Wednesday, Oct 20, 2010 at 14:28
Michael
Pumping up hard when the engine is not running is normal. You should not get a hard pedal if you had left air in the system.
The pedal going down a little and feeling slightly softer when you start the engine is also normal. That is because the booster has now started working and is helping you push the pedal down. If it does not work the pedal will stay hard.
If it is now going down further than before then maybe the petrol engine is producing more vacuum than the diesel vacuum pump. I am not sure how much vacuum is produced by a diesel pump but it would not surprise me if the petrol engine is higher.
Another possibility is you have created a leaking master cylinder while bleeding the brakes. This is not uncommon if the cylinder has been there for a long time and the fluid has not been changed regularly according to the servicing schedule.
Dirt and corrosion builds up in front of the piston seals but the piston only travels over the same area while driving so it does not come into contact with it. When you bleed the brakes, it goes a lot further and slides over the damaged area. This can damage the seals instantly.
Try pumping the pedal without the engine going until it is as hard as possible. Keep your foot on it with very light pressure and wait. If you feel it going down ever so slowly then you either have a leak at the
wheels, which is easy to see, or a leaking master cylinder.
If it passes that test, increase your foot pressure and start the engine. The pedal will immediately sink down a little and feel slightly softer as the booster starts working. If you think it is going down too far then check with a brake specialists. They should be able to tell you if the engine is producing more vacuum than you had before.
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