brake master cylinder + booster

[newreplica Junior Member Find all posts View Profile Close newreplica]

Hi,

i have a fiero brake booster with wilwood aluminium tandem master cylinder.
but my brake pedals need a long way.

between the booster and the master cylinder is a bolt. i constructed a longer custom bolt.
now i press the pedals a little bit and the car stop (that's perfect). with this construction i can drive all the day.

problem:

next day i start the car, but i can't drive because the brake is pressed alone. first when i unsrew the master cylinder i can move the car.

What is the problem between the master cylinder and the custom bolt?

[msaby Active Users Find all posts View Profile Close msaby]

Re: brake master cylinder + booster

It sounds like you may need to bleed the brakes some more. Did you bench bleed the master cylinder before installing?

[txbuilder Senior Member Find all posts View Profile Close txbuilder]

Re: brake master cylinder + booster

Make sure that the pin between the master cylinder and the booster is not too long. The piston in the master cylinder has to completely return to the stop or it might not release the pressure on the brakes.

[newreplica Junior Member Find all posts View Profile Close newreplica]

Re: brake master cylinder + booster

i bench bleed the master cylinder and bleed the complete system.
when i make the pin 5 mm longer, i can brake perfect all day day. but next day i can't move the car.

[jdinner Senior Member Find all posts View Profile Close jdinner]

There should be an air gap between the pushrod and the master cylinder piston. To test to see if you have this air gap, remove the master cylinder reservoir cover so you can see the brake fluid. Now hit the pedal. You should see a shot of fluid go straight up out of the master cylinder. If you do not see the fluid shoot upward it is too tight.
The master cylinder piston must return to the top of its stroke every time the pedal is released or else the heat of the fluid at the calipers will start to apply the brakes slowly.

What you have done is cranked the pushrod to simulate pressing the pedal down so now you would only need to press it a short distance.
If your pedal stroke is still too long check for air in the system and sticking or misaligned brake calipers. It could be your Tilton pedals have the pivots in the wrong spot.

Did you setup your balance bar correctly between front and rear master cylinders?
Your center point should be much closer towards the front master and not in the middle.

[txbuilder Senior Member Find all posts View Profile Close txbuilder]

His post says he has a tandem master cylinder rather than dual master cylinders so the balance bar issue will not apply in this case. I still think, as you said, that he has the rod between the booster and the cylinder too long. Also check and see that there are no residual pressure valves for drum brakes in the system. Some of the Wilwood master cylinders come with them. If the brakes are locked up, jack up each end of the car and see if the front or rear is locked or both. That will help pinpoint the problem. It helps to have a return spring on the pedal itself.