83 300SD trans slipping/flairing when cold

I replaced the modulator and adjusted the pressure to factory spec about 3 months ago when I first got the car. Also at the same time I replaced most of the vac hoses and connections under the hood. The trans seemed to shift pretty good for its age, with a very small 3-4 flair.

One night after getting off the interstate 3rd gear just didn't engage. After trying to limp home for a couple minutes, I got angry I just gave it gas and all of a sudden it shifted and worked. The next day I changed the trans fluid/filter and added some Lucas. Now first thing in the morning it slips VERY bad going into 3rd and has a VERY noticeable 3-4 flair. If you floor it all gears engage solid, but it seems like it doesn't want to downshift and it seems to be shifting early too.

This sound like a vac or bowden cable adjustment or internal trans?

Forums

Transmission / Suspension Specific Aid

Chassis Model Number

W126

Sounds suspiciously internal

Try driving first with the Bowden cable disconnected at the valve cover. Any difference in the slipping? Next unplug the vacuum line going to the modulator. If it still slips then check modulating pressure again. If that pressure reads ok then you have an internal problem.

83 300SD trans slipping/flairing when cold

check the vacuum going to the modulator (the only line diving at the firewall to the transmission). it should be between 9 and 10, with an ideal setting at 9.4. high vacuum = slipping, low vacuum = jerky shifts. if you find your vacuum too high, simply work the little white dome cover (plastic) off the side of the fuel pump (on the outside of the pump near the back) and adjust the little screw. i forget which direction, but just leave your mighty vac hooked up during idle to confirm which way you need to go. this worked great on my '83 300D. fyi, don't be surprised to find your vacuum in the 13 to 14 range initially. that'll be enough to cause massive slipping.

IF you still encounter slipping after adjusting your vacuum, you may need to replace your K1 and K2 springs (kits sell for about $10 each) in the transmission. it's a simple job if you don't mind getting a little messy. the replacement requires you to drop the transmission pan and remove phillips head screws off of small square cover plates. pull the old springs out, and reinstall new springs. just get a transmission service kit from mercedessource.com and follow the directions. it's pretty simple, just don't strip the phillips heads when removing the square cover plates.

i did the above 2 items in reverse order, but in retrospect the only issue i had was high vacuum and it is a very simple fix. please post back and let us know how you come out with the vacuum adjustment.