I have a 79 300td. I had a used tranny installed, which flared and shifted poorly, so the shop said i should rebuild it. Did, and problems weren't solved! initially, they blocked off the check valve to the door locks, and the green ac line. The car shifted very softly and early. However, since i got it back, it is late shifting at the top of the RPM range, kickdown won't engage, and it won't shut off.

The shop found the 't' fitting too large, so the filled it and drilled it out to 20 tho/inch...The gauge pulls 12.5 in vacuum at the 't' fitting, and at the line to transmission from the 3-2 valve atop the valve cover.

I have replaced all the rubber vacuum lines/connectors--both in the engine and at the key shut-off terminals. I have replaced the two brown vacuum lines.

The shut-off switch functions, but only periodically and takes a while to engage (hitting the thottle). Sometimes it only seems to get 4 hg

At some points i get NO vacuum reading at the line to the trans modulator. Then it will kick in, and the vacuum control (proportioning) valve does it's job--leaking down vacuum with throttle opening/rpms.

SO...sometimes it shifts like butter, sometimes hard shifting. I've also tried blocking the line to the shut-off valve, to no effect.

Is my vacuum pump leaking?

**Just read the long sticky thread on transmissions: it would seem possible/likely that the vacuum line going from the 3-2 valve after the VCV might be cracked/leaking! This would explain the intermittent shifting. I don't have a vacuum pump gauge, just a dial gauge. So i will go get one tomorrow to see if the vacuum line to the modulator on the tranny is holding vacuum!

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Mike
Vancouver, BC
'79 300td 60k miles!
import from Japan