300SD Shifting Problem
 

Yesterday, I got in my 1980 300SD and drove it as usual (It had been sitting for about a week). It shifted between 1st through 3rd just fine, however, at about 40mph, it suddenly down shifted, then a second later shifted to third again. It does this consistently. I noticed something really strange as well, as I pressed the accelerator, the speedometer needle would behave like a tachometer, where it would move up the speedometer in tune with my foot. I checked the fluid and it's clean and appears to be at the correct level (I checked it with the engine running and in park). If I accelerate quickly, it'll get to third and stay there fine. Am I looking at a lot of $$$$ here or is it possible an adjustment of some type would work? The car has 353k miles on it and I've never had one once of tranny trouble with it until now.

Thanks,

Paul

What about the other gears?
 

Have you checked reverse and is that normal. Does it engage reverse quite quickly. Then you refer to third gear as though it were the top gear. What happened to your 4th gear, or is that part of the problem, that it just doesn't find 4th gear.

Sorry, I goofed
 

Reverse is fine. Yeah, I knew I goofed. I should have written that it shifts between 1st through 4th okay and that it downshifts into 3rd then back into 4th and repeats that process. Sorry about that.

Bad Translation!
 

You might want to lookup DIESELGIANT.COM and check information on the transmission vacuum valve levers. They're located under the black plastic cover on the valve cover. I just picked up a pair real cheap from him and they arrived within just a few days.

I had gremlims in my dash. Sanding the ends of some fuses resolved the problems.

kickdown checkup
 

You might want to check to see if there's a problem under the accelerator affecting the kickdown switch. The kickdown solenoid on the tranny might be acting up; a leaky o-ring?

I'm assuming the '80 is similar to my '84, but my repair programs don't go back that far.