What could cause brakes to lock-up
I was driving my '64 FI with J56 brakes to cars and coffee this morning, about a 40 mile round trip, on the way home, about a 1/4 mile from my garage, it started slowing down and finally just stopped on a hill up to my place. It would not move. The rear brakes (maybe front too?) were locked up, like the emergency brake had been set. That brake was not set, and cable was loose. I noticed a drip of brake fluid from the rear brake circuit at the MC, (the reservoir was full), so I took a wrench and loosed the fitting at the MC and let some fluid flow out (maybe a few teaspoons) as it seemed under pressure, I also disconnected the vacuum on the booster. Then I was able to drive it but the brake pedal was hard and had hardly any travel. When I got it in the garage, I topped off the MC, and started working the pedal while the car was running with the vacuum hooked back up. It then seemed normal. Any ideas on what went on here? Thanks.
-
Big Tanks In the High Mountains of New Mexico -
Re: What could cause brakes to lock-up
I have seen where a miss adjusted rod between the master cylinder and pedal cause this exact thing. It apparently does not allow the piston to retract enough to bleed back into the cylinder. How much altitude change did you have on the trip?
Rick In WA State -
Re: What could cause brakes to lock-up
I've seen this on my 63 but it's a very different system. I agree that the backing off the rod from the pedal to the cylinder will help.
Comment
-
Re: What could cause brakes to lock-up
A common problem with old brake hoses is that they swell up inside and restrict flow either way, often locking up brakes. Those rare J56 and the J65 metalic brake shoes both have many small segmented pads which sometimes come loose and can jamb into the drum. Both conditions are easy to check without to much work. That kelsey hayes master is one rare piece, and there could be an internal problem there. There's probably a small number of members who could speak from experience with that master. I would guess it to be same as any other dual circuit one, the valving balance only difference. Sounds like a very interesting car.Comment
-
Re: What could cause brakes to lock-up
hoses probablyFounder - Carolinas Chapter NCRSComment
-
Re: What could cause brakes to lock-up
Mike , on a second thought, did the car pull left or right ? Also don't know if you checked but if one wheel is dragging you can feel more heat on it's wheel center and sometimes a burning smell. The rod adjustment sounds very possible. Only worrying thing is any brake fluid leak is bad .Comment
-
Re: What could cause brakes to lock-up
Thanks guys, the altitude change was only about 1000 feet to and back. I will check the rod adjustment, the pedal was pretty low when the lockup occurred (and it happened slowly over the course of about 1 mile), I even tried to pull it back up but it was frozen. There were and are no leaks anywhere except the one small one at the MC on the rear circuit line, and after I released the pressure and tightened it back down with my line wrench, there was no leak now. I will drive it around carefully tomorrow and see it doesn't happen again. I have only had the car for a few months, and it is newly restored and obviously needs some sorting out. That '63 Z06 style MC is an odd item, and I am hoping it is OK.Big Tanks In the High Mountains of New MexicoComment
-
Re: What could cause brakes to lock-up
It sounds like you have a plugged compensating port in the master cylinder. The small hole to the left in the pictured master cylinder allows brake fluid to expand back into the reservoir as it heats up. If the hole is plugged, the brakes will slowly lock up because the fluid expands, applies the brakes, which further heats the fluid, and the car grinds to a halt. I used a paper clip to clear the plugged port and that fixed it. Be careful because if the seal is blocking the port you don't want to damage it. If the seal is blocking the port you need to adjust the rod so the seal is behind the compensating port. As soon as you apply the brakes, the seal covers the compensating port.
Comment
-
Re: What could cause brakes to lock-up
Thanks very much Bill, that sounds exactly what it would be. The slow, progressive application of the brakes as the car gets hot, without my foot doing it, until total lockup. I am wondering, since I released the pressure and the brakes are now working as normal, did whatever plugged it get removed, or maybe I should drain, clean, and refill the MC? The fluid is almost new, as the car was restored recently.Big Tanks In the High Mountains of New MexicoComment
-
Re: What could cause brakes to lock-up
That's the odd thing, the brakes released when I cracked the big nut on the rear circuit and released the pressure, and everything was still very hot. I drove it around some immediately after that and all was working as normal.Big Tanks In the High Mountains of New MexicoComment
-
Re: What could cause brakes to lock-up
Replace the hoses if for no other reason SAFETYFounder - Carolinas Chapter NCRSComment
-
Re: What could cause brakes to lock-up
Thanks Jimmy, will do. I have now drained and cleaned the MC, and ran a small wire into the holes, drove it around this morning with no issues, hope that is it. Thanks to all.Big Tanks In the High Mountains of New MexicoComment
-
Re: What could cause brakes to lock-up
Not odd at all. When you cracked the fitting some fluid escaped thereby decreasing pressure in the system and allowing the brakes to release. Continue driving without freeing the relief port, the fluid will again expand, will again pressurize the system and the cycle will repeat.Comment
-
Re: What could cause brakes to lock-up
After checking the hoses and ports check for push rod clearance between MC and vacuum booster- stock 65s have an adjustable rod.Comment
Comment