Muncie id question

[Chris H.]

Was underneath a 65 396 coupe today and saw what appeared to be an M22 as evidenced by the two drain plugs. The part number was 3925661 with a patent number of 3088336. The date code appeared to be P1K28C. Can anyone id the transmission. Thanks, Chris.

[Rodney Armstrong]

Re: Muncie id question

Chris,

I could not find any information on the 3925661 main casting number. The closest number I found was 3925660 and it was used in 1968-1969 passenger cars, corvettes, chevy II, chevelles and camaros. A 1965 M22 had a main casting number of 3851325. All of this information came from the book Chevrolet by the Numbers 1965-1969 by Alan L. Colvin. This book contains a lot of good information. It also has a chapter discribing the difference between M22 Muncies.

Rodney

[Bob Patton]

Re: Muncie id question

[paste] The part number was 3925661 - The date code appeared to be P1K28C

Chris ~

1 = year ~ K = July ~ 28 = day ~ C = M22

Gleaned from Chev by the Nbrs

HTH, Bob P 21991

[Terry M.]

Re: Muncie id question

If you were looking at a Muncie the code is:

P=Muncie HD 4-speed

1= Model year, in this case 1971

K=Month produced, July

28=Day of month produced, 28th

C= 2.20:1 Rock Crusher M-22

The two drain plugs have nothing to do with whether the transmission is M20, M21 or M22 after 1969 or so. All Corvette four speeds had two drain plugs from 1969 to 1972 and likely for some time beyond 1972.

The fact that the case was marked for M22 does not mean that the gears inside are correct for M22. Either a brief drive to listen for gear noise or open the side cover and look is the final proof of the tale.

Terry

[Tom B.]

Re: Muncie id question

Chris,

I think Terry has nailed down the whole thing. Also, I believe the A, B, or C designation part of the code isn't found on the casing until the start of the 1968 model year. TBarr #24014

[Joe L.]

Re: Muncie id question

Chris------

In addition to agreeing with the information provided by others, I'll also add that if this is a complete 1971 transmission, the 1965 driveshaft would have to be shortened to fit and have a 4-5/16" finger diameter u-joint yoke attached at the transmission end. Otherwise, a 1971+ driveshaft could be used, but the pinion shaft companion flange on the 65 would have to be changed to accomodate the 4-5/16" finger diameter u-joint.

You can tell if the complete transmission is the 63-70 or the 71-74 style by looking at the tail shaft extension housing. The earlier style will have extension housing casting number 3819113, 3846429, or 3857584. The later style will have casting number 3978764.

Considering the fact that the main case is from the 1971 model year, if this transmission has the 63-70 style extension housing, that probably means that the transmission was "built up" from parts and there is, consequently, no certainty of what other parts might have been changed, including the gearset.

[Joe L.]

Re: Muncie id question

Tom----

The suffix coding started in October, 1968 just after the beginning of the 1969 model year.

[Tom B.]

Re: Muncie id question

Thanks for the clarification Joe. I had been additionally curious all this time, since my 68 M21 (December 67 build) didn't have the suffix either. Now that clears it up for me as well. Thanks again. TBarr #24014

[g.r.rogers]

Re: Muncie id question

Chris, Sounds like the responses have answered your question. Try to pick up that Corvette Black Book,you can see under options that the M22 wasn't optioned in the corvette until 1966 and only 15 were on the road then. If you really need info about transmissions or repairs call Darrel Shepard of Darrels 4 speeds. He builds transmisions and rear ends and rebuild a M22 for me about 10 years ago. He is not cheap but does great work, at least from my experiences. His Tech line number is 217-275-3743.Regards GRR#33570

[Chris H.]

Re: Muncie id question

GRR, thanks for the info.

However, Al Grenning wrote an article that documents that 30 M22s did infact make it into some late production 65s, one being a documented car bought by Peter Fonda.

I thought I may have stumbled upon one but alas, it appears to be a 71 box.

Chris

[g.r.rogers]

Re: Muncie id M-22 question

Chris, that may very well be. I just use the books that have the facts so I can be armed against those that try to rip off good people who have owned or want to own a corvette for either a driver or hobby. If you feel that my quote from the corvette black book was wrong I'll always say your right. It's your bread. I just hate to see someone get ripped off. The black book shows "ZERO" M-22s in 1965 and this could be a way to get the price down. Ask the owner if he has the book and if so where did the M-22 come from.I was just trying to help and always keep an open opinion and will pocket your findings.Best Regards GRR#33570

[Curt Worden]

Re: Muncie id M-22 question

As far as the 1965 M22 facts are concerned throw the Black Book in the garbage ! The ZERO production total for the '65 M22 has been a mistake perpetuated by hobby authors. GM never said M22 production total was ZERO. GM said the records were n/a .... a big difference ! Curt

[Mike]

Re: Muncie id question

When you take the side cover off, what are you looking for?

[Chris H.]

Re: Muncie id question

The gears should be visible and M22 gear angles are much less (more vertical)that M20 or M21

[Terry M.]

Re: Muncie id question

Look in Chevrolet Chassis Overhaul Manual for photo of transmission internals. I believe there is one in almost every year Muncie was available. That will show M-20, M21 gear angle. Compare to gears in trans in question. Significantly less angle is M22.

I also believe the size of the side shaft (I know that is the wrong term, but I don't have the correct one at hand.) is larger on M22, but this is not easily seen with just the side cover off. Others might chime in on the accuracy of this last info. I am just a little uncertain of it.

Terry