Asiandude

Hi all
My '87 S4 auto has a clunky gear change. I bought the car with only 5K miles on the clock and did the following to try and improve the transmission action:
1, Fluid and filter change (shell synthetic atf), reckon the old fluid was original from 1987!
2, Checked and adjusted cable adjustment
3, Adjusted the servo valve on the side of the transmission (anti clockwise)
4, Checked and retorqued the forward flex plate on the torque tube
These improved the gear change quite a bit and if accelerating smoothly everything's fine. If in slow traffic however, the 2-3 change is a right old "clunk", is this normal? I don't have any other 928s to compare!!
The transmission is oil tight and the fluid level is correct per wsm. The old filter looked clean enough, with no clutch material or metal in it.
Any thing I can do to smooth out the "clunks" (apart from buying a manual 928!)
Thanks
Joe.

WallyP

When you adjusted the vacuum modulator (the "servo" on the side of the transmission) did you check the vacuum level? There should be manifold vacuum at the modulator.

Not unusual to have a leaking/disconnected/blocked line to the modulator.

blown 87

I agree

Not having manifold vacuum will make one hit hard, it thinks you are harder on the throttle.

That line may have been there for 23 years, lots of time for things to happen.

86'928S MeteorGrey

If the transmission checks out fully, it could be a suspension bushing, linkage, or a CV joint.... Is it just an abrupt shift, or a solid metal clunk?

Angel84-928

Joe, Thanks for asking this question!
I seem to have the same exact problem. In slow speed it clunks but if I'm on it a bit, it shifts nicely. Hmmm Does anyone have a pic of this vacuum modulator? How is the Vacuum line routed?

WallyP

The vacuum modulator is a round device on the left side of the transmission. There is a round black rubber cap in the center, and a vacuum line on the side. The vacuum line runs from the intake manifold along the top of the torque tube to the modulator. Check the vacuum line to make sure that you have full intake manifold vacuum.

Asiandude

Thanks for the suggestions guys, your help is always appreciated. I've changed engine and transmission mounts, checked the CV joints (and done the boots) and the suspension seems tight. If I wind in the modulator the shift/change gets harsher so vacuum must be getting to it (I guess), I'm afraid that 22 years of very little use has maybe caused problems in the transmission. Why do people pay huge sums of money for quality cars and then hardly ever use them???

WallyP

Very easy to check the vacuum, then you will know for sure...

shadowknight

What is the process of removing the vacumm modulator?

blitz928

Could be trans mounts, I replaced mine a couple years ago and it was money well spent, shifts smoother with some "cushion".

JHowell37

It's not enough to simply check the line with a hand held vacuum pump. You need to visually inspect all of the plastic portions on it. When the line breaks down from excessive heat, it can collapse on itself. When it does that, the vacuum modulator loses vacuum, but since the end of the line is sealed, you don't notice the problem in the form of a vacuum leak.

GlennD

I had the same problem (self induced) when I was cleaning up and re-seating the vacuum lines at the back of the engine (86.5 auto). I created a vacuum leak by having one line (from that small multi-headed rubber vacuum manifold) not in all the way.
The result was the transmission clunked each shift when driving slow. Stepping on it resulted in a slightly softer shift.

Perhaps you (inadvertently) pulled the vacuum line from the engine to the tranny. That is where I would check before pulling the modulator.

Good luck
Glenn

WallyP

That is six times for the recommendation that the vacuum to the modulator should be checked - a free five-minute check.

So far, no indication that the check has been done...

Asiandude

Ok, so a bit of an update then....
I live on the other side of the world from you guys where tools like a mityvac and then the spares have to be ordered on line which can take weeks or even months to obtain, so I'm afraid the thread got a bit cold. A vacuum check revealed that there was indeed a leak so I routed-in a new vacuum line (the original goes over the torque tube!), unfortunately the modulator was also leaking so got one of those in from Singapore. The transmission now shifts smoothly - new mounts new fluid new filter new modulator new vacuum tubing - probably my most successful repair to date (just took awhile!)
Thanks again for all your ideas and assistance with this.
Joe

WallyP

Joe,

Congratulations on getting the problem solved, and thanks for closing the loop.