Air Sound When Pushing Brake Pedal

[Bangalorre]

So, my kids and I are about 4 weeks into restoring a 1990 325i. We started with brakes. Today we completed rebuilding all the calipers and attaching everything back on the car including new brake hoses.

When we started bleeding the brakes I heard air coming from the engine compartment when my son pressed the brake pedal. After bleeding the brakes they seemed to work fine. I took it on a 10 minute test ride and gave the brakes a good test. However, I don't know how "strong" the power assist is supposed to feel since I've never driven another e30. It certainly doesn't brake like my 2009 BMW.

So, my concern is that the vacuum booster could be toast. However, when I press and hold the pedal it seems to hold pressure although I must admit that I don't know exacting how much it would move over 15-20 seconds if it was leaking. So, my question is - anything else that would leak air around the master cylinder / vacuum booster that could be heard when pressing the brake pedal?

I haven't started testing check valves yet but wanted to post this question to see what sort of help I could get.

Thanks!

[turbo55]

The brake booster is a big diaphragm inside. A vacuum line is connected to one side of the diaphragm. When the engine is running, the pressure difference makes the diaphragm push on the brake master cylinder piston, helping you brake. I'm thinking when the car isn't running and you push the brake, you'd be pushing that diaphragm manually, causing air to be pushed into the vacuum line, so maybe that was the sound? Or maybe you have a leaky connection to the vacuum line, so the air would be pushing outside as well. If you have a vacuum leak there, that would result in weaker brakes as well.

[vpilarrt]

If the booster wasn't working at all you'd know it - brake pedal would be hard as hell to push. Once you've pushed the pedal to a certain position and hold it stationary the booster isn't really doing any more boosting. Sounds like your booster is OK. You could get a vacuum gauge and see if you're loosing vacuum while the engine is running to see if there's a small leak in the booster.