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-   -   Modulator Valve replacement (https://rennlist.com/forums/928-forum/596237-modulator-valve-replacement.html)

Landseer 10-13-2010 05:21 PM

Modulator Valve replacement
 
7 Attachment(s)
86 automatiic is shifting harshly.

Vacuum check showed expected high vac on hose at modulator valve.
But, modulator valve, when checked with mighty vac unit, wouldn't hold vac.

Here are a few pictures of replacement.
Mounting bolts are 5mm hex allen.
Shift acutation rod was popped off stud for access.
Exhaust was dropped a bit.
Heat shield was removed.

Will need to get a shift rod boot, as this one broke-up.

karl ruiter 10-13-2010 05:55 PM

In my S4 I just swapped the cracked rubber cap and it really helped. I will replace the whole assembly later on when I can afford to have the car down for a while if something goes wrong.

Landseer 10-13-2010 05:58 PM

I didn't see that until after loading the pictures!

Dictys 10-13-2010 11:07 PM

What was the part number and cost of the part, as I am thinking of replacing this part myself? Thanks.

karl ruiter 10-13-2010 11:25 PM

Don't remember the exact price, but Roger has it and it is quite inexpensive.

BIMMERMIKE 10-13-2010 11:47 PM

Did you need to drain transmission fluid?
I only have harsh shift from 1st to 2nd and 2nd to 1st but not always, other gears are okay.



Originally Posted by Landseer (Post 7972002)
I didn't see that until after loading the pictures!


Landseer 10-14-2010 12:25 AM

No need to drain / no leaking.
Similar shift behavior here before switching (haven't tried it yet / might need to adjust).
The heavier the acceleration and throttle, the less noticeable, but at light throttle 1-2 had become very abrupt. Valve itself wouldn't hold vac, maybe the cap as pointed out by Karl.

Check with Roger or others on price / part #. Reasonable.

Cosmo Kramer 10-14-2010 12:26 AM

If the valve is leaking vacuum it will shift harshly in all gears. You can replace the valve without draining the transmission.


Originally Posted by BIMMERMIKE (Post 7972797)
Did you need to drain transmission fluid?
I only have harsh shift from 1st to 2nd and 2nd to 1st but not always, other gears are okay.


BIMMERMIKE 10-14-2010 01:50 AM

Could this be my source of vacuum leak?? I used my mityvac to check vacuum at front and was pulling 21 inches

M. Requin 10-14-2010 08:15 AM

Excellent - thanks, Chris. Have to be doing this soon.

Cosmo Kramer 10-14-2010 10:32 AM

If it is holding vacuum at the T at the back of the motor then no. I had a crack in my T that I fixed and it would only hold vacuum for 3 seconds!

You said your car shifts hard on 1-2, is that all the time?

I am trying to find a decent check valve to put on that vacuum hose. On a NA car the modulator sets the maximum line pressure at 0 vacuum. On the boosted car it continues to increase the line pressure with manifold pressure, but I still have 18 hg at idle and vacuum under light throttle. If I adjust the modulator to have a smooth shift at WOT, I get shift flares at light throttle. If I set so it shifts properly at light throttle it shifts really hard at WOT. I have tried a vacuum check valve and it just messes up the shifting, they must accumulate vacuum or they don't react fast enough :(.


Originally Posted by BIMMERMIKE (Post 7972994)
Could this be my source of vacuum leak?? I used my mityvac to check vacuum at front and was pulling 21 inches


Tom in Austin 10-14-2010 10:48 AM

What position did you set the t-handle to on the new valve? Ideally, you'd measure and set the correct modulating pressure when replacing the valve.

underdog928 10-14-2010 12:25 PM

I found a leak where the rubber hose from the modulator connects to the metal line on the torque tube. The hose end was frayed and missing a chunk of rubber. Cut off the bad end, reattached and held vacuum fine. YMMV.

karl ruiter 10-14-2010 03:14 PM

Cosmo, do you still even have vacume there? The boost must change things quite a bit.

Cosmo Kramer 10-14-2010 03:42 PM

I have vacuum until about 1/4 throttle then it is positive pressure. The positive pressure really makes it shift hard under boost. I called Steve Cattaneo at Master Tech today and he suggested getting a check valve from a 1987 300D Mercedes as they are a turbo diesel and are fitted with one from the factory. Unfortunately Mercedes says the part is NLA.

I am going to try hooking my check valve on a T fitting with the check valve venting to the atmosphere under pressure and closing under vacuum. This should stabilize the vacuum signal and make it work a lot better.


Originally Posted by karl ruiter (Post 7974272)
Cosmo, do you still even have vacume there? The boost must change things quite a bit.



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