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Evan_90SC
06-01-2015, 08:49 PM
Hey guys, haven't been around much lately as my SC doesn't get driven as much as it used to, but I ran into a problem the other day that I'm tired of trying to diagnose so I figured I'd consult the experts...

I had it up on jack stands for something unrelated, and happened to notice that my front brakes are locked up. About 4-5 years ago I did the dual piston caliper swap in the front. Drove it for a couple years with no problems, then over the last few it has been driven only a few times during the summers. Still started up and moved around frequently, just not driven a bunch.

Anyways, fronts are locked up. Pulled the calipers off and took them apart to inspect, everything is fine. Replaced the front rubber brake lines to the calipers, bled the system, fronts still locked up. ABS system seems to be functioning just fine. When I crack the bleeders it doesn't relieve any pressure on the calipers which I find kind of strange. It's definitely getting pressure to the calipers just fine, but won't release the pressure. What have you guys run into? Am I looking at a faulty valve in the master cylinder somewhere that isn't letting fluid return? What else is in the system that I'm not thinking of...

Word Man
06-01-2015, 09:49 PM
If opening/removing the bleeder doesn't relieve any pressure, the problem is mechanical and not hydraulic. Try loosening the caliper mounting bolts several turns and see if thw wheel frees up. If so, it sounds like the caliper isn't floating as it should.

Mercutio
06-01-2015, 10:36 PM
Pads rusted to the rotors?

Evan_90SC
06-01-2015, 11:16 PM
Nope. I've had it all apart, nothing is rusted, and the guide pins are lubed and slide just fine. Had the calipers all disassembled to check condition of the pistons and bores. The only way to release the pressure is to pry the calipers off and compress the pistons. Then reinstall, step on the pedal, and the process repeats, they seize up again.

I think the distribution block/pressure switch on the inner fenderwell is for the ride control as well as acts as a proportioning valve for the rears... I'm wondering if it could be internally compromised and acting as a one-way check valve for the fronts possibly.

Word Man
06-02-2015, 07:14 AM
I'm wondering if it could be internally compromised and acting as a one-way check valve for the fronts possibly.

If you are opening the caliper by opening the bleeder (assuming the bleeder isn't clogged), and the brake caliper does not release with the bleeder open, it cannot be a hydraulic problem.

Mike Puckett
06-02-2015, 08:45 AM
I had a similar problem a few years ago with my PBR calipers. I swapped them out with new calipers, rebuilts from Advance actually, and the problem went away.

S_Mazza
06-02-2015, 12:29 PM
Nope. I've had it all apart, nothing is rusted, and the guide pins are lubed and slide just fine. Had the calipers all disassembled to check condition of the pistons and bores. The only way to release the pressure is to pry the calipers off and compress the pistons. Then reinstall, step on the pedal, and the process repeats, they seize up again.

I think the distribution block/pressure switch on the inner fenderwell is for the ride control as well as acts as a proportioning valve for the rears... I'm wondering if it could be internally compromised and acting as a one-way check valve for the fronts possibly.

From what I read, the little square cut rubber seal between the caliper piston and the bore actually has an important function besides keeping the brake fluid in. It is supposed to flex when you apply the brake to allow the piston to slide outward a tiny amount and apply braking pressure. Then it is supposed to spring back and pull the caliper piston back a tiny amount. Ideally, the only reason the seal moves within the bore is because pad material gets worn away.

My point is that, if you have a piston that doesn't retract, I would check the rubber seal. Maybe it's swollen or lost its elasticity.

90tbird4.7l
06-03-2015, 03:45 PM
sounds like the rubber line is internally collapsed, blocking the fluid from returning (kinda like a one way valve). i have only seen this happen 2 times but it happens

Word Man
06-03-2015, 04:34 PM
sounds like the rubber line is internally collapsed, blocking the fluid from returning (kinda like a one way valve). i have only seen this happen 2 times but it happens

But that wouldn't keep the pistons from retracting when the bleeders are opened.

820
06-03-2015, 08:28 PM
I have a set of PBR twin piston calipers that I rebuilt and powder coated black. Just sayin if your interested pm me. I think that the S_Mazza has your answer.

Evan_90SC
06-04-2015, 03:54 AM
Well, you all had me convinced that I had overlooked something when I disassembled and inspected my calipers, so I went out today and dropped $100 on a new set. Got them installed and the system bled and what-do-ya know, still locked up...

I will say that the left front feels a tad better than the right front, but should still spin more freely than it does. Things were promising before I got the system fully bled, brakes were applying and releasing properly. But as soon as I got all the air out, same old problem.

Rubber lines to the calipers were the first thing I replaced. I'm past the comically frustrated stage and into the straight pissed frustrated stage. It doesn't make any sense to me. There's got to be a blockage somewhere else, or a failure in the master, I'm just surprised no one has really seen this before.

Mike Puckett
06-04-2015, 07:53 AM
Try pumping the brakes to get the fronts to lockup. Then open the bleeder on one to see if the pressure releases and the caliper loosens its grip. With the new calipers it should. If it doesn't I would say it isn't a hydraulic problem but maybe something mechanical at the wheel.

820
06-04-2015, 10:40 AM
What calipers do you have on the front? What rotors?

S_Mazza
06-04-2015, 06:51 PM
Well, you all had me convinced that I had overlooked something when I disassembled and inspected my calipers, so I went out today and dropped $100 on a new set. Got them installed and the system bled and what-do-ya know, still locked up...

I will say that the left front feels a tad better than the right front, but should still spin more freely than it does. Things were promising before I got the system fully bled, brakes were applying and releasing properly. But as soon as I got all the air out, same old problem.

Rubber lines to the calipers were the first thing I replaced. I'm past the comically frustrated stage and into the straight pissed frustrated stage. It doesn't make any sense to me. There's got to be a blockage somewhere else, or a failure in the master, I'm just surprised no one has really seen this before.

Have you driven the car? Does the wheel get hot?

What is the level of fluid in the reservoir like at this time? Does it look overfilled? If the accumulator has been emptied by pressing the pedal, the level in the reservoir will go up. I have seen it vent fluid at the cap if it gets full enough to build pressure inside the reservoir.

Evan_90SC
06-04-2015, 06:51 PM
What calipers do you have on the front? What rotors?

PBR calipers, no idea what brand rotors.


Try pumping the brakes to get the fronts to lockup. Then open the bleeder on one to see if the pressure releases and the caliper loosens its grip. With the new calipers it should. If it doesn't I would say it isn't a hydraulic problem but maybe something mechanical at the wheel.

Been there, done/checked all that.
____________________________________

Alright, well today I decided just to flush the system all out, so I did a gravity bleed for awhile before I just pumped a bunch of new fluid through it. Had the lines off the calipers, and with no fluid in them I could successfully actuate them with compressed air. They applied and retracted just fine, which makes sense why they functioned properly for me yesterday when the brakes weren't totally bled and there was still air in the system. So that meant I was back to the hydraulic side of things. Ended up forcing a bit of compressed air up the lines towards the master to maybe clear anything that was clogged in the lines. Did that, flushed a bunch of fluid, bled the system, and they feel better now. I still think there's more drag than there should be, but they don't completely hold anymore, so I threw the wheels on and went for a drive to get them hot. All seemed ok, came back and jacked it up, fronts still spin ok for now.

I think that just running air and a bunch of new fluid through the lines cleared something up somewhere, who knows if it'll last though. But for now it'll work. Still frustrates me thinking about it though that's for sure.