Vacuum Pump Replacement 91 300D
 

So I took my 91 to my mechanic to diagnose my vacuum problem (slowly retracting headrest, bumpy shifts, and slightly diminished braking ability). As part of my diagnosis, I was going to get a vacuum reading from along the brake booster line, but in the process I broke the fitting to the line that goes to the shut-off valve....so that was the first thing that had to be fixed.

My mechanic replaced the line and then measured vacuum. He was getting 18" along the fitting in the middle of the booster line...eventually it went to 20". He has another 91 in the shop right now and got 20" right away with that one. He's run through all the MB recommended tests, brake booster is fine, etc., etc...

HOWEVER, when he had that line off he noticed oil in it....which obviously should not be. So he thinks what makes most sense is to replace the pump. Since it's an original style pump, I need very little encouragement to get the pump replaced. But I thought I'd run it by you guys before I actually pull the trigger.

One forum member has already mentioned to me via email that the pump, in the nature of the case, can't push oil....rather, it's getting sucked from somewhere and that I need to find out where that is. But, I still wonder if a compromised VP diaphragm could result in oil in the line.

The car only has 113k miles on it so I was hoping to keep the original pump for a while....but it is 23 years old so perhaps age is a factor.

Thanks.

Transmission vacuum modulator...potential source of leaking oil?

So there's evidence of a bit of BLACK oily mess BOTH at the vacuum pump output to the brake booster AND at the hose that connects to the shutoff valve. As far as I know, the VP and the SOV are the only two possible places where engine oil could enter the vacuum system.

I have the car back....my mechanic still suspects the VP.

I have the old brake booster line....need to slice it open and see what I find, although I imagine I'll find evidence of oily mess throughout.