Brake booster check

Suspension related stuff goes in here.
micbrody
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Posts: 443
Joined: Tue Nov 04, 2014 4:50 pm
Your car is a: 1981 fiat 2000
Location: Munster, IN (Northwest Indiana near Chicago)

Brake booster check

Postby micbrody » Tue Sep 08, 2015 10:02 am

On my quest to improve starting and running of car, I went to test the vacuum seal of brake booster, since if there was a big leak, I would expect it to alter idle; maybe starting issues. I put mityvac on disconnected end (manifold side) of booster hose . I was first able to get a vacuum of 15-20, but then it went to zero. I tried again; but as pressure went to negative 5-10, it would suddenly release. I fully disconnected hose. It has no leaks. The check valve works. However, again, the booster seems to only hold a 5-10 vacuum. I was curious if booster was working at all. I drove it without it connected. very difficult to to brake. When reconnected, brakes work very well.
So my interpretation: I have small leak in brake booster diaphragm. Not enought (yet) to dramatically affect booster function; but enough where my idle slightly varies, probably every time the booster diaphragm's tiny leak looses vacuum. Am I correct?
Or is my mityvac brake booster vacuum test flawed, in that booster is suppose to lose vacuum???

DieselSpider
Posts: 2130
Joined: Wed Dec 24, 2014 10:21 pm
Your car is a: 1978 124 Spider with Isuzu Turbo Diesel

Re: Brake booster check

Postby DieselSpider » Tue Sep 08, 2015 12:37 pm

In general the booster should maintain vacuum to assist stopping the car after the engine has stalled. Most will maintain boost for a few applications of the brake pedal after the engine has been turned off even after 24 hours or so.

micbrody
Patron 2018
Patron 2018
Posts: 443
Joined: Tue Nov 04, 2014 4:50 pm
Your car is a: 1981 fiat 2000
Location: Munster, IN (Northwest Indiana near Chicago)

Re: Brake booster check

Postby micbrody » Tue Sep 08, 2015 1:08 pm

So does my test procedure with mityvac confirm a small, abnormal leak?

DieselSpider
Posts: 2130
Joined: Wed Dec 24, 2014 10:21 pm
Your car is a: 1978 124 Spider with Isuzu Turbo Diesel

Re: Brake booster check

Postby DieselSpider » Tue Sep 08, 2015 9:27 pm

micbrody wrote:So does my test procedure with mityvac confirm a small, abnormal leak?


It would appear too unless the MityVac itself has a leak. If you plug the line does it hold vacuum by itself. You have to test the tester and verify it holds before you can do a proper leak test.


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