The Stovebolt Site Forums The Shop Area Driveline Proper SM318 Syncro Rings?

Hey Guys,

My SM318 needs to be rebuilt and I found these syncro rings online. Do these look legitimate?

https://www.parts123.com/parts123/yb.dll?parta~dyndetail~Z5Z5Z50000014a~Z5Z5Z5AAEKZ~P25.00~~~~S4Q90UTWJD18417913050e~Z5Z5Z5~Z5Z5Z50000014x


I'm in Baton Rouge and looking for someone to rebuild it. It's from my running and driving '53 3100 that is starting to grind in 3rd when the trans gets warm. Some of the Shop Sharks on here have helped me determine the syncro rings need to be replaced.

Those would be the correct rings.
If you haven't already, you may want to look at my blog post on this.

Thanks so much for confirming the rings are correct. Nice blog post too! So in your experience, would you agree that if I'm using thick gear oil (first 90w mineral oil and then 85w 140) and I still have 3rd gear grind only when the transmission warms up that this is a syncro ring issue? I always double clutch when I drive it by the way. Thanks again for the very helpful information!

Are you able to put it in first or reverse without it grinding when warm?
A clutch that is dragging can make it hard for the synchro's to bring the gears to speed.

Yes, no problem in first, reverse, or second gear. It's just third gear that grinds. When the truck has been sitting for a day or two, I can drive it around the block a few times with no grind at all, then it slowly and steadily grinds more as it warms up. It never gets really bad and once it does start grinding as I shift into 3rd, it will grind less if I let the truck decelerate a little and ease it slowly into gear.

I should probably also mention that even when it does start grinding, I can bring the truck to a stop and shift into all gears fine. The issue only happens while in motion. Thanks again for your help.

It sounds like synchro then.

While in there, do them all as well as pilot bushing or bearing and throughout bearing.

Thanks for confirming the syncro problem Dave. Yeah Ed, I definitely planned on doing both syncros while it was being rebuilt. I'll look into the bushings and bearings suggested as well. I was going to buy the syncros as well as a rebuild kit from the same site. I just need to find someone to do the work. My understanding is that these transmissions are dead simple to work on. However, I have zero transmission experience and may not even have all the tools I need to do the job. I really appreciate all of the great advice guys!

If you don't mine me asking....where are you sourcing your parts from? Thanks.

It would be a good learning experience plus make you proud of yourself to do it yourself. Lots of help here, after all, none of us were born with these skills.

On my first tranny rebuilding used a piece of EMT to take up cluster shaft spacing.

Ed

Hey beltfed,

I'm finding the parts on a site called the filling station. They have a parts site called parts123.com. See the link I posted in the first message at the top of this thread and it will bring you to the page for the synchros. These guys have pretty much everything and prices are reasonable.

I may take a swing at doing it myself. On the Old Online Chevy Manuals site, there's a manual for rebuilding the later SM318 (7 bolt side cover) but not one for the 4 bolt side cover SM318 that I can find. Are there any resources like that for the earlier SM318 transmissions?

I, like you had never rebuilt a tranny. I decided to take it on several months ago with a buddy who agreed to help. They are as simple as a tranny can get. Collecting the 2nd/3rd grear synro hub plus new engerizing springs proved to be a task as they don't make them anymore. A couple of special tools are required like the wide snap ring pliers, No tool necessary was expensive and adds value to my toolbox for the next job. I used the large service manual for my year of truck. It covered the tranny quite well. There are several guys here that helped me at every stage and when I did something wrong. I have around $200.00 in parts for the rebuild which included the $115.00 for the synro hub. Then needle bearings are a pain but with grease and patience will go back in, just be sure to count them and not leave one in the bottom of the tranny. There is a big grear set in the bottom of the tranny that I didn't have to mess with and most likely you will not either. Good luck

The 7 bolt side cover trans is a Saganaw full syncro trans. No similarity to the earlier Muncie units. The 48-54 transmissions are completely different from the 55-65 version. There is an interesting snap ring operation holding everything together in the torque tube end.
If you notice in Dave's picture of the brass syncro ring, it will have a dimple in 4 places on the ring. This process was performed at the factory which actually presses the brass outward into specific holes in the sleeve. Without having the means to do this press operation the syncro ring will not be properly held into the sleeve which can ultimately cause it to pull out. Also the brass syncro rings are not the only thing that wears out. You can also have wear on the lugs on the steel syncro ring and on both the clutch gear and the 2nd gear engagement points.
Fred

Hey Fred,

Thanks for the info and that's exactly what I was worried about. It's kind of why I really need to find someone who can rebuild it properly. I don't feel comfortable trying to dig into something like that and not having the tools or means to do the job right the first time.