Porsche Enthusiasts Club Forum

I wonder if I could enlist your help.....

I have lost my kickdown 2 weekends ago on my way to a TIPEC garage day. Topped up the oil with 1/2 litre of oil in the box as the oil level when running was on the lower line. Hoped this would have sorted it for the Merry Miller meet but still no difference.

The autobox was running OK and shifting up & down OK up until this. During my run to the meet I had auto shift when I started out but then fist I lost full kickdown on the switch and then I lost fist kickdown from pressing accelerator moderately. The stick shift works OK and the gears change up & down OK but normal auto change up and kickdown has gone. The Porsche garage quickly checked that the cable was still fitted and not slack for me.

When I start off from rest the box does change up the gears but if give it any accelerator it sounds like its trying to change down - but doesn't sound like it can quite get there.
- I will check the oil level again today on the ramp
- I will also check the vacuum spider under the air box
- MAybe I need to get the oil changed with new gasket & filter - if that would solve my problem?

Has anyone suffered this loss of auto shift & kickdown before or has anyone any idea or pointers to what can be wrong?

Many Thanks

Steve

Just checked the vacuum spider by the brake vacuum valve - this is a Euro car - and I can't hold vacuum even without ignition on? I can get up to about 15mg then it very slowly drops. When I turn ignition on it drops immediately and I cannot hold any vacuum at all?

** The vac line that is loosing vacuum is the one that goes into the left hand side inner wing [Left hand side - sitting in the car that is] this doesn't hold vacuum at all.

Thanks

Steve

On a similar issue, I can see a vac pipe that has been "blocked off"? The pipe seems to go back under the MAF area and under the Inlet manifold - anyone come across a blocked off vac pipe here before?

Thanks

Blocked the y-piece vacuum pipe off to the Cannister and tested the vacuum from the brake check valve side and it was v.good but would gradually start to fade. So I took her out for a test drive to see if my kick downshift up & down was now working - but alas no different!

So back to the drawing board!

Tried to test the kick-down switch as well with the ignition on and couldn't hear any solenoid clicking in? Got my wiring diagram out and found the relay XV position doesn't have a relay in that position on my fuse board on MY88? Seems I need to do some more checking to get to the bottom of this!

check kickdown cable tension??

Hi Steve have posted to the Rennlis thread with info on the vacuum reservoir and y- piece

Cheers

Adrian

Well After finally finding a Union nut very kindly supplied by Paul Thorn off the list - Many Thanks - I fitted my new union nut & seal to the Auto oil pan and tightened everything up & re-filled the auto box. Everything runs as sweet as a nut and no leaks - but my gearbox doesn't kick down still!

To refresh, the symptoms are; as I drive from start the gearbox will change up normally. If I want to go faster and drop a gear by the kick-down {not double kick-down via the relay] then as I apply the gas peddle some more the revs go up but where it would normally kick-down a gear you just feel a slight hint of an action but nothing happens. I can move the stick shift and drop it into any gear so the gearbox works in that regard. But there is no kick-down form pushing the accelerator further to the floor, just a faint hint that something is trying!

The auto gearbox was working perfectly with full kick-down some 2 months ago and it just disappeared on me whist driving to a tipec garage day
I have changed the filter for new and put new ATF oil in the gearbox
Might the Beldon cable be broken? I have tried it but it seems to still be attached
I have some vacuum @ the 7 way connector but it does seem to drop

Anything obvious I am missing here?

Help needed from the list

Thanks in advance

Steve

Hi Steve,

Maybe problem with the kickdown soleoid or supply to it? Live at rear of transmission close to diff I believe.

Test with ignition on. When you press the kickdown switch (by hand to make su it's not pedal not engaging button) you should hear a click from the solenoid.

Didn't you also have the mysterious missing kickdown relay? Have you found it? I havent checked wiring diagram but presumably the relay energises that solenoid.

I can print out and email to you the kickdown troubleshoot from manual if that's any help.

Adrian

Hi Steve,

Just checked wsm which is typically brief on section you want it to be detailed on, i.e. kickdown problems!

Says this, confirming my suggestion to test solenoid:

Condition: No kickdown downshifts

Correction: 1. Check voltage at solenoid valve. If necessary. check wire
connections against current flow diagram.

2. Remove solenoid valve. Connet removed valve to power
supply and check function. replacing if necessary.

3. Tighten control pressure lever bolt on transmission. Then
check control pressure, adjusting if necessary.

4. Check movement of kickdown control valve in shift valve
housing upper section, replacing shift valve housing if
necessary.

Point 4 interesting. I don't know what the control valve looks like so maybe PET shows location and appearance clearly?

Cheers

Adrian

I should have really corrected my title for this post as "Downshift" not working to be more accurate.

Its the Bowden cable / vacuum modulator down shift that isn't working not the floor mounted kickdown switch.

Just for clarity.
Steve

Control Pressure Cable!
Spent Sunday trying to readdress this probelm and take a fresh look at it. Got the Auto trans oil pan off again to check if the Bowden Cable /Control Pressure Cable was attached to the hook in the valve body. Well to my dissappoointment it was connected & working the plunger! Damn!

So, what to do next? I have a new modulator valve which I can try and then its major surgery I think. Not much more I can do with time available other than take it down to Paul ANderson in Stroud and let him sort it out!

Need the gearbox working mint for my trip to the Laon Historique in France on May 11th

Steve

"A Porsche 928 gives you a sense of being someone special, you drive as if you have to live up to the car. Your temper improves miraculously; if anyone overtakes you or cuts you up, it's because you have given them permission to do so, or because they are suicidal, not because their cars are more powerful or their driving more skilful! "

Hi Steve

If I were you I would pop down to Pauls...take the valve with you and he will pop it in a in a few minutes if needed...

All the best Brett

I reckon Steve's 928 just wants him to keep his license!

You could be right Adrian . But remember my stick shift still works so I can still unleash all that 928 - Hell hath no fury - when the mood takes. Just the old girl feels sluggish under normal driving conditions as the up shift is really quick thru the gears.

I will let Dr A sort it out

Well at long last I have my 928 S4 Auto gearbox fully back working correctly again! Whooooppppe!

In the end I gave in & took it down to Paul Anderson and he did some investigation & found the oipressureuGovernoror was sticking & not providing reliable oil pressure to the Gearbox. So, we resorted to putting my old Silver S4 auto box back in along with the LSD. Great result to finally find out what was wrong all this time.

So I am all ready for my Laon Historic trip in 3 weeks time with a fully working gearbox. Just have to do a few small jobspreparationtion for the trip overnextnext weeks. Can't wait!

Thanks everyone for their help along the way trying to identify the troubles.

Steve

"A Porsche 928 gives you a sense of being someone special, you drive as if you have to live up to the car. Your temper improves miraculously; if anyone overtakes you or cuts you up, it's because you have given them permission to do so, or because they are suicidal, not because their cars are more powerful or their driving more skilful! "