I just was given a '81 TD300 and I really like it however I just drove it 600 miles and started having problems with the transmission. Shifting really hard into 2nd and occassionally downshifting from 4th into 3rd at highway speed (kind of disconcerting). When I got it home it will now not engage any of the forward gears but has no problem in reverse. Does this sound like the dreaded B2 piston problem that plagued early to mid '80's models. Could there also be a coexisting problem with the vacuum modulator that's a separate issue?

Yes, it could be.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

That's what I thought...second question, is this something I can repair by myself? I understand that some models require the transmission to be removed in order to replace this part. In my owners manual it lists my model as 123.193 type. Can I access it without removal of transmission?

You can do it with the transmission in situ, though there isn't a whole lot of space in the 123 trans tunnel.

Here's how I did it. While you're in there, you may want to replace the K1 spring as well.

Tom

Thanks, I printed the article. I'm a little worried in your description of this problem that if 4th gear is having problems then it is not the B2 piston. It did jump down to 3rd a couple of times on my trip down from San Fran. although for the most part it was rock solid in high gear. It was only when I got off the highway that problems manifested themselves. As of now I can't even drive it in forward anymore, only reverse seems unaffected.

Hm. The B2 piston only engages in first and second. When mine broke, I drove 600 miles in one night, fourth gear never flinched. I don't know nearly enough about these transmissions to further speculate on your problem, but you may want to post this in the diesel discussion. You will get more response there.

Good luck,
Tom

B2 is actually engaged in 1st through 3rd gear. During disengagment of B2 part of what is improved is a valve that participates in the driving of B2 off and then the filling of K2 (4th gear).

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician