Brake booster question / problem
Thread Starter
|
New User
Joined: Jan 2016
Posts: 14
Likes: 0
Brake booster question / problem
I recently did a disc conversion and put on a new master cylinder. After bleeding I have a firm brake pedal and all brakes engage, with the truck not running. When I start it up and the booster is on, the pedal goes almost to the floor before engaging the brakes. The difference where brake pedal stops between truck off and on is about 5 inches.
I realize the pedal should fall a bit when the booster comes on, but this seems like way to much.
Bad booster? Other thoughts?
Thanks,
Jason
I realize the pedal should fall a bit when the booster comes on, but this seems like way to much.
Bad booster? Other thoughts?
Thanks,
Jason
Fleet Mechanic
Joined: Sep 2003
Posts: 1,716
Likes: 15
Always a good idea to list what vehicle, year, etc. you are working on for others to try to help. Especially since you are doing a conversion!
The pedal should drop when starting the engine, as you noted (but not 5"!).
Another test for the booster is let engine run with foot off of brake, then shut engine off. Then press brake pedal firmly, let it up, press firmly again, repeat. A vacuum-assisted brake system usually has enough vacuum reserve in the booster assembly to allow 2 1/2 power-assisted brake applications. After that, the pedal gets hard as assist is gone.
If your booster passes the test above, I really doubt that you have a problem in the booster itself. The booster multiplies pedal force tremendously, so anything not quite right in the brake system itself will show up under high line pressure.
The pedal should drop when starting the engine, as you noted (but not 5"!).
Another test for the booster is let engine run with foot off of brake, then shut engine off. Then press brake pedal firmly, let it up, press firmly again, repeat. A vacuum-assisted brake system usually has enough vacuum reserve in the booster assembly to allow 2 1/2 power-assisted brake applications. After that, the pedal gets hard as assist is gone.
If your booster passes the test above, I really doubt that you have a problem in the booster itself. The booster multiplies pedal force tremendously, so anything not quite right in the brake system itself will show up under high line pressure.
Thread
Thread Starter
Forum
Replies
Last Post
F-250 WARHORSE
1973 - 1979 F-100 & Larger F-Series Trucks
15
Jan 21, 2017 01:33 PM
91dirtydiesel
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
56
Jan 23, 2010 06:02 PM
loudfords
Brakes, Steering, Suspension, Tires, & Wheels
5
Mar 3, 2005 03:34 PM
