C2 4 Speed Transmission Shim(s)

[Ken K.]

When I removed my '66 M21 transmission, I noticed that it had two shims. The shims where between the rear rubber mount and the lower mounting bracket. My question(s) are: Is this factory? If not, why would someone put these in this location? Is there something I should check to see if I should reuse these shims, or leave them out when I put the transmission back into the car?

This car originally came with an "Under car exhaust" system. Someone converted to a "Side exhaust." Are the shims under the transmission mount there because it is now missing the bracket that the two exhaust pipes would clamp to?

Was this normal for side exhaust cars? Or did those cars get a thicker rear rubber mount?

Is all this that critical for proper alignment?
Thanks Ken

[Joe L.]

Re: C2 4 Speed Transmission Shim(s)

Ken-----

Cars with side exhaust used a spacer plate in lieu of the "ox bow" bracket used for under-car exhaust. This was a simple rectangular bracket with 2 holes. One can easily be fabricated from steel flat stock or, I believe, such plates may be available in reproduction. The plate is necessary to establish the correct position of the transmission as mounted in the car.

[Jim R.]

Re: C2 4 Speed Transmission Shim(s)

Ken any corvette supply company has this plate for about 7 dollars ,or it can be made without much effort.

[Timothy B.]

Re: C2 4 Speed Transmission Shim(s)

Is the 63 corvette transmission mount different because of the different hanger assembly used for 63?

[John H.]

Re: C2 4 Speed Transmission Shim(s)

Joe -

I've always wondered about that shim. Logic would say that if the output shaft angle was indeed that critical, that the shim thickness would make up for the lack of the "oxbow bracket" on an N14-equipped car. However, the shim isn't shown or called out in the '65-'66-'67 Assembly Manuals, and I seem to recall someone posting about a year ago that it was only used on 69's with N14, and shows in the N14 section of the '69 Assembly Manual (I don't have one).

[Joe L.]

Re: C2 4 Speed Transmission Shim(s)

John-----

I agree. The shim is not specified for the N-14 installation in any of the 65-67 AIM's. Also, it's not found in any P&A Catalog for 65-67 models. So, it makes one wonder. My belief that the shim was ever present on 1965-67 models is only rooted in what I've been told by others. Obviously, my knowledge of side exhaust cars is limited (and, will forever remain so).

A spacer is shown in the 1969 AIM for N-14. This spacer was GM #3949179. That's a 1969 part number, so that part could not have been used for 1965-67 although, presumably, if a part existed for 65-67 it would have been identical. However, I also find that GM #3949179 was not supercessive to any other part number. So, that implies that there was no equivalent 65-67 part, although it could just mean that there was no 65-67 part that was ever available in SERVICE.

Also, the 3949179 spacer is shown in the P&A Catalogs as being uniquely applicable to 1969 with N-14, with no earlier applicability. However, once again, that could easily happen if there was no SERVICE availability of any 1965-67 part which may have existed.