300TD B2 piston replaced, still no forward movement - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 05-09-2017, 10:19 PM

My friend brought his TD over with no forward movement, and was told it had a bad B2 piston. He provided the new part, and I read a few threads on the subject. After removing the cover (real hard job with the limited space), I found the B2 to be in pieces.

I installed the new B2, and put everything back together. After filling up the fluid to the proper level, it still had no forward movement. I did more reading, and thought that maybe the bushing and/or seal was bad. I procured the parts, made a puller as described in another thread, and pulled out the old seal and bushing. I installed the new bushing and seal, making sure the seal was installed properly. After replacing the filter and gasket and putting everything back together, it still has no forward movement. It is kind of discouraging doing all this work with no positive results. Yes I did use grease to hold up the "dogbone" so it would be in the right spot on the brake band. Anyone know what could be the problem? Thanks in advance, Rich

EDIT: Reverse gear works fine, both before and after B2 replacement

dude99 · #2 05-09-2017, 11:19 PM

Hmmm, I would start by pulling a transmission cooler line and making sure that the pump is working.

kerry · #3 05-09-2017, 11:22 PM

X2

ROLLGUY · #4 05-09-2017, 11:55 PM

Reverse gear works fine, so I am sure the pump is working.

DeliveryValve · #5 05-10-2017, 12:58 AM

Was there tension on the new piston when installing it?
i.e. the piston is being forced outward.

If it slid in freely with no tension, most likely the brake band it toast. You'll need to overhaul the trans at this point.

.

dieselbenz1 · #6 05-10-2017, 07:46 AM

Sherry ex had a similar problem with his w124 and turned out to be something (broken spring) in the governer.

Forget that thought he had 1st gear
What's the likelihood the valet ruined my transmission?

ROLLGUY · #7 05-10-2017, 10:00 AM

Yes there was spring tension against the band before putting the piston in, and also afterward.

Mxfrank · #8 05-10-2017, 01:00 PM

Check the pressures. If they're ok, the most likely explanation is that the band itself it toast.

83TD · #9 05-10-2017, 01:08 PM

This is a long shot, but many years ago I decided that it would be a good idea to replace the original B2 piston in my 83 300TD with the newer design in order to avoid the problem. To make a very long story short, I used a chrome plated socket to tap in the new seal and bushing, a flake of chrome came off the socket(despite my efforts to keep things clean) and lodged in the valve body where I eventually found it wedged in by one of the tiny valves, causing the B2 piston to become inoperative in somewhat spectacular fashion(noisy) resulting in a tow home.

If the failed B2 created any tiny pieces that could have been carried away in the fluid, this could happen. I don't know if you can check for fluid flow to the B2 piston cavity with the transmission in drive and the motor running, but that might be easier than dropping the valve body for inspection.

Peter

jake12tech · #10 05-10-2017, 01:41 PM

I second the though of the band being an issue. When these problems happen and you do the b2, it is usually a bandaid. Eventually you will get reverse issues, flares, slips etc. I've learned when one thing goes wrong, pull it all and rebuild it. These trans are cakes. I could have one done in 30 minutes on a bench. Getting it in may be a little longer!!!

Diesel911 · #11 05-10-2017, 03:26 PM

There is an old style metal bushing (replaced by a Nylon one) and a lip seal that also should have been replaced. The lip of the lip seal faces outwards which is contrary to the way you might think it goes.

But, I have never read what happens if you get the seal in backwards.

Can some one verify this. I think that if you remove the Pan there is a tiny area where you can view that Pin (Dogbone) where it goes into the Band. If you can see that you might be able to get something in that and see if the Band is loose.

ROLLGUY · #12 05-10-2017, 03:59 PM

Quote:

Originally Posted by Diesel911

There is an old style metal bushing (replaced by a Nylon one) and a lip seal that also should have been replaced. The lip of the lip seal faces outwards which is contrary to the way you might think it goes.

But, I have never read what happens if you get the seal in backwards.

Can some one verify this. I think that if you remove the Pan there is a tiny area where you can view that Pin (Dogbone) where it goes into the Band. If you can see that you might be able to get something in that and see if the Band is loose.

I pulled the cover and replaced the bushing and seal (described in the first post), after I replaced the B2 piston, having the same results. Again, yes I put the seal in properly. I suspect there was nothing wrong with the original bushing and seal, as replacing them did not fix the problem. I also looked to see if the dogbone was in the right spot, but it appears the valve body will need to come out to see up inside......Rich

chasinthesun · #13 05-10-2017, 05:21 PM

Dieselgiant describe having to do a do over ,if this is any help he has it on his site.

Diesel911 · #14 05-11-2017, 12:14 PM

For anyone interested this is a quote from the Diesel Giant site.
"Because I was too lazy to remove the pan to insure the push rod was secured into the B2 piston properly. I got the car stuck in the street in because it would not go forward. Getting 3 of my neighbors to push my car back into the driveway and up the ramps was a little embarrassing. Please learn from my errors."

The below is without revmoving the valve body.

"Looking up into the transmission you can barely see the brake band to the left of the brown plastic piece. You will need to look at this after you install the piston and push rod to ensure the push rod engages the brake band. I did not do this simple step the first time and caused me to do the whole job over."
For more info on that you can go to the site (I am not recommending buying parts there).

I believe I also read back in 2008 where someone claimed that they did not get the Pushrod in the right pisiton and it broke the B2 Band but my memory is ver hazy about that.

Note that in the picture apparently due to the camera angle (?) you cannot actually see the pushrod/dog bone. And I can't remember what I saw when I did the job.
But it is nice to know there is a way to verify without removing the valve body.
Note I edited the original pic trying to lighten the shadow.

ykobayashi · #15 05-11-2017, 11:59 PM

I'm guessing the dog bone fell out as you put the piston in. Just a guess.

The other possibility is a broken band.

I know, it was all mentioned and you checked tension. But it sounds like it has to be opened again.

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