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Q: Vacuum leak and transmission on 1995 Ford Taurus

I still have not found the vacuum leak. Is there a vacuum line to the transmission or would vacuum cause the transmission to shift differently? Would the vacuum leak cause the automatic transmission to shift hard. When putting it in drive, the car jerks forward, it also jerks hard from 1st into 2nd gear. I don't want to put a used transmissiom in and still have same problem.
Thank You in advance for your answer!
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No and No -- No vacuum line to this transmission. The transmission is electronically operated and controlled.

A vacuum leak will cause the engine performance to suffer, causing possible load and throttle position issues, which could indirectly affect transmission shifting. But that's kind of a stretch, really.

What is telling you that you have a vacuum leak?

Is your transmission full will clean fluid?
Thank You for answering my question. On the vacuum leak, my heater and vent air are directed to the defrost under moderate to hard acceleration. Also I lost about 4 mpg.
On the transmission, I had it back flushed at local garage (take off transmission lines at radiator) and it did not change the hard shifting from park to drive and from 1st to 2nd gear.
It was doing this before the transmission flush.
I wanted to make sure these two problems are not related. Thanks Again!
You are keen on the vacuum leak - although I would guess that your leak is under the dash, not under the hood. Your fuel economy may be telling the story, though - these engines are not known for intake leaks or anything like that, but more for a PCV hose or other hose leaking.

The fuel economy could be caused by many things, of course...

I am very familiar with the AX4N / AX4S transmissions in this vehicle; they were fairly notorious for forward clutch problems, although it's been 16 years now and anything goes. Your concern sounds characteristic of what I've experienced in the past. You can probably live with it as long as you can deal with the jerking, as I don't believe catastrophic failure is imminent.

Another quick note - have you had a look at your motor mounts? Not as likely to fail for a 3.0 compared to a 3.8, but it can happen, accentuating any kind of jerking feeling.

Good luck!
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