PeachParts Mercedes-Benz Forum - View Single Post - Transmission shifting response vacuum span (Stevebfl are you out there)

stevebfl · #2 06-24-2001, 04:29 PM

Wow, yes it makes perfect sense. I think you actually understand at least one of the inter-related effects that can be mixed to fool the beast.

The adjustment of the proportioning valve is done at the end of the shaft that has the pivot arm. It is done on the other end. This end has a plastic cap over it on the outward side of the device (away from engine). The cover is about the diameter of a nickel. It will pull straight out with a firm grip.

NOTE: there are at least three different valves, only one is adjustable that I know of. On one the cap doesn't pull off (don't force it, it should be easy). On one, the nut on the end of the rod is crimped on and doesn't readily turn (I have not tried too hard as these are the way new valves come). The one that is adjustable will have two flats on the nut which will be 8mm apart (use an 8mm open end wrench).

The width of the vacuum range is different in each valve. Broad range can fix certain problems. On others a short range moved relative to the throttle is the best answer.

Unfortunately, it sounds like you have a 83 or earlier 300SD. The basic problem with that tranny was that they had too strong of a band application in second gear. The fix was a new band and a new servo piston which is also involved with the band going away in fourth gear. The servo piston can be changed externally and probably would help.

To a certain extent the shift overlap can be controlled by changing some springs in the valve body on the accumulator pistons. There is a company that makes a spring set with instructions for "calibrating" these shift irregularities. I have used it a few times. The real answer though is often to rebuild the tranny as there are so many improvements that can be made.