'57 Corvette transmission question

I've been tapped to overhaul a 3-speed manual box out of a '57 Corvette. I have not seen it yet and I am not having much luck finding any information on it. What box is it and who makes it? Anyone got a good parts source for it? Any help will be much appreciated, thanks!

 

Should just be a regular 3 speed Chevy tranny,nothing special just because it came out of a Corvette.

 

I'm not so sure - it's a '57 model - GM used a few different 3-speeds over the years. I do know for a fact the early ones (like this one) do not even have a synchronized 1st gear. I'm trying to identify it so I can check on parts. Is it a Borg Warner, a Saginaw or a Muncie? I have no idea. Whats the model designation? Etc.

 

I think I found it - GM SM318. Anyone know much about it?

 

Seem to remember those were Muncie but they also had a gear ratio change , don't recall if it was 1st or 2nd gear and there was a different extension housing to mount a floor shifter. Guts and bearings will work from a std. pass car though. I'd dig in my old Hollanders if I could remember where it is ! (darn oldtimers disease !)

 

The main differences I think were between the 6cyl and V8 models - the 6cyls got a lower 1st gear ratio and the Corvette models had a unique tailshaft housing - I THINK. I'm surprised how little information is available.

 

Muncie transmission.

parts book is here

http://chevy.oldcarmanualproject.com/

have fun!

 

The Corvette is a close ratio, different from passenger car. I just helped my buddy put one together, my first time inside a trans. I have a good source for rebuild parts. I doubt if you will find any gears though. I will look tomorrow night for the guy's card we got bearings and seals from.

 

Same bearings etc 55-64 . I killed about 3-4 sets of them close ratio gears back in the late 60s before I got smart and put in a Muncie.

 

Thanks for all the input guys - I already know this is a weak transmission, however it is original to the '57 Vette that it came out of - which it will be going back into once its overhauled. This will be a very high dollar restoration and the car will probably only rarely be driven and certainly never abused.

 

Actually there were three different gear ratios used in those old three speeds. Six cylinder cars had a 2.94 first, standard V8 cars had about a 2.54 first and Corvettes had a 2.20 close ratio gear set. As long as you aren't going to need any gears, there should be no problems. Gaskets, seals and synchronizer drum should be the same as used on standard passenger cars from 55 through 64. It's pretty much a piece of cake once the trans is out of the car.

 

I found them a PITA. The double row of needle bearings in the input are all loose. The closer ratio boxes required the cluster to be put in loose and then the input inserted. Good luck getting the synchro in the case. I have spent a day with that trick. The boxes were designed in the 30's and were not designed for the later gear sets.

 

Oh I figure I won't have too many problems with it as long as all the hard parts are still usable.

 

Muncie 318, the 319 was the same unit with a Borg-Warner R-10 overdrive attached. For parts, DriveTrain.Com. The only weaker 3-speed was the 54 and earlier units. The largest amount of damage comes with a reverse gear clutch dump; the whole cluster gear assembly comes out of the case taking some of the case with it; very weak support. Had friends who did that, I was always breaking 2nd gear in my 56, 283 equipped, hot rod. Butch/56sedandelivery.

 

So, on a high end restoration such as this, if you had the correct transmission, but it needed gears, and you decided to use a nice passenger car set instead of a worn out close ratio set, would this be something that the Corvette cork sniffers would ever check out and get their gold chains in a knot about?

 

The guy we bought parts from is Ed Hartnett at 610-623-9381. VERY knowledgeable, and helpful.

 

lol...I was waiting on someone to bring this up. I have also pondered that same question. Undoubtedly those vette gearsets for this transmission are rare as hen's teeth. If it has broke shit in it I would imagine its going to end up with non-vette parts in it. The real question is this....should I let the owner make this call or should I just fix it and deliver it a good working transmission to the customer? Chances are no one would ever know the difference.

I really hate those fart-sniffing corvette guys you speak of.

 

Thanks for this information fellas, I am sure it will come in handy.

 

The 348 3 speed transmission used the close ratio gears, probably the same, if I remember right they were the same transmission, just shorter tailshaft and tailshaft housing. I have some parts for the Corvette transmission, for sure the tailshaft housing with the shifter boss. Had a set of the close ratio gears out of a 348 car in my '56 Chevy in the '60s, had a 3.08 rear end, would shift from 2nd to 3rd at 110 mph.

 

Welp - its been just a few months since I posted this thread, but I have finally taken custody of this transmission. As it turns out it's a Saginaw and not a Muncie. I can find parts kits for the Muncies all day long, but so far I cannot get one valid return in a web search for these early Saginaw 3-speeds.

Looking closely at the parts kits that are sold for the "Muncies", the look to be identical. Are these transmissions the same?

The box I have has the following casting numbers on it:

Main case: 3845122 ('56 and very early '57)

Side cover: 3731911

Tailshaft housing: 3737460 (might be 3737450, can't tell for sure) If it's a 450, then it would be from a '60 model, but the owner claims this is the original un-molested gearbox from the car. I can't find any information on the 3737460 at all.

The date code is C297

The serial (stamped on the pass side rear face of the main case) is S404. "S" designates it as a Saginaw box from what I have read. Would be "M404" if it was a Muncie. This is what makes me wonder if they're actually the same gearbox.

Anyone?

 

The trans you have is basically the same design as most Chevrolet passenger car three speed transmissions from 55 thru 64. As long as no gears are required you should have no major problems. Why not rip it apart and decide what parts are really needed before you start throwing money at it, or describe the problems that the transmission has so we can help diagnose it.

A picture of the parts you need wouldn't hurt either.

 

I don't think it needs any parts to be honest with you. The owner just wants it "rebuilt". Probably the main shaft bearings, gaskets and seals is all it will get. Its in very good shape otherwise.

 

Here's some pictures of it:



Main case numbers:



Main case serial - there's actually an "S" in front of the 404, its just very slight. Didn't show up in this photo:

 

Big dilemma here; some guys SWEAR the early 3 speed is a Saginaw, some say Muncie. I say MUNCIE, because that is what ALL my books refer to it as, and the DriveTrain.Com site refers to them as MUNCIES. The Saginaw 3 and 4 speeds I'm used to had a 7 bolt side cover, all the shift levers (including the 4 speeds) were in the side cover (not like Borg Warners and Muncie 4 speeds that reverse is on the extension housing). So, I still say it's a MUNCIE 318, even though you're going to hear differently. I've even dealt with a very knowledgeable Corvette restorer, and he refers to them as SAGINAWS, even though I've given him all the info I have calling them MUNCIES. Look on the bright side, at least it's not a Dearborn! And it could have been in 66-67 Pontiac GTO's with the Dearborn (Ford) supplied 3 speed. Figure that one out. Butch/56sedandelivery.

 

Same transmission, everyone calls that one a Muncie. There was only one design back then, even if it was made in two different plants.

I did find the reference to the S vs. M in the literature.

 

Per "Corvette By The Numbers" by Alan Colvin, its a Saginaw 3 sp. The 3845122 maincase is correct for 55-57, and that particular case has a casting date of March 29, 1957 (C 29 7) and an assembly plant/date of Saginaw/April 4 (S404). Tailhousing should be 3737450, sidecover 3731911.

 

That's the problem, right there. We hot rodders don't do "by the numbers" restorations.

 

Thanks for all the input guys. This is exactly what I was also thinking.

I'm almost afraid to touch this thing. What if the tail housing falls off my bench and gets busted? I'll be SOL. lol

 

I'd sell you one if you really need one. Just picked up a complete trans this morning dated E 11 5 . Sometimes I hate myself for buying things that are hard to ship.

 

I will try to be careful. lol

I bought a kit for a 318 this morning. We'll see how it goes. All the parts look to be correct for this transmission.