RIO68

Drove my 77 to the NC mountains yesterday and by late evening I had no brake to panic stop, all the way to the floor, only enough to slow down and stop after good distance. Got the car home last night (long and slow) and put up and this morning brakes are back.

Can fluid boil like that or is there any other ideas?? Thanks for any direction to go or check!!

...Roger...

Probably air got into the system due to rotor runout , common problem. Just a guess but I bet if you crack open the rear bleeders air will come out of 1 or more. Whatever one air comes out of ,check the rotor runout on that wheel.

CA-Legal-Vette

Brake fluid can certainly boil, especially if it's old and hasn't been flushed in a while. That can lower the boiling point considerably.

Get yourself some Motul brake fluid and a Motive bleeder. Flush all four corners and if boilling was your problem, it should be gone.

It's also possible that you had simple brake fade from overheated pads and rotors but that shouldn't make the pedal go to the floor.

Roger certainly could be right as well but typically that won't get better with cooling.

Mike Ward

The fluid itself does not boil, water trapped in the calipers can and will- if the temperature exceeds 212F. The resulting steam pockets created pushes fluid out of the caliper giving the low pedal.

These steam pockets collapse when the surrounding fluid drops below 212F again and brake operation returns to normal.

68-427Rich

While your there, flush the old fluid from the system. I do this at least once a year.

RIO68

Well, the system is new-rotors, master cylinder, flex lines, porprotional valve, fluid and calipers. All the metal lines were blown out to get junk out of those. Don't know where to start??

mds3013

No answers but a couple of questions. Do you have o-ring or lip seals on caliper pistons? And what type fliud are you using? mike...

RIO68

Good question-don't know on either one. I thought about fluid being at issue but don't know if flushing it out and putting more in would help. I'm pretty sure it's Dot 3 at least. I know I didn't use silicon base. Calipers I don't know about seal type.

7T1vette

Was the brake fluid "old". If sitting in a damp/moist environment for years, it can absorb moisture...and you can't tell that by looking at it.

RIO68

Don't think so--it's been 3 1/2 yrs putting car together fld good 3 yrs old now. Fld purchased from parts house.

turtlevette

If you're going to be hard on your brakes you need to flush the whole system about every 6 months. They tell you to flush everytime before a road course event.

Unfortunately that even may not be enough. They stock calipers use aluminum pistons which is a great conductor of heat.

You'll have to learn to use the gears to slow the car in the mountains if you want to live.

RIO68

I just finished flushing out the fluid. It was really dark which indicates some contamination, new fluid clear. Got a good feeling pedal but will need to drive it and see. Still not 100% on the master cylinder. Frt bled good but back calipers not as flowing with fluid as frt were.????????

onaqwst

well, i did put my front calipers on the wrong sides before....just saying...

muskegonbrake

Most likely problem. Were the wheels hot when you finally stopped? Did you smell hot brakes? If so then you could have boiled you fluid, and that usually indicates another problem in the braking system.

RIO68

No smell at all. Just weak on brakes. Trip just short of 100 miles once 3/4 way home brakes felt somewhat better still on floor but resistance was just a little bit more. Still could not panic stop---gradually slowed. ?????

Easy Mike

I'm betting your new rotors have excessive run out. Check all four.

RIO68

How many thousands is too much? Brakes apply smooth no vibration or pulsing.

muskegonbrake

Should be 0.005" runout or less.

aussiejohn

R1068,

Do you think that maybe the booster is not working properly? If you have a vacuum leak or the diaphragm has a hole, you won't get the proper amount of boost.

Just a thought.

Regards from Down Under

aussiejohn

builder

If the caliper pins are rusty, a caliper could hang to one side and rub the brake pad to the rotor. If a caliper is corroded on the inside, it could hang up and not release pressure and heat up. If a rotor is ground too thin, and is beyond minimum thickness, A caliper puck could go out too far in its bore and catch (not return). That would create a lot of heat. If your proportion valve is clogged, that could be a problem too. If at any time the pads remain in contact with the rotor and heat up, your brake pads could be glazed and no longer function as they should.
If I ever had a problem such as you described, I would thoroughly go through the entire brake system, flush, replace pads, and check for run out on the rotors.