Booster pushrod clearance
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
There should be no clearance between the booster pushrod and the piston in the master cyl. You can easily verify that you have the correct adjustment of the pushrod by removing the m/c reservoir cap and watching the surface of the fluid as you push on the brake pedal. As you begin to push on the pedal, you should see a disturbance on the surface of the fluid as a jet of fluid is forced out of the small port between the m/c bore and the reservoir. If your fluid is clean, you should be able to see the piston move by looking into this port in the bottom of the reservoir. Push gently, or you may see a geyser!
I can do this test on my car while standing in the open doorway while pushing on the brake pedal with my right foot.
If the pushrod is too long, this port won't be opened to relieve the pressure in the brake lines when your foot is off the brake pedal. This will result in dragging brakes as the fluid expands due to the rising temperature of your brakes.
I can do this test on my car while standing in the open doorway while pushing on the brake pedal with my right foot.
If the pushrod is too long, this port won't be opened to relieve the pressure in the brake lines when your foot is off the brake pedal. This will result in dragging brakes as the fluid expands due to the rising temperature of your brakes.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
You need some clearance for expansion from heat or the brakes might start dragging after things get hot especially in the summer. The master needs to retract all the way also for proper operation. I'm thinking at least 1/16 or a tad more but I don’t have an exact measurement and is difficult to do.
Thread Starter
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
It sticks in my mind that 0.020 to 0.030 is the number as the piston in the master cylinder is fully back if off the booster and the booster in it's full back position if no vacuum. The previously mentioned zero is a tough number to hit as there is no tolerance in zero. The stack up in manufacturing would have to be zero as well and rather certain they are not hand fit on each car even in '91. In my mind the problem with too much is the ratio of pedal movement to pushrod movement. This will mutipy the pedal movement to take up the slack.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
