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  #1  
Old 11-16-2013, 05:45 PM
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:( 82 300d transmisison vaccum hose

how hard is it to replace a 1982 300d vacuum hose.
i did a mityvac vacuum test, it went to 25 gh then dropped to basically nothing in a few minutes. is this the line or the little blue modulator?
i replaced the short little hose on the transmission peice
does the transmission need to be dropped to replace this?
also have squeaking nois and no vaccum hold at brake booster line
ugh.

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  #2  
Old 11-16-2013, 06:15 PM
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Which vacuum hose? The hose between the VCV and transmission isn't difficult to replace. If you don't like fishing around under the car, disconnect one end and tape the replacement hose to it. Pull out the old hose to feed the new hose.

Where did you apply vacuum with the MityVac? You should isolate systems to find the leak, if there is one. The brake booster is a big hungry reservoir. It takes a lot of pumps of the MityVac to evacuate it.

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87 300D
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Old 11-16-2013, 06:43 PM
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If you checked the vacuum line from above, keep in mind that there are two likely possibilities of leaking at the transmission:

Flex line connected to the modulator
Modulator cap 1982 Mercedes-Benz 300D Sedan - Automatic Transmission - Page 4
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84 300SD 350K+ miles ( Blue Belle )
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Old 11-16-2013, 07:43 PM
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To add to what the others said, I don't think a drop over a period of minutes on a vacuum test is a huge issue. When I use the MityVac I give it 10-20 seconds tops....

Or is someone going to tell me I'm wrong ?
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2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

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Old 11-17-2013, 09:44 AM
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its drops from 20hg to basically nothing. I did the test on the black line that goes directly to the transmission. is there any way to test the modulator?
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  #6  
Old 11-17-2013, 02:39 PM
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Quote:
Originally Posted by minsk View Post
its drops from 20hg to basically nothing. I did the test on the black line that goes directly to the transmission. is there any way to test the modulator?
See SDBlue's answer. It is more likely a nick in the line or a leaking modulator cap than the modulator itself.

You can access the modulator cap from under the car on the passenger side. Take a short(er) length of vacuum tubing from somewhere else and hook it up to the modulator and the mityvac and see if it holds vacuum.
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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22
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Old 11-19-2013, 10:27 AM
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are you guys referrring to the little black cap that should be on the side of the modulator?
mine doesnt have one.

knee jerk minsk ordered a new modulator...****
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Old 11-19-2013, 10:52 AM
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Yes, the little black cap on the modulator itself. Trust me, you only want to change the modulator as a last resort. It has to be adjusted, determined by transmission pump pressures, the model of car, and at a certain speed range. You will likely need to replace the pin that needs to go with it as well. It's best to clear up all of the related vacuum leaks, including the ACC system, beforehand.
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84 300SD 350K+ miles ( Blue Belle )
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  #9  
Old 11-19-2013, 11:34 AM
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so i should replace pin and cap...but not the modulator itself yet?
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  #10  
Old 11-19-2013, 12:51 PM
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Sorry I wasn't clear about what was written. The cap should be replaced right away, as it will cause a vacuum leak.

The pin I mentioned is a separate, internal transmission part and part of the modulator set up. I replaced mine when I replaced the modulator and found the pin was broken. Shifting was all over the place, sometimes smooth and usually not. Here is a pic of the pin: Pelican Parts - Automotive Parts and Accessories - Porsche & BMW
Likely, it was broken when a previous owner tried to replace the modulator to fix hard shifting on the transmission.

I've gone through the PIA of replacing the modulator, pin and adjustments and that is why I recommended clearing up all of the other, especially vacuum, problems first. From what I've read here, the modulator on the MB's, of this era at least, is designed to smooth the shift not to determine the shift point as is typical of U.S.-made cars.
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  #11  
Old 11-19-2013, 12:57 PM
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Quote:
Originally Posted by SD Blue View Post
From what I've read here, the modulator on the MB's, of this era at least, is designed to smooth the shift not to determine the shift point as is typical of U.S.-made cars.
You are correct for 85 or 90 percent of the transmissions being discussed on the forum, but from my experience the modulator plays a larger role on this model of transmission, where there is no control rod or Bowden cable.

With no other control in play, the shift points are controlled by the governor - which on this model is internal and not accessible/adjustable - and the modulator, and the vacuum to the modulator.

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2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22
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