Auto Transmission Leak

[n/a]

Hi.  My 280SL has a pretty bad transmission fluid leak coming from either the front of the transmission or the fluid coupling.  The fluid collects on the coupler and leaks through the inspection plate.  The drain plug on the coupler is tight.

Several years ago I replaced the front pump seal on the transmission, as I assumed this must be the problem.  But the leak has remained.  Assuming that seal is good, must the leak be coming from the coupler, or is there another place at the front of the transmission that could be leaking?

[ja17]

Hello,

The riveted hub on the fluid coupling is probably leaking. You can test this by removing the coupling and filling the valley around the rivets with water and blowing compressed air into the coupling. You will see the air bubles if you have a leaky hub.
You can weld the seam and around all the rivets to cure the problem. A good transmission rebuilder can probably do this and test it afterward. Otherwise a good welding shop can tig or brass weld it for you. Be careful to flush all the fluid out it will ignite during the welding (singed eyebrows and hair speaking!).  Fill the valley with water afterward and test with compressed air for leaks.

The third option is to find a good used one, or replace with a very expensive new unit.

Joe Alexander
Blacklick, Ohio

[n/a]

Thanks for the advice Joe.  My mechanic and I did the compressed air test on the coupling and have decided it does not leak.  Are there any other possibilities?

[ja17]

Hello Bob,

The front transmission pump has a large o ring around it also. This is not usually the problem, however I would change it if you can't find the culprit. Unfortunately the front cover will need to be removed to unscrew the four bolts holding the front pump on.  So you may need the front transmission cover gasket also.

Take a good look at the front bronze bushing in the front pump also. It normally is a silver grey color. If the bronze base metal is showing through it may be worn.

Also be aware the riveted hub my leak only after the transmission warms up and parts expand. May be you should retest after heating the converter in an oven?

Good Luck,



Joe Alexander
Blacklick, Ohio

[hands_aus]

do these transmissions have a breather on the top of them that, if blocked, can cause high internal pressure (just like the differential/axle) and consequent oil leaks?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ja17]

Hello Bob,

Good point!  These transmissions do have a breather on top. It does look like the one on the differential. As stated, it must be clear or could cause a leak.

Joe Alexander
Blacklick, Ohio

[n/a]

I replaced the front pump seal and the coupler seal at the front of the transmission and sealed the rivets on the coupler.  No more leak!  Thanks to everyone who replied on this thread.

[dean]

Hi Joe,

i have a major transmission leak as well.
Changed ALL the seals on the transmission but the leak is still there.

The front pump seal that was in the car had part no.--34-52-10 but the replaced seal from MBZ is 34-52-8/7.  could this be the problem of the ongoing leak?

i found this thread after we changed the seals so we did not pressure test the fluid coupling.


Thanks



Dean

[ja17]

Hello Dean,

First make sure that  the transmission fluid level is correct (engine warm, running and on perfectly level ground). Check and snug up all bolts and fittings you can get to. Clean the outside well enough to identify the general area of the leak. If you still have a leak originating from the front bell housing area, you will need to look at all the possibilities mentioned in this thread.

Mercedes frequently chages part numbers and part configurations (materials etc.)  I cannot cross this number for yo but I would double check fit if you need to take it out again.

Keep us up to date.

Joe Alexander
Blacklick, Ohio

[dean]

HI Joe,

All levels etc correct.  the leak seems to be coming from the front bell housing.

i guess we have to take it out again  !!!

so the two suspects are the front pump seal and the coupling.

is there any way to check on the front pump seal no. because my mechanic is not happy with the part no. MBZ is recommending.

thanks for all your help.

Dean

[ja17]

Hello,

You may want to give the Classic Center a call.  If I were taking the unit out again I would replace the new seal anyway just in case it gets damaged along the way.

[dean]

HI Joe,

The classic center confirmed the part no as below:
"The numbers you are providing must be the manufacture number what is the Mercedes part number if you bought it from a dealer it should be on your invoice the correct Mercedes number is 008 997 91 46 let me know"
008 997 91 46  is what we bought from MBZ dealer.  But as advised before the new seal is all rubber and stamped part no.34-52-8/7  while the one that was in the car was metal/rubber and stamped 34-52-10.  since I have to take out the transmission AGAIN I want to see if I can find the same seal metal/rubber 34-52-10.
Also my mechanic is not able to line up someone that has experience welding the Torque Converter, any recommendations ( I am located in New York City area)?
Do you recommend a shop that I can send the torque to that has done this type of welding?
Your help is greatly appreciated.
Thanks

Dean