Dragging front brakes

[Stewart]

I'm dealing with a weird front brake issue. The front brakes will intermittently drag when cold you can feel the slight resistance when moving the car by hand. WHen they are warm they will drag enough to slowly bring the car to a stop and hold it on a mild slope. While driving the pads are being held enough against the rotor to hear them along with that lovely burning brake smell. Both front wheels feel to be at the same temp.

75 mgb with the brake booster

Heres what I've noticed

I can do a couple of hard stops and get the brakes hotter than the sun and they will still work perfectly with out dragging however if I get into city traffic a few stop signs even with cold brakes is enough to get them to start sticking. When the brakes start sticking the pedal goes rock hard. When they stop sticking the pedal returns to normal.

So far I've replaced the calipers, pads, front hoses and even the rotors. I'm I looking at a bad master or something else?

 

[Deleted member 8987]

Crack a line.
If you crack the line at the master, and it goes "poof!", and rolls freely, it's the master.
If it doesn't, it's in between.
Start cracking fittings until you find it.

 

[PAUL161]

Stewart, If the front flex lines are old, they can separate on the inside and create a valve effect which will cause a pull on one wheel or another. It's rare, but has happened. If that's not the problem, look for the piston in the MS not returning all the way back and letting the pressure bleed back to the reservoir. The hard pedal at times you indicate, makes me feel it's a Master Cylinder problem. JMHO. PJ

 

[bob67bgt]

Be sure the vent hole in the cap is clear. Bob

 

[Stewart]

Update

Changed out the master with a new replacement and checked the hard lines for kinks there were none.

With the booster connected felt great for a while then the brakes pumped up and the front started dragging again. Bad enough that you could not move the car using your foot to push with an open door. When the brakes are working normal no effort to do so.

Jacked the car up fronts locked up rear perfectly free.

Cracked the bleeder on the left front it spurted and the brakes released enough to move the car. Front brakes were HOT.

Started the car up and the over the space of 30 seconds the front brakes bound up. Shutting the car down and pumping the brakes to bleed off the vacuum released them.

Disconnected the vacuum from the booster.

Drove the car again and it felt fine for about a mile then the same old feeling of the system pumping up and the rock hard pedal and bound up front brakes returned.


I'm completely baffled.

 

[bob67bgt]

Any chance there is no free play between the master and the booster push rod? I know very little about late booster car brakes.
Good luck on the repair! Bob

 

[Deleted member 8987]

Back to what I said earlier.
First, don't just throw parts at it, figure out what is wrong FIRST.
When it locked on the old MC (and now new MC), did you crack the line at the master?
Did it go "poof!" and release?
If so, it's the master (or pushrod too long, or some such...identifiable by tighting line, applying brakes until locked, and unbolting MC to icrease free play and see if it rolls).
If that doesn't do it, crack at the MC end of the booster FIRST, if that doesn't do it, crack it at the wheel end of the booster.
Dave

 

[PAUL161]

<span style="font-size: 10pt">Check this also for proper operation and internal obstructions! They are reparable! PJ</span>