i have 2 muncies in front of me. 1 is the original off of my 69 that was #734 off the line. it's casting date p8m1, the casting number is 3925660, and it has 2 large 6's castied into it, and my vin#. the 6's are not the same size. the tail section says gm #3857584. now i know for a fact that this is the original trans, but what i am not sure is how to tell if it is a m21 or m22. that part of my tank sticker is torn. the other trans i just bought, i am told is from a 69 also. but the numbering dosent jive with my original. for example, where my date, and vin is stamped on the other, this one is stamped with a 39095 and than underneath it is stamped cc4. the casting number is 3925661. and this one has a large 6 cast into it. the tail section has the same gm 3857584 as my other. according to my ncrs tech guide, there is a a-c suffix at the end of the casting date. niether has any letters like this. there is also differences between the linkage levers. anyone have any idea how to tell which trans these are, and why the 2nd one has a odd stamping.
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Re: 1969 muncie 4-speed questions
Scott, that's a lot of questions, but all I can tell you if it's a M-22, the main case will have an oil drain plug tapped into the boss, and no grooves around the input shaft. The easiest way to tell M-22 gears is to remove the side plate and look at the helical gear angle cut. M22 gears have a relatively straight cut of 21 degrees, while a M-21's are 37 degrees. Side by side it's easy to tell the difference. Patrick -
Re: 1969 muncie 4-speed questions
i will try not to ask so many questions next time. anyway should i use my drafting protractor to measure the angles on the gears? thanks for the info.Comment
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Re: 1969 muncie 4-speed questions
Just take a piece of graph paper and draw a horizontal base line, and then a perpendicular line 90 degrees towards the top. Then measure 21 degrees counterclockwise from the top with a protractor and mark 21 and 37 degrees and draw the 2 lines back to the intesection of the x and y axis. Then place the baseline on the paper up against the centerline of the mainshaft and match up your measured lines with the angle cuts on the gears. This should be close enough for you to tell. PatrickComment
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Re: 1969 muncie 4-speed questions
i was joking about the protractor thing! you didn't really think i was going to try to put one in there did you? that would be like the new designer that we got at work, he tryed to measure a part on his computer screen using a scale.Comment
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Re: 1969 muncie 4-speed questions
Scott-----
First of all, unless the car is an original L-88, the transmission won't be an M-22. For 1969, the M-22 was only available with the L-88.
Second, the A, B, C suffix codes are NOT part of the transmission case or extension housing CASTING numbers; they are part of the transmission production code STAMPING found on the rear, vertical surface of the paasenger side of the main case. If the trans is original to the car, it WILL have this stamping. A= M-20, B= M-21, C= M-22.
Third, the transmission which you have with the 3925661 main case and the 3857584 extension housing would be a combination uniquely used for 1970 model year Muncies only; not just Corvettes, but most Chevrolet cars. Most, if not all, of the '661' main cases have a main case drain plug which often fools folks into thinking that they're an M-22.In Appreciation of John HinckleyComment
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Re: 1969 muncie 4-speed questions
the numbers that are stamped, not casted, verticaly are cc4, an directly underneath are 39095. again those are the stamped numbers. usually those numbers would be the date code, and the serial numbers. like on my original trans which is p8m1, and then my serial number. but not even my original trans has the a,b,c suffix which designates which trans it is. and this area is very clearly stamped, and undamaged. there was never a letter stamped there. so how again can i tell what this trans with cc4 stamped into it is? is the 39095 maybe part of the serial number from the car it came from. the guy that sold it to me said that it came from his 69, and he was in fact the original owner. it does have the tapped out drain in the bottom, which at first made me think it was a m22.Comment
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Re: 1969 muncie 4-speed questions
The ABC code was not used until the '69 model year was underway. If your car is an early build, it would not carry the code. If your extra trans has one or two rings around the input, a visual comparision of the gears in it and the trans from your car would quickly answer your M-22 issueComment
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Re: 1969 muncie 4-speed questions
what are the numbers that are stamped into it, cc4 and 39095. they do not reflect anything described in the tech manual. and yes my car is very early, #734 off the ass'y line.Comment
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M-22 Rockcrusher....
As you know the input shaft and 1st gear are one piece; Darrell Sheppard told me these are virtually impossible to buy these days. As Bill mentioned, no grooves and straight cut teeth on the first 3 gears are the clue. 4th gear is, I believe, the same as an M-21.
An M-22 produces an unmistakable whine going through the first three gears, hence the name Rockcrusher, but in 4th, the transmission quiets down considerably.Comment
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Re: 1969 muncie 4-speed questions
Scott----
This transmission must be a SERVICE transmission which was originally sold over-the-counter. That's the only explanation I can think of for the stampings which are not typical of the numbers stamped on transmissions originally installed in vehicles. I am a little surprised that the transmssion does not have at least the production code stamping, but SERVICE transmissions may have used a different system just like SERVICE engine assemblies.
If the transmission is out of the car, you may be able to tell which version it is by looking at the input shaft. If there are 2 circumferential grooves, it's an M-20; if there is 1 circumferential groove its an M-21, and if there are no circumferential grooves, its an M-22. This only works, though, if the input shaft has never been replaced. Many aftermarket and, even, GM replacement inputs did not have the grooves regardless of which trans version they were used for.In Appreciation of John HinckleyComment
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Re: M-22 Rockcrusher....
Patrick-----
The input shaft and FOURTH gear are integral; first gear is a seperate gear as are second and third. All M-22 gears except reverse are unique to the M-22. For M-20 and M-21, first, second, third, and reverse gears are the same. The input gear (fourth gear) and the cluster gear are unique to M-20 and M-21.In Appreciation of John HinckleyComment
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Re: 1969 muncie 4-speed questions
both of these tranmissions have 2 grooves on the input shaft. on my build sheet i can read 4-speed close ratio trans, but i cant read the "m" number. is the m20 called close ratio on the build sheet? was it even a option with the 427/390 hp?. the trans with the funny stamping was rebuilt by the previous owner, both of these are suppose to be m21. i would just like to make sure.Comment
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M20 Is The Wide Ratio Transmission...
Scott,
It sounds like to me both transmissions are M20s in spite you have been told.
Another thing you can check is AC: C60 option was only available on the 427/390hp with M20 or M40 (Turbohydramatic). If your car has AC, then the tank sticker says M20; M21 was not available with C60.
Chuck SangerhausenComment
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If you're real quick ...
... you can catch a photo comparing the M22 helix angles to the M20, on eBay, item 562108462Comment
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