Front Brakes Staying Engaged

[82BlazerMan]

The front brakes are staying engaged for some reason and their hot to the touch after driving.  I suspected something was'nt right when I did the brake job and the wheels seemed to be hard to turn, obviosly thier engaged.  I checked the rears and their cool.   

I've replaced the following:

Master cylinder
rear shoes and drums
front rotors, pads, calipers and rubber lines.

Any help would be greatly appreciated since I've done all the work and now their worse than before.

82
Blazer
2WD
305ci
700r4...........

[jt1200r]

maybe the proportioning valve,how are the hard lines?

[82BlazerMan]

I'm not sure about the hard lines.  I did'nt figure they could really go bad except to crack and leak.  I did'nt do a flush either.

[bake74]

     Need to check the calipers and piston assy. For the front wheels, they may be stuck on.

[mehunter1]

Also check the metal connection on the rubber line that connects to the caliber.  Sometimes that metal piece squeezes down on that rubber line just enough that it won't allow any brake fluid to get in, will in turn keep the caliber from fully disengaging.

[82BlazerMan]

Holy Moly, it's all brand new.  I know I know, sometimes new parts are bad, but it just seems so unlikely.

I will do the checks and post back my findings.

Any tips for flushing the system?

[bd]

Did the calipers/pads slip onto the rotors easily and did the rotors spin easily before depressing the pedal the first time?  Did you thoroughly clean/burnish and lube the slides, pins & o-rings? 

Remember, brake calipers don't have return springs.  The pistons rely on the elasticity of the piston o-ring to retract.  So, typically there is some inherent drag associated with disc brakes.

Crack the bleeder screw to see if there's any residual pressure and whether the rotors spin more easily.

[82BlazerMan]

I'm not sure if the calipers/pads slipping on easily, a buddy of mine did all this for me, I'll have to get back on that one.  He's a little dumbfounded too.  But, they did spin freely before pressing the pedal.  Once we bled them, they were very hard to turn.  Not sure about the slides, pins & o-rings, my buddy did this so I'll have to get back on that one too.  I did crack the bleeder screw and it does relief the pressure.   Once I drive it again, it begins to stay engaged again.

[Tx_Phil]

NOTE..... I've never done brakes on a GM square body so this post might be useless. If nothing else maybe it will help you troubleshoot things.   

Are both sides hanging up basically the same or is it just one side?

I had an 84 Ford and they used Bakelite pistons. I had one warp right after changing the pads. Replaced the piston and all was well.

Several years later I did a brake job on the front of my 2001 Dodge. Had the rotors turned and put in all new parts. About 6 weeks later the front brakes were gone and it was metal on metal. It seems I got in a hurry and forgot to put that high temp grease on the slide part of the caliper and the brakes never disengaged.

[bd]

Crack the line connecting to the front brakes where it attaches to the master cylinder then recheck rotor spin.  If it frees up, the master cylinder isn't releasing pressure and may contain a residual check valve on that half that's designed to maintain ~7 PSI in the brake line. 

Residual check valves are used with drum brakes to help improve brake application.  Disc brakes don't use residual check valves, because there are no return springs or inherent gaps between the friction material and the rotors.  Using a residual check valve with disc brakes is akin to resting your foot on the brake while cruising.

Another possibility is that the M/C piston seal isn't completely uncovering the compensation port, so pressurized fluid is prevented from completely escaping the brake line back into the reservoir.

If cracking the line at the M/C doesn't relieve pressure, you should look for a restricted line between the M/C and combination valve, or at the combination valve itself.

[82BlazerMan]

Thanks guys, that's a lot of good advice, I will be checking on it this weekend and let you know my results.  Thanks again.

[Engineer]

bd is on the right track. If cracking the lines releases pressure you have a hydraulic problem, and not a mechanical problem.

Good luck.

[82BlazerMan]

Hey guys, just wanted to let you know, I bought the wrong master cylinder.  My mechanic said, the rod that goes into the piston was too long.  I really did'nt want to replacee the master cylinder, so he just ground off a little of the rod until it stopped holding on.  Hopefully, I'll never had to replace the master cylinder again and the next guy will have fun trying to figure out what idiot would do such a thing. 

[diphthong]

In over 25 years of fixing trucks and cars I've seen this problem (the master Incompatibility with the rod) two times.  And in two posts a few months apart on this forum this guy and the guy with RV have the same problem.

I'm not sure if that indicates it's big or small world.


I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)

[BADAZ chevy guy]

I saw a similar issue when working at a front end shop once. The guy had put headers on the truck and they were to close to the cross over tube on the front brakes. Heating the break fluid so it expanded, and closing the calipers down against the rotors. It took us 3 weeks to figure it out. lol