vacuum leak/brake booster problem

[rattfink81]

Hi i have 1988 528e. problem is i have a vacuum leak causing a horrbile idle problem. I sprayed carb cleaner and seemed to pinpoint the brake booster right around the seam. makes sense but when i removed the vacuum line from the intake to the booster it still held a vacuum as it made a "wosh" sound. So how can the booster have a vacuum leak yet hold pressure/vacuum? i just dont want to go through the work of throw a good used one i have from a e30 parts car i had if im just crazy.

[a]

If you pulled the hose off the manifold , then a check valve would keep the vacuum in the booster.

[rattfink81]

i pulled the hose from the check valve and the booster. my question is if the booster is the soucre of my vacuum leak how can it still hold a vacuum?

[tschultz]

I have an early e12 based e24 with vacuum brakes. I confirmed a suspected vacuum leak through the booster. If I suck on the hose, it never holds a vacuum, always keeps leaking air through, although I can't tell exactly where. Maybe some 528e owners have had this problem before.

Can i repair it somehow? Do I just need to replace the booster? Brakes work fine otherwise...

I know it's an old thread... but I am just wondering how they usually leak from the inside via vacuum if no brake fluid leaks?