Modulator Valve replacement
#1
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
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.
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.
#2
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
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.
#6
Rennlist Member
#7
Rennlist Member
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
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.
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.
Trending Topics
#8
#11
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
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
.
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
![Frown](https://rennlist.com/forums/images/smilies/frown.gif)
#13
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
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.
#15
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
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.
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.