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1975 Mercedes 300D
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225 Posts
Discussion Starter #1
I have a 1980 300D and it recently developed a problem where it is having trouble shifting. I didn't drive it for awhile and when I went to drive it reverse wouldn't work, I heard it could be vacuum so I played with some vacuum hoses and it still wouldn't move in neutral, but it would move fine in the forward gears. So I let it sit for awhile more and now it wont move in any gears. I was wondering if you guys could help me figure out whether I need a newe transmission or is it just a vacuum problem. I think it's probably vacuum. I got the Haynes manual for it but that was pretty much useless.
Thanks
 

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1975 Mercedes 300D
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225 Posts
Discussion Starter #2
Could it be the vacuum pump?
 

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2008 PT, 1998 neon--1965 VW 1200
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2,533 Posts
you let it idle in park for a good long while to get the vacuum going? after having been parked for a while, id assume all the vacuum would have been long gone since these cars all leak a little.

im not a big help, i know but i just had to say amen to the haynes manual comment, i read somewhere on this board that they only include enough information to get you into trouble on these cars.

i wholeheartedly agree. i pretty much only use mine as a road map, cuz i know where nothing is on this car yet! the guys here will get you fixed up though, they even put up with my (much similar to this posting...) uneducated, silly newbie questions and long posts about nothing at all!

id say check the vacuum and maybe even the shift linkage? if the shifter doesnt tell it to go in gear, it prolly wouldnt, eh? good luck!
 

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1975 Mercedes 300D
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225 Posts
Discussion Starter #4
The door locks are vacuum and they had started to work really slow when this happend, and they don't work at all now, thats what makes me think it's a vacuum problem. I'll take a look at the shift linkage one of these days it warms up and stops snowing.
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2008 PT, 1998 neon--1965 VW 1200
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heh heh yeah, i live in birmingham and its 71 and sunny here today, so i can understand your not wanting to go out in the cold to do it!

it could be that the vacuum leaks have gotten so bad that you need only to hook that back up wellenough to atleast see if the tranny is good!

i thought my car had vacuum problems because it kept running after i'd turn it off, and the doorlocks were so slow, rough shifts too.

ive heard since that these cars dont shift super smoothly even when theyre perfectly adjusted/running! i could be just talking out of my ass though!
 

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To the best of my knowledge, the only vacuum line running to the transmission is for the modulator. The modulator simply modulates hydraulic pressure within the transmission (sort of like a pressure regulator on a gas grill) to control shift timing and quality. If this vacuum is not hooked up you will simply get early HARD shifts. How about some more background information. Did the problem develop suddenly? Did it start but get worse over time? Did or do you hear any noises? Did you say the car can't be pushed with the transmission in neutral but can in drive or other gears?
 

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1975 Mercedes 300D
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225 Posts
Discussion Starter #7
The problem got worse over time, but it did shift hard early. Thats pretty much it for the problem but as of now it just won't move in any gears. It worked in all the forward gears and reverse didn't work but then one day I went to start it and see if I could move it in the forward gears and it wouldn't even move in any of the forward gears and reverse, I think I mis-stated that in the first post and said neutral instead of reverse.
hope this helps solve the problem
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I don't know a lot about transmissions but it sounds like you have lost hydraulic pressure within the transmission. This could be due to a bad pump or something else. I would suggest calling some transmission shops and trying to mild them for some information. Of course, most of them won't tell you anything on the phone but be patient and eventually somebody will talk to you.
 

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W123 280E
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112 Posts
Is there oil in the tranny? What colour (should be red, not brown or black)? Does it smell burnt?

Start the car, kick the handbrake and put D on. Tell your friend to stand on the brake. Check the oil and add if needed. The engine must be hot, and running idle all the time.

If oil is ok, let the engine run idle and go slowly through all the gears couple times. Check the oil again.

Again, dont push the gas until a gear is connected. The tranny may kick very hard in some cases and that will break the differential, driveshaft, or something.
 

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1983 240D auto..soon to run a generator in the country.1984 300D turbo 4 spd
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149 Posts
I was lucky to buy someone's 240D that stayed in 1st gear. After reading other posts I plugged the EGR switchover valve,(under the black plastic on top og the valve cover, left hand side, facing engine compartment). The vacuum to the right hand side swichover valve was improved but the plastic cam had worn away at the valve lever. $17 later with a new switchover valve, (transmission only) I chased down other leaks. Changed fluid 1st,(draining the torgue converter through the little plug) filled it up too much, ran it, drained it and changed the filter. The car had 96k miles and the transmission was the reason the owner got frustrated, left it under some pine trees for a couple of years and then I got it. Hydraulic problems would encourage me to junk the auto trans and chase parts to go manual. If it ran well before sitting I'd guess a fluid, filter and possibly modulator change is still a cheaper way to go.
Vacuum will always be a concern till you've gone over it time and again and feel more confident to use a vacuum gauge or process of elimination.
 

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1975 Mercedes 300D
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225 Posts
Discussion Starter #11
Hey thanks everybody, I called one guy who works on Mercedes and he said I needed a whole new transmission. I really doubt it. I still think it's vacuum. I'll give what you guys said a try.
Thanks
 
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