1982 300sd transmission

[willrev]

I have scheduled a trip to the mechanic tomorrow, but need to know what to ask him to look for.

First - I have a clunking sound when car is in park and engine running. Have looked at many posts on this site. Possibilities in similar situations - flex discs, center driveshaft bearing, transmission mount, or exhaust system banging due to broken exhaust mount.

What are flex discs? They are discussed in many of the posts but no technical information is given.

Second - clunking with each downshift. Possibilities have been said to be the T fitting to the modulator gets a clogged orifice and needs cleaning - i.e. it is a vacuum problem - not enough vacuum during downshift.

Thank you very much for your feedback. I want to ask educated questions.