changed ATF & filter, and now it's leaking - PeachParts Mercedes-Benz Forum

Desert Panther · #1 03-10-2012, 01:10 PM

This just recently happened to my 1978 300CD, which previously didnt leak a drop of trans fluid. As the car is a semi recent purchase, I am in the process of going through and changing all fluids, everywhere. The ATF that was in it looked a little "off color", but definitely wasnt the worst i'd ever seen or smelled. Put the new filter & gasket in (from Fastlane - of course!) and all was well. For a few weeks anyway. Now I am getting a few quarter sized spots of ATF underneath the front of the trans when I park the car after driving it any distance. A mechanic at a local indie Benz shop put the car on a lift & said it is likely the front seal (or front pump seal?). The transmission shifts just fine, like it always has, no complaints there. But this new fluid leak bothers me, obviously. I am going to take an educated guess here & suppose that the addition of new ATF somehow dislodged some dirt or debris around that seal, thereby enabling the leak. Is there any "magic additive in a can" that may possibly remedy this situation? I am pretty sure that other folks on this forum have dealt with this exact issue at some point in their Benz owning life.

Stretch · #2 03-10-2012, 01:47 PM

I know of no magic in a can solution.

Sorry.

First you need to find out exactly where the leak is coming from.

Did you by any chance drain the torque converter when you did the fluid change? (Hint - check the torque converter drain plug)

scottmcphee · #3 03-10-2012, 02:22 PM

Over-tightening the tranny pan bolts will distort the gasket and allow leaks.

I'd take the pan off, re-examine the gasket fit, surgically clean all surfaces in the area, put the pan back on, and using a star pattern tighten the bolts down... not too tightly. Snug and then a bit, like you would a tapered spark plug. Reinspect in a day, a week, and then a month, and then you're good.

Desert Panther · #4 03-10-2012, 03:02 PM

Quote:

Originally Posted by Army

I know of no magic in a can solution.

Sorry.

First you need to find out exactly where the leak is coming from.

Did you by any chance drain the torque converter when you did the fluid change? (Hint - check the torque converter drain plug)

No, I didnt drain the torque converter, just the fluid in the pan. The owner/head mechanic at the indie Benz shop said it was the front seal.

Quote:

Originally Posted by scottmcphee

Over-tightening the tranny pan bolts will distort the gasket and allow leaks.

I'd take the pan off, re-examine the gasket fit, surgically clean all surfaces in the area, put the pan back on, and using a star pattern tighten the bolts down... not too tightly. Snug and then a bit, like you would a tapered spark plug. Reinspect in a day, a week, and then a month, and then you're good.

I am certain the leak isn't coming from the pan.

Stretch · #5 03-10-2012, 03:25 PM

Well the only way to fix a front seal is to remove the transmission and replace the seal.

There's some pictures of the front seal etc etc here

722.118 Automatic transmission rebuild (Monster DIY)

I guess you've got a 722.1 there...

layback40 · #6 03-10-2012, 06:26 PM

The front seal will have hardened with age/heat & the spring that keeps it tight on the TC tube will have stretched.
Its great to see that you are not going down the path of trying snake oil. There are many products that claim to rejuvenate seals & gaskets. They dont work or if they do its only for a short time.ATF will get out of any where, thats why its such a good ingredient for penetrate/un seize products.

A good indie can have the trans out in about 2 hrs.
I would replace the seal with a viton one. ~$20 instead of $5 but they will outlast the car. We have never had to replace a viton seal. Had to do standard seal again many times in various applications. The heat kills them.

Desert Panther · #7 03-10-2012, 07:20 PM

Quote:

Originally Posted by layback40

A good indie can have the trans out in about 2 hrs.

Really, 2 hours?!?!!?

So then what, about 2½ hours to put it back in the car and maybe a half hour to r&r the actual seal for a total of 5 hours? The shop quoted me 8 hours to R&R the seal/trans. At 105 an hour labor rate!

Needless to say, I think i'll hold off for a while until I have that kind of money to throw at it.

I dont have the skills or the tools to be doing this job myself. Not at this point in time, anyway.

I will just keep an close eye on the ATF level in the transmission & top up when necessary.