Can anyone explain how the modulator valve works on an automatic tranny? I know what it is used for, just don't know how it works. On my 69, I have an FMX tranny and it is giving off a buzzing noise. I have narrowed it down to the modulator valve. But the car is shifting fine and no problems with the tranny.

 

Thats weird,, I dont know why it would be buzzing.. If it is shifting fine, then you may just have a little leak that is whistleing and makeing that buzz sound.. the modulator is not an expensive thing to replace. How loud is the buzz?

 

It is pretty loud. And only at certain times. When I shift into reverse, it ususally does not buzz. Last week I found that the vacuum line was split, I replaced the split and the buzz did quiet down some. If I can ever find a FMX pan, then I will change it all out (pan, gasket, filter, mod. valve, etc).