Hard shiftin' SDL
 

Ever since I got the car it has shifted pretty hard, but I learned to live with it. But crawling in traffic or going slow when it shifts gives a very noticable jerk and an associated snap/clunk sound which I assume is play in the driveline.

Anyway, tonight I went under and turned the trans modulator 2 full turns BACK, and this seemed to have very little effect.

In the morning, when the engine is cold, it will shift nicely, not too hard, not too soft. I think this is from a cold-start vacuum valve that allows it to shift softer when it is cold, because these normally shift hard when they are cold, but it only does this for about two minutes.

Did I turn it back far enough? Maybe I have a leak in the line to the vacuum modulator?

Any suggestions?

What RPM do you get before it shifts? My SDL shifts harder then my 300D. One thing I noticed SDL shifts at a higher rpm 3200+ while 300D does it at around 2300+ under normal light throttle. Since I just got that SDL I haven't got time to mess around with the linkage. Have you done that?

TD

My 86 SDL did just as you discribed during a trip last week. This was new and when we stopped for fuel. I started looking for a disconnected vacuum hose.

Sure enough, the small hose leaving the pump was loose.

Reconnected and its back to normal.

Harry
86 300 SDL
85 300D Euro

Another common problem is a restriction in the system. Either a leak or a rescriction can cause a hard shift.
I would check out the ports on the power brake booster hose, where the 2 smaller vacuum lines connect. The can plug up with soot or minor amounts of oil over the years. You should be able to spot which one goes to the vacuum contols for the modulator. The other one is for the door locks and engine shut off and so forth. You can try cleaning out the ports with a small diameter drill, just do it by hand. If this seems to fix it, you may want to consider just replacing the booster hose, it's not that expensive.
Gilly