I've searched this site regarding late shifting and early shifting. My problem with my 81 300Cd non turbo is when I measure vacuum to the modulator its 23 hg at idle and the second I move the throttle it goes to zero! my series number is 123150-12-006942, my vin is WDBAB50A0BB006942. I've replaced the white switching valve on the valve cover, verified no vacuum leaks there. Replaced vacuum regulator valve on injec. pump with 2 used ones, all to no avail. My trans shifts from 1st to second on light throttle at 20 mph, from 2nd to 3rd at 39 mph, then to 4th if I let up on the throttle slightly. All shifts seem late and harsh and moving the adjuster pin in the modulator has drastic affects which I attribute to no vacuum present at any postion except for idle. I notice an adjustable rod attached to the vac regulator valve but have no reference for adjustment. Should I have varying vacuum i.e. 23 at idle 10 to 12 at half throttle, none at wide open throttle? Any assistance would be appreciated, thanks Bill. We want to give this car to our 17 yr old daughter as a first car because the engine is great, 150k miles, body great, a/c and cruise work and she likes the 2 door hardtop look, but I dont want to spend $1000.00 on a $1500.00 car! trans was rebuilt 2 yrs. ago.

 

This problem sounds familiar to me as I just went through it with my 81 300 CD. The problem with mine ended up being the white vacuum valve on the valve cover. My car has 3 of them. One of the nipples had broken off which caused no vacuum at all. When I ordered replacements, and checked them with a vacuum gauge before installing them, I found one was defective and would not flow air through it. So I suggest you check the vacuum valves to make sure they're working properly. To the best of my knowledge and I can check this again if you want, when you apply vacuum to the single stem on one side, vacuum should flow through one or the other stem on the other side, depending on whether you have the valve pressed or released. All of my shifts were late and extremely harsh. My car is 26 years old with 68,000 miles on it and believe me they were hard earned miles as this car received very little in the way of maintenance its whole life. It is my opinion that these valves are not extremely stout. So to me, they're prone to failure and at the cost of $35 a piece, I saw no need to not replace all three because one had broken. My car went from giving me whiplash to almost imperceptible shifts for $100. If you want help adjusting those rods, I suggest you post again and ask for help with that specifically. There are two or three people that view these posts that work on mercedes vehicles for a living. That's where I got my direction from. Good luck - and don't sell the car, it's worth spending $1000 on because these cars go 300,000 plus miles with the right care.

 

Thanks so much for the quick and very informative reply. I will ck the other two valves tonight.

 

This is promising. I'm purchasing a similar MB diesel tomorrow with similar tranny symptoms. I've owned several VW diesels including new TDI's and an 83 Chevy G20 conversion van w/ a 6.2 diesel. I've always wanted an early MB diesel and found one for sale on the side of the road.

 

Thanks to poster 81 300cd, I rechecked all the switching valves on the valve cover. The other two were, in fact, leaking as well. I replaced all 3 valves and the problem is resolved!. As an aside, I also drained all trans fluid and replaced with Dextron/Mercon 5 which is synthetic. Thanks all for their assistance. so glad I found this forum. Bill.

 

hey, nice of you to post a reply! i am glad i could help at least point you in some direction. and the valves are cheap compared to labor in some shop to troubleshoot the problem. glad it helped. andrew