greg928GTS

Noticed some slipping between gears. This is the one disappointment I've had with the car.

I'm quite conflicted. At times I feel as though I may have made a mistake buying the car. Have you ever gotten that sick feeling, like you've just done something really stupid, like paid top dollar for a car that might have a major problem? This is when I get thinking about how major a problem this might be and I start thinking that I should have done more to have the car checked out better before I traveled such a long distance to get it and paid so much money etc...

Then there are other times when I think about how nice the rest of the car is and how happy I am to have this car, and of course it could be something really simple and not really a major problem anyway, and all 12 year old cars have something wrong with them, it's just the way it is. When you decide to play the expensive German toy car game, you've got to expect to shell out some cash, etc...

I first noticed this problem when I got to Pittsburgh and started driving around the city. Starting from a stoplight, in second gear, at low-speed, low rpm's, very light on the gas pedal, the car would rev up just a little bit before switching into 3rd.

When I test drove the car with Jason, I didn't notice this, although I did try a couple of times to get it to go down into first gear and Jason and I both had a hard time telling if it actually did get into first gear. We really weren't in a very good place to really give the car a good go through all the gears.

There was one time, coming out of a toll booth, that I was accellerating at a fairly brisk pace, and the car revved a little between 2nd and 3rd when I let up on the pedal a little just as it was switching gears. This was different than the low-speed, low rpm version because I was going much faster with much higher rpm. But it still happened when I let off the gas and it switched gears right at that moment.

I can make this problem happen or not, depending on how much pressure I exert on the gas pedal. Light pressure will make the problem appear, and heavier pressure results in prompt solid shifts between gears.

Is this really a problem? It's more of an annoyance for me, but I wonder if it's going to get worse.

Jason said he never noticed it during the few hundred miles he put on the car over the few months that he owned it. He said Stan never mentioned anything to him. The PPI mechanic never noted anything in his report. So it seems that this is a new problem that popped up during my trip home.

Jason mentioned a pressure adjustment on the transmission. Anyone have any information on that?

Stan put a kickdown switch in the car and I had that engaged for the whole trip. I tried disengaging it for a short time and the slipping problem was the same. But why would someone put a kickdown switch in anyway? Is this an indication that Stan was perhaps not satisfied with the shifting of the transmission and used the kickdown switch in an attempt to make it shift better?

Thanks for any input.

Rod Underwood

A lot of people put in a kick down switch to allow them to more easily start in first gear. Probably our American infatuation with jack rabbit starts and street racing instead of high speed cruising.

Under normal driving conditions, the Mercedes transmission actually starts out in second gear. If you hit it hard, you can get first gear, but the kick down allows this downshift to occur without full throttle.

Rod

Garth S

There are a couple of active threads on slipping transmissions .... read below.
The first thing to do is check the ATF level in the reservoir. Assure that it is between the marks with the car warm, running in park .... and absolutely level.

greg928GTS

Ahhhh. O.k., so maybe this is why I wasn't sure I was in first gear when I test drove it. I wasn't going full throttle because I knew the rear tires would spin (not much tread left). I have to floor my 89 to get it to go into first, and all hell breaks loose when that happens. It's quite dramatic. Don't get me wrong, there was plenty of accelleration happening with the 93, but it wasn't as dramatic probably because it was going into first easier with the kickdown switch, at lower rpm's, and not as abruptly as I'm used to with my 89 at full throttle.

I plan to conduct more tests on this in the weeks to come , when the weather allows, and I have time.

Ispeed

I don't think the trouble free 928 exists. They all suffer from age or use or bad maintenance or neglect. Don't let this stuff get you down. These are THE greatest cars, but you will have to get involved with it in some way.
You might want to consider relocating closer to Dave C, Wally P. or Earl Gillstrom. Pick a guru and call a mover.
You've got a really nice car, time to get dirty.

Shark_gts

I would look at 1. Cable adjustments, then move to 2. modulator tweak if necessary. May want to check the trans level too.

When were the plugs last changed and how many miles on her?

Paul

WallyP

Congratulations on your purchase - no, you didn't make a mistake...

To repeat some of the good advice from above:
First - check the transmission fluid.
- With the car warm, parked in a level spot (front/back and side/side), and idling in park (parking brake set):
- Using a good flashlight, kneel beside the right rear tire and find the fluid tank on the side of the transaxle. There will be three lines on the plastic tank. The fluid level must be between the top two lines.
- If it is not, use a squeeze bottle and attached tube, or a long hose and attached funnel run outside the wheel well, or a gear-oil pump, to add Dexron until the level is correct. There is VERY little fluid needed to go from the middle line to the top line, and you don't want to over-fill the transmission! Be very careful to avoid getting dirt in the tank, and to avoid getting burned on the exhaust.

If that doesn't help - check the adjustment on the transmission modulating pressure control cable.
- Look on the left side of the engine, and find the throttle cable quadrant - a lump of mechanism with several cables attached.
- These cables are:
One running between the firewall and the quadrant - this is from the throttle pedal.
One running to the left front fender - this is from the cruise control.
One running up under the intake manifold - this is the one that operates the throttle.
One running back under the firewall - this one tells the transmission how much throttle you are using, so the transmission knows whether to shift early and softly, or late and hard.

First, make sure that there is just a tiny, tiny bit of free play in the cable that operates the throttle, and not a lot of free play.
Next, make sure that there is no free play in the cable from the throttle pedal.
Next, make sure that there is no free play in the cable that runs to the transmission. You can tighten this cable just a little, then drive the car and see if the shifting is better. If you over-do the adjustment, the transmission will shift a little late - that is, it will stay in second a little too long.

As mentioned above, you can try tweaking the vacuum modulator. Look on the left side of the transaxle, forward of the half-shaft, and find a round device about the size of a catfood can, with a rubber cover in the center and an attached vacuum line. Pop the rubber cover off, and pull the handle out. Try one turn in (to the right, or tightening direction) and see if this helps. You can continue to tighten one turn at a time to see if it makes any difference. This modulator affects primarily the smoothness of the shifts, and not the timing of the shifts on the 928. You should feel the shifts getting firmer as you tighten the modulator.

If that doesn't help, it may be time to ask for expert help. Steve Cattaneo is one of the most knowledgeable techs in the USA on 928 automatics. He can be reached by email at MASTERTECHatMASTERTECHTRANS.COM - change the "at" to "@".

There are a couple of internal repairs that can be done without dropping the transmission. Steve can give you advice on this, and in the worst case you should be able to find a local independent shop that specializes in Mercedes Benz transmissions that can handle the problem.

Shark_gts

An '89 or 90 trans has quite a bit different personality than the '93 GTS. The '90 (& all other) I was driving was more willing to downshift into first or second.

In general upshifting I haven't had any issues. I've got my fluid chock full. I did have revs bumping a bit when shifting PRND - that went away with the fluid level.

The GTS has a slow speed coast zone that will cause a slip and hard grab 3->2. Couple of drivers have noticed this. So going into certain corners on our country road I drop into 2 manually before hitting the apex and getting back on the throttle.

greg928GTS

Great information guys, thank you. Makes me want to get out there and work on it.

Oh, I'm not really down about this problem. I have a realistic outlook when it comes to the issues with a 12 year old sports car. Besides, with support from the 928 community, fixing this problem will be easy.

I think a 928 guru mechanic should consider moving to Maine, right nearby to where I live!

Greg

greg928GTS

I've learned a few things since I first generated this thread.

What I have happening is known as a 2nd to 3rd shift flare.

Today I brought the car to a mechanic who specializes in German cars, recommended to me by a rennlist member that I met on the 928 email list, and he changed the tranny fluid and filter for me. He noted how clean and light colored the fluid was and he felt the tranny didn't need to be flushed. We found a few tiny pieces of metal in the pan, which he thought was normal or maybe just a little concerning. He said normal, but his face said a little concerning. Anyway, the pieces clung to a magnet, so they were steel. He throughly cleaned the pan and filler reservoir, put a new rubber gasket on the pan and fitted it back onto the car. He filled the tranny, started the car and ran it for a while, and then topped off the reservoir. He put a small container of additive into the tranny too, not really sure what that was, he said it would help.

He went to his computer and looked up the instructions for cable adjustments. I'm not sure where he found these, but I do know a rennlist member has given him the CD with the manuals, so maybe it was there. He works on another 928 regularly. He adjusted the cable that goes from the engine to the transmission two turns of the nut.

We test drove the car and the flare was just as bad as before. On my drive home, I would say it actually got worse. The car seems to shift slowly in all gears, but 2nd to 3rd flares a lot sometimes. It does it more when the car is cold. Throttle pressure does seem to make a difference as to whether it happens at all, but I have a hard time making it do the flare or not on a consistent basis.

Am I looking at a rebuild?

P928Drvr

My car was having some shifting issues also. 4 weeks ago I put it in the tranny shop to get a good understanding of what it was. FYI I drove the car to the shop and it had good power to the wheels with the exception of my third to first gear shift. Turns out my tranny was going down a very bad road. I'm really glad I had it checked. The inner parts have been hard to find, that is why its been 4 weeks. At least I will have a tranny that will take me another 100k. My advice is to get the internal workings inspected. Tear down and rebuild only takes about 3 days from what I understand (if you don't need to replace parts).

ErnestSw

It may be that he adjusted the cable in the wrong direction.

greg928GTS

When he took the end of the cable off the round ball, it was lined up exactly in line with it, not shorter or longer. He tightened it up by two turns, meaning that the end of the cable was theoretically slightly shorter. I say theoretically because it didn't seem to be any different to me when he snapped it back on. I paid close attention to the procedure and how to put the little "oh crap" spring back in so I can fool with it myself if I want.

I'm not sure about the resources I have available to me for transmission work in rural Maine.

G Man

If you need parts you might try these guys. They have a huge selection of parts for the MB trans. Good prices too!

http://www.bulkpart.com/Merchant2/me..._Code=Mercedes

Schocki

Have you tried to adjust the vacuum modulator?