The transmission in my 1983 300d flares on the 2-3 and 3-4 shifts (at least that is where I think it is flaring). I have searched the board and I am guessing that the prior owner may have fooled around with the modulator. What I am thinking of doing is plugging the vacuum line to the modulator to see if that will give me harder shifts without the flare. Has anyone tried this and is there any potential harm?

I just had my tranny rebuilt. Currently have no vacuum to the modulator.
I have a vac leak or something else wrong but how long will tranny
take the harder shifts without damaging it? Or is it ok to leave as is.

The transmission will take the harder shifts forever. It prefers a very fast shift and it causes less wear on the clutches. You can certainly plug your vacuum line and not cause any harm to the trans.


However, if the shift is very fast, the shock to the driveline is quite high and you will cause the flex discs to wear much faster than normal. Additionally, this shock is transmitted through the differential and it does not do the gears any good. Finally, the same shock is transmitted to the axles, which also will not be too happy about it.

For testing purposes, the removal of the vacuum completely is fine.

Here is an excellent source of info for trans. woes. www.mbz.org Click on Articles, then Transmission, then Adjust. For vacuum leaks, I found it easier to just replace all the 3-way connectors and flexible connections. Takes about 10 min. and less than $15. Then search further if you are still having problems.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I did it and it didn't affect the shifts at all. Maybe my modulator was bad, however I adjusted the modulator, and the shifting is good now. Smooth and no flaring.

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'83 240D with 617.952 and 2.88
'01 VW Beetle TDI
'05 Jeep Liberty CRD
'89 Toyota 4x4, needs 2L-T
'78 280Z with L28ET - 12.86@110
Oil Burner Kartel #35

http://i16.photobucket.com/albums/b1...oD/bioclip.jpg

Once you're set up with a vacuum gauge and some T pieces testing the vacuum system is not at all difficult. There are plenty of articles that tell you what vacuum reading to look for at various places in the system - it's not hard to do.

It may be that the line to the control valve on the injection pump is blocked, preventing it from reducing the vacuum as the throttle is increased. The white control valve has another pipe that allows air to enter, to replace the vacuum and lower the reading, which may be blocked - mine leads off into the dash somewhere and appears somewhat restricted.

A flare is caused by too much vacuum to the modulator, hard shifts by too little. Most failures seem to be the result of not enough vacuum leading to hard shifts. There's really nothing particularly mystical about the way it all works.

Kevin

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'85 300SD

I just went through all of this with my 1982 300sd. My modulator tested fine with a vacuum pump. It was the vavles preceeding the modulator that were leaking that sent pressure to it. There are two vavles on the valve cover in a black box. One of them operates the EGR, the other white colored cam and valve affects pressure to the modulator. If it is leaking as mine was - and this is according to the MB dealer in Raleigh NC and the indy mechanic I deal with then the modulator will not get sufficient pressure. Replace the valve for about $40-50 on the valve cover then check the pressure going to the modulator and adjust the modulator to soften the shift. We adjusted my modulator 2 whole turns and you dont even feel the shift from 1st to 2nd and 2nd to 3rd. First used to be hard and squall my rear tire and second was hard too. Now it drives like a dream. The vavle on the injection pump can go bad too and throw off the modulator, but is more like $125 to replace. Try the one on the valve cover first. Your problem sounds similar to mine.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

Thanks to the post of the diagrams and testing my system, I found
the oriface (0.5 mm) plugged with soot in the main booster line.
Then I also found the double valve assembly on top of the valve cover
was not holding vac. So I am ordering two 3/2 way vac valves today.
Then I go back to my Transmission rebuilder to have him readjust
the modulator. I should be back in business after Christmas.
I hope to keep the old girl for at least another 200K miles.

Over the holiday break I am going to tackle the cruise control and
climate control. Both are intermittent.

Thanks, Matt