1985 300DT: 2 issues - vacuum + windows - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 10-17-2010, 01:22 PM Thread Starter
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Post 1985 300DT: 2 issues - vacuum + windows

Hey there,
I have a 1985 300DT that I've been getting back into daily running shape after it had been sitting for 4 or 5 years.

Around 170k miles.
I don't know if it is a California version or not, and I'm not sure how I can find this out.

The issues:
1. Vacuum leak(s)
The car was shifting terribly, and would not shut off when the ignition was turned off, key removed.

After doing some reading I did a little experimenting and now know that if I keep the doors locked while driving it shifts much better (still pretty heavy from 1-2, but pretty smooth from 2-3), and the engine shuts down with the key as long as the doors remain locked. It also seems to brake much better, though I could be imagining that, but still seems to be lacking in pick-up power when accelerating.

I know this should be telling me something fairly important, is it that the leak in the system is somewhere in the locking?

I've also been having a tough time finding a diagram for the vacuum system that matches what is under the hood, or that I can decipher. Any ideas/ help? I've done a lot of searching of forums both here and otherwise, and got some resolution, but I'm not sure where I should go from this point.

2. Power Windows
All four windows stopped working at the same time, they are all currently in the down position and won't roll up.

The fact that all four stopped working at the same time leads me to believe that there is some common switch that went bad somewhere, but I can't seem to find it. Fuses were replaced and made no difference.

Any ideas?

Any input would be awesome.

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post #2 of 3 (permalink) Old 10-17-2010, 01:48 PM
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Try also asking on the W123 forum, at least I think that's what you have. Look in the sedans section, locate the proper forum, and you should get some quicker answers.

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post #3 of 3 (permalink) Old 10-17-2010, 03:09 PM
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1. check the appropriate section as MM suggest
2. check the fuse for the windows. Common issue on those cars is that owners put aluminum fuses into brass holders. That generate electrocorosion. If you have those -replace alum fuses with copper ones.
3. your conclusion about vacuum leak sounds right on the money. This car has one engine-mounted vacuum pump for everything. Even the brake booster is having bigger tube than the rest of the system -leak in small tubes might affect brake boosting as well. I rebuild the locks on W123 years ago and it was lot of fun. From what I remember most of the tubes are under floor mats. The main tubing goes into driver door valve and than the valve distribute it to door elements. The best way for me was install tee on the main tubings with vacuum gauge on it, run the engine with pump and than disconnect and plug the tubings "down the road". This way you can easily diagnose which branch of system leaks. On 25 years old car , all door elements could use new diaphragms or all new elements.
4. observing which door lock is the slowest might give you quick indication about evident problem.

Last edited by Kajtek1; 10-17-2010 at 03:12 PM.
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