros. About 120. Also, and this one you will want to beat the bushes for, get a new pair of shift forks. One of the forks is used on both the four speed and three speed and so is pretty easy to come by new. The other is four speed only so that one is a little harder to do.

I paid 250 for my 2 groove sag. (3.11 first gear and its a ball, gets you going from a stop and no its not too low at all. Stock 50s three speeds generally were in the range of 2.94 first gears so pretty close). I paid 120 for the rebuild kit, a few dollars for degreaser, anaerobic sealer, probably another 140 for new forks, and a few dollars for paint. So I have like $550 into a fully rebuilt four speed. That is pretty hard to beat compared to the cost for a rebuilt muncie or BW T-10 or something of that nature.

Hurst still makes an installation kit if you want to use a Hurst shifter, otherwise the factory shifters will do. Its not a terrible choice for a transmission if you are trying to be careful with the money.

Sounds Bueno, need a service manual, and I will be on my way, Thank you....

Here is a link for a Pontiac service manual, it covers the basic Saginaw 4 speed. You can print this.

http://ronspontiacpage.com/1968PSM/pages/7C.4.speed.saginaw.manual/7C.001.html

I did dry pavement clutch dropping rev limiter burnouts with mine every day with well over 500hp getting smashed through it. Only reason it probably lasted so long was it was in a 3150lb car on a 245 tire so it was up in smoke no mater what😂

Thanks for all the help there Bolters...᠁.

Never had much luck with saginaw 4speeds. One good speed shift from first to second would usually break it

They were not designed to be speed shifted from the start!

Ed

Respectfully disagree Dragsix, about the only bad info I have seen you give. I have rebuilt many of these aluminum models and cant say anything redeeming about them, sorry. They have the lasting ability of a 16 year old boy on his first date.

Had one of these pos in my factory cosworth vega and it couldnt even take the torque of a 140 cu inch (115hp)four cylinder motor. Complete junk transmissions that one should think twice about before putting in their stove-bolt truck.

I understand, I do, but I ran that cast iron Saginaw down the drag strip I cant tell you how many times between 2015 and 2017 behind a 261 without a single hic up. It was what I could afford at the time and it turned out to be very reliable. You just had to be easy with it. Like I said, no burn outs, slicks, big tires, dry hops, speed shifting, and other abuse. I replaced my sag in 2018 with a Muncie but my son is going to use the sag in a 57 car he is rebuilding. For an inexpensive traditional four speed it really can’t be beat $ wise. If you want to engage in abuse, it is not going to be the trans for you. But for everything else, it’s a pretty good choice if you are trying to be careful with the bread. Frankly, it was installed behind hundreds of thousands of vehicles over the years and provided dependable service, as long as it was not abused.

People break t56 transmissions at less than 300hp everyday. Its pretty easy to yank it into gear and “break” it. Yet in stock form they will hold over 800ft lbs all day long. Usually its a clutch or driver issue. My saginaw 4 speed was speed shifted behind a beastly powerplant and never broke during a shift but rather when the power came on rolling into it with tons of torque in a turbo setup. If your clutch releases clean and your shifter is set up right it should have no issues. I wish my T56 shifted as good as my old sag 4 speed. I have a video on my phone of how i treated my 4 speed but i cant really post a vid on here. Mabey i will put it on YouTube and link it.

Here ya go. Drove it like this everyday for at least 2 years and drove it to and from drift events and ran it on the tracks all day long with no issues.
Saginaw 4 speed beat down