I have a 1998 Hyundai Elantra. The front calipers are locked up pretty tight. I can’t turn them by hand. I’ve been hearing the passenger side rear grinding too. I checked all the lines and there’s no damaged/collapsed line anywhere that I can find. I lossened the bleeder at the master cylinder and forced the caliper pistons back in a little way (it was hard even with the bleeder open) and then closed the bleeder. Started the car and pumped the brakes a couple times. The calipers are tight again. The pedal has been getting harder and higher over the last couple weeks and now has no freeplay at the top and is hard as a rock. Is this likely the master cylinder gone bad and not releasing or what? Any ideas?
Your symptoms are consistent with a bad master cylinder, but I can’t say for sure that is the only possibility. I once had that happen to the front brake on a motorcycle causing the brake to lock when it got hot, that was “interesting.”
Okay. So I pulled the master cylinder off and the seals and springs and everything look okay. The bore isn’t pitted or scarred up. The fluid was pretty gnarly looking though. Complete flush of the system is the next logical step, no? Is there an easy or, more importantly, effective way to determine if the caliper pistons are moving acceptably freely?
If you are that far into the brake system, why not take the brake calipers off, take out the piston, examine the bore, wipe it down, put a new seal on the piston, put the caliper back on, put in fresh brake fluid, and try it out?
Please make sure you have some free play at the master cylinder to brake pedal pushrod. Without perceptible clearance, an internal ‘relief’ passageway may be blocked, causing exactly what you describe, locked brakes. Check the servicing manual for proper clearances and methods of adjustment. Opening a bleeder on the system will not always relieve this pressure due to redundancy plumbing of modern systems. When pushing caliper pistons, they can be difficult, particularly when cocked to one side and binding occurs. This binding can happen very easily and can cause internal damage. So be gentle and enjoy.
You need new brake calipers. If it’s still hard to force the pistons back in even with the bleeder open, and the brake fluid looks that bad, that’s the only thing it can be.
Is rebuilding the calipers as the last poster suggested a good option?
check around for rebuilts. they should cost around 50 bucks after the core charge.