Testing Brake Booster
Thread Starter
Pro
Joined: Jul 2006
Posts: 505
Likes: 25
From: Buxton Maine
Testing Brake Booster
I'm hoping to find out how to test the power brake booster on my 69. The master cylinder isn't installed yet. The dash is not installed either. I thought now would be the time since it would be a lot easier to replace it while the dash is out and I have access.
Yesterday I hooked up an electric vacuum pump that pulls 25 inches and the booster is only holding 1 inch of vacuum. It must be no good? What do you think? Thanks for any advice, Rick
Yesterday I hooked up an electric vacuum pump that pulls 25 inches and the booster is only holding 1 inch of vacuum. It must be no good? What do you think? Thanks for any advice, Rick
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
It may be bad, but the master cylinder helps the front seal to seal better. I would try bolting a master cylinder up to it and try the vacuum test again. It will help push the front seal in place.
Last edited by '75; Dec 28, 2014 at 09:36 AM.
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
The way to test your booster. You have to have brake master cyl installed and brake system bled.
Now with a solid pedal. Hold brake pedal down, apply vacuum to booster via the vacuum check valve(usually this is done by starting the engine) your brake pedal should sink a inch or two and become firm. without bottoming out against firewall.
If pedal goes to the floor= brake system not properly bled.
If pedal doesn't move when vacuum applied = bad booster.
Now with a solid pedal. Hold brake pedal down, apply vacuum to booster via the vacuum check valve(usually this is done by starting the engine) your brake pedal should sink a inch or two and become firm. without bottoming out against firewall.
If pedal goes to the floor= brake system not properly bled.
If pedal doesn't move when vacuum applied = bad booster.
