The Stovebolt Site Forums The Shop Area Driveline 1953 3100 3-Speed Transmission Rebuild

Hi
I am looking into doing a rebuild on the transmission for my 1953 Chevy 3100. It's the original 3-speed (I believe it's called the SM420) and is running/working, but needs new synchro rings and I have sourced a place to buy those: Syncro Rings

I have found gaskets at The Filling Station also, but I'm wondering what bearings I need. I'm a little confused on that. Any help would be appreciated.

One other thing that may help some people working on these, I found a couple of great disassembly/reassembly videos on YouTube that I wanted to share:

Disassembly

Assembly

Thanks in advance!

Hello, mattconrad5150

If you are working with a 3-speed, it is not called an SM420 (which is a 4-speed transmission). Internal parts and most gaskets/seals for are different for 1953 truck 3-speeds and 4-speeds.

http://chevy.oldcarmanualproject.com/chevyresto/53153.htm

Your transmission's model code/name/number might be SM318 (but I am not sure about that for the enclosed drive-shaft 3-speed)?

Thanks for the correction; SM318 got it! I'll search around and see what I can find.

I found this rebuild kit, which has the gaskets and bearings included for a pretty great price. If this works, I can just buy the synchro rings from The Filling Station and I should be good to go.

Any opinions on this rebuild kit?

SM318 Rebuild Kit

If the transmission has a lot of miles on it, please check first gear carefully. First gear isn't synchronized and I've seen many these having first gears with broken teeth or teeth worn at rough and jagged angles from people forcing them when they should have been a little more patient. Also if your truck spent time in a mountainous area, first gear might have been used frequently as a downhill brake and this will eventually cause first gear to wear very oddly over time. The last one of these I repaired howled like a jet engine and would jump out of first unless you physically held the shift knob constantly. Good luck. Wade's Transmission and Gear in Dallas used to be a great source of gears and parts for these. They're still in business but I don't know about their supply of old stuff.
Jon

In 1953, the three speed received an upgraded clutch gear with 2 sets of needle bearings in the clutch gear. This was to cure popping out of third like earlier transmissions had, so it is a good transmission for a rebuild. I have personally rebuild 2 of these and it was pretty straight forward. Like it was said before, check first gear if any teeth are chipped or worn bad, it can be purchased on ebay, still available. I have used the second and third synchros that you are referring to and they worked just fine. That rebuild kit is the one I used too. Second gear is constant mesh so if the gear is worn and you replace it without replacing the counter gear, you could pick up a little bit of gear noise in second, but second is pretty whiney anyway.

I am having popping out of third problem also bought used trans used 2 to make 1. Now looking for part numbers for gears inside the transmision pictures breakdown. I see parts on eBay but is there a source for new? One stop shopping? Mattconrad5150 did you get yours working right?

Dave Waugh in Santa Fe Springs, CA rebuilds those transmissions and has parts.
Waugh Transmissions
11965 Rivera Rd.
Santa Fe Springs, CA 90670

562-693-0855

Good guy & fair prices

Fred

Thanks Fred I’ll check it out!

I am glad to see that the synchro rings are available again. The complete synchro drums are getting very hard to find and are very expensive. 50 years ago rebuilding the synchro drums with new rings was common. 1953 was a transition year that GM made some improvements and there was an early 53 and a late 53. The quick way to tell the difference is the early one has two lugs on the synchronizer and the later one has four. There are also some changes to the gears and one of the bearings. Other than the synchros, almost all the rest of the parts appear on eBay quite regularly.

The rebuild kit shown above is primarily for the open drive line (55 up) version as it has the rear housing gasket and rear seal. The other components are likely the same. Be aware that the brass syncro rings are pressed in and then staked in 4 places to press the brass into small holes in the drum. This is likely a factory press operation as the holes in the 3rd gear end are blind once the ring is inserted.
It could be a challenge replacing them. I would be interested If someone has successfully done this operation.
Fred

Roll the synchro around and you will notice slits on each end which gives you access to the snap rings that hold the collars in. Remove these and remove the collars and this will expose the rings. Once remove these, you can see the rings and get them out. They are brass and don't worry about ruining them on removal. The new ones can be pushed in with the proper size bushing driver. Or they can be tapped in with a brass drift punch. 50 to 70 years ago hardly anyone bought the whole synchro from GM. We went to the local auto parts who sold made in USA stuff at the time and bought a pair of rings. This is why there were quite a few NOS complete synchros available a few years ago. GM dealers never sold many. And the after market rings worked just fine.

The steel end rings are relatively easy to remove but can be a challenge to reinstall. The brass syncro rings press in relatively easy also, but that is not the point I was trying to make. The factory staked them in for a reason, there is a lot of load on those parts and they didn't want them to turn in the drum. The factory and/or re-builder's had to have some sort of tooling to stake them in properly.
I took a syncro out of a 57 trans recently that had a loose brass ring. It was obviously worn out which would cause it to grind going into gear and likely pop out at some point.
Fred

I admit that finding a NOS synchronizer would be the best route to go, but they are not always available. I have not installed the rings that are available now. However, the ones that were available 50 years ago were a very tight fit. I had access to a hydraulic press, but I have known them to be installed with a brass drift punch and a pretty good size hammer. I have been around a lot of Muncie 3 speed that were fixed. The aftermarket rings are a tight press fit. I have never known anyone to use any other special equipment. Aftermarket parts are not always installed in the same fashion that the factory used. I use a lot of Moog "Problem Solver" suspension parts. They are made in USA and make an easy fix of inferior factory design. If the currently available rings press in like the ones we had 50 years ago, they will be an improvement over what they factory did. They Muncie synchro design was much inferior to the Borg Warner design of the same period. I think that is why Saginaw kind of copied the the BW design. But if you own an old Muncie, it needs to be fixed.