Brakes seized

[SCOTTGTK]

Good am all, so brakes started to seize up fortunately as I was pulling into my driveway. Very little peddle action at all. No leaks anywhere..dual master cylinder was filled to where it should be... brake system was within the past week flushed and new fluid put in. I loosend the front brake line off the cylinder just enough to allow a little fluid to come out and then tightented it and this fixed it for the time being. my concern is this will happen again... thoughts? Thank you in advance, Scott

[davez]

One or both of 2 things. Either the calipers need rebuilt. Pistons are not retracting when pressure is released.  O rings have degraded not allowing the piston to slide properly .
Or rubber brake lines are collapsing on the inside not allowing the pressure to release.  When you opened the line it releases the pressure allowing the piston to back off.

Somewhere you've got something not allowing the pressure to release

Most of our rubber stuff made these days degraded much faster than the original from 60 years ago.

[SCOTTGTK]

Thanks davez! Original diagnosis was that master cylinder needed to be replaced?

[davez]

Sorry i was thinking that the master cylinder was new and didn't read that properly. So you also have a piston with o-rings in your master cylinder as well so that could be. How old is everything?
Since you're able to open the line and the pistons release, it's probably not the caliper. Something is holding pressure somewhere.

[SCOTTGTK]

Can't say age of, but certainly not new... consensus was the master cylinder was over pressurizing. This came from the shop that did the flush, bleed and refill. All 4 wheels/calipers etc were "checked" and found to be fine... pads as well. a google search on my part turned up possible pushrod was to long... pushrod was not replaced.

[Lincoln tech]

Power or manual brakes ? did you try pulling up on brake pedal ?

[SCOTTGTK]

No power... 65 factory K code, factory GT cloned to GT350 in the early 70's. All wheel disc with proportioning valve in the cabin. Peddle does lift back towards you (inch or 2) if that's what you mean by pulling on the peddle. The current position of brake peddle is the same since I've had it, no change there.. No seizing up the past several rides since the flush/fill etc.

[Lincoln tech]

So at this point the system is working properly , therefore there is nothing to fix. Keep an eye on it and address it when it comes back .

[SCOTTGTK]

Yeah, I get parinoid with brakes and I feel like it'll happen again. Going for a ride shortly so we'll see. Thanks for everyone's help... if anyone thinks of anything else... please post.

[s2ms]

Also possible the proportioning valve is sticking, is yours adjustable? If it is and this happens again you might try that.

[SCOTTGTK]

It is adjustable... I'll keep that in mind, thanks s2ms... I just got back a good ride and tried to duplicate the ride yesterday when they seized up and nothing happened? I'm glad nothing happened, but feel like there's still a possible underlying problem.

[Chris Thauberger]

Are you using synthetic brake fluid?

[SCOTTGTK]

No synthetic.

[KR500]

Scott
If both front brakes are (were) dragging and loosening the line at the M/C released the brakes then it is more than likely the M/C at fault.  If it is just one wheel dragging then open the bleeder screw on that caliper. If the dragging goes away replace that hose. If it is still dragging after opening the bleeder replace the caliper. You said that you just had the fluid replaced/system bled so more than likely some debris or sediment could have gotten into the M/C bore and caused the piston to stick, although most of the time when that happens it causes the fluid to bypass the piston seal resulting in no brakes. Scary sh*t on a single chambered M/C vehicle. One other possibility is that whoever replaced the fluid put in the wrong fluid , like a petroleum based fluid that can swell all the rubber parts and wreak havoc on the system. DOT 3 & 4 brake fluids are water soluble. Take a small sample and mix with water it should dissolve. If it dos not that's bad.

Rodney

[SCOTTGTK]

Thanks Rodney, I really couldn't tell...if I had to guess, all wheels were affected. I was coming down my home street and into my driveway so it was a short amount of time, not at speed to feel any type of pull one way or another. This is a dual chamber and as soon as I cracked one of the lines coming off the MC and a little fluid came out, I tightened it and all was back to normal.Peddle action etc  I will test the fluid for accuracy though. Thanks for your help!

Scott