88porsche928

Hello, I have a problem with my transmission. For some reason yesterday when driving normal the car will not shift out of 2nd to third until the RPM is very high or when it gets high and i let of the pedal. I read some other post and it seems like I need to adjust the modulator. Does any one know where or how to reach this modulator? Is their any other test I should do before attempting this?

Tails

I attended to this yesterday on a friend's 1989 928 S4 auto as he was having similar problems.

This operation is best carried out with the car on jack stands, safely supported as you will be working under the car, that is if you do not have access to a hydraulic hoist.

Before this operation was undertaken we carried out a full diagnostic check on his car and neayl all sensors etc., were working correctly, a very well sorted and clean car.

It was noted that his 'kickdown" switch was not being fully depressed and his bowden cables to the accelerator quadrant were generally slack and out of adjustment and the Idle Stop Valve was not opening and closing freely. The ISV was given a good dose of WD 40 done the inlet tube to give it a clean and advice was given to give it a few more doses of WD40 over time to try and get it operating correctly to control stable rpm at idle.

It was also noted that the WOT (wide open throttle switch) was not giving a clear signal that it was alway achieving a fully opened throttle butterfly valve every time, so it was deduced that that the applicable bowden cables were not adusted correctly.

1st. You need to adjust the accelerator cable, so that the spherical end of the bowden cable fits on the quadrant arm ball without any tension on slackness when the quadrant is in the fully opened position. To get this correct you have to ensure that the kickdown switch is fully depressed when the accelerator is fully depressed and then this adjustment is made.

2nd. Let the accelerator come back off to the idle position and then adjust the inlet butterfly valve bowden cable so that the butterfly valve is fully closed at idle with no tension of slackness in the cable, so that the ISV controls the idle speed via the LH computer.

3rd. Adjust the bowden cable to the auto box so that it has no tension or slackness in the bowden cable at the idle positon (butterfly inlet valve is full closed). This cable controls the shift positions of the auto box, so it is imperative that it is adjusted correctly.

4th. Adjust the cruise control cable that if fits onto the spherical ball conection on the actuation arm with no tension, but a little bit of slack is accceptable.

5th. Detach the vacuum tube to the auto box from the spider in the LHS engine conpartment , as viewed from the drives seat and seal off the end going to the auto.

6th. Remove the LH section of exhaust pipe from behind the cats to the rear muffler and the heat shield to give you access to the modulator valve (green capped valve with a rubber cup on its outside) in the LHS of the auto box.

7th. Remove the vacuum line end from the modulator valve and check that you can obtain and hold a vacuum on this line. This vacuum is essential to get a correct modulation valve operation.

8th Leave the vacuum line off the modulator valve during testing and adjustmrny. Remove the test port bolt for the modulator valve, this is the bolt located at the aft side of the modulator valve and fit a pressure gauge to a suitble nipple that can be screwed into the test port.

Start the car and bring auto box up to operating temperature and check the modulator pressure, it should be approximately 61psi ( for you model auto box) at idle. To check this correctly it should be done at 50kl/hr or 140 kl/hr, however this can be accomplished by having the car on jack stands, place the gear selector in "D" and take the rpm up to 2000 and the box will shift through its change up cycle to "D" and this is equivalent to 50kl/hr highway speed. Check the pressure on the pressure gauge is at 61psi. If it is higher or lower you will need to remove the rubber cap and adjust the valve via the "T" handle until you achieve the pressure of 61psi at idle and then take it up to 2000rpm as previously described to confirm the correct pressure at 50Kl/hr.

When all the above is done and all items are reassemble take a test drive and you should be surprised how smooth the gear changes will be. My friend was really pleased with the results and his kick down worked really well and surprised him. During the test drive we undertook a knock count (17 knocks in 10,000 firing cycles)

We also checked the rpm at idle and in "D" when car was stationary to check the drop in rpm when in "D", so it would be a good idea to check this WYAIT.

This is a simple and brief description of the opertions that should fix your problem.

All the above procedures are contained within the WSMs or within Jim Moorehouse's Technical CDs and will require you to undertake a fair amout of reading to safely undertake this quite simple opertion if you are a competent DIYer.

Tails 1990 928S4 Auto

Leon Speed

Before you do any adjusting make sure that the ATF level on the fill tank is correct and ATF and filter are fresh (change every 40,000 KM).

Tails

+1 to Aryan's comments.

Prior to starting work auto level was checked at operting temperature. It is advisable to ascertain the last time the filter and fluid was changed.

Tails 1990 928S4 Auto

88porsche928

Sorry for the late response I had alot of things to do since my last post. Today I went to see where everything was before messing with stuff. I looked at the transmission fluid level and it was on the max line, the container looked old so I don't know how accurate the color guage was. the cap had alot of gunk on it as well as the cover you would take off to replace the transmission filter. I also found where the modulator is and it has a black cap over the t handle thing. I am alittle confused about some of your steps. You basically want me to disconnect the vacuum line from the modulator and to part that connects to the spider / auto box (i don't know what that is) and see if the line can hold vacuum pressure? Then with the vacuum line unplugged from the modulator start the car and remove the test bolt? then plug a pressure guage in the test port then at idle it should be 61ps then at 2,000 rpm with the car on drive? how do i know the modulator is good or bad?

Leon Speed

The transmission oil level needs to be checked on operating temp. if the car sits without moving a few days, the oil drains back into the container and you won't get an accurate reading.

WallyP

Hopefully, you checked the transmission fluid level correctly, but just in case...

These items are mandatory to check the level correctly:
- Car must be level both front-to-rear and side-to-side.
- Engine must be running. The level is meaningless otherwise.
- The transmission must be in Neutral or Park.
- The fluid level must be between the two upper marks on the tank.

Oli928

I don't know if this will help, but I had a similar problem on my 1989 928. It turned out to be fairly simple. I had a vacuum leak (at the vacuum line junction below the air filter area). The line pulled loose from the junction. The line had enough slack to cut off the end (to get a semi-fresh end) then reinserted. Worked perfect. As mentioned in other replies, if you have the proper tools, check for vacuum leak.

Alan Almoradie

Hey all,
I have a 89' porsche 928s4 w/95,500mi and needed a torque tube overhaul so I found a salvage(but in great condition)90' 928s4 TT w/60,000mi that would swap out easily and I just assume the loud whinny noise would disappear but unfortunatley it's still loud and the whin is suddle but still there??!! what gives;(. My mechanic said my TT was trashed and needed to be replaced and said the new TT was tight when hand spun(no loose bearings). So can it be that the new TT just went bad?? Any thoughts would be appreciated. Thanks all

Landseer

Why a swap? Did you considering a rebuild instead using new upgraded bearings.
(good find on the donor car, though)

One of us hobbyists would have rebuilt the tube using the new Constantine bearings, else bought a rebuilt tube from 928 International. Not used a donor tube as-is.

But it might not be the problem at all. Several of us have had whining from auto trans units, bearings or primary pump have been implicated. Curious how yours developed and how you decided on the torque tube being the issue. Try some searching here.

What is the crank endplay on your car? Mechanic should have measured that also and explained to you how he would take precautions to ensure that after the tube swap the engine wouldn't be in jeopardy of thrust bearing failure. Probably not core to the whine sound, but now more than ever you need to learn about this situation that affects S4 cars. There are a couple of auxilliary clamps that can be used to inexpensively help protect the car.


Where are you located? You might be near a good support group of 928 rennlist guys.

hb4

Hi Alan,
Welcome to the 928 Forum. If your car is an Auto, then it could be the Torque Converter bearing gone bad, assuming you and your mechanic are convinced it's not the used TT.

It always helps to put your car info in your signature, and give your location as well. And we are photo hounds, so start a new thread and introduce yourself. Lots of good advice here; likely one of the experts (not me) will chime in with more detail.

dr bob

Your post deserves a thread of its own, since there is no relation at all with the original poster's problems except that the parts live under the car. Perhaps one of the mods will help you with that.

---------------

The torque tube bearings are wearing parts, so you may have bought another 20k or so of life with the used TT you swapped in. Considering normal labor costs for R&R that part, it only makes sense to put a rebuilt tube in with new bearings to eliminate the problem for another 25 years or so.

Meanwhile, there are several things that might cause a whine, none of them the torque tube bearings. The TT bearings rumble more than whine as they go south, more a grinding noise than a whine, louder as engine speed increases rather than higher pitch. They are rather easily diagnosed with a stethoscope under the car with the engine running in neutral. Same stethoscope can be used back towards the torque converter housing to diagnose input shaft bearings there. After that, the stethoscope loses effectiveness as you get to the transmission housing since there are a lot more bearings and bushings inside, and sounds transmit from all of them to the case. At that point it gets to symptomatic diagnosis, with noise relative to engine speed forward in the box, more related to road speed is at the rear. Then you get to narrow it down from there.

Bill Ball

I've never heard torque tube bearings whine, although I suppose it's possible. When they fail, the TT usually emits a low rumble/rattle and there is often noticeable vibration throughout most of the RPM range. I would lo0ok for that whine eslewhere. I will tell you that my transmission has made a whine like a bad fuel pump when in park or neutral (goes away in gear) for over 5 years. I have no idea what the actual source is, but it has not changed at all during that time. So, I decided to just ignore it.

Alan Almoradie

Thanks all for your helpand knowledgeable comments. I'm from Chicago(very few sharks around here)but after making the swap I should've just rebuilt through Constantine. So that'll be the next 90k mi. I consider you all shark enthusist my best friends

the flyin' scotsman

My S4 TT whines........like a loud supercharger so it does happen.