67 Transmission

[Richard S.]

Is a 67 435 with 4:11 gears likely to have come with M 20 or M21?
Thanks.

[Joe L.]

Re: 67 Transmission

Rick-----

It's not only likely that it was originally equipped with an M-21, it's a virtual certainty. The L-71 was only available with the M-21 transmission. The M-20 was not offerred with ANY rear axle ratio.

[Tom H.]

Re: 67 Transmission

I have the close ratio "rock crusher" Muncie in my '65 and the quickist way to very its authenticity is to look for an oil drain plug in the case. I haven't drained mine since '81 when the car was stored (soon to be "unstored")but I remember that the drain was a npt plug of maybe 1/2 pipe diameter.

[Norris W.]

Re: 67 Transmission

Tom, I wasn't aware the M22 "rock crusher" was available in 65 as an RPO. My "old" NCRS spec guide, which is first addition, and may have been updated since, shows 0 M22's installed in 65. As far as identifying them with the lower drain plug present, this is true in some years, but not all. Chevy installed Muncies in the early 70's in some cars, including Corvettes that had the low drain plug and also the large output shaft like the M22 and Turbo 400, but had the small gears. I assume these were all M21's. I have at least one of these that came from a Corvette, but I can't recall the year model off the top of my head and I've seen one in a Chevelle also, probably a 71 or 72.

[Tom H.]

Re: 67 Transmission

I've had mine since it was brand new. Took delivery on a snowy January 19,1965. Trans was replaced by GM in March or April 1965 because of a bad countershaft (severe knocking sound at idle). Car came with several parts missing because of a 60 day strike in the fall of 1964 as the car was ordered in August .Among the missing parts were the radio, clock, knock-off hub cone or pin covers, visors and side exhaust covers. These parts were added as they were shipped (between early January and delivery to me on the 19th) at Anderson Chevrolet in Baltimore. The radio installation was so bad that I eventually replaced the original knob bezels with 67's to cover up the sloppy dash work around the knobs. The trans was rebuilt in the summer of 1968 by Bob Creager at Marsden Chevrolet in Baltimore after some "abuse" in Solo events at the old Marlboro Speedway. I'm currently in the process of putting the car back in service as it was set up for autocross and Solo events in the late 60's- both mechanically and aesthetically.

[Joe L.]

Re: 67 Transmission

Norris------

Although a controversial subject for some, I believe that a few 1965 Corvettes were actually delivered with the M-22 transmission. There were not too many; just a handful. Al Grenning has pretty well documented this and I'm a believer. For 1967, though, I don't think that any were ever originally installed behind L-71 engines. So, if you got an L-71 for 1967, then the only transmission available was the M-21. The same was true for 1968. For 1969, either M-21 or THM-400 was available with L-71.

As far as the drain plugs go, for 1965-69 Muncies, only the M-22's got the drain plug (although the plug could be added to any Muncie case).

In 1970, all GM cars with Muncie 4 speeds changed to the 3925661 main case and this case continued to be used until the end of Muncie production in 1974. All 661 main cases have the drain plug, regardless of which variant (M-20, 21, 22) which the transmission was built as.

For 1971, the Muncie main shaft, extension housing and input shaft changed. The main shaft was about 3/4" longer, of greater diameter in the rear section, and of 32 spline output configuration. The extension housing changed to accomodate the revisions in the main shaft configuration. The output yoke became the same as the one used since 1968 for THM-400 Corvettes. The input shaft changed from 10 spline configuration used from 1963-70 to a 26 spline configuration. All 1971-74 Muncies use the 26 spline input, although the input shafts are different for M-20, 21, 22 due to gear difference.