C3 1969 Thm 400

[Jimmy B.]

The 69 I just purchased is leaking a considerable amount of automatic tranmission fluid (thm 400 13 bolt pan if memory serves me correctly). I noticed that the 6 inch or so rubber hose connecting the modulator valve to a tube coming from the upper engine compartment down past the starter was swollen to at least twice its size and had fluid dripping out of it.

What does the modulator do and does the connecting tube connect to a vacuum source up above (this is all very greasy) and could this be the cause of my "leakage"?

Would this leak when the car is just "idling" or must the car be in gear?

Modulator valve located on the RH side of the transmission.

I found a square tag on the rh side of transmission farther back but it is also covered with grease.

Should I steam clean the underside of the car or what?

Thanks in advance.

Jim Blakely

goodnews: rear end AV 3 28 69 W exactly what my protecto plate says

[Paul Y.]

Re: C3 1969 Thm 400

Jimmy, the modulator valve works off the vaccum of the engine and helps the tranmission shift smoothely. It has a diaphramn in it and will leak if ruptured. Replace it and the hose and clean off the underside of your new acquisition to see if the leak stops. Let us know how it works out please.

[Jimmy B.]

Re: C3 1969 Thm 400

OK, now as I do more research I see a ton of adjustable modulators on the market, is this what I want or does anyone have a replacement # from NAPA or some other source? I found this number in my old GM catalog
GRP 4.205 8625976 but apparently this is obsolete.

Thanks,

Jim Blakely

Paul, you better start that fuelie up before the gaskets dry out! Thanks for your explanation above amigo!

[Joe L.]

Re: C3 1969 Thm 400

OK, now as I do more research I see a ton of adjustable modulators on the market, is this what I want or does anyone have a replacement # from NAPA or some other source? I found this number in my old GM catalog
GRP 4.205 8625976 but apparently this is obsolete.

Thanks,

Jim Blakely

Paul, you better start that fuelie up before the gaskets dry out! Thanks for your explanation above amigo!

Jim-----


The part number you mentioned is discontinued. The current part number is GM #89057785. This part will SERVICE the application perfectly but it's not configured like the original piece. You can also use a Standard Motor Products #TM-15 which is likely the exact same piece as the GM.