Are TH350 and Muncie M21 yokes the same? [Archive] - Chevelle Tech

: Are TH350 and Muncie M21 yokes the same?

Jul 10th, 99, 3:54 PM
I am in the process of swapping my TH350 with a M21 and am having difficulty inserting the yoke from the TH350 into the M21. Both output shafts are 27 spline and the mounts of the M21 are in the same place as the TH350. The drive shaft used on the TH350 looks to be the correct length. The yoke slides up the shaft about 3/4" into the trans tail and stops like it is hitting the end of its travel. Still about 2" of yoke is sticking out of the trany. The splines on the yoke and the trans look good. I used a hanger and was able to feel at least 3" of output shaft beyond the yoke seal.

I read and article in Chevy High Performance that made me beleive that the yokes were the same and the only difference being that the M21 setup was a 1/4" shorter.

Does anyone have any suggestions? Is an other yoke used? If so does anyone know the part number and where I can get one? Or is somthing wrong inside my trans?

Thanks for your help. I can't wait to bang some gears.

Jul 10th, 99, 4:17 PM
Years ago I had a 70 SS Nova that had a M21 in. The tranny blew so I went the T350 route. Everything stayed the same, crossmember, driveshaft. I never had a problem doing the swap or driving the car.

The only thing I would have done differently was to keep it a 4-speed. Manual trans cars are just a blast to drive!

Jul 11th, 99, 11:18 AM
They are exactly the same (although 71-74 Muncies were larger, the same as a turbo 400 yoke). That yoke should slide all the way in until hits the rear of the tail housing. If you are unable to gently persuade the the yoke to go on into the rear of the Muncie, something is wrong. That concerns me. I have this fearful feeling that you may need to remove the tail housing. If, and when, you do, sight down the tailshaft splines to be sure the shaft is not twisted. That's rare, but it happens. Let us know.


[This message has been edited by DZAUTO (edited 07-11-99).]

Jul 11th, 99, 6:41 PM
I'd like to add a bit to what DZAuto said about spines being twisted. The yoke should twist long before the tailshaft does. Try a different yoke, and see if it goes in all the way before you try swapping it on the driveshaft. if it goes in all the way, then you should be ok. Try to push your current one in before you do anything else with the shaft, if it doesn'y go in, try another one. If the other one goes in, swap them. If it doesn't, then there is something wrong with the tailshaft housing, or the splines on the tailshaft.

70 & 1/2 RS Camaro
SB406 & M20 4spd
9" Rear
70 Malibu
SB350 & TH400

Gold Member # 103

Dave Birdwell
Jul 11th, 99, 9:20 PM
hey DZ- Are you sure they're 'zactly the same? I remember reading that one yoke, the automatic, I believe, has a hole in the center for a vent. really small hole, like a 1/16". Or am I all wet???

Gene Chas
Jul 12th, 99, 8:11 AM
In a related matter, Sparky, if I remove my drive shaft from the Muncie, do I need to plug the output shaft to stop fluid from leaking out? I need to do a driveshaft check.

Jul 12th, 99, 9:10 AM
Dave, you are correct that some of the yokes have a small hole in them, but im not sure what the applications are that use it. I used to work at the Parma GM plant that made these and there was one yoke we made with a small hole that was the same size as the Turbo 350 yoke.
Gene, you may be able to pull your driveshaft out without the trans draining if you jack up the rear of the car, ive had that work a few times but other times it didnt.

70 Chevelle SS396, 71 Z28-RS, 95 Z28 Convertible. Aces 3081, TC #54 Gold

Jul 14th, 99, 6:24 AM
I probably should have been more clear. The configuration of the splines is exactly the same. By that I mean that a 70-earlier Muncie, P-glide, turbo 350, and a 3sp yoke should all physically slide all the way in and bottom out against the rear of the tail housing (actually, the tailshaft itself since it sticks out past the tranny a little bit). Now, there are several differences between yokes as far as the part where the u-joint cups fit. For example, Corvettes use clamps like the rear end yoke. Chevys use a snap ring just inside the hole to retain the cup. Olds has the snap on the back side of the hole with a groove in the bearing cup. but they will all slip onto your Muncie shaft. And the tiny hole? I don't know. I, personally, have used both, no problems.
Can anyone for sure tell us the purpose of the tiny hole?

Oops. Left out one thing. On 62-older trannys, the tailshaft and yokes are the same size as 63-later, BUT, they have course splines and will not interchange (don't know the spline count).


[This message has been edited by DZAUTO (edited 07-14-99).]

Jul 14th, 99, 11:53 AM
Guys thanks for all your help. I removed the end seal from my trans and it appears that the brass bushing in the tail shaft is a little buggered up and may be preventing the yoke from going past it. With the help of YearOne they identified my tail shaft as a 1965 to 1970 muncie and had a bushing that they are overnighting me ($20.00 shipping ouch!). My cousin has a tool to remove and replace the bushing.

I'm going to try it tonight and I will let you know how it goes.

I know this is not the forum for this but I need a headlight knob for my 68 Chevelle. If any one has one can you E-Mail me and we can work something out.

E-Mail: or

Jul 14th, 99, 9:53 PM
Dear Sparky,
With this letter I am informing you that:
Most Chevy parts depts and auto parts stores stock this bushing for about $6-8. It is an extremely common bushing. Sorry.