Thread: 2001 Volvo v70 brake booster problems

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A friend of the family owns a 2001 volvo v70 they took it in to have brake work done and replace the brake booster. The booster and vacuum check valve has been replaced five times from supposedly 3 different suppliers because of booster defects and they still have problems. Each time they hear a hissing sound from the booster when it goes out.
Anyone have any idea how/what may be making this happen...TIA joe

The booster is just a big canister that captures a diaphragm between the two halves, with valving that puts vacuum on both sides at rest, and then when the pedal is pressed allows atmospheric pressure to press on the area of the diaphragm to assist pedal pressure. What this simplified diagram leaves out is that the "piston" against the diaphragm allows vacuum to pass by at rest, and seals when the pedal is depressed, trapping the vacuum downstream.
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brake-booster-1.jpg
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Sounds to me like the diaphragm is failing for some reason.

Originally Posted by rspears

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Sounds to me like the diaphragm is failing for some reason.

Yes I know what a brake booster is and how it works but 5 diaphragm failures from different sources??...joe

Originally Posted by TooMany2count

Yes I know what a brake booster is and how it works but 5 diaphragm failures from different sources??...joe

Joe, I'd look at the adjustment of the actuating rod from the pedal to the booster and be sure there's some freeplay there, not adjusted too tight. They may not be failing, but just being pushed off of their rest position with no pedal action. Just a thought.