Auto trans reverse pressure switch problem

[wwheeler]

On my '68 W111, occasionally when I shift into reverse, the engine RPM drops almost dying and then will pick up to the normal idle RPM after a second or two. Operation usually is normal and never happens cold, only sometimes when hot. Drive switch always works well. Trans is about 50-60K since rebuild and runs well. Switches are new about 5 years ago. Solenoid also new 5 years ago. It almost sounds like pressure isn't building fast enough in the trans to activate the switch. What other problems could it be?

The trans will start over filling the pan with oil after a month or two if not driven. I assume this is coming from the torque converter. I know this happens, but seems like it is normally a much longer interval. Could that be related to the reverse switch issue? Otherwise has very little trans leakage.

Thanks for the help!

 

[wwheeler]

An update to this problem. The brief slow idle when going into reverse only seems to occur when hot AND when there is a slight white smoke in the exhaust. Hasn't happened in two months, now suddenly on consecutive days. Any chance it could be the vacuum modulator leaking?

Maybe a leaking diaphragm would allow trans fluid to go into the intake and then get burned. If it was leaking, it would also not have as much pressure and may not be activating the pressure switches immediately. I checked the fluid level. It is a bit low when warm but just a bit above when hot.

Any thoughts?