Still sorting the freshly restored 65 f85 out.

I added a new disc brake conversion from inline tube during the resto. (These are manual disc)
I noticed that the brakes were dragging very badly when I went around the block.

Today I had some time to inspect.
-I checked the pressure differential and it is indeed centered in the prop valve(both manually and with a test light)
- checked the Clovis rod to make sure it’s not depressing the MC
-I removed the calipers and pushed the pistons in(they were out about 1/8” from caliper body
-lubricated the guide pins(again)
-cracked the lines at the calipers a bit to release any pressure

And everytime I step on the brakes the pistons return to a position that locks up the brakes.
Thoughts?

 

Peter, these calipers adjust for pad wear by purposely pushing the piston out to the point of pad contact and leaving it there. The seal is designed specifically designed to hold the piston out. This should provide a drag on the rotors with the pedal released, but it should not be locked up. If the calipers are, in fact, clamping too hard on the rotor with the pedal released, then the problem is almost certainly the fact that the piston in the M/C is not being allowed to move backward sufficiently to allow pressure in the line to release. The only way to prove this is to put a brake pressure gauge on the system and watch the pressure at the caliper from applied to released pedal. What M/C do you have? Are you sure it doesn't have a residual pressure valve in the outlet port to the front brakes? If not, then double check the pushrod adjustment. If the calipers are locked up, try backing off on that adjustment and see if the pressure relieves. If not, the aftermarket M/C might be machined incorrectly.

 

Thank you, Joe.
I’ve adjusted that rod multiple times trying to get as much slop in it as possible just to be sure.
the master cylinder was part of the in-line tube brake kit. I’ve used these kits before with good success.
but I don’t doubt for one second that I could have gotten a faulty one.

would it be a problem to re-bleed just the front Reservoir of the master cylinder (on the car) and bleed the front lines all over again?
The rears are fine.

 

You can bleed one end of a dual circuit system as much as you want. Excessive air won't cause this problem, as air is compressible and would relieve a lockup problem.

 

I was just thinking I should drain everything and start from scratch with the front.
It was a while from when I bench bled the MC to me actually hooking up the brakes...just wondered if that would help.

 

If you suspect air in the system go ahead and bleed it; but, as JoeP said it won't reduce a binding situation. If anything because it is compressible air might reduce binding but not through a good way.

Raise a front wheel to see with everything hooked up and bled, does the binding release if the master cylinder to the booster retaining bolts are loosened?

 

There is no booster Sugarbear

 

Raise a front wheel and loosen the firewall attachment a little to see if it releases a wheel.