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Discussion Starter #1
My brakes work fine under normal conditions but if I pump the brake pedal pressure builds on the pedal but I lose the brakes. Normal brake pressure returns a few moments after releasing the pedal. I seem to be losing vacuum pressure somewhere. Anyone know if this is a common problem?
 

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Not really a problem - It takes the vac pump about 30 secs to get back to full vacuum after you discharge it at idle - will be quicker at higher revs.
Under normal operating conditions this is quite acceptable as you would not normally pump the pedal repeatedly at idle.
 

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Discussion Starter #3
Thanks. Unfortunately it's doing this at higher revs as well. Can't find any obvious leaks on vacuum hoses etc.
 

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It is not that fast at higher engine speeds either - If you have a vacuum leak you will loose the servo effect soon after you stop the engine. To prove it -leave the vehicle overnight without touching the brake pedal after stopping the engine. Next morning apply steady pressure to the brake pedal and start the engine - you should feel no appreciable difference in the pedal if all is OK.
The 'standard' MOT check is to stop the engine, pump the brake pedal until it goes hard (!) - Start the engine whilst holding steady pressure on the brake pedal. If the vacuum pump is working the pedal should go down slightly within 30 secs.
 
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