Brake pedal, Master cylinder

WEJONES

MEMBER
FORD F-150

1994 F150, 4.9L, 2 wheel drive, rear abs, 214K miles

I just had to change my left front shock tower and as a result all of the front brake lines, left caliper hose and while I was at it the pads. I bled all of the lines and flushed all new brake fluid through the lines, including the back brakes. The brake pedal is solid with no indication of air in the lines when the engine is off. When the engine is running the brake pedal goes down about 3/4" and does not always return all of the way causing brake drag. I thought there might be some air in the lines, so I bled the lines with a vacuum bleeder. Pedal still drops when the engine is running. There is plenty of pedal when stopping. Any ideas?

5 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Sir

Did you bleed the master cylinder before you bleed all the wheels. Good brake job includes inspecting for wear and tear and adjusting the rear brakes before bleeding.

When air is trapped inside the hydraulic system, it usually migrates to the highest point. This may be the master cylinder, but it can also be trapped behind the caliper or wheel cylinder pistons, or inside an ABS unit.

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Saturday, August 18th, 2007 AT 1:22 AM

WEJONES

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6 POSTS

Yes, I did bleed the master cylinder with a loop to the reservoir.

I repeated bleeding today, including the master cylinder and still have the same problem. The brakes grab when the engine is running. The pedal does not return all the way. If you pull back on the pedal, it releases the front brakes.

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Saturday, August 18th, 2007 AT 4:59 PM

RASMATAZ

MECHANIC
75,992 POSTS

Try adjusting the pushrod on the back of the brake booster. When this is done and it continues-its probably the M/C it not return the fluid back to the resevoir and applying the brakes or a brake hose acting like a one way check valve.

Did you push the caliper piston all the way in?

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Saturday, August 18th, 2007 AT 7:58 PM

WEJONES

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6 POSTS

Seems the problem was with air in the rear wheel cylinders. Replaced the shoes which pushed the pistons back together and forced the air into the path from the brake line to the bleeder screw. Even thought the shoes were still good and properly adjusted, the pistons were out far enough that the the air was not getting drawn out during bleeding, even a hard bleeding.

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Thursday, August 23rd, 2007 AT 7:39 AM

RASMATAZ