Trans vacuum module, keep or replace?
 

After searching and reading extensivly I am trying to resolve my wickid 2-3 and 3-4 shift flare. My initial check of the vacuum pot on the drivers side of the trans reveals a slow leak.

When pumped up to 15 hg it will zero out in about 12-15 sec so I know its not as new as it leaks ~1 hg/sec. Im asking beacuse I have read that a slow leak like this (if it is indeed considered slow) is not ideal but still servicable, I have also read if it does not hold vacuum its garbage and should be replaced before further adjustments and trouble shooting are performed? Which is true and if replace what do I need to know to get another (besides trans #)?

Thanks. I want to resolve this before I pull out the hyd psi gauge and set internal psi.

87 300SDL

I'm probably not one of the more knowledgeable people who could offer an opinion, but at this point I seem to be the only one. So-----if your car has a Bowden cable, you might want to adjust it first. Last spring I bought a 300SD with a pretty pronounced 3-4 flare and a simple adjustment of the Bowden cable cleared it right up.

My less than perfect understanding is the bowden cable alters shift points and the modulator/vacuum system status will effect shift quality. Again my understanding being less than perfect. I dont think Im going to chance it, I'll order another one, I have to keep this car for a long time.

Perhaps after I replace all the defective components I can begin dialing it in to shift correctly. I have been reading about shift correction kits to, I think its time for a call to Phil.

I have something like 3 different issues going on this car right now trying to get it roadworthy.

Agreed --- also an adjustment on the vacuum control unit might help. I was of your same opinion about the Bowden. As stated before, my 300 SD was flaring and I suspected that I had larger project ahead than it turned out to be. A simple adjustment of the Bowden made shifting superb. On the other hand, when I bought my 300D a few years back, I wanted to tweak the shift. First I replaced the transmission modulator (it would not hold a vacuum) but no real improvement in the shift. Finally adjusted the vacuum control module (behind the injector pump on the 300D) and got the shift I wanted. Was prepared to repeat that trick on the SD but was relieved that the Bowden took care of it. Not quite what I expected, but was happy that a 5 minute job with no tools cured the flare.

Completely unplug the vacuum line from the transmission. It should shift ultra firm with no vacuum, that would also be my assumption from a leaking modulator. Change your fluid and filter before going crazy....if that doesn't solve it plus the vacuum unplugged, then I would move on to the springs in the valve body and/or worn clutches.