Brake engagement point rises, brakes drag

[tastyratz]

This has been an ongoing issue with my car I have been struggling with but is now seemingly worse. Over the course of a drive my brake engagement point will get higher and higher until brakes are stuck partially engaged and dragging.

If I park the car and drive it the next day, 0 issues when I first start driving it. car rolls 0 resistance in neutral on a flat surface. It does not have to be from the car driving spiritedly, this can even get worse when idling. I do not have any single locked calipers, and all brakes are dragging not just some. If I crack the bleeder screw on the bmc itself, fluid spurts out under pressure. When I close it again I can drive the car normally no problem for a period of time till it comes back.


I have:

replaced my bmc
my fluid was freshly flushed with dot 4 valvoline synthetic 100% when I changed the bmc
adjusted the pedal adding lots of slop to the top
replaced the check valve and my booster is sealed well, vac after 24 hours exists (if I pull the pushrod it gets sucked right back in)
I even adjusted the 7mm lock nut in the booster where it is retracted MORE than stock fsm spec.

I left work early today and decided to say screw it -changed my booster - NO CHANGE!
The bmc came out of another known car with 0 braking issues therefore working + aadjusted within factory spec.

I pulled the car in the garage just now, in neutral, ebrake off. Jacked the front and tried turning either front wheel by hand, neither moved and both equally stiff.

grabbed the bmc bare handed and it was warm to the touch, but not too hot to stay held onto for however long I wanted, so it is not turbo mani heat soak.

removed vac line from booster, big whoosh so it was sealed.

Removed the bmc from the booster completely so no pushrod was in it, 0 change.

Bmc rod seat fully retracted & fine as normal.
Attempted to push in with a screwdriver and it was stiff (obviously with brakes locked) but the small amount I got it to move was smooth, no sticking and returned 100% as it should be Just like my old bmc on the shelf. Looks like it is not the bmc binding there.

HOWEVER

I yanked the ebrake hard several times then let it back down. When I did that, the front brakes loosened up considerably. They were still stuck, but could be rotated without much difficulty by hand.

As the cars cooling and the friction coefficient is dropping it is slowly becoming more movable.

Man this is just TOO weird...

short of driving it off a cliff which I can't do right now with the brakes stopping me short, other ideas?

edit: this car is non abs

[rcdad123]

your proportioning valve might be bad. when you replaced your fluid with synthetic fluid, did you flush ALL of the non synthetic fluid out? i`ve seen this happened when one of our tech accidentally filled the brake master cylinder with power steering fluid. all of the rubber parts in the brake system expanded and had to be replaced.

[tastyratz]

I actually tentatively might have it fixed and will post to help others that search.
I went out last night and bled the whole system doing a huuuuuuge flush. Inspected the distribution split block in the rear no jams. Pull passenger front wheel and caliper is looking naaaaaaaaasty. Felt too loose to me, almost thought it might be seized. pad faces were all rotted looking and different from the other pads. Bleeder screw missing cap and looked like hell. I had all sorts of sandy rusty goodness coming out of it when I bled that corner. I think with the bleeder grody and letting bad news in the caliper causing all this crap. Took my caliper compressor and compressed it all the way down without any issue, no visible tears in the boot or rust ingress near piston face. replaced the screw with one I had and after bleeding and hitting the brakes a million times it re seated properly/felt fine.

Did about a 35-40 minute jaunt up and down twisty roads in the neighborhood last night. took a few minutes of settling but so far no issues have cropped up. Drove it to work today also 30 min drive 0 issues.

(fyi valvoline synthetic is not silicone fluid, the only dot brake fluid you can't mix is silicone)

[Howlermonkey]

If it happens again, add some free play to the pedal.

If you don't have enough, you get the exact symptoms described in the first post.

Also check for a rust stain on the booster below the master cylinder because I have seen water intrusion cause the retainer in the back to rust and swell which didn't allow the cylinder to fully come to rest.

[nissanfreak317]

I used to drive this old Ranger for a machine shop that I worked at, it used to sit a lot until we needed to pick up parts or whatever. One day the brakes started grabbing while I was driving, turned out that water had gotten into the brake fluid and water is denser so it collects down in the caliper and boils causing the caliper to grab when hot, then gradually let go once cooled. Sounded a bit like your problem, so I just thought I'd mention it. A good bleed took care of the issue.