Slow leak around B2 Piston--change piston?

[Rob124]

I've had a slow leak from around the pan on my 722.3 transmission, and just today found the likely cause--the cover for the B2 piston.

Given that the '87 cars have a reputation for bad B2 pistons, should I just cough up the cash and buy a new piston, or is exploratory surgery a good idea first? I already have a B2 piston seal ring, but not the big o-ring.

The transmission performs properly, so I have no reason to believe the piston is bad. Right now, I'm thinking I'll lower the transmission and replace these two seals, and stop at that. If it ain't broke...

Recommendations, please? I know there have been many threads on B2 issues, but I haven't found what I'm looking for with the searches I've done.

[Diesel911]

If it is the same setup as the 85 300D on the other side of the Piston is a Lip Seal and a Bushing.
I do not know enough about the 87s to know if you have the most updated B2 Piston and Bushing in your Transmission.
My 85 still had the Metal Bushing (replaced by a Nylon/Plastic one).

If it is easy to get at when you change the O-ring; I think I would at least inspect the B2 Piston for wear marks and see what type of Bushing it is using.

[pwogaman]

This is exactly what I'm likely going to have to do on my 300TE. Take lots of pictures if you do it.

[Rob124]

One issue has me a bit confused. According to at least one source, it's nearly impossible to replace the large o-ring with the transmission still in the vehicle. Others (and here) seem to have replaced it without difficulty. I'm hoping that's all that is needed. But is it really so very difficult?

[Diesel911]

Originally Posted by Rob124

One issue has me a bit confused. According to at least one source, it's nearly impossible to replace the large o-ring with the transmission still in the vehicle. Others (and here) seem to have replaced it without difficulty. I'm hoping that's all that is needed. But is it really so very difficult?

The O-ring groove is inside of the Bore that is in the Transmission Housing. When you get one part of the O-ring into the groove and go to get the other end into the groove the part that was in pops out.
It is frustrating.
In my case I just kept fooling with it until I got it all in and it stayed. Do not twist the O-ring or for sure it will not stay.
If there is room and you have another pair of Hands to hold the O-ring in the groove; that might help.

In the case of the B2 Piston Cover/Plug take a close look at the not to clear pic. Where the red arrow is pointing notice that the Plug has a beveled edge but that there is still a sharp corner on the Plug.
I took a fine File and went around the Cover and rounded off that edge. After that I lubed the O-ring with STP and did the same to the edge of the Cover.
Do the best you can to press directly in the center of the Cover.
Mine went in OK.

This sharp Corner issue or parts that have a sharp edge often comes up with other parts also. I have the little Jewlers Files or other files and have found rounding the edges and or getting rid of metal burrs helpful.

The new B2 Piston I got had a similar sharp edge issue and would not push into the new Lip Seal I installed easily (the lip faces towards the B2 Piston and also makes it harder to install the B2 Piston).
I again very carefully rounded of the edge with a Jewlers File and lubed it with STP and while I still had to play with it; it went in OK.

[Rob124]

Up to this point, the most challenging problem is getting access to the B2 piston cover. Although suggested elsewhere, I found no merit in removing the fan or shroud--there's plenty of clearance between the fan and the radiator. Unbolting the dipstick tube wasn't necessary, either.

Loosening the motor mounts may help somewhat in providing freedom to move the transmission laterally, but the limitation on vertical movement of the transmission seems to be caused by the engine oil filter housing contacting the firewall. The tail housing of the transmission doesn't drop as much as I'd like, and prying it sideways helps only a little. I have difficulty imagining pulling the piston out of the transmission while still attached to the engine and in the car.

We'll see how this turns out!

[Rob124]

Is this the appearance of the old-style, high-risk piston?

[Diesel911]

Originally Posted by Rob124

Is this the appearance of the old-style, high-risk piston?

There is a part number on the Aluminum Casting.
Unfortunately I did not put it in my notes but there is a thread somewhere where the Poster listed the Piston Numbers showing the changes.

You need to pull the Piston out to see if it still has the Metal Bushing behind the lip Seal.

In the thumbnail the Brass colored part is the Metal Bushing behind the Lip Seal. The Metal Bushing has been replaced with a White Plastic/Nylon one.

The part number (red circle) is on the front of the Piston. So it would need to be pulled out. Note the direction the central Pin goes (there is a groove or grooves on one end of the shaft); it is loose.

[Rob124]

This was a much easier repair than I'd expected. Changing the o-ring took about two minutes. I had no trouble at all getting it to stay in place. Pulling and replacing the piston was also quick and uneventful.

Best of all, there are now no transmission leaks!