Ok so I have a 79 300td, so there is no vacume modulator on my model, but get this:

shifting from 2nd to 3rd under load or up hills, I get a sound at the trans that is described as follows: a hiss, or like air and fluid being forced out a small opening. It switches on as the rpm climb (to about 3000) and fades out before or a little after the shift(with a jerk). Otherwise the shifts are firm with no slipping (I know slipping defined as rpms suddenly climbing then dropping back)

In fact The performance of the trans is the same as its been for the 20,000 miles Ive driven so far, except for now that hiss.

Well not exactly...I always would get that sound or a simular sound only if my fluid got below the lower line on the dipstick.

Now the bushing connecting to the rod that comes down from the manifolds is gone, so theres a little slop. Also I havent changed the trans filter yet. Is there a pressure relief valve? there is a lot of oil caked up around the passenger side of the trans.


So what is that hiss sound if it isnt vacume? Its getting worse.
Thanks!
Mike

PS I checked the other threads, but not much is there to give me a clue to a hissing sound on a non-vacume controlled trans.