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Old 01-02-2009, 02:20 AM
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Brake system

Have a 1986 Ford F150. Replaced m/c (new, not rebuilt), front and rear brakes, rebuilt wheel cylinders in rear, bench bled m/c, bled all four wheels, found no leaks anywhere. Am getting several inches of pedal travel before brakes are engaged. Disc brake calibers are sliding and engaging. Rear wheel adjusting screw has been adjusted. Brake pedal is firm before engine is started. Once engine starts brake pedal goes down several inches before brakes engage. What could be the problem? Brake booster?

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Old 01-02-2009, 07:01 AM
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Descibe how you adjusted rear brakes.

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Old 01-02-2009, 07:07 AM
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that is normal for the booster to do that, in fact it is one way of checking to see if it is working correctly.

Have you driven it , it is a little deceptive the way power brakes feel. When power is added you can not feel all that is going on because the assist is helping by applying the pressure for you ... So brake engagement will be happening/ slowing the car before you start to feel it in the peddle..

I would say this if you are getting a hard or firm peddle without power assist and it holds the peddle, meaning does not slowly drift to the floor you are good

Keep in mind that the brakes work exactly the same with or without the assist. I am saying that you either have a hard firm peddle or you don't.

I think you have a good set up working for you and you maybe just over analyzing what is going on.

Just a few things to ask yourself cause I can not tell from your post

Was this a disk/drum set up before ?

If not two items to verify, is there a proportional valve plumbed after the MC in the hardline before the wheel cylinders and calipers?

Also you mentioned a MC just replaced do you know what it came off of.

MCs have two variances
1. two different fluid containers , large and small volume , large side for disk and small side for the drums.
2. some have a 10 psi valve that keeps the rear shoes out close to the drums, and gives one more peddle, without knowing the part number it might be hard to determine this.

If it does not have this then no problem you can plumb one in the rear line too the rear brake system.

Not trying to throw to much at you but trying to see all sides. Just an example of what I ran into recently.

Put a new brake system together and had brakes firm but to low and too much peddle before brakes .... sound familiar here

Well I had all the right parts and all worked so so ok , but not good, the solution was to add the 10 psi to the rear brake system. You have two brake systems working front and rear totally separate, redundant brake system.

You see I am using a remote fill MC and it did not have the 10 psi residual built into the MC , It is a newer style and is for disk/disk ..
Mine are disk/drum ...

Hope I have given you some areas to check and you will be-able to solve your problem ..
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Old 01-02-2009, 09:47 AM
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Thanks for responding. MC was bought at local Auto Zone. Original setup is disc on front and drum in rear. Rear wheels adjusted manually (I spun each until there was minimal spin). Checked proportioning valve and it's fine. Vehicle doesn't slow down or stop until I apply brakes hard at near bottom. Pedal is not spongy and does not go down further after I stop, but there is a lot of pedal travel.
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Old 01-02-2009, 10:00 AM
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I would try bleeding the rear brakes again. It sounds like you may still have some air in the line. Bleeding the brakes can sometimes be difficult depending on the method of bleeding. I had the same problem and had to bleed my brakes several times before I finally got clear fluid coming out. Usually, not always, but if the lines are bled completely, the play in the pedal will go away. I'm running disc on the front and rear. The fronts are easy to bleed and it gives me a decent pedal. After the rear lines are bled properly, I get a solid pedal and can feel the difference. Hope this helps.
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Old 01-02-2009, 01:13 PM
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agreed, all the work done on the system all at once could require a bleeding or two., it is sounding like there is some still air. Sounds like the parts match ok.
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Old 01-02-2009, 02:06 PM
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Quote:
Originally Posted by 86Ford
Thanks for responding. MC was bought at local Auto Zone. Original setup is disc on front and drum in rear. Rear wheels adjusted manually (I spun each until there was minimal spin). Checked proportioning valve and it's fine. Vehicle doesn't slow down or stop until I apply brakes hard at near bottom. Pedal is not spongy and does not go down further after I stop, but there is a lot of pedal travel.
I would take a hard look at the master and make sure the flange and all mating surfaces look the same as the one you took off. There are some minor differences and if the flange is a little thicker or doesnt seat quite right it could have the same effect as if the pedal rod was to short. You may be able to adjust the pin from the booster to be a little longer to raise the pedal. be careful not to make it to long or after 3 or 4 stops your brakes wont release. There is a bleedback hole in the master that needs to be open.
Also to PROPERLY adjust drum brakes, you lock them up then back them off 7 clicks. This is sometime difficult and it is wise to make a tool first that will go through the adjuster hole and hold the self adjuster arm out of the way. I like to use a piece of coat hanger.

Most people dont take the time to do this, but it is the proper way.
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Old 01-02-2009, 04:11 PM
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Quote:
Originally Posted by 86Ford

Rear wheels adjusted manually (I spun each until there was minimal spin).
Quote:
Originally Posted by T-bucket23

Also to PROPERLY adjust drum brakes, you lock them up then back them off 7 clicks. This is sometime difficult and it is wise to make a tool first that will go through the adjuster hole and hold the self adjuster arm out of the way. I like to use a piece of coat hanger.

Most people dont take the time to do this, but it is the proper way.
There you go. Brake pedal height (considering correct pedal/linkage geometry) is dictated by rear brake adjustment.

The shoes have to be locked to center them on the backing plate to the drum. You then back-off and adjust to get desired drag, hit the brakes insuring centering and adjust from there. You will also have to wait until the shoes become seated, i.e. the shoe pad arc is concentric to the ID diameter of the brake drum. Unless one has an old arc-grinder, wear has to take place and then proper adjustment and peddle height can be achieved.

...whew...
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Old 01-02-2009, 07:55 PM
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I bled all four wheels until clear fluid was coming out of the plastic tubing I attached to each bleeder screw. Adjusted the drag on the rear wheels. I went ahead and replaced the power booster. None of this made any difference. Still alot of pedal travel. Wondering if the master cylinder pushrod from the power booster is too short and not engaging the master cylinder until the brake pedal is almost to the floor? Is this rod adjustable? How about if I used a spacer in the MC to shorten the pushrod travel distance?
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Old 01-03-2009, 01:52 AM
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Quote:
Originally Posted by 86Ford


I bled all four wheels until clear fluid was coming out of the plastic tubing I attached to each bleeder screw. Adjusted the drag on the rear wheels. I went ahead and replaced the power booster. None of this made any difference. Still alot of pedal travel.

Wondering if the master cylinder pushrod from the power booster is too short and not engaging the master cylinder until the brake pedal is almost to the floor? Is this rod adjustable? How about if I used a spacer in the MC to shorten the pushrod travel distance?
...whew...

If the MC travel was good before, just a new MC should not change that unless it is not an exact copy or defective. If when the pedal is low, you pump the pedal a few times, does the pedal gain any height? Does it retain that height with continuous application?

You also may have air in the calipers if the bleeding srews are not pointed directly up. Sometimes you have to loosen the caliper (depending on design) and rotate it (keep pads over rotor) and bleed.
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Old 01-03-2009, 09:26 AM
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The first MC was leaking and the pedal was spongy and not able to hold a firm pedal. With the new MC even when I pump it, the pedal does not gain height. It stays firm when it stops but that's almost down to the floor. I'm just about to give up and take it to a shop.
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Old 01-03-2009, 09:31 AM
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Are you sure you got the right MC? There are two types. One is manual and the other for power brakes. The piston on the end of the MC is different. The power MC has the dimple on the piston nearly at the end of the piston, whereby the manual is approximately 1/2" more inward. Check your old MC if you still have it and make sure the one you have is the same. Sometimes people don't check, especially auto zone employees. If you didn't mess with the rod adjustment that should be fine. You may just have a defective MC too. Just because it's not rebuilt, doesn't mean its good.
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Old 01-03-2009, 10:25 AM
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It didn't occur to me to check that. The MC that I bought (it's the second), does have the dimple about 1/2 to 1 inch deep inside. I didn't know that two different types were made. I'm going to go back and exchange it. That may just solve the problem. I'll let you know. Thanks!
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