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Old 07-26-2014, 12:44 AM
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Front disc lock up

I had power brakes added to my 34 Coupe disc front and drum rear new calipers pads bled master cyl and all 4- the problem is after a 2 mile drive the disc starts locking up. The calipers get very hot like 300 what can I do to get the pads to release after braking. After cooling down they will release HELP!!! THX Orange Tommy

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Old 07-26-2014, 05:43 AM
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Quote:
Originally Posted by Orange Tommy View Post
I had power brakes added to my 34 Coupe disc front and drum rear new calipers pads bled master cyl and all 4- the problem is after a 2 mile drive the disc starts locking up. The calipers get very hot like 300 what can I do to get the pads to release after braking. After cooling down they will release HELP!!! THX Orange Tommy
if you are still using the all drum master.. or system.. that's the problem..
not knowing what you have, there is a residual valve the holds about 15psi in the lines on drum brake set ups so the springs don't back off the shoes and cause you to have a very low pedal or your need to pump to get any pedal ..
some systems the valve is in the master outlet port.. others it's in the metering block or proportioning valve..

you need to remove the one (residual valve) from the front side of the system.. if master is under floor sometime you have to use a residual valve in the fronts but it's almost no pressure.. it just asks like a one way check valve so the fluid doesn't try to drain back into the master if lower than the wheels..

once you have that fixed. then you might need a proportioning valve to balance the front to rear brake bias..
but that residual valve in the front system set up for drums.. is why your disc are dragging and getting hot,, and if lucky you didn't warp the rotors..

you'll have to report back what you are using for master/metering block/prop valve(if any)..
and someone can tell you where the residual valve is that needs to be removed or moved.. you might be in for some pumbing..
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Old 07-26-2014, 06:18 AM
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Ran into a simular problem on a guys bucket. The master wasn't returning all the way at rest and caused the same problem.
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Old 07-26-2014, 08:29 PM
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. If your brake pads are too worn down and/or the rotors cut too thin and/or rotors rusted till they collapse, then the pistons can come out too far and get jammed cockeyed in the calipers and not go back in and hang up the brakes... rusted pistons also do same thing... I lube the pistons/bores with silicone grease which doesn't attack rubber seals... expensive in auto parts stores but cheap in plumbing dept. bought as plumber's grease... make sure pads not worn at an angle...
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Old 07-26-2014, 09:28 PM
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How old are the hose ??? If they are bad inside, It won't release the brakes..
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Old 07-27-2014, 06:16 AM
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Originally Posted by BOBCRMAN@aol.com View Post
Ran into a simular problem on a guys bucket. The master wasn't returning all the way at rest and caused the same problem.
This ^^^^^^^^^^^^^^^^^^^^^

The pushrod for the master needs adjusted. It is too long and holding the master cylinder piston down blocking the compensating port in the master.
When the fluid gets hot, it expands. When the fluid expands it applies the brakes as the compensating port is blocked it has no way to flow back into the master, so it pushes on the brake piston, applying the brake, making more heat,causing more expansion...compounding the problem.
Check the pedal travel to be sure the pushrod has a little free play ,if not make some.Then pull the master cylinder loose(don't remove).Pull it forward then gently try to push it back on the booster. see if it hits the pushrod before it flushes up to the booster, if so shorten the rod in the booster.Some are adjustable, some you gotta grind off a bit.

The compensating ports are the little holes inside the master cylinder where the fluid makes it into the bore then on to the lines . You can see them in the bottom of the reservoir. If the master cylinder piston is applied , enough to block these ports, the system is basically starting to apply the brakes and allows no way for fluid to escape due to thermal expansion of the fluid.
If your system has the wrong residual valves, say for instance 10lb valves in the front disc instead of 2 lb, it would cause a little extra drag on the pads, it would not lock the brakes as it is only designed to hold 10 lbs pressure, not full system pressure. This would however cause the pads to wear down quicker than normal , but would be noticed in the long term(months)
A hose that becomes blocked , can and will lock the brake on that side, and the same principle applies as the blocked port in the master, but will affect only the brake downstream on that hose, not both sides.
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Old 07-27-2014, 06:38 PM
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. If a C-clamp is gently applied to the caliper to push the piston back in, should be able to see a 'bump' in the top of the fluid level as fluid rapidly returns to the master cylinder... if pushrod is adjusted correctly... prolly need two people to do that...

. Next door neighbor had an old brake hose inside lining come loose and block fluid pressure return a couple weeks ago and jam the brake caliper locked... new one on me, hadn't seen that before... usually replace the hoses when showing cracks... last Friday had a brake hose on my truck pull out of the crimp, also a new one on me... I think the metal crimper was rusted enough to weaken it...
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Old 07-28-2014, 04:49 AM
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the O/p needs to comment if when he added those front disc brakes if and what else he changed.. unless I read it wrong..
he only changed the front drums to disc and then bled the brakes..




nevermind I did read it wrong

Last edited by gearheadslife; 07-28-2014 at 04:58 AM.
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Old 07-28-2014, 07:43 AM
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Quote:
Originally Posted by BuzzLOL View Post
. If a C-clamp is gently applied to the caliper to push the piston back in, should be able to see a 'bump' in the top of the fluid level as fluid rapidly returns to the master cylinder... if pushrod is adjusted correctly... prolly need two people to do that...

. Next door neighbor had an old brake hose inside lining come loose and block fluid pressure return a couple weeks ago and jam the brake caliper locked... new one on me, hadn't seen that before... usually replace the hoses when showing cracks... last Friday had a brake hose on my truck pull out of the crimp, also a new one on me... I think the metal crimper was rusted enough to weaken it...
Seen it happen a lot on the older cars and some new ones too..Usually by the time one does it,the other isn't far behind..
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