Bill Ball

I was expecting Steve Cattaneo to see your thread and comment about 4th gear. I honestly don't expect trans cleaner to resolve this. It can improve failure to shift into a gear by freeing up stuck shift valves in the valve body, as it appears to have done for me. But that probably is not your problem. Free-wheeling in 4th gear is something else, and I would expect Steve or borland, the two guys around here who know the AT best, to have commented. I suspect one of the clutches is gone -->rebuild.

Tails

Power Flow in Automatic Transmission (A28 4 speed)

4th Gear Power Flow

Applied Operating Parts:

Clutch K1 engaged

Clutch K2 Engaged

Clutch 'F' One-way -outer race - unlocked

Brake Bands B1, B2 and B3 not applied.

As in all gears , power flows from turbine (torque converter) via drive shaft to the Ravingneaux planet gear set is held by the applied clutch K1, the drive ratio is 1 : 1.

By the application of clutch K2 the sun gear of the rear planet gear set is connected via components of the Ravingneaux planet gear set with ring gear of the rear planet gear set, this locks the rear gear set and the ratio is 1 : 1.

So what does this mean?

My conslusion is that either clutch K1 or Clutch K2 could be slipping when transmission is heated up to towards operating temperature which give the loss of power flow to the transaxle, however Steve Cattaneo is the resident automatic transmission expert and he can point you in the right direction.

When you change out the ATF was there any clutch plate residue in the sump pan?

It was noted that the old ATF had a burnt smell.

Did you inspect any of the exposed surfaces of the rotating internals to see whether there was evidence of high heat (multi colouring of the surfaces)?

In making this assessement I have assumed that you checked that the gear selection lever on the transmission was in alignment with the auto shift, as previously recommended, so that the activation of the internals of the gear box were correctly carried out?

Tails 1990 928 S4 Auto

borland

Your ramps are unsafe unless you have the wheels blocked. Don't count on the Park or emergency brake. I would recommend you use jack stands instead.

If 3rd gear is ok, then suspect K2 clutch. See the diagram below. You might inspect the K2 shift valve after removing the valve body. Cleaning this might find the problem, otherwise you would need to remove the tranny from the car inorder to service the K2 clutch pack.

Tails

Boland is right, as when 3 gear is operational the K1clutch is applied, so this rules out K1clutch not activating correctly or slipping and points to the K2 clutch.

I should have done some more reading/research especially the Trans/tec on the 722.3 and 4 series transmissions.

Tails 1990 928 S4 Auto

evozine

These diagrams will help me diagnose, thanks for posting them. That said, I will get it up on ramp(s) again this weekend, I'll be sure to block off the front wheels if I ever raise the rear only.

I didn't adjust the shifter cable last weekend because I was afraid that I wouldn't be able to get it back on. I agree that I need to adjust this cable before I re-inspect the trans. My guess was that the correct adjustment of this cable would not fix the specific problem I'm having with 4th not engagin- am I correct?

The trans. fluid looked pretty clean, and I couldn't see any shavings or gray powder...

I've been driving the car this week, using gear 3. My goal here is get comfortable with the car, get the detergent engine oil moving through the system, etc.

Bill Ball

There you go - Tails and borland have sorted through this. If it is the K2 shift valve, you might luck out with some trans cleaner additive - they can work on sticky valves where a fluid change fails to do so, as I have experienced with the 1-2 shift valve. Mine was stuck so I had no first gear starts. A fluid change made no difference, but adding some trans cleaner fixed it within a day. It came back a few months later. Another shot of additive and it was resolved. I have since changed the fluid a few times and have not used any further additive. It's been 3-4 years and the tranny is still shifting properly. Here's hoping, otherwise it's rebuild time.

Tails

When undertaking fault finding I suggest that you go back to a starting point and follow a logical pattern to ensure that all is adjusted correctly before moving to any strip down, repair or replacement in the trransmission. This procedure holds good for all vehicle problems.

Repair by replacement to try and solve a problem can become a very expensive exercise, especially with Porsche parts and if you have not identified the problem fully with the transmission I would suggest that you undertake the following steps first:

1. Check gear selector lever on transmission is in sync with auto gear lever and safety lock switch is correctly adjusted so that you can only start the engine in Neutral or Park. WSM gives procedure

2. Check and adjustment the 4 Bowden cables on the throttle linkage on the RHS of the air inlet box (looking aft whilst standing at the front of the car).

There are four cables to be adjusted 1. Accelerator linkage 2. Throttle body linkage 3. Auto transmission linkage (control perssure cable to automatic transmission) and 4. Cruise control linkage.

a. Check idle RPM is 675 +/- 25 (between 650 and 700 rpm)
b. Adjust Accelerator linkage to ensure that the throttle plate is fully opened. There is a spring on this linkage that allows you to go to the floor(peddle to the metal) to ensure the throttle plate is fully opened and there should be some tension on the spring.

c. The throttle cable to be adjusted to be an exact fit with no tension of slackness whilst maintaining the idle rpm to specifications above. Be careful if you disconnect the cable that it does not come off the guide pulley to the inlet butterfly valve linkage.

d. The auto transmission control pressure cable should be exact, no looseness and without strain (no tension). This is import as it will effect you shift points and the harshment of the shifts.

e. The cruise control cable should be exact, no slackness or tension.

3. Check ATF level cold or hot as per WSM (you have already changed the filter, pan gasket and renewed the ATF in the transmission and torque converter?). Also ensure that you have operated the transmission as per the WSM procedure to get the correct fill level. Don't overfill as the ATF can foam and cause problems.

4. Take note of Bill's suggestion of using the Auto Transmission Cleaning Fluid to free up any stuck valves etc. If this works then go no further as the problem maybe solved, if it does not then move to step 5

5. If 4th gear is still not functioning correctly check out K2 shift valve as per Borland's advice. If you remove the valve body, be very careful not to lose any of the small valves, springs etc contained in the body whilst getting to the K2 shift valve. Pretty good description of how to remove the valve body in WSM, but do not use compressed air to blow around the body because of these small spring and valves etc. As me how I know? Been there done that and got the T shirt.

6. Whilst the valve body is out check out internal of the transmission for excessive heat especially the K1 and K2 clutch and the B1 and B2 brake bands. No signs of heat could mean that no slippage of K2 clutch, however, you have to make the decision whether to dissamble the K2 clutch or box up and see how it operates. Whilst you are in there you can check the clearance on the brake band as per WSM.

7. However, before venturing into the valve body removal, the checking of the K2 shift valve operation or the K2 clutch strip out and overhaul I would advise that you wait to hear from Steve or you may decide to give him a telephone call and discuss your problem as he is the expert.

Tails 1990 928 S4 Auto

Tom928

In my 84, I had a B2 piston failure. Delay in drive with intermittant slippage and sometims no forward movement. When it did work it had a flaring shift from 2nd to 3rd. Steve had me install a new B2 piston, bushing and band adjustment pin, a K1 spring kit and adjust the modulator a couple turns.

The B2 piston cleared up the slippage and no movement, the K1 spring kit stopped the flaring. The adjust makes the shifts faster or harder and I am still trying to get this right.

Steve is defintely the guy to talk to about transmission problems.

evozine

Yes, I did get an email from Steve, I sent hime my symptoms yesterday.

Update:
The minor adjustment I made on the transmission cable today fixed the problem with not being able to select second gear, but the problem with 4th gear persists... I suppose driving a 4 speed as a 3 speed will have to do for some time.

This means that all gears are selectable and working except fourth, so I am making progress, learning about porsche maintenance. All in all it was a great day.

We'll see what Steve has to say.

http://www.evozine.com/porsche

evozine

Does anyone know if the k2 clutch is accesible from under the car (without dismantling the entire rear end...) ?

Three Speed Al

borland

No. I already addressed this.

I don't know the progression of your cars problem, but it's likely that the valve body initially malfunctioned, causing the K2 clutch pack to slip. The PO likely drove the car with it slipping, so the K2 clutch pack is probably toast and needs new steels and frictions. Fixing the valve body may resolve the problem, but that may not be enough.

Get a copy of the Morehouse CDs and look at the WSM to see the teardown procedure.

Steve Cattaneo

You have the symptoms of a failing B2 piston, I would check.

evozine

Well I finally took the plunge and attempted to find out more about my 4 gear failure in my 1984s auto transmission. I removed the valve body as one piece, then carefully removed the side plate that houses the K2 shift valve. It was a little sticky, so I cleaned it up and reassembled it, which made it a little smoother.

I put it all back together with new fluid, but the problem persists. Can anyone tell me if the B2 piston is serviceable without removing the transmission, as I think I may have to pull everything apart another weekend to resolve this problem...Since I am a relative novice with auto transmissions, it might make sense to pay someone to rebuild mine if the valve body is in working order.

Al, 3 speed for now, Munevar

evozine

Ok, I may have answered my own question here, but still, I have more:

I found the documentation that references the replacement of the B2 piston for a 1990S4 auto trans.
Will these procedures apply to a 1984S?
Does anyone happen to have a smiliar writeup for a 1984S B2 piston failure?
Lastly, the writeup on the B2 piston failure has different symptoms, but I sounds like it's worth a try...

I must say, the valve body mechanism is quite cool, lots of little springs and plunger devices....

thanks again,

Al

SeanR

The B2 is serviceable with the tranny still in the car. It can be a pretty easy fix.

There was a thread recently talking about the replacement of it and it is the only thing I've done on them. Transmissions scare the hell out of me........because I've not dug into them.

Here is the thread....it was down about 7 clicks from this one

https://rennlist.com/forums/928-forum/429605-question-about-b2-piston-and-b2-band.html