How about the brass rings? Somewhere in there it seems there was a difference in the early muncie boxes and the later ones. I think that changed when they went to the one inch pin from the seven-eights pin.
Talk to these guys. "autogear.net/motorsports/" Located in Syracuse, NY. They can help you out with parts and information.
They are good to deal with. I bought my new side cover for my M20 from them. Good service after the sale too.
Reason I am asking this is that I ran into a problem with some different brass rings once. IIRC, the rings were a different inside diameter and would lock up on the cone of the gear. Wish I could remember more clearly for you. Seems the slider hubs were either an inch or a inch and one eighth long and that was the difference between an early and later box. Also I think the real early muncies had one more snap ring on the main shaft. Been a while since I have seen one of those.
When I rebuilt my m20 years ago I had to buy a new front bearing retainer because the new input bearing was a little thicker by about 1/16”- 1/8”. Got my stuff from Medtronics.
Think the gears are made for the Autogear Muncie supercase there is something different on them cant recall what it is exacty.
Just wondering can a synchronizer hub be put on facing the wrong direction? Aren’t they offset like the early Fords?
Expert came by. We had it together right BUT its just not right. He thinks it's the synchronizer hub. It's NOT oem. You can see where it's rubbed where it shouldn't. You can see how hot the shaft has got. It never would shift right. If I thought it was just buying a new one........a good one. .......
Third gear has been hot on the shaft,,,, was it a new gear from before ? Check the id for any wear or tight spots . Unless you have always owned the transmission,,,,,that could have been from a previous issue . Tommy
Im confused. Your first post would lead someone to believe the trans problems were during the assembly and not put into service yet. You said then it shifts through the gears ok, just can't fit the front bearing retainer. Now you say it never shifted right??? Which is it??? How did the main shaft get overheated and the hub damaged? Did you reassemble it that way??? Bill
Long story. I bought the engine and drivetrain out of a parts car. We took the side case off and it looked good. Nothing obvious. We put it in the car. It never did shift right. No matter what it would grind going into 4th. We knew we had to fix it but it took care of that for us. I bought a new main shaft and input from a reputable source. The end of the shaft and inside the input was all scored. It wouldn't go back together right. I think it was never right. That's why it is scored and the shaft got so hot. It was put together way too tight to start with. The guy that came by said the synchronizer hub was aftermarket. He believes that is the problem. Everything is back together correctly but input just doesn't sit right in the hub. The outer snap ring sits appx 1/16 of an inch high so when you put the bearing retainer on it clamps everything tight.
When you say the end of the main shaft and the inside of the main drive were scored do you mean they were bottomed out hitting each other, or do you mean they were scored where the needle bearings ride? When it was assembled, bearing retainer snugged up and locked up, was there slop in the 4th syncro ring? On the work bench, take the assembled syncro with the rings, set it on 3rd gear. You should see some slop in the syncro ring. Now take the main drive and set it on top of the syncro assembly. The syncro ring should bottom out on the cone and be tight. That means the syncro ring is bottoming out, before the cone on the main drive hits the hub. That is how it should be. If there is slop in the syncro ring, then the cone on the main drive is hitting the hub. I am going to assume you have a late style 1" hub with stepped rings? Or is it possible you have an early wide hub and stepped rings? Not sure if you could even get it together that way or not. I am going to assume you just have the oil singer on the front bearing without any extra shims, like some like to do to reduce clearance in the 4th syncro? I am also going to assume the mid plate is an OE original and not aftermarket. If that stuff checks out ok, then the only other thing it could be, is the main shaft pilot is hitting the inside of the main drive. That wouldn't be the first time I have seen that and have had to shorten the pilot on the main shaft on a few of them. The way to tell if there is sufficient clearance between the two shafts is, when the trans is assembled, you should be able to push the main drive/ bearing further into the case without the snap ring on the bearing. Good luck, Bill
What I would do to rule out possible causes would be to install the main shaft back in the case with out the 3-4 syncro assembly or 3rd gear on the shaft. Tighten up the mid plate and see if the problem goes away. If it doesn't, then the two shafts are hitting. Bill
I'll try and address this. We have the 1 inch hub and stepped rings. There is NO slop. That's out problem. It's tight. When the bearing stick out the end of the case we can't even get the bearing to fit back to the snap ring let alone push it further in. The mid plate appears to be OEM.
Always check the synchro ring fit.Make sure they are not out of round..They can vary in ID size ,the best rings are forged bronze The fit on this is .035, I do believe the Muncie is the same.
New or not they need to be checked for fit.. I have new ones that were out of round and or sized incorrectly...
So I've been busy but still battling this.....until today. I need to do some research before throwing anyone under the bus. Just seeing what anyone here may know. A friend (new friend from trying to figure this out) gave me a name of someone to call. He's actually a big truck specialists but he said he does Muncies. He told me to bring it out (about a half hour away). He looked at it and said right off (you have the wrong bearing). See pic. The one on right is the one I bought from the well known seller. It's the same size that came out. It's the same size as a trashed unit the previous guy let us take apart to try and figure it out. It does NOT work with my transmission. The guy today drug out his old book and looked up his info. Went back and got me the bearing on left. It fits......everything works (not back in car yet). I asked him why is it no one else knows about this other bearing. He just shrugged and said "I don't know". But it was right there in his tattered book. Now mine is one of the last ones built. Fine spline, big shaft. Dates out to 1973. Did GM make some late change most people don't run into? Anyone know before I call the place I bought this first bearing from?
Being a fine spline M21, is weird for a start. Chevy parts book shows one bearing for all of the Muncies from 64-74, in non Corvette applications, ND41307B What numbers are the bearings you have sitting there?
The new bearing is N1307L. I called a couple places to see about buying an entirely new unit and they noted that they have a hard time getting the big tailshaft. I have no idea what the trans initially came out of. I also have no idea how it left the factory.
My '71 cutlass had an m-21 with a fine spline input , could have easily been bolted in any GM product of that vintage with a matching disc ? Pretty sure the inputs were the same lengths ?
So anyways.....in the shop putting things back together.......before I call the place I bought my parts from I still like to be right or know what I am saying. I'm looking at the input from the junk trans we got and it has the thin bearing. I guess I didn't look close enough before. This the bearing I was sent.
Well this is the HAMB and I expected all kinds of answers. LOL. The place I bought this from sells new "upgraded" cases. Any chance they use the larger bearing and that is what I got? Still doesn't explain why the larger bearing was in it to start with. (obviously not the original bearing)
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