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1980 F150 brake pedal not returning

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Old 11-18-2011, 07:36 PM
Alclem Alclem is offline
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1980 F150 brake pedal not returning

My question applies to an 1980 F150 with a power brake booster. I've just completed replacing the front calipers and emergency brake cables including bleeding everything. Brakes work fine but the pedal does not return (brakes stay applied) until I pull it up with my toe.

Is there a brake pedal return spring somewhere that could be bad? I've looked but can't see where any spring would connect and don't see a spring.

If there's no such thing, then I'm thinking I have either a master cylinder hang-up or a troubled brake booster. Is this right?

Thanks for any help you can provide.
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Old 11-18-2011, 07:43 PM
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No such spring, I would be looking at the master cylinder or booster.

Pump the pedal a few times without the engine running and see what happens; then, disconnect & plug the vacuum line to the booster, start it up and see how it reacts when you push the pedal.
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Old 11-18-2011, 08:16 PM
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My truck does this same thing. Do you hear any air when you apply the brakes?

On my truck, I'm pretty sure both the booster and the master cylinder are shot.
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Old 11-18-2011, 10:18 PM
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I've seen a bad o-ring in a brake caliper cause this, although that was on a motorcycle. However, the principle is the same.

The o-ring in the caliper is actually square, not round. (So, is it not an o-ring?) When you step on the pedal the pressure goes up and the piston moves out but, up to a point, the o-ring just rotates in its recess and doesn't slide on the piston. When you take your foot off the pedal the o-ring is supposed to rotate back and bring the piston back. That pushes fluid back into the master cylinder and brings the pedal back up.

Again, that was on a motorcycle with the result that the brake lever wasn't coming back out and the pads were dragging on the rotor. Replacing the o-ring fixed both problems. In this case maybe the o-rings in both calipers are old and have lost their "spring"?
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Old 11-19-2011, 08:46 AM
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Check the rod, and components, and brackets, between the pedal, and the booster, make sure something is not worn, and binding
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Old 11-20-2011, 06:16 PM
Alclem Alclem is offline
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More data about problem

I did a bunch of experiments with engine off, engine on, vacuum disconnected, car on level and on a slight hill down. Here is what I observed:
-when emergency brake on, pedal does not return
-on a hill slightly down, as soon as car begins to roll the pedal pops up
-on the level, pedal does not return and the brakes are partially on
-no difference in behavior when engine off or vacuum line removed

So, it appears that turning the (rear) wheels a bit causes the pedal to pop up. Maybe turning the rear wheels (remember, no pedal return when emergency is on) causes pistons to push in a bit and push up the pedal. I did replace the emergency brake cables and readjusted the shoes - could this be screwed up somehow??

When the engine is off, the behavior is very similar as noted above but the pedal requires quite a push to apply the brakes.

I tried to push on the pedal and than start the car. The pedal went down a bit after the car started. If I remember right, this is a positive test of the booster.

So guys, does the above suggest anything other than to spend money replacing the booster and master cylinder? Thanks a bunch.
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Old 11-20-2011, 06:22 PM
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And some more data

I hear a bit of noise (air) when I apply brakes. This seems to be normal from what I can tell.

I looked under the dash and watched the pedal push the rod into the booster. I don't see anyplace where it could be binding.

The rod pushes into the booster and appears to move a rubber piece (shaped like a donut) that is inside the booster body and around the rod. Is this supposed to be happening or could this be hanging up the rod? I could try to pull this out with needle nose pliers but maybe it has some function I don't understand.
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Old 11-20-2011, 09:27 PM
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Quote:
Originally Posted by Alclem View Post
I did a bunch of experiments with engine off, engine on, vacuum disconnected, car on level and on a slight hill down. Here is what I observed:
-when emergency brake on, pedal does not return
-on a hill slightly down, as soon as car begins to roll the pedal pops up
-on the level, pedal does not return and the brakes are partially on
-no difference in behavior when engine off or vacuum line removed

So, it appears that turning the (rear) wheels a bit causes the pedal to pop up. Maybe turning the rear wheels (remember, no pedal return when emergency is on) causes pistons to push in a bit and push up the pedal. I did replace the emergency brake cables and readjusted the shoes - could this be screwed up somehow??

When the engine is off, the behavior is very similar as noted above but the pedal requires quite a push to apply the brakes.

I tried to push on the pedal and than start the car. The pedal went down a bit after the car started. If I remember right, this is a positive test of the booster.

So guys, does the above suggest anything other than to spend money replacing the booster and master cylinder? Thanks a bunch.
Guess I'm a bit lost. If you are on a downhill the pedal pops up as soon as you start rolling, but not if you are starting on the level. But then you say that "turning the (rear) wheels a bit causes the pedal to pop up". Those statements seem to be at odds with each other - yes?

As for the e-brake, if it isn't installed correctly I would think you may have the shoes bound up such that the springs aren't pulling them back in. And, if they don't retract the wheel cylinder pistons don't push fluid back into the system and the pedal won't come up. Also, the brakes drag. So, I'd check the e-brake setup before doing anything with the booster or master cylinder.
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Old 11-27-2011, 06:56 PM
Alclem Alclem is offline
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Problem Solved

The problem was a sticking master cylinder. Thanks everyone for their comments.
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