PeachParts Mercedes-Benz Forum - View Single Post - 722.120 Transmission Shaft Seals Not Replaceable Without Rebuilding Transmission?

Squiggle Dog · #14 06-12-2019, 02:01 PM

I found a fix for the control pressure rod shaft seal without having to rebuild the transmission!

The leaking control pressure rod shaft seal is the one leak my car has had and it's been driving me crazy. Here is what the shaft looks like from the outside, with the lever removed from it:

The seal is not located at the outside of the case, but rather it's on the shaft close to the inside of the case. In order to replace the seal, the shaft has to slide out from the inside of the transmission, but one of the drums is blocking it. I really dislike this design and want to change it. I thought about having the case bored so a lip seal could be installed on the outside of the case. But, this wouldn't work because the shaft steps down at the area where it would need to seal.

Then I had another thought--the lever welded to the shaft on the inside of the transmission is keyed, so if the weld was ground off, the lever could be removed and then the shaft could be drilled, threaded, and the lever made to be removable with a screw, allowing the shaft to be removed from the outside. I had envisioned removing the valve body on my transmission, taping a plastic bag around the area where I would need to grind off the welds to prevent contaminating the transmission with metal particles, and then doing the modification so I could replace the seal without taking apart the transmission. But, there is just not enough room to reach a tool in there. Oh, well. I still might do it when it comes time to rebuild the transmission.

In the past I had attempted to stop the leak by putting an O-ring on the shaft, sliding it up against the case, and then letting the force of the nylon washer and the spring washer push against it. It did not work. But, I tried it again using a thicker Viton O-ring, size 8mmIDX12mmOD.

I put the nylon washer and spring washer and clip in place against the O-ring, and though it felt like they were pressing hard against it, I noticed the nylon washer was deforming at the open end of the clip. So, I replaced it with a steel washer from a flex disc bolt of similar dimensions (11mmIDX18mmODX1.5mmT)--I think the nylon washer had a 10mm inner diameter, though.

It was a bit difficult to get the spring washer and clip on after the O-ring and steel washer, but it was putting firm pressure against the O-ring.