300sd shifts funny when going uphill.

[avacadogreen779]

Hey everyone, here's my story....

I have a 1979 300sd w116. It runs smoothly in city driving, but whenever I'm at freeway speeds 45+ (i live in hawaii and we drive slow here) and going uphill the car boggs down dramatically as if it's in 4th or 5th gear when it should down shift to be in high gear to go up hill. It feels like the car should be in high 2nd or 3rd gear to climb up hills and keep up with traffic. But instead it feels like it goes straight to 4th or 5th thus struggling to gain momentum on an up hill climb.
Hope that makes sense. During city driving and freeway driving on flat ground, the car shifts perfectly. The turbo kicks in when it should, it's just the down shift to climb up hill that doesnt seem to be working.

Could it be a vacuum thing? Turbo release valve or something? Or the tranny?

Would love to hear your thoughts and ideas.

[jbach36]

I don't know. In fact, I know less than the just-enough-to-dangerous stage.

But I just put synthetic in mine, and it does seem to shift smoother.

Maybe yours is low on fluid? Have you checked to make sure you have enough (check after you've run the car a bit). When's the last time you did a fluid and filter change?

It's possible the transmission needs adjusted, but I don't know.

Good luck.

[kerry]

Probably a bad kickdown switch. Check it, it could just be unplugged. Your transmission does not have a 5th gear. What you need is a lower gear to go uphill, not a higher gear.
You could also be getting stacked shifts, a quick shift from 3rd to 4th. Not on unusual problem on a W116 300sd. An adjustment of the bowden cable might solve that.

[clackclack]

Sorry,I love that movie.