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  #1  
Old 02-20-2007, 06:10 PM
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Transmission adjustments adjusting vacuum modulator & throttle pressure cable

anybody have any pics on how to adjust the Throttle pressure cable & vacuum modulator. My 1983 mercedes 300SD isn't hard shifting but when it goes into the next gear it get louder and hesitates. It then shifts and quiets down.
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  #2  
Old 02-20-2007, 06:15 PM
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Originally Posted by chosenberg View Post
............but when it goes into the next gear it get louder and hesitates. It then shifts and quiets down.
"Flaring" is what happens when the transmission disengages from the engine during the shift. The engine runs up in rpm and a split second later the trans engages the next gear the engine returns back to a lower rpm.

Do you have "flaring"?

If so, which shifts are affected? Is it just the 2-3? Or is it both the 2-3 and the 3-4?
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Old 02-20-2007, 06:32 PM
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Thats what it sounds like "flaring" can you give me some tips please. Actually its three and four that are being affected.
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Old 02-20-2007, 06:39 PM
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The best thing to do for flaring is to reduce vacuum to the transmission.

Do you have a Mityvac that you can use?
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Old 02-20-2007, 06:40 PM
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What is a mityvac and how do I reduce vacuum?
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Old 02-20-2007, 06:49 PM
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What is a mityvac and how do I reduce vacuum?
A mityvac is a portable vaccum pump that allows you to provide vacuum to troubleshoot most functions on the vehicle. It's nearly mandatory for any work on these vehicles with extensive vacuum controls for the transmission, brakes, and door locks.

Once you get the Mityvac, we can go over the proper procedure to set vacuum to the trans.
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  #7  
Old 02-20-2007, 06:56 PM
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I own a craftsman vacuum pump. That should work fine right?
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Old 02-20-2007, 06:58 PM
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I own a craftsman vacuum pump. That should work fine right?
We could make that work although it's not as convenient. You'll need a vacuum gauge in addition to the pump (and separate from any gauge that might be on the pump).
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Old 02-20-2007, 07:07 PM
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so this alone wouldn't be sufficient? I'll need and extra vacuum gauge other than this? Can they be purchased at autozone or pepboys?
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Old 02-20-2007, 08:20 PM
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Old 02-20-2007, 08:28 PM
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so this alone wouldn't be sufficient? I'll need and extra vacuum gauge other than this? Can they be purchased at autozone or pepboys?
That's the "Mityvac". You won't need anything else.

What to do:

Find the Injection pump.

On the top of the pump, near the rear, is a white plastic valve. There will be a vacuum T above the valve. The bull of the T goes into the valve. There's a green and white dampener valve on the line. The far end of the line goes to the transmission. The near end (closer to the front) is the supply vacuum.

Remove the supply vacuum from the T and connect up your Mityvac.

Pump up the Mityvac and obtain a reading from the guage. It will pump up to about 14" or so.

On the side of the white plastic valve (properly called a Vacuum Control Valve, or VCV) is a small domed plastic cover. Carefully pry this domed cover off the VCV. Beneath it will be a slotted screw and a small locknut. Release the locknut and turn the slotted screw about 5 degrees clockwise.

Observe your gauge.

It should drop down from the 14" reading. You want it down around 10". Once you reach 10", lock the locknut and put the cover back on.

Reconnect the supply vacuum to the T and take it for a drive.

Flaring is now gone..........hopefully.......
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Old 02-20-2007, 09:24 PM
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Thank You Brian. I will try to do it tomorrow. Would you happen to have a link to some pics of a demonstration?
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Old 02-20-2007, 10:34 PM
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Thank You Brian. I will try to do it tomorrow. Would you happen to have a link to some pics of a demonstration?
I don't believe we've got any DIY's on that procedure. Just post if you get into trouble........however, I'm away most of the day tomorrow........but others know the procedure as well.
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Old 02-21-2007, 06:52 PM
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Originally Posted by Brian Carlton View Post
On the side of the white plastic valve (properly called a Vacuum Control Valve, or VCV) is a small domed plastic cover. Carefully pry this domed cover off the VCV. Beneath it will be a slotted screw and a small locknut. Release the locknut and turn the slotted screw about 5 degrees clockwise.
FWIW, I checked the vacuum as Brian described today. My trans shifts pretty well once warm but I figured if there was room for improvement.....

When I removed the small domed cover there was no slotted screw and locknut. There was a small threaded cylinder with two flats on each side threaded onto a stud (sorta like a 'tard nut). An 8mm wrench fit the flats perfectly. The mityvac indicated 12hg so I adjusted it to 10hg. I tried the whole range of adjustment, almost 1/2 turn and it ranged from 8hg to 15hg. Very sensitive little bugger. It was either 8hg or 15hg with just the slightest change but I got it to stay at 10hg after fiddling a bit. The shifts are just slightly more crisp. RT
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Old 02-21-2007, 07:23 PM
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I have a question, which may or may not pertain to the info in this thread? I have been looking at a 1987 190D, well havent seen anything besides pictures, but have corresponded with the owner several times a week for the past few weeks. He stated he had the transmission rebuilt about a year ago, but instead of letting the technician finish "tuning" the tranny, he took the car, as he was tired of renting one while that was in the shop, and he needed his car back. Here is a quote from what he told me about his transmission..."Work was done by AAMCO and I've got the receipts.
Only the rubber seals needed replacing, but, I needed a working car, and decided to get the transmission rebuilt. With 20/20 hind sight, time and
the car being home near it's local mechanic, I wouldn't have done it. No major motor work. It does use a bit more oil than it should. There's a leak
around the head gasket that I haven't bothered to repair. The vaccum modulator or vaccum to the transmission might be needing attention. I'm not
sure. It seems to shift late, but, that transmission can be 'tuned' so by so many variables, I haven't played with it. If I need a 'jack rabbit' start. (ok,
with a non-turbo diesel, a 'jack turtle' start), I simply downshift into '2' and then when it gets speed up, I pop it back into "D". Do you think making the adjustments you guys have been talking about in this thread, would help his problem?
thanks,
coadman
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