99+ GT PBR calipers sticking

[paul351w]

I put some 99+ GT calipers and rotors on my car a few years ago, and the last few years I've been doing a few open track events with the car. It doesn't get driven much so I still have the original pads that came with it, but I noticed that after the last event, the front brakes are dragging.

I compressed the calipers back with a C clamp, and the wheel will spin freely, but if I press the brakes hard and try to spin the wheel then, it drags pretty bad. My slide pins are free moving, so I think the caliper is sticking.

I haven't taken them apart yet, but I'm worried they might be junk, anyone have any experience?

[Mars_302]

remans shouldnt be much from a parts store. Hell Cobra calipers last I checked were $50 a piece plus core. Try a fluid flush first

[paul351w]

The calipers only have maybe 1500 miles on them total, so I hope they're not junk already. If they turn out to be, I might have to upgrade to Cobra pieces.

I changed the front brake lines last winter, so it has fairly fresh fluid in it. I'll just have to see what I can find. Hopefully I didn't cook something.

[Mars_302]

Well if they are only a few years old and have a only 1500 miles I would say chances are they probably seized up a little.

[huesmann]

If they haven't been operated a lot, corrosion could be a factor.

[Han Solo]

If they aren't leaking you should be able to take them apart and clean them out. Then you can look at the pistons and see if they are pittd or anything. Lines can also clog up and cause sticking brakes. I know you said you replaced them but if the calipers look okay make sure the lines are open, hard and flex.

[ESPSteeda]

Originally Posted by Han Solo

If they aren't leaking you should be able to take them apart and clean them out. Then you can look at the pistons and see if they are pittd or anything. Lines can also clog up and cause sticking brakes. I know you said you replaced them but if the calipers look okay make sure the lines are open, hard and flex.

Are you using the rubber brake lines to the caliper? I ask because i have seen several times on cars and trucks where the inside of the rubber brake line deteriorates and collapses causing it to be almost a like a check valve. It seems to be caused by corrosion or excessive heat. May be something to look into.

[MFE]

Especially when the calipers are allowed to hang unsupported from the rubber lines during work, or they're clamped too tight with square-edged pliers.

[paul351w]

I put stainless steel lines on them last year, and made sure to always hang them by a heavy wire if I took them off.

I took the driver's side caliper apart last night, and the first thing I noticed was a metallic gray color to the brake fluid coming out of the caliper... Got the pistons out and both have scoring in the same spot orientation wise. Not sure if it was corrosion or something in the caliper, but they both were dragging on the bore on the back 1/4 of the piston. I can't even get them back in by hand.

I might just have to upgrade to the 13" Cobra brakes I've been thinking about for a while...

[MFE]

Did you mess with the MC for any reason?

[paul351w]

The MC is a 94/95 unit that I installed with matching booster back when I put these brakes on. They've worked fine until now, I noticed I was using up some pads at the track, which I usually am pretty easy on, and when I got home I found the front brakes were dragging.

I do have a Wilwood adjustable prop valve, could that have any affect on what the front calipers do? And as an aside, do you know how they work? If they're cranked down to keep the rear brakes from doing much will it make the rears release slower?

[MFE]

Originally Posted by paul351w

The MC is a 94/95 unit that I installed with matching booster back when I put these brakes on. They've worked fine until now, I noticed I was using up some pads at the track, which I usually am pretty easy on, and when I got home I found the front brakes were dragging.

I do have a Wilwood adjustable prop valve, could that have any affect on what the front calipers do? And as an aside, do you know how they work? If they're cranked down to keep the rear brakes from doing much will it make the rears release slower?

The prop valve does two things: 1) It starts reducing line pressure to the back brakes relative to that of the front, and in a linear fashion, after a certain threshold is reached (think a graph like a hockey stick where the slope goes up then tapers off, in straight lines), and 2) Adjusts the pressure at which that breakpoint or "knee point" starts. So even when you have the back fully "closed off", it's not closed off, it just starts getting reduced pressure at the earliest point possible, and when fully "open", it still gets reduced pressure, but at the latest point possible.

And with that said, it's not your proportioning valve. I think it's the booster rod behind the MC, and I think it needs to be adusted just a hair shorter because I think it's preloading the brakes ever so much and making them drag.

[huesmann]

Did the dragging start to happen as soon as you put the new MC on, or were they fine for a while after that?

[paul351w]

I didn't notice any dragging until after the last track event this summer. Brakes have been on the car for several years. I noticed it was creating more dust than normal, and just thought I was using the brakes harder. When I went to check things out in the shop, the wheels were harder to turn than normal. I compressed the caliper, and it spun fine until I pushed on the brakes again, then it would drag.

[huesmann]

MFE, do you think the booster rod would spontaneously extend that way? I suppose anything is possible.

[paul351w]

I'm more curious what could've gotten in the piston bores that caused the pistons to scuff the bores so badly. It almost looked like water or something settled in the bore and the aluminum just corroded, but I don't really know.

I'm thinking about Cobra style 13" brakes, would those be sufficient for open track weekends, or should I drop some coin and get some Wilwoods or something of the kind?

[huesmann]

If they sat for a long time...you know brake fluid is hygroscopic?

[By-Tor]

What kind of brake fluid are/were you using? If it happens to be silicone based it can create steam in the lines when used in a open track/roadrace situation.

[paul351w]

The longest its sat in the last few years is over the winter(s).

I had some valvoline synthetic (tan and blue bottle) DOT 3/4 brake fluid that I used when I changed the front lines last winter. I hadn't been flushing the brake system every year, but it had gotten dissassembled partially enough times that I didn't think I needed to.

About the steam idea, the problem areas in the piston bore were on the bottom inside of the caliper, like something separated out of the brake fluid, could've been water?

[Mars_302]

as mentioned above brake fluid absorbs moisture from the air. The calipers are only $44 a piece from advance

http://www.partsamerica.com/ProductD...e=5003&PTSet=A, you can go that way, and they have a lifetime warranty and all that jazz