W126 trans leak, common sources?
 

Ok, probably the pump seal. But hard to tell where the leak is coming from. Any issues with something like the dip stick tube o-ring, etc?

Fluid is oddly clean and smells good. I have never changed it since the reverse is pretty much dead.

If it's coming out the bell housing it's probably the radial pump seal.

Other common leak points are the servo bores on the passenger side.

Agree
 

This is common..

The dip stick O-ring is almost as common a failure, in Michigan.


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Agree
 

The radial pump seal is common..

The dip stick O-ring is almost as common a failure, in Michigan. :(


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I assume you mean the dipstick TUBE o-ring, yeah they leak too. If it is leaking out of the bellhousing, it's probably a pump radial seal. Unless someone botched a trans fluid change, because sometimes the TC drain will leak if there is no seal or someone has 2 seals on the drain plug. That will make a pretty good mess too.
Gilly

Yes to all the above, with the addition of the small inserts that go into the transmission case opposite the B1 and B2 servos. They install from the inside of the transmission case, so disassembly of the transmission is required. I don't remember the proper technical name for these parts at this time; they have a spring and piston inside them but are serviced as an entire part except for the o-rings which are replaceable. The opposite end of the bands from the servo pistons attaches to these "inserts".

The "radial pump seal" I'm guessing refers to the large O-ring around the pump body and not the hub seal. The o-ring I have always found to be rock hard and leaking. If that O-ring is hardened, there will be others inside the transmission hardened as well, so it would be best to do an entire reseal of the transmission. Most often the O-rings internal to the K1 and K2 clutch drums will be found hardened. They are included in aftermarket transmission rebuild kits along with self tapping screws and instructions for installing the O-rings. Otherwise the K1 and K2 drums would have to be replaced. Not doing so will leave you with leaking clutch drums and possible slippage.

It's also a good time with the transmission out to inspect and replace the B3 clutch discs if necessary. They sit directly behind the fluid pump and can be replaced without removing the gear train. Look for clutch material flaked off of the friction discs.

Most likely the reverse disks will be gone too, seal kit is best; wonder if the new plate material is better and lasts longer .
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