I'm having a problem with my transmission. 1966 200 cubic inch six cylinder, 1968 c4 automatic tranny.

After my engine gets hot, my idle will rise and my shifts will begin to get a lot harsher than what they should be. Once in a while after sitting in traffic, a white smoke (which looks and smells like transmission fluid) appears (smells like burning candle wax) which I assume is boil over. Whenever checking my fluid after this happens, it is always filled with airbubbles, and sometimes it will be filled with air bubbles when just checking the fluid on a regular basis. Replaced the modulator recently. Also just replaced the cooling lines and routed them away from my headers to try to help this problem. While it hasn't boiled over since, the fluid still has air bubbles in it whenever I check it.

 

Just guessing but it sounds like an internal trans issue to me (pump cavitation will cause air bubbles and overheated fluid) I'd check with a trans shop to be sure.

 

Check and make sure the vent is clear. It could be building up pressure if it's stopped up. By the way, did you install a new modulator valve? Pull the hose off of your MV and if fluid comes out you need another one. A cracked diaphragm in it will cause your fluid to be pulled into the intake and burned.

 

That's what I was thinking from the white smoke - fluid getting into the intake from the modulator. Did you replace the hose on both ends of the vacuum line going from intake to modulator?
How old is the fluid/filter and I take it the fluid is at full on the dipstick when checked in park with the engine running?
Jon

 

If anyone here hasn't experienced a blown/leaking modulator diaphragm - it looks like the car is on fire there's so much smoke coming from the tail pipe.