Jchiodi

I will be redoing my torque tube bearing and repacking cv joints so while I'm in there.......

I do see evidence of a leak but not the leak. Trans fluid drops on front of trans below the torque converter. Can't see where the heck its coming from. Torque converter itself? It's not a horrible leak, and I really don't feel like pulling the trans out to deal with it....

Also, I have rough shifts, and am checking to see if the vacuum line is still attached and the modulator pressure is correct. I have a problem with trying to adjust while moving, or even with the engine running!

The modulator is within an inch of the heat shields and cannot be accessed with exhaust in place. Any ideas on this???

Any help would be appreciated.

dr bob

Thr front pump and torque converter have seals that, when leaking, will dribble from the grate under the converter. If it's a real slow leak (so far) and you aren't quite ready to pull the trans to fix it, consider one of the better transmission conditioner products as part of your next fluid change. In the past I've seen good results from some like K&W TransX. If thet doen't do it, you next option is a transmission stop-leak additive. I used Lucas auto trans stop leak in my lift cylinders... I'm sure there will be some suggestions.

On the hard shifting -- There's a vacuum line that runs as hose from the 7-way connector at the top rear of the engine, to a steel line that runs back towards the transmission above the orque tube, then a hose section that connects to the modulator. Before you start adjusting the modulator, make sure the hose is intact, in fact make sure ALL the hoses connected there are intact. For the line to the transmission, use your MitiVac tester to draw vacuum on the whole rear section from the hose at the 7-way. You should be able to draw and hold vacuum there. If you can't you'll need to find what's leaking. Popular failures include the hose at the rear where it loops to the modulator, since it gets baked over time from exhaust heat. The front section can be disturbed when doing service under the air cleaner housing, as can the line from the intake throttle body to that 7-way connector and the other connections there. No vacuum at the modulator tells the transmission to shift as if there is a high load, even though the throttle valve and pump pressure may be telling it otherwise.

Pfc. Parts

XX

Schocki

Help me out I don't understand completely: you are replacing the torque tube bearings and the automatic transmission will stay in the car? I thought this is only possible with manuals, the automatic is to big to remove the TT while it stays in place? Or not?
No the torque converter itself will not leak (unless the drain bolt leaks). It's either the shaft seal or the primary O-ring.

Here is a good video about your typical lekas on a MB 722.3

More about the typical leaks at the torque converter..

If you are pulling your trannsmission, I would highly recommend to change the friction discs B3. They are responsible for reverse and this is what fails first on a 722.3 MB four speed.

Enough siad about the vacuum to the modulator get a Mytivac and check.

Jchiodi

I'm not sure about having to remove the trans? I helped a guy in our club do his (manual trans). Now I'm not sure about doing this as I don't seem to have any noticeable rumbling? I want to get the car back together within about 45 days or so, lol. and I do have a lot of other little things to do. I will try the fluid treatment options first definitely!

On the modulator vacuum hose. I have done the intake refresh and think I have all the vacuum hoses okay. But I think there are two different hoses heading back toward the passenger compartment. One to the computer and the other to the trans modulator. I think?

I will do the mighty vac thing and see if I can hold pressure. Kinda cold so I will wait for weekend, start up the heater and spend a day playing with it. I wish it was warmer, but then I would be wanting to drive the damn thing, not fix it.

On a side note, any tricks to getting steering rack boots to slip on.. I about got a hernia trying to pull one side on. I just can't quite get it over the rack side bump. Need one or two more hands, lol.

Thanks for the replies.

Captain_Slow

Wow! At 2:10 of the second video is hugely helpful info. Mine only weeps a few drops through the grate after driving. Completely dry after those few drops for as long as the car is parked. Thanks a lot Schocki!

Pfc. Parts

Oh.

Schocki

Steering rack side note: if you changed the bushings to DELRIN, only put the upper ones in first. Lift it into place and use oversize washers to pull pull the lower bushings into place. With this you have a little more movement.

Bill Ball

On pre-S4 the torque converter (TC) is small enough that it is POSSIBLE to remove it and replace the seal and primary pump seals with the trans still in the car. Dan Brindle (podguy, R.I.P) did it successfully. Of course, the torque tube (TT) must be removed, which is a bit of a trick, but that can be done in any year 928 with the engine and trany still in place. I've done that numerous times. The tranny needs to be loosened and slid back and the bellhousing removed to lower the front of the TT and remove it. Then the TC cover can be removed. Good time to do the TC cover bearings as well. That's as far as you can go with an S4. There is just not enough clearance for the TC to be removed, but the smaller, earlier TCs can be removed. I'm not necessarily advocating this. The TC is heavy and hard to handle in this orientation and I would think there is high risk of tearing the seal on reinstallation. The correct procedure calls for the tranny to be standing upright on its tail so the TC can be dropped directly down into place.

Schocki

I would not mess around and spend a lot of time trying to fix a TC leak in an installed tranny. Rear axle removal is not that difficult and as soon as the automatic is out of the car it is easy to do some WYAIT stuff.
I just did it this month on my liftbars and with a transmission adapter on my 3.5 ton sear hydraulik floor jack. It is time consuming but not difficult.
IMHO take it out, replace B3 and all accessible seals and O-rings (on the automatic and also differential housing). This way you can be sure that your car will be leak free for many years to come.

Good time to buy some tools....

Here is my post about this: https://rennlist.com/forums/928-foru...ement-diy.html

Jchiodi

Since I do HAVE to replace torn cv covers, and since i've already dropped the entire exhaust system to get to modulator, i may as well pull tranny and do what i can to overhaul it.


Didnt want to do this, but what the heck.

May upgrade the modulator while i'm there also.

I wil be back, soon...

Bill Ball

Of course, I agree with Schocki. My note was just FYI. Some people just like to be different. :-/

Captain_Slow

This guy must have very little enamel remaining on his teeth This is the part 2 of the second video Schocki posted. It provides a bit more information on how to replace the pump seal and O-ring. The most interesting part is how brittle the old O-ring is. Do the O-rings get this brittle on the 928? Could the crispy example in this video be the result of the torque converter being mounted right behind the MB engine? Diesels run cool, so this got me wondering if we can expect the same brittleness.

Mrmerlin

If your working on a transmission,
I suggest to use the Dow Corning 111 on all of the O rings,
this will keep them soft

Schocki

Yes they harden over time. The bigger the temperature difference, the quicker they harden. Just imagine the amount of thermal stress that this little piece of rubber faces over 20 years plus.