92 Bonneville brakes

My Bonneville lost pressure in the brake pedal. The pads are good and it's leaking no fluid anywhere. What could cause pedal to be VERY soft?? Car still stops but pedal goes almost to floor.

Reply to
thinman
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Sounds like the master cylinder is shot.

Reply to
=?x-user-defined?Q?=AB?= Paul

Replaced master cylinder about 5 years ago. Wii do it again. What does the round booster on the driver's side firewall do if bad?? Hard to replace?

Reply to
thinman

If there are no external brake fluid leaks, then it's likely fluid is going around the plunger seals in the master cylinder. Inside the booster is a large diaphram. If brake fluid or water gets sucked into the VAC side of the booster it will rust out the vac side of the booster, or if the diaphram breaks, there will be an engine vac leak and no power brakes. If the ATMOSPHERIC side develops a leak or bad valve, touching the brakes tends to immediately apply full power assist. IMO, the booster is harder to replace than the MC. If you replace the MC, be sure to do a complete system flush. Otherwise, dirt from the lines will get sucked into the new MC and ruin it again.

Reply to
=?x-user-defined?Q?=AB?= Paul

Thats the power brake assist. If the pedal gets really hard and it takes a high amount of effort to stop the car then the booster is usually bad.

Reply to
Dennis Smith

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