x98boardwell

I have searched and can't seem to find what I'm looking for.

I have addressed the shifting issues with the cable on the throttle body and it seems to shift better. The transmission was rebuilt almost 5 years ago but hasn't been driven more than 2,000 miles in that time from the PO.

The issue is when driving and putting the gas pedal to the floor to pass another car or just for fun (depending on my speed) it will downshift one gear too far and will be at 6500+ RPM's, which is scaring me so I haven't really pushed it as I don't want to hurt the motor at that RPM.

Is someone familiar with possible adjustments or is this somehow related to the internals of the transmission with springs rather than the Bowden cable or any other outside adjustment options? Could it be fluid related..?

Thank you for any help on this... I'm at a loss.

Bryan

Mrmerlin

put the shifter into the next lower gear when your looking to pass this will shift the ns one gear lower and dont press the pedal to the floor thius engages the electric kick down otherwise loosen the bowden cable half a turn till you find what you like

x98boardwell

Thank you for the quick response. I adjusted the Bowden cable tighter as it was shifting too soon, which now is better. Before I adjusted the cable it was doing the same thing regarding the downshifting early so unsure if that will help with loosening as it will just shift too soon again and now will have two problems. Thoughts on this behavior? Any other ideas on why it could/would be doing this?

Bertrand Daoust

The cable at the quadrant is too tight.

Like Stan said, try loosing it half a turn and see.

If not enough, another half, etc.

Dont forget, the cable adjusts shift speed, the modulator adjusts shift firmness.

Edit: Just read your last post. If you loose it, it will upshift sooner but will need more pedal action to downshift.

x98boardwell

Thank you for the insight. If I tightened the cable since it was shifting too early and now with the cable tighter it shifts correctly and my issue is when hitting gas pedal to pass someone and it shifting into too low of a gear, will loosening the cable help me at all? Wouldn't the old problem of shifting too early just come back? Also, the downshifting issue was still present then as well? Just making sure I'm not going backwards. It seems as these two problems may not be related.

Edit, just read your edit, haha. Yes, so loosening would bring back my previous problem. Could anything inside the transmission be causing/allowing this?

Kevin in Atlanta

The white car I have on eBay had it's kickdown switch bypassed. A PO added a wire that set the kickdown on all the time. I spent a lot of time dialing back at the quadrant with no success. It wasn't until I was detailing the interior that I found the bypass wiring. Once removed the car was a pleasure to drive. Hope your solution is that simple.

x98boardwell

Thanks Kevin, mine doesn't kick down unless at 95% plus with the pedal so it does take a lot but when it does, at certain speeds it shifts into a gear it shouldn't as the appropriate opportunity has passed but it does it anyways throwing the car into a very high RPM range which doesn't help performance as it's at the end of its torque curve and also could damage the engine down the road.

I dont' think my issue is what your referring to but to clarify at what pedal or how often did it kick down? Based on your post it seemed almost all the time?

wpgshark

a vacuum leak can mess with the shifting.

OTR18WHEELER

When you say down shift, it seems you descibed an up shift at 6.5k while at Wide Open Throttle.
I believe that the shift points from 1st to 2nd while WOT from a dead stop is up to 45 MPH in 1st, (~65k rpm) 2nd gear to 85MPH (~65k rpm), ..
I've never carried third out while WOT, but on the lighter side, tooling around town my car will shift smoothly all the way into 4th in under 50MPH., ***a slight lift of the throttle will induce an up shift at low- mid rpm range.
....as for 6.5k RPM, it was designed that way, or else the red line would not be 6.8k.

Kevin in Atlanta

There is a switch behind the gas pedal. It is independent of the kickdown achieved when pressing the accelerator pedal. One form of kickdown is cable induced, the other is the switch I just described. When the jumper was in place the transmission would remain at a lower gear and higher RPMs until I removed my foot from the pedal. That can be unnerving.

Bertrand Daoust

This.
If you're car has been modified to have the kick down switch engaged all the time (which would not be a good thing) or when you're activating it (pedal to the floor) like when passing a car, it's totally normal that the transmission downshifts two gears, depending at what speed you're going and in what gear you're in.

If it's up shifting at the right moment (not too early/late) under normal driving condition, the cable is probably fine. It will also downshift from fourth to third when pressing the accelerator pedal. Not much if it's adjusted on the tight side, a bit more if it's adjusted on the soft side.
If you need to press the accelerator pedal quite a lot to downshift from fourth to third, it is not tight enough. Maybe it is very loose and you need to hit the kick down switch for the transmission to downshift causing it to downshift two gears all the time. This can be unnerving like Kevin said!

x98boardwell

Thanks everyone for the input.

My dilemma surrounds 3rd to 2nd gear as that is the most viable scenario and speeds at which I drive.

Sometimes when downshifting from 4th to 3rd when passing someone it will downshift all the way to 2nd when it's viably past that opportunity. This means it shoots to 6500+ rpm's and seems to be a bad decision that the transmission has chosen.

Before I tightened the bowden cable I had upshifts too early meaning it would go to 2nd, 3rd and 4th too soon even under hard acceleration and would seem to bog down for a lack of better terms as the rpms would be too low while trying to accelerate. Under normal driving conditions I can see where this would be fine but not when the pedal is pushed down a fair amount in a spirited drive scenario.

Does this make sense in terms of what's happening?

GregBBRD

Because the '94 and '95 GTS's have dynamic kickdown, proper correlation between the throttle and the TV (kickdown cable) is essential.

Randomly shortening and lengthening the TV cable usually just results in a confused mess, with these particular cars. (At this point in time, more are messed up than are correct....especially if the transmission was removed by someone who was not extremely familiar with this particular model.)

Adjust the throttle cables and kickdown cable properly, in order to get perfect correlation. When you are done doing this, you should not have to move the kickdown cable more than 1 turn to perfectly "tune" the kickdown to the desired result.

Confirm that the dynamic kickdown system properly functions. It is common for the special throttle switch that is required to not be working. (Note: At one point in time, these special switches were NLA....not sure about right now, but I'm pretty sure we still have them.)

If the engine revs too high on shifts (6500 is way too high, especially if you have an early '94 with the weak connecting rods) with the cables adjusted properly, the rebuilder did not properly adjust the transmission shift point, internally. (Also common with rebuilders that are not really familiar with this specific 928 application.)

When everything works together, these automatics wirh the dynamic kickdown are great fun to drive!

x98boardwell

Greg, what you are mentioning seems like it could be the culprit.

I did print out your directions on how to properly adjust those cables. I will do that and report back. It is very possible that the internal portion you mentioned is also a potential issue. I local german shop here in the Central Valley rebuilt the trans after it wouldn't go into or come out of reverse.... can't remember as the PO told me the story.

I think when I was adjusting the Bowden cable I must have turned 5-7 times tightening it when attempting to adjust the shift points, clearly I was adjusting too much but it did seem to help. I shouldn't have adjusted it that much.

Regarding the internal adjustment, is that something that is adjustable with the pan off or would it need to be removed to be serviced/adjusted?

On the last part regarding the revving too high, it only does it on downshifts when passing. It will never run anywhere near that RPM range when just accelerating from a stop. The last 8 of my VIN are RS820146, do we know where this is in the run of the 94' models?

Thanks for the help!

GregBBRD

Reverse clutches are the very first thing to fail in the GTS automatics....I generally see failures as low as 100,000 miles and as high as 240,000 miles....totally depends on how much reverse was used. (As well as how it was used.....people that wait for reverse to engage completely, before giving the car any throttle get longer life.)

The fact that your car doesn't hit excessive rpms on an upshift probably means that your issue is completely related to the TV cable adjustment. Proceed to adjust the cables at the throttle quadrant.

Disconnect the TV cable. Get full throttle without activation of the electrical kickdown switch on the floorboard. When the kickdown switch is activated, you should see the spring on the throttle cable from the pedal (at the quadrant) compress. Spring should not compress at full throttle without electrical switch activation! This spring allows one to get full throttle without kickdown and full throttle with kickdown, without breaking the cable. Note that when adjsutment is proper, the levers on the throtyle quadrant will not move....only the spring will compress.

When done with this, have someone hold the throttle down to full throttle (with or without kickdown switch activation) while you manually extend the TV cable to its full travel. Simply adjust the ball cup piece on the TV cable, so that it snaps onto the ball. (Good time to lubricate all of the throttle ball cups, BTW.

You can change the cable tiny amounts, from this initial set-up to change shift points, if you find the need.

Notes:

It is common for the bearings inside the levers on the throttle quadrant to significantly war the actual shaft on the main bracket. I replace the bracket and the internal bearings on many cars.

The cables do not seem to stretch much. Most all of the throttle cables that I replace are do to broken plastic end pieces.

One of the things to watch for, when adjusting cables is the cruise control cable. It is common for the plastic ears that secure this cable to be broken, which allows this cable to pop out of the bracket and allow the forward edge of the plastic piece to catch on the bracket. This will keep the throttle open and can be very dangerous! A couple of tie wraps on the square portion of the cruise control cable (where the tabs were, originally) will keep this from occurring.


I'm not very good at translating VIN numbers to engine numbers. This is also am uncertain thing to do, given that Porsche replaced several engines, under warranty, for excessive oil consumption. However, the connecting rods got updated starting with engine numbers 85R00533 and 81R50597. There's a technical bulletin (#9401) on this change in BOOK K, page 11. I've seen several sets of the "updated" rods that still have the 1R designation, which is mentioned on page 12 of the same bulletin. Very interesting to see these.

The '94 GTS models are extremely interesting, to me. I think that the first 17 (?) 1994 models that were made from 100% 1993 pieces (in 1993, with option code 718) are very, very interesting and stand out as being very unique in an already fairly unique series of cars. Obviously, all of these cars had the weak connecting rods.