transmission Modulator Valve ?
 

I am new to this forum and Mercedes Benz / Diesel. I have owned and driven air cooled gas VW's for 20 years. I wanted to be different, So I Bought a MB diesel. To drive. Powered by the biodiesel I am planing to make on the side of my house... I figured, with the direction fuel prices are going :sad: . I Better get on early .... early on the band wagon that is.

Anyways, I bought A 1982 300D. and the transmission has a hard shift.

My question. On the transmission's vacuum modulator..... If the little black dust cap ( The one that retains the little adjusting key from falling out ) is removed is there suppose to be a vacuum leak?.

From under the car. With the car running, my vacuum gauge at idle shows around 15 in,

If I hook my hand vacuum pump straight to the modulator. Pump it up. It holds a vacuum, with the cap ON.

With the cap OFF..... It will not hold a vacuum. I am thinking it should..... and I am thinking my modulator is bad. Am I right with this assumption?

PS: I think I see this question being answered, on another post. But not sure...

I thank you in advance, for sharing your knowledge.