I noticed last year the brakes felt quite un-responsive. I thought it might just be me but before getting it back on the road ready for the summer I would just check if the brake servo was OK. I did the usual test of holding the brake and starting the engine and indeed the pedel did pull down. However, when I applied vacuum to the servo via a hand pump; well I couldn't apply a vacuum! There was a major airleak and I heard that it should hold vacuum for a good 5 minutes.
In a previous life it was evident there was a failed brake master cylinder. The paint was all peeled from below it and the master cylinder had been replaced - but I guess not the servo / brake booster. I found removing it quite hard, I had to remove the clutch slave cylinder and slacken off the turbo downpipe to get enough space to rotate it around past the struct tower. The pin (clevis) that attaches to the brake pedal is quite long so stops it all from just sliding out.
It seems impossible to find a new or re-manufactured servo unless I get one shipped from Aus to UK.
When I got the old one out I used my hand pump to apply a little pressure this time, much easier to find the leak. In fact it was so bad I could just blow with my mouth down the pipe into the servo and hear the air hissing. It was coming from the pin that pushes into the master cylinder. I carefully with a pick worked around a sortof washer / seal retainer thing. Then I carefully prised the seal out - which has a metal backer washer. I gave everything a good clean.
With the retainer and seal (Part No 222-24100) removed, you can see its all got a lot of surface rust and the area around the seal was full of gritty rusty old peeled paint stuff. Looking at it, I'm not sure its the seal to blame. The shaft was quite dirty and in the picture you can see its actually pitted. Cleaning it all up helped a lot but I had an idea to improve the surface of the shaft
Here is 50mm of heatshrink (which is actually Viton). I got a piece that only just fit over the shaft and carefully used a heat gun to shrink it onto the shaft, without getting anything else in the booster too hot. I the applied a good amount of red silicone based grease on the outside and inside faces of the seal, pushed it back in and drove the retainer back home with a 27mm socket.
I managed to pull 0.5bar of vacuum and it held that for 1 hour before I decided it was working well!