My brake servo isn't working, as evidenced by the brake pedal test and having to press really hard on the brake pedal to stop the car. Having stripped down the servo the only thing I can find that may be the cause was the air valve piston which was stuck in the bore of the slave cylinder. Following the workshop manual I applied air pressure to remove the piston, but it didn't budge even up to significantly high air pressure. I eventually got the piston out with a bolt removal bit which produced enough bite to twist and pull it out.
After cleaning up the piston and bore they seemed to be in a reasonable condition, and the piston slides in the bore when inserting the reverse way round ie leaving the rubber cup outside the bore. When inserting the piston cup first into the bore it's a tight fit and I'm doubtful whether the spring tension from the air valve could push the piston down the bore. Looking at the manual it says the cup should be fitted with the lip facing the shouldered end of the piston - which I take to mean lip facing upwards to the top of the bore. However, the cup is fitted the other way round. See photo.
The odd thing is the servo has been working fine for several years until recently, without touching these components, so maybe a red herring!
Can someone confirm which way round the cup should go.
Thanks
Peter

After cleaning up the piston and bore they seemed to be in a reasonable condition, and the piston slides in the bore when inserting the reverse way round ie leaving the rubber cup outside the bore. When inserting the piston cup first into the bore it's a tight fit and I'm doubtful whether the spring tension from the air valve could push the piston down the bore. Looking at the manual it says the cup should be fitted with the lip facing the shouldered end of the piston - which I take to mean lip facing upwards to the top of the bore. However, the cup is fitted the other way round. See photo.
The odd thing is the servo has been working fine for several years until recently, without touching these components, so maybe a red herring!
Can someone confirm which way round the cup should go.
Thanks
Peter
