hard shift on 85 300sd Calif. model
 

I have very hard shifts on all shifts on this car. Being a CA. model, the trans appears to be electronically controlled.
I found threads talking about vac adjustements etc. But I do not know if that applies? the trans also does not kick down as I expected it to when slowing down. I have not checked the kick down swithc under the pedal, but thought this info may be important.
It has been doing this since I got the car.

Any ideas? or things to check.
thanks
Doug

Hard shifts on my 85 300 TD have always been an indication of a vacuum leak somewhere. Try plugging the vacuum lines to the doors and climate control and see if it shifts smoother.

Ah, another CA car guy!

Our cars do have a vacuum transducer that is supposed to calculate the proper amount of vacuum to go to the tranny. I know one of the things this is based on is boost, but I'm not well-versed on exactly how the transducer does its thing. The transducer is the blue plastic thing on your driver's side fender that sends a vacuum line down to the trans. modulator. It's pretty close to the fuse box.

That being said, your problem sounds like a vacuum leak somewhere and probably has nothing to do with the transducer. When I got my car it shifted very hard, too. I discovered the line to the modulator was not actually connected! You've probably checked that already but it took me a while to figure that out. In my case there was so much oily crud stuck in the unconnected line that all the vacuum in the system didn't leak out of it.

If you haven't tested for vac. before there's a great pictorial on www.dieselgiant.com. However, be aware that since you have a CA car, your vac numbers will not necessarily match up with the ones shown on his pictorial. When my tranny is functioning properly I've discovered I have 22.5 inches hg going to the tranny at idle, and I think the regualar federal cars are supposed to have 15". 22.5" is the full amount my vac pump puts out.

The vacuum leak could be anywhere in the system. If you have any vacuum components that aren't working as well as they should be like your door locks or your vents, that would be a good place to start testing. It's also possible you have a leak in the modulator itself or in the rubber part that's also down there. You could test those things by taking the vac line off the transducer and using a vac pump to create a vacuum in the line going to the modulator. The modulator should hold vacuum; if it doesn't there's a leak down there somewhere and you've isolated the problem.

I've had a number of vacuum issues and I've already asked a lot of questions about them, so you might not have to. I would suggest doing a search on my user name and 'vac' or 'vacuum.' You might also search for ConnClark, he's another guy on here with a CA car. His info. has been valuable to me and might help you, too.

Sorry if you already knew most of this. Good luck!

Oh yeah, to see if your kickdown switch works, just floor the pedal when you're driving sometime. The car should downshift to give you more power. If not it may be need to be fixed but it shouldn't cause the hard shifting you describe.

wow!
 

I knew almost none of this. For some reason this car still gets my goat! But I must start. I thought these were completely electrical. My vents do not work right, so that is where I will start I guess. Could I just clamp off the hose to those and go for a drive?
The kick down does not work. That is another on the list.... And it keeps growing. Do not know If I can keep up between this and the f-series truck. But I will try.

I will also do more searches.

Thank you.
Doug

vacuum lines and diagrams
 

Be diligent young man!
Every one who works on these puppys has the dire need to f**k up the vac lines for some reason.
I even found a bb shoved in my modulator line!
There are ALOT of diagrams available and I had to extract something from each of them and even compare pictures for weeks and test drive around the hood about 25times till I got it right ~but in the end my 265k tranny shifts like a new car!
The modulator adjust was the final tweek!
I wish I knew all this info when I had the 300d cause I lived with the headjerk from 1to2 for two years!

Pushing the far right climate control button will eliminate alll the ACC vacuum pods from the equation. If shifting improves your problem is with those pods. If it doesn't, the door locks are the next most likely culprit.

An exception..........
 

On the W126, the door locks are on a completely separate vac/press system operated from a pump mounted in the trunk. (Just didn't want you to go on a wild goose chase.);)