Weak brakes on emergency stop

[fmmv]

The brakes on my (300tdi) 90 seemed  weak.  They worked fine, there was power assistance, and they felt normal on mild use but an emergency-type stop needed a massive shove on the pedal. The calipers were recently rebuilt, with LOF performance pads.  I suspected the servo or vacuum pump might be struggling, so I attached a Mityvac pump to the servo and it would not hold a vacuum. It's not the original servo, it was fitted new in 2010 about 60,000 miles ago, so it has had some use .

We are both knocking on a bit, and I thought it needed addressing as if we did have to do a hard stop maybe we wouldn't shove hard enough. I knew the servos are prone to splitting, so I decided to go with a new servo, in the event I went for a LOF dual diaphragm servo kit. When I took the old servo off, I found that rust had crept under the O ring sealing the servo to the master cylinder. I suspect that was the air leak.  So I would suggest if you feel the brakes lack the bite they once had but the servo is working, to detach the master cylinder and have a look. The photo makes it look way worse than it actually is, it seems to be just paint missing and I think a clean up, and new O ring would restore the power.

[fmmv]

Of course, one other thing on a 300tdi is the vac pump exhausts into the crankcase, so an air leak means air is constantly pumped into the crankcase - not good.

[Maverik]

Good bit of info sharing 👍

On this same topic *different vehicle - being a D2 (Td5), but I also found I had poor emergency stop type situations happening, on checking out the vacuum circuit, the previous owner had removed the EGR system, but not done a great job of sealing up the supply ports for the EGR solenoids etc thus the vacuum circuit wasn't tight, after I fixed it properly, it vastly improved brake performance.