Porsche 3 speed auto kickdown problem - PeachParts Mercedes-Benz Forum

#1 07-27-2002, 03:02 AM

Hope I'm not imposing on you guys.
I have an 83 Porsche 928 Auto, 44k miles. The box is reputed to be MB unit out of the 6.9 sedans. Fluid & filter changed, works fine except the kickdown doesnt happen. Electric switch under throttle pedal, solenoid on RH side front of box above the pan. It audibly clicks somewhere down there, but nothing happens. The Porsche list cant seem to help me, and the Porsche workshop manuals dont address it much, so here I am.
The solenoid gets 12V on it, can hear a click. Can I remove the solenoid easily - will I get fluid everywhere? Does this box have an MB model/type number? Could it just be O ring problem?
When I changed the fluid it wasnt badly discoloured, the filter didnt look too bad, only a small amount of soft crud in the bottom.
Also, when selecting reverse, there is a delay in taking up drive - is this something I can adjust easily from outside - reverse band?
TIA,
jp

stevebfl · #2 07-27-2002, 04:09 PM

I could have swore the 83 was the first year of the 4spd. My 84 928 has the 722.3 4 spd. The earlier car had the 722.0 3 spd trans (as used in 450's).

The kickdown solenoid dumps governor pressure in both units. The three speed did commonly have a winding problem such that the solenoid didn't work. You won't loose much fluid in removing it. You should replace two o-rings if you take it out.

I would take it out and see if it moves when energized.

The control pressure cable adjustment is also important to kickdown. The three speed does have a band adjustment for reverse. The four speed does not.

#3 07-28-2002, 01:26 AM

Steve,
Thanks for the response!
I think this is still a 3 speed because its a Euro - I know USA and Japan got the 4 speed first.
OK, so solenoid out is not a big deal - screws out, retained how?Check for action with 12V, if not, replace? Also replace any O rings visible - I assume these are on the solenoid body somewhere? There are many MB parts shops over here (only 1 Porsche dealer, and 928 parts are rare), so I should try them for a solenoid? Any idea of part number - same as the 4 speed by any chance?
The cable seems pretty good - I took some slack out once and the shift points moved up quite high, so I slackened it off again.
Is it fair to say these boxes are fairly robust, considering the 928S is 300hp? I have seen a post suggesting the reverse band can be adjusted - cut a slot in the headless bolt, screw in to bottom, back out 3/4 turn - sound right?

Many thanks for your help.
John P
Riyadh

stevebfl · #4 07-28-2002, 01:00 PM

The way to tell whether its a three speed or four is the shape of the pan. The three speed is square with four bolts. The 4spd is rectangular with a narrowing to the rear (in the MB) with six bolts.

The kickdown arrangement on the 3spd is a plunger bolt/housing surrounded by the electromagnet. The pieces are bought separately. The plunger bolt unscrews from the case, tightens on the magnet and is sealed internally by two o-rings. The rings seal both ends of the bolts protrusion into the pressure passage. Leaks from either can simulate a engaged kickdown as its job is to leak away the pressure in the passage.

#5 08-04-2002, 08:35 AM

Steve,
Mine is definitely 3 speed - square pan.
Problem is the solenoid is getting 12V, energising - audible click, but not going down. Is it possible the moving part that should dump pressure is stuck in place? Is the end in an O ring that could hold it? If its not moving, what is making the click noise? Could I have a blocked passage that is not letting the pressure off?
Thanks,
jp

stevebfl · #6 08-04-2002, 10:08 AM

I have never heard one of the kickdown solenoids. I have tested them electrically and never really heard anything. If the solenoid can be heard then I imagine it is working. All the problems I have seen with the o-rings are internal leaks which cause delayed upshifts rather than the opposite.

I would take a big look at the control pressure cable. I would probably make a huge adjustment to it and see what happens. By big I mean a quarter inch or so. make the cable shorter or the housing longer. (I don't remember how the adjustment goes on the 3spd Porsche application.

#7 08-10-2002, 03:48 AM

Steve,
On the button - cable adjustment problem! Just took it up a bit, and electric switch worked fine. I obviously wasnt giving it quite enough travel. I have a parallel switch with the kickdown one so I can drop it down without giving it all the throttle.

Thanks again,
John P
Riyadh

PanzerSD · #8 09-21-2009, 10:59 PM

Where does a guy GET a new Kick down solenoid? I can't seem to find them in the regular channels (fastlane, ect)

whunter · #9 09-22-2009, 04:02 PM

Quote:

Originally Posted by PanzerSD

Where does a guy GET a new Kick down solenoid? I can't seem to find them in the regular channels (fastlane, ect)

It may be a dealer only part.

Porsche provides technical service information on the Porsche TechInfo website:

Technical Service Information

you can also try these links.

http://www.porsche.com/usa/accessoriesandservices/porscheservice/

https://techinfo2.porsche.com/PAGInfosystem/VFModuleManager?Type=GVOStart

Have a great day.

Medmech · #10 09-22-2009, 04:07 PM

Quote:

Originally Posted by PanzerSD

Where does a guy GET a new Kick down solenoid? I can't seem to find them in the regular channels (fastlane, ect)

Shoot me a PM with your email I have a friend neighbor that knows all things 928 he has 2 and I helped drop the tranny and torque tube a few weeks ago.