1969 THM400 Transmission Code PR
 

I have a 69 GP with a 428 H.O. 390 hp engine and matching Thm400 trans. The Yellow ID plate on the side of the trans reads PR -69-. I’ve read that in 1969 the PR code was exclusive to the GP with the 428 HO engine. I also read that the PR transmissions were equipped from the factory with extra large forward and intermediate drums for additional friction plates. Are there any other differences between the PR code and other Pontiac Thm400 transmissions? I’m planning to get this transmission rebuilt and want to know what if any special parts may be needed.

Unlike the fullsized Pontiac that used a specific TH400 for the 428 HO that was not the case on the GP. In that case the regular and HO (the 370 and 390 horse) versions of the 428 both used the same code transmission. There were different TH400’s for the 400 engines however.

Thank you for the clarification. Do you happen to know what code transmission the Fullsized Pontiac’s equipped with the 428 HO used?

TH400 codes for fullsized cars:
400-290 & 265 horse: PB
400-340 horse: ?? (I've never found factory documentation for the trans code for this engine (it was a mid year introduced 4bbl engine option)
428-360 horse: PA
428-370 horse (police): PH
428-390 (HO): PC

While most variations between these codes relates to different internal components in the transmission to better suit engine characteristics sometimes you can have two different codes where the only difference is the speedo drive gear teeth count to reflect the standard axle ratio difference between two engine choices. I don't know what are the differences in the above transmissions. btw, the 400-340 engine was a four barrel version of the standard 400-290 standard engine. Both were high compression small valve and shared the same heads and cam etc. The 428-370 on the fullsized car was police only and basically the 428 HO without the chrome dress up or long branch manifolds. In other words it used the same 62 heads, 067 cam, carb, distributor and 4 bolt main bottom end from the HO. Interestingly the manual transmission version of the 428-360 was identical to the police engine while the automatic version used a two bolt block and the cam and small valve heads from the 2 bbl 400-290.

Grand Prix transmission codes:

400-350 horse: PW
400-265 horse: PT
428-370 & 390 (HO) horse: PR

The 428 370 (standard SJ engine) was very similar to the HO with dress up kit and same heads, carb and 4 bolt block but without the long branch and it used the 066 cam instead of the 067.

Grand Prix