I started a few threads on this forum a while back on my car not having enough power. I still feel like this may be a problem, but I'm thinking maybe the feeling of little power is actually a shifting problem. My question is why is my car shifting too early? Too early by definition can mean many things, but when I sometimes get to 4th gear by 25 mph and can't get back up to speed, that's a problem. I feel like the car has plenty of power especially at high speeds, or if it is in the correct gear. For example, I can't get out of 4th to go back into 3rd if I need it unless I push REALLY hard on the accelerator. If I really need the power, I usually just manually shift the shifter to another gear. Since I don't have a tachometer, I can't help with giving what the shift points are, but if I floor it, and I mean really floor it hard, it will shift into 4th at about 45-50mph. It seems like unless I give my right foot a serious workout, my car won't go anywhere. I checked out the throttle linkage and didn't seem to find much play or any problems. Is this more likely a vacuum problem, or a trans problem? Don't forget, this is an earlier w123 with the auto trans that starts out in 2nd gear, just as a sidenote. Also, when my car is cold (as in an outdoor temp of 65 degrees here is southern California) it seems to have MUCH more power and stay in gear for a much more appropriate amount of time, at least until the car warms up. Thanks for reading the long post.

Sounds like a vacuum problem to me. Have you checked your system for leaks? Your car doesn't have a bowden cable so you can't adjust the shifts that way.

__________________
1981 230E, 1984 300D.
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www.ranwhenparked.net

I don't really know how to check it for leaks, but I'll run a few searches and see if I find any DIY's or how-to's.

diesel giant has a pictorial on vacuum troubleshooting.
http://www.dieselgiant.com/mercedesvacuumtroubleshooting.htm.

http://www.dieselgiant.com/mercedesvacuumtroubleshooting.htm
try here

Don't think it's a vacuum problem. Vacuum controls softness and hardness of shifts but not shift points. The fact that it shifts later when cold is entirely normal, accounted for by the fact that shift points are controlled by the accelerator (rack) position and when the engine is cold it has less horsepower so you have to push the rack further to get the same horsepower. The further down you push the accelerator, the higher the shift points move.
Shift points are controlled by one of two things, either a bowden cable or a series of rods. I don't know which version the 79 has (my 77 had the rods) but you need to adjust the length of the cable or rods to move the shift points upward. Bowden cable would be on the top of the valve cover and have an adjustable nut there to change its length. Rods would begin at the valve cover (hooked to the accelerator linkage) and go down thru the manifold area and then back to the transmission on the right side.
I can't remember which way to adjust. But changing the length will move the shift points up or down.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

thanks, I'll check it out.

I'll jump in and try to help, though my knowledge is pretty limited. On my '83 300D I adjusted shift points by adjusting the vacuum control valve. At least I think that's what I did (was blindly following advise on this forum and it worked). Don't know if your model works that way or not. If I'm correct, maybe someone more knowledgable can add some wisdom.

__________________
John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

I'm not sure when the vacuum control valve for the transmission was introduced, but I think it's possible that the 79 does not have a VCV. I suspect it may have been introduced with the turbo, so it would be found on a W116 79 300SD but not on the 79 300D. This is speculation.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thanks for the involved post. Someone earlier in this thread said that the 79 300D didn't have the bowden cable, so I would assume the rods would be on my car. I'll have to search for some pics or more info on this topic, thanks again.

looks like there's an unknown; does anyone know for sure if the 79 300D has a vcv?

Any links on what you followed to do this? Thanks.

It's white, on top of the back of the injection pump with a bunch of vacuum lines going to it and one heading down to the left side of the transmission.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Not too good at moving things around on the computer, but if you look in the DIY section under vacuum control valve (not vacuum modulator) I think you will find lots of info.

__________________
John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

I can tell you from experience (I had a 1979) that there is no bowden cable. Kerry brings up a good correction to my point though.

__________________
1981 230E, 1984 300D.
-
www.ranwhenparked.net