front brake locks up

Growler

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199
My brakes lock up and I don't know why. I recently was out for a short drive and felt like the brakes were dragging. I stopped and they seemed to free up. when I got back to the garage (a mile or two away) they were locked up again (I could drive - creating heat and smell, but could not push the car). I jacked the car up and found that I could turn the rears, but that both fronts were unable to turn by hand. Lightly pressed the brake pedal and it immediately freed up to the point I could rotate the wheels while up and it rolled it easily. I have a recently rebuilt master (original single circuit) and servo. What else could it be? Any help would be appreciated. Thanks, Josh
 

Forrest39

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406
sounds like a sticky booster, but very odd that the rear brakes aren't stickling too. Perhaps try bypassing the booster to see if the problems persists?
Cheers, -Kevin
 

Growler

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199
Sticky boister

We just rebuilt the boister... It seems to slide fine but does it take time to work properly like a break in period? How would 1 bypass ? Just disconnect vacuum hose?
 

michael-king

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4,132
I'll go with perished front brake hose, they will look fine on the outside but internally are deteriorated. They will work OK initially then you push the pedal and they collapse inside and don't let fluid return keeping the brake on... They will then sometimes release giving inconsistent lockup, the brake calliper stays clamped
 

Forrest39

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406
I'll go with perished front brake hose, they will look fine on the outside but internally are deteriorated. They will work OK initially then you push the pedal and they collapse inside and don't let fluid return keeping the brake on... They will then sometimes release giving inconsistent lockup, the brake calliper stays clamped

I've seen this before as well. I had TR4 clutch that would stick and slowly release. Fixed the problem by simply replacing the hose. How old are the brake hoses?
I got a new booster from Randy last year. worked perfectly right out of the box.

To bypass it, you need the bypass hose available from the CAT store or just make your own.

Other possibilities are stuck caliper pistons - SS has replacement seals and pistons.

Cheers - Kevin
 

Growler

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199
Brake hoses are only a few years old (3?) and I had purchased and installed good quality HEL steel braided hoses ... also, I cant imagine both locking up at the same time. Very confusing because I rebuilt the booster very carfully with good quality parts from SS and made sure that the large piston was centered, lubed and moved freely. I would typically suspect the calipers but again can not imagine that they both lock up at the same time.
 

Growler

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199
This whole thing started because the booster was sucking up all my fluid, so all seals were changed. As long as I had the system apart, I rebuilt the master as it hadn't been done since I owned the car.
 

Warren

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3,872
Plus 1

on blockage and or collapse of the squishy internal line inside the steel braid. Bleed and test on stand with any luck it is the line and not the caliper. I don't have much faith in the steel braided lines though
 

0neoffive

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Test This

Test the booster: Jack up the car's nose, start the car and bury the brake pedal. Keep the motor running. If the callipers are locked up , crack the "out" brake line on the booster and see if they free up. If they are now free, turn off the car; it's the booster.
Otherwise, take a hard look at those braided lines again. General manufacturing costs force the competition to wrap fancy braid around a crap piece of rubber . . . . . .
 

Bryan

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418
booster

also testing booster is to pull the filter housing off the manifold run engine then turn off-step on brake pedal listen for a release of air thru filter hole- booster diaphragm should hold for a couple of brake applications with engine off.
 

Growler

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199
Bryan, are you talking about the small air filter on the booster? Curious you mention that because when rebuilding the booster, I had a metal washer just a bit smaller than the small rubber diaphram in the air filter but when I saw the parts pic in the SS cat., there was no washer, so I left it out (it didn't look original either) .... Anybody else have a metal washer under the small air filter or just the cork and rubber ... Could it be that simple?
 

Forrest39

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CAT Member
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406
Bryan, are you talking about the small air filter on the booster? Curious you mention that because when rebuilding the booster, I had a metal washer just a bit smaller than the small rubber diaphram in the air filter but when I saw the parts pic in the SS cat., there was no washer, so I left it out (it didn't look original either) .... Anybody else have a metal washer under the small air filter or just the cork and rubber ... Could it be that simple?

I just pulled mine to look. No washer - just cork and rubber. Mine came freshly rebuilt from Randy last year and works perfectly.

-Kevin
 

Bryan

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418
yes-inside is a filter element- with a rubber gasket- with 2 small holes which should be clear-not cover up- I don't know what this cork thing is?
 

Growler

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Messages
199
Update

Booster seems to be holding air. As suggested tested via air filter. Then jacked the front end up, started the car and stepped on the brake hard...no lock up. Did that several times and couldn't get it to lock. It happened twice yesturday wich was the 1st time driving since booster rebuild....hopefully the leather seal just had some working out to do. Ill drive it a bit (short trips) and see if it happens again.

In the meantime, when I had the car up, I found this (wet spot is directly under the drip line on the backing plate)... wheel bearing (wheel sounded fine) or ???

 

Growler

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Messages
199
Fluid is black and thick (doesn't appear to be brake fluid) and the brake system seems to be holding pressure and maintaining fluid level....
 
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