This is my brake servo.
I removed it from the car as part of the "refurbish the brakes" subproject of the "financially ruinous Rover P5" project. It's a separate unit from the pedal-activated cylinder unlike it is on almost any other car, because Rover loved overcomplicating things back then.
The vacuum chamber (the large cylinder on the right) was half-full with brake fluid. As the name "vacuum" implies, there is not meant to be any fluid in there at all. That was quite the surprise when I took it apart, and also a surprise which caused me to lose a full set of clothing. There was little way the servo could have been functioning, and I suspect that aeration of the brake fluid would have caused the braking system to be minimally-functional even without the servo's assistance.
I suspected this seal may have been the problem:
But, the unit was so ugly that I cannot say for sure that any single component was at fault. The photos you see here were after a blast of electrical contact cleaner (which is great for cleaning up anything that isn't an electrical contact).
I take a lot of photos in the course of doing things as reference for how things need to go back together. In the above one, you can see quite a lot of mank in the servo's internals.
Under other circumstances, I would have considered giving it a wire brush on the outside, a soak in petrol and a skim with very mild abrasives to clean the cylinders. But while I was ordering an electroplating kit for the various fasteners I have removed from the car, it seemed a good idea to order an electrolytic cleaning kit` as an experiment! As if I didn't have enough new things to learn...
Electrolytic cleaning is, in my head, electroplating in reverse. Rather than using an electric current to attract material onto a thing you want to plate, you operate it in reverse so an electric current attracts material away from a thing you want to clean.
It works quite well. In the process of working quite well, it turns the electrolyte (this is water mixed with powdered sodium carbonate) into the only thing I would like to drink less than brake fluid or Foster's.
The exterior of the servo still required some love from a wire brush on the outside after the cleaning. The two bores feel very nice after the cleaning, so I will leave them be.
And the part that makes me happiest, is that the Girling wordmark is now visible!
And that...means that after two weekends I am half-way through rebuilding one of the components of one of the sub-projects of the P5.