Landseer

Filter change is pretty straightforward on them. Filling is a bit of a pain. So is lining-up torque convertor for access to the drain plug.


I think when the 86 throttle cable is set and the bowden is set, he will get the 1st gear start in drive. Such is how my 84, 85 and 86 transmissions are setup. ( The 84 is now replaced with an 89 donor box, which operates in the car quite differently.)

Well, here's some information to help us rationalize when the transmissions went to 2nd gear starts:

Turns out with the S4 transmission the shift program was changed to cause a 2nd gear start under certain conditions when moving off in Drive. The change was made gradually during spring 87. Lots more on this in the 1988 Service Info by Year document, here's some of the information:

Changes on Upshift and Downshift Program (Introduced in Spring of 1987)
I n the past cars with an A 28 automatic transmission always moved off in 1st gear and shifted down
into 1st gear with a noticable jolt shortly before stopping while rolling to a stop . A changed shift
program in the valve body now makes it possible to also move off and roll to a stop in 2nd gear for
certain operating conditions .

If the throttle valve is not opened by more than about 260 (26 degrees) while moving off, the car will accelerate
in 2nd gear before it shifts up into 3rd gear and later into 4th gear (curve A - B) .
If, on the other hand, the car is moved off with an almost wide open throttle valve, the transmission
downshifts into 1st gear before rolling away (curve C - D) .
The moving off shifts 1 - 2 - 3 - 4 are then the same as in former transmissions .
Another Possible Moving Off Version :
Acceleration is slow at first and wide open throttle valve acceleration takes place at about 12,5 mph .
The car rolls away in 2nd gear and shifts down into 1st gear at 12,5 mph . The shift up into 2nd gear
then takes place at a road speed faster than 31 mph (curve E - F - G - H).
Advantages of Changed Shift Program
- Less tendency to creep, since the car stops in 2nd gear (e .g . at traffic lights) .
- Soft, comfortable moving-off is possible .
- Lower fuel consumption in city driving .
- No 2nd - 1st gear downshift jolt while rolling to a stop .
- Still possibility of moving off in 1 st gear .
The changed moving-off program was introduced gradually in Spring of 1987 .
New Upshift and Downshift Program in Selector Lever Position 2 :
The car rolls off in 1st gear and shifts down into 1st gear again briefly before stopping while rolling to
a stop . The braking effect in 1st gear is still effective while coasting up to about 50 mph, before the
car shifts up into 2nd gear .


Bill Ball has pointed this out before in old, old postings on the subject, but its one of those subjects that emerges from time to time.

rexpontius

Thanks again for all your input

I will start with the vacuum check and oil change this weekend and let you know if that solved the problems (hope so verrrrry much)

I intend to bring the car back into a very good condition, but off course I have to start with major things first.

WallyP

Try turning the engine to TDC (shown by 0|T on the crank dampener) before you start changine the fluid. If you are lucky, this will still put the torque converter drain plug at the bottom.

rexpontius

Quick update:

Today I had some time to take a quick look and removed the air-filter box, which was pretty straightforward.

I soon found the rubber vacuum line coming from the torque tube and while trying so see where it went, I had one end loose in my hands. Looking more closely I found the T-piece connector where the vacuum for the passenger side fuel pressure regulator was also connected to the vacuum.
While test-fitting the plastic pipe (straw is perhaps better word :-)) into the t-piece it felt as if the straw was too thin, it was just not gripping into the rubber t-piece.

So I cleaned it up some more and managed to get a small tie-wrap around it tightly. Finally I reconnected the vacuum line from the torque tube and also secured it to the plastic straw by fitting a small tie-wrap.

I am not 100% sure it had no vacuum at all, but is was surely a very bad connection, so I hope it will bring some improvement.

While working on the vacuum line I also noticed a completely cracked 3-pin bosch connector (black). I will fit a new connector (luckily Alfa also used the same connectors, so I will use a donor connector from an Alfa :-)) tomorrow. Does anyone know what this connector is for? It has a black, yellow and a blue cable.

Finally I noticed quite a bit of engine oil in between the cylinder banks (under the manifold where the MAF slots in). I hope this is caused by some spilling of engine oil by the previous owner, otherwise there is something leaking oil.
Just to make sure I will remove the inlet manifold completely this weekend and see whats underneath it.
Nice opportunity to clean the manifold as well. The previous owner painted it with some kind of very crappy silver paint which is now starting to chip off.

Last but not least I noticed quite some slack on the throttle cable which also goes to the gearbox, I will tighten this as well to the point there is no/minimal slack.
Could this explain why the gearbox seemed to take ages to downshift when accelerating firmly?

Cheers
Michel

Richter12x2

Yup, I think you nailed it - that cable tells the transmission where to downshift. I think you're going to be much happier once you test drive it.

Sadly, that galley between the cylinder heads catches all kinds of stuff - I spent about 2 hours cleaning it when I had my intakes apart, and it's already collecting dust and grime again.

Landseer

On the 85 and 86, the oil vapor hoses that attach to the cam cover seem to breakdown chemically and ruputure. When that happens, the top of the engine gets misted with oil and it can collect on the top of the motor. There are other ways, too, but this is almost universal on the 85 / 86 it seems.

rexpontius

Ok thanks for the info.
Will I be able to replace these hoses with the intake manifolds off?

Landseer

its the only way / time to really access them. Also, the TPS switch on the throttle body.

rexpontius

Today I worked on the car a couple of hours and have been able to sort the oil leak (indeed cracked hose), repaired the vacuum lines (tested it, held vacuum OK) and removed the slack from the throttle cable going to the gearbox.

The car drives much better now, downshifting beautifully, and upshifts are now significantly less harsh.

However they are still not as smooth as I think it should be. Especially from first to second still goes with a harsh 'clunk'
I also checked the vacuum at the gearbox side which also seems fine (rubber hose stuck to my finger with the engine running, so there is definately vacuum).

Furthermore I noticed there is a high pitch whining noise > 2.500 which seems to come from the gearbox and/or driveshaft.
I check the oil again to see if there were any metal particles (dreaded thrust bearing issue), but fortunately did not see any metal in the oil. Oil pressure is also perfect (5 bars under load, approx 3 bars on idle with warm engie)

I suspect the car sat for approx 2-3 years (only 1k miles in 3 years), so I wonder if the gearbox issue could be caused by the ATF oil in the gearbox. I plan to change the oil + filter anyway next weekend, but it would be nice to know if low or old oil could cause this type of behavious of the transmission.

Many thanks for your feedback
Cheers

Landseer

They seem very sensitive to ATF level. Replace filter and fluid and see if it helps.

How is 2-3 upshift?

It is possible to back-of on pressure slightly at the modulator valve. Search the forum for guidance on that. Proper procedure is to attach pressure gauges and set the valve based on pressure readings. But you could empirically change the setting by a turn, I think counterclockwise, to try to soften the transition. But your 2-3 might not be as solid.


But good filter and right fluid level are important.

Not sure on your whining sounds, I have them on the 89 box, but they have nearly gone away during the couple weeks I've driven it.

Note that the fluid may be yellowish/very dark/black and chemical stinky, that's normal due to a transmission fluid specified by Porsche sometime during the early use of the 4 speed trans. They say specifically that you can't judge trans band condition by fluid smell/color if that is used. Saw that in some obscure documentation.

BTW, the three 4spd transmissions that I have used, all exactly like yours, have had a fairly abrupt 1-2 upshift. And its torque and temperature dependent it seems. And perhaps phase of moon.

rexpontius

2-3 upshift is much softer than 1-2, if 1-2 would feel like 2-3 It would be fine for me.

It also seems that the changes are less hars when I have driven a couple of miles, but that could also be my imagination :-)

I will change the oil next weekend and see what happens.

Must say I have really fallen in 'love' with the 928, it just drives brilliantly, especially for a relatively old car.

I will keep you posted what happens when I change the oil

Landseer

Another thing that you might dive into, next, is the throttle position sensor. It has great effect in electronic shifting of timing under heavy acceleration. There is a way, I'm into it today, to work on the switch without removing the entire intake again.

G Man

Did you check the modulator to see if it will hold vac? You have vac to the modulator which is good, but if the modulator will not hold vac you will still have issues. Simple test if you have a vac pump. Just remove the vac line and attach the vac pump and vac down to around 15 and see if it will hold.

rexpontius

Yep the modulator valve holds vacuum, tested it with simple vac tester, so I think this should be fine.

How does the throttle position sensor affect the gearbox behaviour?
Is it a potmeter type sensor of WOT sensor?

thanks
Michel

mj1pate

+1

You've figured out how to (safely) get the car up in the air by now it seems. Check the transmission fluid level while underneath the car in the exact way the manual describes. Don't be surprised to find the level low. Top it off exactly using the procedure in the manual. You'll probably find that the transmission behavior is much more to your expectations.

Oh, nice choice on the 164s! I tried to help my son locate a "good one", but the pickings are usually slim. He settled for a nice '98 540i. Really want a GTV6 Callaway, but just can't quite get back into the mode of chasing rust on those beautiful cars. Kind of got spoiled by Porsche's Teutonic pragmatism.