1969 435HP auto transmission pan

[Joe L.]

Re: 1969 435HP auto transmission pan

My memory is that sucker had a date code stamped into it too.

On the other hand the point Chuck makes about some of these details being hard to see is valid; but the TH stamping on the bottom of the pan should be a no brainer.

Terry------


The original transmission oil pan was GM #8625766. This same part number was used for many years. Of course, the Hydramatic Division embossment could have been added at any time without a change in part number.

The GM #8625766 was discontinued from SERVICE in August, 1985 and replaced by GM #8655021. I know nothing of this pan.

GM #8655021 was discontinued in February, 1993 and replaced by GM #8679995. The latter is still available from GM to this very day. It has NO embossment and appears very similar to the original, 1969-era GM #8625766. It may be zinc plated, though; the 8625766 was natural steel (I believe these were designed to be rust-free as a result of engine and transmission oil leaks which provided a "protective" covering of oil).

[Terry M.]

Re: 1969 435HP auto transmission pan

Terry------


The original transmission oil pan was GM #8625766. This same part number was used for many years. Of course, the Hydramatic Division embossment could have been added at any time without a change in part number.

The GM #8625766 was discontinued from SERVICE in August, 1985 and replaced by GM #8655021. I know nothing of this pan.

GM #8655021 was discontinued in February, 1993 and replaced by GM #8679995. The latter is still available from GM to this very day. It has NO embossment and appears very similar to the original, 1969-era GM #8625766. It may be zinc plated, though; the 8625766 was natural steel (I believe these were designed to be rust-free as a result of engine and transmission oil leaks which provided a "protective" covering of oil).

LOL. And I thought it was only Powerslides that were supposed to mark their spot.
I have had several TH400 equipped vehicles (none of them Corvettes) and all were daily drivers. You are absolutely right. The accumulation of oil and grease in my experience did a good job of keeping the trans pans, and other under car parts, rust free.

[Richard M.]

Re: 1969 435HP auto transmission pan

Jeff, I checked my original 1969 CY transmission this past weekend, the pan is smooth, with the two dimples, the vacuum modulator which I believe is original is black, the oil leakage problem on early 400's was mainly from the fill tube, early ones used a o-ring for sealing at the case, later they went to a larger rubber grommet type seal, about the #3868810 underpan it is still available and it is stamped metal like the original. Richard

[Jim T.]

Re: 1969 435HP auto transmission pan

I replaced my original owner 1970's THM-400's transmission pan in May 1990 with a new one from the Chevrolet dealer. It is a GM #8655021. I was surprised at the weight difference. The #8655021 is a thicker metal pan and sure does a much better performance of sealing. The seepage of transmission fluid I experienced with the original pan was gone with the installation of the #8655021. Only wish I had replaced the original transmission pan before 1990. The #8655021 has three dimples, one is small and the other two larger and are the same size. It is has the lettering HYDRA MATIC and below that DIV OF GMC.
My modulator is black and the transmission's underpan is metal and still has the original black paint.