I'm looking to buy this winter beater for 1000$. It has a transmission issue. This is how the owner describes it;

As far as the transmission, when the trans shifts into second and third it wants to return to the previous gear for just a second until the rpm and speed raises slightly, if this makes sense. Cottman Transmission rebuilt the transmission and told my father that the problem was with the vacuum system. I remember my father telling me that a mercedes dealership had to clean oil out of a vacuum valve several years ago. This problem does not act like a slip, but more of an adjustment needed. Once you get into third gear, the ride is smooth.

Now, I thought that a vacuum issue of that sort in an 81' would prevent upshifts and that these symptoms sound like something other than a failed vacuum modulater or simple leak. What do you think is wrong with it?

Thank you.

Sounds like bowden cable needs to be adjusted. Vacuum modulators are relatively cheap. If it shifts and goes forward in all gears without major slipping, then make an offer.

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1987 VW Jetta Mk II - Daily Driver
1992 W201 2.3 - sold
1985 W126 380se - sold
1985 W123 OM617.952 - sold
1981 W123 OM617.912 - sold
1986 W201 2.3 - sold
1979 W123 OM 617.912 - sold

It sounds like what is commonly referred to as "flaring", and is typically caused by too much vacuum.

Search "flaring".

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Gone to the dark side

- Jeff

If I understand your thread this $1000.00 car is an 81. If it is, it has no bowden cable. Its controlled thru metered vacuum. There are vacuum check valves upstream of the modulator that control vacuum to the modulator by leaking off vacuum. There is also a valve on the top of the valve cover that is opened/ closed as the linkage pivots. They are prone to leaking or the little lever on them breaks off. Yes I agree, it sounds like too much vacuum is getting to the trans, not too little. On a car that old it could have many issues, threaded throttle rods misadjusted, ck valves leaking, modulators sticky, etc. Make an offer once you find a mechanic that is well trained on this older car. Not before.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Is the vacuum not contolled by the vcv on the ip?

Yes, that meters it as throttle is opened, but then check valves hold or meter vacuum after that. Do you have the white vac valve on the top center of the valve cover?

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.