Front Brakes Binding

[richinwaco]

I've been fighting with brakes on my Chally for over a year now.  Got the 4 wheel disc kit from Dr Diff with 15/16 bore manual master cylinder and stock front calipers.  It included distribution block.  Never could get any pressure after changing master cylinder and front calipers more than once.  Put pressure valves on the rear lines, still couldn't get good pressure.  Put a 1 1/8 bore master cylinder on, brakes were binding badly so took pressure vales off.  Now I get good pressure with good pedal travel when cold but the front brakes bind when they get warm and the pedal barely moves when braking.  Then they turn loose after driving on the highway awhile.  I'm guessing they're getting so hot they're letting go.  Front pads are semi metallic.
Is the bore too big on the master cylinder?  Or is it something else?  I don't think it's the calipers because the car doesn't pull to one side or the other when brakes are binding, or when stopping.  Any suggestions are appreciated!

[Skunkworks Challenger]

I don't know anything about this particular brake system but in general binding is caused by shoes or pads not retracting after application or there is not enough free pedal before application begins.  I would adjust pedal push rod so the pedal has free travel of 1 to 2" before brakes apply. 
The size of the master cylinder bore should not affect this problem and only controls how much pedal pressure is required to stop the car.  A larger master cylinder bore requires more foot pressure but less movement while a smaller bore works the opposite.

[richinwaco]

That's the strange thing about this, the pedal travels 2 inches when the brakes are cold.  After they get warm, no pedal travel and front brakes bind.  And after they get really hot, pedal travel is back to 1-2 inches and no binding. 

[farmboy70]

A couple things to look at would be is there any kinks in the hoses.
Also and it is possible, are all the bleeder fittings pointed up.
If the calipers are mounted with bleeders down you'll never get all the air out.
Dave

[burdar]

What year Challenger?  Are you using the factory prop valve or just the supplied distribution block.  The larger bore master can cause a hard pedal.  The 15/16 is recommended for less pedal effort on manual brake setups.  Is this a power or manual setup?

Stay close to home while you test.  When the brakes are acting up, jack the front wheels off the ground and see if they turn freely.  If the wheels are locked up, loosen the master from the booster/firewall and see if the wheels turn freely then.  Do you have the pushrod adjusted correctly?  It could be adjusted too far out causing the brakes to stay slightly engaged.  Brake hoses can go bad from the inside out.  They could look fine from the outside but be collapsed internally.  Also check to make sure the piston in the caliper moved back into its bore freely without a lot of effort. 

[HP_Cuda]

Call Cass at Dr Diff he will help you pinpoint the problem.

Heating up the brake fluid makes me wonder if you are near a heat source or you are massively using the brakes?

[richinwaco]

I spoke to Cass when I couldn't get pedal pressure with 15/16 bore and he sent me another m/c with 15/16 bore.  It didn't work either, so I took the car to a professional garage who put the 1 1/8 bore m/c in it.  They obviously didn't test it well since it went from no pedal when I took it to them to binding when I got it back.
I will drive it and disconnect m/c from firewall when front wheels are locked and see what happens.   

[richinwaco]

Turns out the pushrod was causing the brake binding.  Adjusted it backward then had weak brakes.  Obviously there's a happy medium, and I probably need to put the 15/16 master cylinder back on and adjust the pushrod properly for best results.  Thanks guys!