All 4 disc brakes locked up while driving

[Vref]

Was driving the 65 yesterday and without any notice, boom all 4 brakes lockedup, braked pedal was hard and not moving. I am using silicone fluid.

Seems like a master cylinder thing, (not releasing). After it sat for a couple of hours. the brakes released again and worked just fine.

Anyone else have this problem?

 

[61 Silver]

Brake lock up

This happed to my 65 after restoration. I installed original rebuilt stainless sleeved brake calipers and I rebuilt the master cylinder my self. The problem was the small holes in the master cylinder bowl that allows the line pressure to release back into the master cylinder were plugged. You can try to release the pressure by loosing the break line and to allow some fluid to escape. IMPORTANT!! (Do not get fluid on the paint) if this frees up the breaks you will probably need to clean the two small holes in the main cylinder bowl. I used a torch tip cleaner to clean the holes and it solved my problem.



Ray

 

[Vref]

This happed to my 65 after restoration. I installed original rebuilt stainless sleeved brake calipers and I rebuilt the master cylinder my self. The problem was the small holes in the master cylinder bowl that allows the line pressure to release back into the master cylinder were plugged. You can try to release the pressure by loosing the break line and to allow some fluid to escape. IMPORTANT!! (Do not get fluid on the paint) if this frees up the breaks you will probably need to clean the two small holes in the main cylinder bowl. I used a torch tip cleaner to clean the holes and it solved my problem.



Ray

Thanks, That sounds exactly like the problem. When I loosen the break line and allow fluid to escape, It solves the problem temporarily.

 

[67HEAVEN]

That must have been a tiny bit freaky. :eek


How fast were you going?

 

[youwish2bme]

With the way that I normally drive I think that I would have needed a change of my shorts....Dave..

 

[Vref]

About 50 mph with no shoulder on the street, we went left across traffic where there was an open spot to put her, smoke from the wheels and everything. And there she sat until the tow truck came, Then we couldn't move her since the brakes were locked.

Sat there with no tools to release the pressure, finally she slowly released on her own.

I wouldn't recommend the experience.

 

[youwish2bme]

COOL....... Glad you had a place to point her.... Most of the time I'm on two lanes so I would have been screwed.....Dave

 

[JohnZ]

Two possibilities:

1. How old are your flex hoses? When they get old, they deteriorate from the inside out (swelling) and act like check valves - they'll pass fluid under pressure, but when you take your foot off the pedal, they won't pass fluid back toward the master cylinder, causing the brakes to drag. The more they drag, the more the fluid heats up (and expands) between the restriction and the caliper, and eventually they lock up solid.

2. Brake pedal free play isn't adjusted properly - this causes the master cylinder piston seal to cover the outlet and compensating ports; the brakes work when you step on the pedal, but the return path for fluid is blocked, causing the same result as in (1) above.

 

[Vref]

Two possibilities:

1. How old are your flex hoses? When they get old, they deteriorate from the inside out (swelling) and act like check valves - they'll pass fluid under pressure, but when you take your foot off the pedal, they won't pass fluid back toward the master cylinder, causing the brakes to drag. The more they drag, the more the fluid heats up (and expands) between the restriction and the caliper, and eventually they lock up solid.

2. Brake pedal free play isn't adjusted properly - this causes the master cylinder piston seal to cover the outlet and compensating ports; the brakes work when you step on the pedal, but the return path for fluid is blocked, causing the same result as in (1) above.

They were changed to in 1992, It would think the flex hoses if only one wheel locked up, But since all 4 locked up at the same time it seems the issue has to be in the master cylinder. I just cannot imagine all 4 of those lines swelling at the exact same time.

 

[JohnZ]

Yup, I'd go after the master cylinder first - could be as simple as inadequate pedal free play adjustment (check that first - should be 1/8"-1/4"); if that's OK, rebuild the master cylinder.

 

[Glassman]

I agree on the free play in the brake pedal. I just worked on a 72 where the last person who worked on it set the push rod for no free play it would not release the rear brakes and neutralize the pressure in the rear. This caused a vacuum to hold in the line the rears would suck air. That was a problem to find. Fixed to 1/4" free play and worked great.
And yes you do have a bleed back problem, I am just relaying this info to make you aware so as not to have another problem.