I'm stumped! - '93 300E transmission flaring

[rgnprof]

I just reinstalled this rebuilt transmission and I have a significant flare from 3-4. I have tried to adjust the vacuum modulator w/o success. I made 3 separate adjustments, turning the modulator 'key' approx one full turn each time, and it doesn't seem to help.

I have checked the vacuum at idle - 18 psi and at half throttle (give or take) it is 22-23 psi. Is this right? How far can I - should I - adjust the modulator?

ryan

[C32AMG]

You have a vacuum respose problem, vacuum shold drop with open throttle.



Install a vacuum gauge directly into the modulator vacuum hose at the transmission, with the engine running on a healthy engine there should be a steady reading of manifold vacuum present, ”18 to 15 ”HG.

A quick opening and closing of the throttle should drop the vacuum to below 5”. The needle on the gauge should act as an extension of your foot, foot down needle drops foot off needle comes up. The needle MUST RESPONE Quickly, with no lag. Any delay means a restriction in the vacuum line.

This is very important; a slow vacuum repose drop in the needle will cause no line/ working pressure rise, a sure way the brunt the transmission; too much vacuum under throttle will also cause no line rise, low working pressure, soft slipping shifts and flared shifts.

To optimize the shifts you must check and adjust if necessary, working pressure. Install a pressure gauge to the working pressure port, with the modulator line disconnected, in drive at 1400rpm stall; pressure should be 16.0 or 15.8BAR depending on your transmission.

Then check working pressure repose, a quick opening of the throttle should raise working pressure to spec

[rgnprof]

Steve,

Thank you for your help. You helped confirm my thinking and led me to turn the car over to a pro. He confirmed that I was getting too much vacuum and was messing up the shift points. So far, so good...

Related question - I have a '72 250 - does the vacuum work the same way on this car??? I have a similar problem with flaring shifts on this car - through all gears. If I let up on the accelerator, it will shift fine.

ryan