brake problems
Thread Starter
|
New User
Joined: Nov 2003
Posts: 1
Likes: 0
brake problems
I have 91 Aerostar with RABS. The antilock light, and the brake light stay on. I have replaced the calipers, and bled the brakes to no avail. The brake pedal will build up when the engine is not running but as soon as the engine is started it goes straight to the floor. Any suggestions would be greatly appreciated.
Elder User
Joined: Dec 2002
Posts: 624
Likes: 0
From: Georgia
Postmaster
Joined: Apr 2001
Posts: 3,818
Likes: 3
This happens frequently after brake work. The '91 uses a different master cylinder than other years and the internal floating piston is easily upset by bleeding. If you allowed the fluid level in the MC to run low you may have air trapped in either the master cylinder or the RABS valve unit. When bleeding, DO NOT push the brake pedal more than half way down - this overextends the piston in the master cylinder past the differential pressure valve switch. Since you state the pedal goes all the way to the floor, you may have inadvertently done this already.
Disconnect the electrical connection on the driver's side of the MC. Jumper across the connector, start engine and see if the lights go out. If so, the switch is grounded because the piston is off center.
To fix this, locate the small bleeder on the front of the MC. Use a small length of tubing to run from the bleeder into the MC fluid. Clip the tubing to the MC to keep the end of the tubing in the fluid and so as not to interfere with the float. Unsrew the bleeder several turns and pump the brake pedal halfway down four or five time. Close bleeder and check brake pedal for firmness.
If you are confident you did not allow the MC to run low during bleeding, then the soggy pedal sounds like the dump valve on the RABS unit is stuck open. Sometimes tapping the valve LIGHTLY will close it. The following link will walk you through how to test for a stuck dump valve. It also sheds lots of light on this RABS oddity.
http://www.babcox.com/editorial/bf/bf69936.htm
Disconnect the electrical connection on the driver's side of the MC. Jumper across the connector, start engine and see if the lights go out. If so, the switch is grounded because the piston is off center.
To fix this, locate the small bleeder on the front of the MC. Use a small length of tubing to run from the bleeder into the MC fluid. Clip the tubing to the MC to keep the end of the tubing in the fluid and so as not to interfere with the float. Unsrew the bleeder several turns and pump the brake pedal halfway down four or five time. Close bleeder and check brake pedal for firmness.
If you are confident you did not allow the MC to run low during bleeding, then the soggy pedal sounds like the dump valve on the RABS unit is stuck open. Sometimes tapping the valve LIGHTLY will close it. The following link will walk you through how to test for a stuck dump valve. It also sheds lots of light on this RABS oddity.
http://www.babcox.com/editorial/bf/bf69936.htm
