Rodrv6

I believe you are looking at the kickdown solenoid on the transmission. I've never removed one, so I can't help much there..........

NSW928

OK well the good news is that I've potentially found the problem. I think I should be able to get enough play to take it out completely if I undo the bolts holding the linkage cables in place. Now to find a new kickdown solenoid.....

NSW928

Here are the filling capacities for the ATF:

Filling capacity approx 8.0 l (from model 87 approx. 9.3 l)
Oil change capacity with converter approx. 6.0 ltr.
(from model 87 approx. 7.3 ltr.) ATF-Dexron II D

I'll change the ATF again when the filter and solenoid arrive, I won't really be driving it until then - it looks like about 7.3L is what I should be expecting?

In the meantime I'll devise a plan to remove the busted solenoid and will post the procedure when I get to it, it might be useful for someone down the track.

NSW928

I'm confident I've found my problem. As a test I glued the solenoid back together with some 2500psi epoxy and let it set overnight. The problem was still there however it took a lot longer to happen for the first time, and I was able to get it to shift from 2nd back into 3rd after slowing down to about 60kmh.

Upon rereading the above, Speedtoys' symptoms are very similar to mine and part of me fears that I broke the solenoid myself when I was undoing the hex head pin next to it!

Greg, are you inferring that if I still have the problem after replacing the solenoid, the next step would be to replace the governor gears, or the secondary pump parts, or both?

antlee928

Hi. I like this colour a lot in the 928 S4 shape. Did you buy this car from an owner in the western suburbs of Melbourne? If so, this owner had undertaken quite a bit of his own maintenance on the vehicle.

Cheers

NSW928

Update.

I replaced the kickdown solenoid with a brand new one. While I was there I changed the ATF, filter and gasket. I have checked and triple checked that the ATF level is right. BTW, the refill amount was 7.5L.

But I still have my problem. The thing I find strange is that it's fine until the ATF warms up. So it seems to have something to do with the changing characteristics (viscosity or expansion) of the ATF once it is heated.

That aside, from Greg's post here and also the troubleshooting section in the manual I am led to believe that the cause could be the centrifugal governor. My next step is to take it to an expert to diagnose the actual problem so that I then know what I am up for.

GregBBRD

If you drop the filter, the valve body, and the intermediate plate, you can actually see the governor/secondary pump gears.

I assume that since you have messed with the kickdown solenoid, you realize that the "O-ring" on the actual solenoid should be not visible and inside the electro magnet?

NSW928

Thanks Greg. I spoke with the Porsche service people out here before I put it in and I'm pretty sure I did it all correctly. I've decided it's best to get a pro to look at it now so I've got in booked in for Thursday, I'll make sure they check my solenoid work while they're at it.

Will report back when I know more.

Avar928

Greg, did you ever find that information on removing the secondary pump?

GregBBRD

No, nothing.

Even more amazing is that Porsche, in Pet or the Workshop Manual doesn't acknowledge that many pieces got changed when they eliminated the darn thing.....no changes in part numbers even though the pieces are completely different visually.

I did finally get into the Mercedes factory parts program and was able to go through every single model and year of the 722.3 transmission....one at a time! I was able to determine when and which model the secondary pump was removed and I have ordered some pieces from Germany to compare to the GTS pieces (GTS does not have the pump.)

I have details of all the differences in the valve bodies, from year to year...and there is only a couple of subtile changes in the GTS valve body.

Speedtoy's transmission works with the pump removed...it has got one glitch that needs to be solved. (Won't shift out of 2nd gear at WOT, when manually shifted.)

Hopefully, a couple of these obscure pieces, from Mercedes, will solve this.

GregBBRD

No, nothing.

I think figuring out how to build and then get the pieces to build a nuclear weapon would be easier that figuring out this.

Either there are very few people that understand all of the changes in these Mercedes transmissions and understand what each chang does, or these guys are the most secretive people I've ever run into.

Even more amazing is that Porsche, in Pet or the Workshop Manual doesn't acknowledge that any pieces got changed when they eliminated the darn thing.....no changes in part numbers even though the pieces are completely different visually!

For instance: The B1 operating piston got updated to a self adjusting (compensates for band wear) piston in the later 928 transmissions. Fantastic upgrade....keeps B1 band pressures optimized as thing wear!

Good luck figuring out what that part number is....even though there are Mercedes part numbers stamped into the pieces!

I did finally get into the Mercedes factory parts program and was able to go through every single model and year of the 722.3 transmission....one at a time (crazy tedious). I was able to logic out when and which model the secondary pump was removed and I have ordered some pieces from Germany to compare to the GTS pieces (GTS does not have the pump.)

I have details of all the differences in the valve bodies in the 928s, from year to year...and there is only a couple of subtile changes in the GTS valve body.

Speedtoy's transmission works with the pump removed...it has got one glitch that needs to be solved. (Won't shift out of 2nd gear at WOT, when manually shifted.)

Hopefully, a couple of these obscure pieces, from Mercedes, will solve this.