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Front brakes sort of locking up?


Google

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Ok. Before I tell you the problem, let me preface this by telling you what has been replaced.

Calipers - Both sides
Rotors + Pads - Both sides
Wheel Bearings - Both sides
Rubber AND Metal lines - Both sides

When the rubber and metal lines were put on, the lines were obviously drained ( they were all brand new ), and brand new, clean brake fluid was used and they were THOROUGHLY bled to make sure that all new brake fluid was in the lines.

NOW, here's the problem.

When I start the truck and drive it, no problems at all. Drive it for 15-20 minutes, make 10, 15+ stops, no problem. I get on the highway.. After about 5 miles ( or sometimes less ), the front end starts shaking, and it's everything I got to get the truck to go 35... Brakes have somehow ( without me applying any pressure to the pedal ) decided to act like someone is standing on the pedal. THEN, if I get off of the highway, truck is driven slowly for 15 minutes or so, they start working again, then I have no issues, the rest of the day. When I go to drive it the next day, rinse and repeat.

There are NO issues with the rear brakes, what so ever. It should be noted though, that within the last 2 years, they have also been completely replaced ( lines, wheel cylinders, shoes, hardware kits, adjusters and drums ).

This truck is a 1992 standard cab with a 2.3. 5 speed manual transmission. No ABS, no power anything. It's probably about the most plain jane you could get for that model year.
 


RonD

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Welcome to the forum :)

So no power brakes?

Master does have two separate lines, one for front and one for rear brakes but can't see Master adding pressure on its own, unless its power brakes, and even that would be very very rare


Reads like you are getting excessive heat build up in the front rotors/calipers, fluid is expanding and adding pressure to the pads causing more heat and pads dragging even more, the higher the speed the hotter it gets
After it cools back down it works again

Did you tighten the new bearings up and then back off the nut a bit, so they rotated freely but didn't wobble?

If you jack up a front wheel can you spin the tire easily?
Pads will rub a bit but tire should spin.

Did the new pads and caliper go on to the rotors easily didn't touch at all and then caliper expanded when bleeding to push pads against rotor.
If you get the wrong pads or caliper or rotor then they can be hard to install very tight squeeze onto rotor and thats a warning sign of the wrong parts

You should be able to open bleeder and pull caliper towards you, pushing in its piston, this will show you the "sliders" are loose enough to not hold caliper and pads against rotor.

Picture of slide pin here: http://www.explorer4x4.com/bjpinin.jpg

And you can see piston is out a bit with new pads installed, which is correct
 
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Google

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Welcome to the forum
Thanks!


So no power brakes?
It has, like you said, a brake cylinder with 2 out ports. One to the front, one to the rear.. Both connected to the master cylinder.


Reads like you are getting excessive heat build up in the front rotors/calipers, fluid is expanding and adding pressure to the pads causing more heat and pads dragging even more, the higher the speed the hotter it gets
After it cools back down it works again
Yeah, this would seem correct.


Did you tighten the new bearings up and then back off the nut a bit, so they rotated freely but didn't wobble?
Yes.
The tire spins pretty freely. When they are working correctly, the truck will roll VERY easily. If it's on a flat surface, I can literally push it with one hand and it will roll.

If you jack up a front wheel can you spin the tire easily?
Also, yes.

Did the new pads and caliper go on to the rotors easily didn't touch at all and then caliper expanded when bleeding to push pads against rotor.
Yes. When I put everything together, it went together easily and I was able to spin the rotor with it all put together by hand, and it would still keep spinning.

You should be able to open bleeder and pull caliper towards you, pushing in its piston, this will show you the "sliders" are loose enough to not hold caliper and pads against rotor.
I will try this tomorrow when I pull it apart for a closer look.

I checked out the picture you linked, looks exactly right. The more I think about it, I am thinking it's the master cylinder. I have replaced everything except for that and the booster. It's just so strange that it will drive ok, heat up.. Then cool off, then I can drive it the entire rest of the day with no problems. It's gotten the rotors so hot now that they are warped and I am going to have to replace them.. But I need to figure out what is going on for sure before I go doing that.
 
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55trucker

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I have replaced everything except for that and the booster.
You do have a booster

Hmmmmm...what is the pedal travel under your foot cold vs hot........

does the pedal seems to firm up & there is less travel (as in the brakes are RIGHT there) when this situation occurs?

try removing the master & check the pushrod on the front end of the booster to see if it has clearance to the master piston. The pushrod is on a thread & is adjustable.
 

RonD

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Yes, if you have power brakes then booster is most likely the issue

Atmosphere valve on cab side could be leaking
 

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You do have a booster
Yes.

Hmmmmm...what is the pedal travel under your foot cold vs hot........

does the pedal seems to firm up & there is less travel (as in the brakes are RIGHT there) when this situation occurs?
I should have addressed this in the original post. When the brakes are working ( without the hanging up issue ), there is what I guess you would call " normal " amount of travel before they start to engage. Now, when they are hot.. The travel in the pedal is gone, and I mean gone. You touch the pedal, and it stops REALLY hard, really fast.

try removing the master & check the pushrod on the front end of the booster to see if it has clearance to the master piston. The pushrod is on a thread & is adjustable.
This is exactly what I am going to try. I didn't have a chance to tear the truck apart today, but over the next few days, I will do this.

I know the rear brakes are not nearly as powerful as the front, so for all I know the rear could be hanging up as well ( they just wouldn't get nearly as hot or wear as quickly as the front ). As you suggested that the pushrod on the front of the booster might be getting stuck.. I was wondering if it WERE getting stuck forward ( causing the locking issue ), would this affect the travel in the pedal at all? I guess what I am asking.. If the pushrod that goes into the master cylinder was getting hung up, would the pedal be further down? Because it has been all the way up. That's why I never considered the master cylinder or the booster.

I am not against replacing both, as I have replaced the rest of the brake system on the truck, and that truck is what puts food on the table. I will work on it, if not tomorrow ( Friday ), this weekend at my dads garage for sure.

Thanks for the input!
 

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Atmosphere valve on cab side could be leaking

I will check into this as well. Thanks!
 

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Thought I would let you know what happened!

I ended up replacing the booster and master cylinder ( they actually ended up being cheaper at my local Auto Zone than I could find anywhere online.. Not to mention, I had them, same day ). Anyhow. Total repair time, about 1.5 hours. That's from pulling the truck in the garage, to test driving it with new parts installed.

Cleared it right up! Now, I won't ever know if it was the booster, or the master cylinder. They were rusted together. I beat on the master cylinder with a small sledgehammer.. Nothing. It just bent the metal on the booster.

Amyhow, thanks for the suggestions and advice! It's driving great again :)
 

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