722.317 Transmission Front Seal Leak - Is it dead? - PeachParts Mercedes-Benz Forum

jonbobshinigin · #1 01-20-2011, 12:26 PM

1987 300TDT - 195,000 miles

I posted something about this briefly in another thread but decided to make my own also.

I acquired this vehicle when it had 155k on it...it was not shifting like it should, which turned out to be a vacuum leak/issue. I went ahead and changed fluid and filter but it did not help. At the time I did not know about chasing down vacuum leaks so I adjusted the modulator down and made the shifts very soft to compensate. I just did it by feel, not pressure gauge. At this time a did have a small leak.

It was probably like this for 10-15k before I finally messed with it again and tightened up the shifting. During this time I also changed a few associated parts; Differential Mounts (all), both flex discs, and tranny mount. There was a little improvement but not much. Now I have driven an imperfect transmission for 30k+ and it has not gotten any worse.

Currently, the leak is pretty bad and Trans-X has not helped so I am getting ready to pull the transmission. Current shifting, when fluid is where is should be is not bad. It does not flare, but if feels like there is slack in every gear as it shifts. Not very firm and smooth. I probably have it adjusted too high, but even when it was softer, it was like this. Couple questions:

Would a front seal leak cause this kind of shifting symptoms?

Do you think I have done damage to, or worn out discs from running modulator too soft?

If I pull this transmission out, other than front seal, is there a list of factory updates for this transmission such as valve bodies, pistons, etc?

My main concern is that I pull the trans and replace the seal but erratic shifting persists. I have a parts car with same trans and 225k on it with no known history that shifts better that I might could use but I'd rather keep it intact because I am not parting it yet and it can still drive on and off a trailer.

Thoughts?

jonbobshinigin · #2 01-23-2011, 12:56 AM

Bumpage

kerry · #3 01-23-2011, 12:25 PM

Have you tried running it with the vacuum disconnected completely? Shifts should be very harsh. If you can't induce no-vacuum harsh shifts in the transmission with adjustments, then perhaps it is worn. If I had the transmission out I'd do the b-2 piston and install the Superior shift kit.

leathermang · #4 01-23-2011, 12:40 PM

It took a couple of weeks of having the Trans-x in my Lincoln ( quart per 75 miles leak ) for it to seal up... and that was running it regularly.... and adding fluid as needed... I mixed up Trans-x into my trunk reserve supply so as to not be diluting it as I had to add fluid just to drive the car...be sure you have the suggested ratio in there...

300D85 · #5 01-23-2011, 02:10 PM

Quote:

Originally Posted by jonbobshinigin

If I pull this transmission out, other than front seal, is there a list of factory updates for this transmission such as valve bodies, pistons, etc?

fwiw ran across info that talks about 2 important front seals

Quote:

For a lasting leak repair both the torque converter lip seal and the pump o-ring seal should be changed. If your transmission is leaking and you think all you need to do is replace the torque converter seal - you may be doing the job again soon!

jonbobshinigin · #6 01-26-2011, 12:28 AM

TransX has been in for months...also, removing vacuum does make or shift hard, adjusting modulator valve does control it, although I do have a new one in hand to install.

Hit Man X · #7 01-26-2011, 04:21 PM

Too soft is not enough line pressure... so you could have some worn clutch plates more than usual but probably not much. I was under the impression these were supposed to shift firm/crisp but not harsh. Mine shift that way and are fine.

You have to recall, this is a 25 year old transmission now with 200,000+ miles (provided the odometer has functioned its entire life). I do not believe in magic in a bottle is going to cure your ails. A reseal is going to fix this but I would not spend the time and money to simply reseal this with the mileage. How much time is left is unknown, after 200k you are on borrowed time. If the car is a 'keeper' I would just have the current unit remanufactured and then get on with life. If something did happen to the vehicle, you can just pull the trans and install it in something else.

I would not waste my time installing a used, 225,000 mile transmission from the parts car. That is just chasing good money after bad.

whunter · #8 01-26-2011, 06:27 PM