PeachParts Mercedes-Benz Forum - View Single Post

dafuzball · #1 11-16-2012, 06:38 PM

Long time lurker, first time poster!

I know there are TONS of posts on this and other forums on transmission topics, and honestly, I feel like I've read through all of them, but to no avail.

I've got a 1984 300SD (722.303 transmission) with ~170k miles. I just bought this car (in near perfect body shape), but it came with one issue, the shift from 1=>2. If I give it any more than, say, 1/4 throttle, the transmission will get past its shift point and then flare (I believe I'm using this terminology correctly) into high RPMs (basically as high as I will let it go). As soon as I back off the throttle some, it will shift into 2nd; and the rest of the shifts are just beautiful. I have been conscious of this, and by keeping it at about 1/4 throttle until I get into 2nd, I have no problem (except that the shift is still very stiff); and I can then give it through full throttle.

Since I wasn't sure of the maintenance records, I have been going through and doing most everything that 'may' need done. I changed A/T fluid and filter (fluid did not have any noticeable wear material, emptied both trans and T/C), engine oil/filter, 2 oil filters and under tank screen, ran a diesel purge, replaced the wastegate hose (the old one was barely hanging on), and cleaned out the banjo bolt from the switchover valve (both to the intake and to the ALDA). I also went ahead and replaced the modulator, as it was original and even if it had not failed, I read that it was a good PM item. After I replaced that, I adjusted it to the recommended level with no vacuum (I don't have it in front of me, but I think it was 48PSI), and it maintained that amount while giving it throttle in park. Of note is that there is a small amount of fluid leaking from under the T/C, but I'm assuming a seal leak shouldn't be a problem if the trans is adjusted to the right pressure?

Here are the transmission specific checks I've tried:
-After replacing the modulator and adjusting pressure, I drove the car with the vacuum unplugged to rule out vacuum problems. Same issue.
-I reviewed several pictures of the adjustment on top of the valve cover for the bowden cable, and mine looks to be correct with a slight amount of slack and a very tiny space between it and the throttle linkage. I adjusted it a small amount both directions to see if that made a difference, and it didn't seem to.
-I took some pictures (couldn't see otherwise) of the bushings connecting to the selector rod, and those appear to be in tact.
-I unhooked the kickdown switch from under the pedal, and that did not do anything (however, I have not verified that there is movement in the solenoid when it IS plugged in)
-I took a spin around the block with the intake banjo hooked directly to the ALDA (bypassing the switchover valve) to assure that my switchover valve wasn't preventing pressure from getting to the ALDA. No improvement.

Here are my next steps:
-Adjust valves
-Check turbo pressure on road test

And if neither of these are the problem, my best theory thus far is the B2 piston is sticking / has some wear and needs to be replaced.

I know there is a lot here, but hopefully one of you experts out there has read through this and has some insight for me, things to try, encouragement/disagreement with my theory. Thanks in advance for the help.