jacal128

When I first got the 86.5 the transmission shifted fairly hard ( mainly when cold ). I did the top end refresh and must have left a vaccum line disconnected because it had started shifting a great deal smoother, while doing the TB and WP I found the line disconnected ( under the master cylinder ) clipped it back put new connectors on it and now it is shifting harder again. Is this normal ? I have read about an adjustment to the transmission to smooth out the shift. Any ideas would be great. Thanks, Jack

SQLGuy

I actually had the opposite problem with my 85: shifted hard with the vacuum modulator disconnected.

That vacuum line should be connected to a little rubber manifold near the DS rear fuel damper (vacuum inversely proportional to engine load). If it's getting vacuum from the other side of the check valve, where the cruise control and brake booster are getting it, then that might cause shifting problems.

Bertrand Daoust

Do a search on "modulator".
You will find alot of informations on how to check the vacuum an do the ajustment on it.

Good luck.

Calgary Ole

Not familiar with your model but a 928 tranny shifts smooth under all driving conditions. Sounds like your vacuum to the tranny is not connected. Time to get the Mity Vac out to check HG at the tranny. Driverside on most cars and then Bowden cable might need adjusting.
What do you mean by hard shifting?

jacal128

It dosen't slam in gear but it is pretty hard 1st to 2nd and 2nd to 3rd. Harder when cold.

jacal128

I found the vaccum line thru the fire wall to be disconnected, the car runs pretty good but shifts hard. The problem is I have large hands and getting into that point is impossible, I guess I need to drop the exhaust, are their any items that may need to be addressed while under there with the exhaust off. I did notice what seems to be a small leak on some lines going to the front of the engine ( transmission cooler ? ), it is where the hard line meets the rubber line and goes back under the exhaust and maybe thr TT. I am Going to soak the bolts tonight maybe to be able to remove the exhaust tomorrow. Thanks for any info. Jack

SQLGuy

New O2 sensor WYIT? And maybe new bolts for the collectors? (since they tend to rust from the heat.)

Bill Ball

The vacuum line from the engine to the modulator, if hooked up to manifold vacuum, reduces shifting firmness at idle and partial throttle, when manifold vacuum is high. You should check that you have it connected to manifold vacuum (high vac at idle and decreasing as the throttle opens with the engine running). You should also check that the line going back under the firewall to the tranny holds vacuum. It is common for it to come off the vacuum modulator back at the tranny. IF your full throttle shifts are harsh as well, then the vacuum modulator isn't the only issue.

neilh

You need to hook up a vacuum gauge - if you have a Mityvac, at the modulator pull off the vacuum line, hook the mityvac to the modulator, and pump it. You should see 17 - 19 inches of vac, and it should hold or leak down very slowly - like over 10 minutes or more. Replace if bad.
If that is good - use the mityvac as a vacuum gauge and hook it to the disconnected line coming from the 'Tee' at the engine and start up. look for about the same vacuum at idle, going to nothing as you increase revs.
If you do not see the vacuum from the engine go back up to the 4 or 5 way 'tee' and check it there.
If the problem is between the 'tee' and the modulator, you need to replace the line. I did this on my 86 with a steel brake line from a land rover ( $12 at Kragen) and some high temp silicon tube to make the connections. May sound like a lot of work, but 2 - 4 hours max, including run to buy parts.

Tails

After you have checked the vacuum line to the modulator valve and if you still have a harsh shift you will need to set the vacuum modulator pressure as per the chart contained in the WSM for your model car.

This can be done at idle by fitting a nipple fitting to the connection port just forward of the modulator valve and installing a pressure gauge.

The WSM describes the adjustment using various gauges and running the car at various speeds, however this can be done with the car on jack stands and adjusting the modulator valve pressure via the "T" handle under the modulator valve rubber cap whilst running the engine and transmission in "D" at around 1,500rpm IIRC.

I have done this myself and now my shifts are silky smooth up and down through the gears.

Tails 1990 928S4 Auto