Last weekend when I was moving my 'vette out of the garage, the brake pedal went to the floor and the brakes completely failed. Fortunately I was going 0.5 MPH in my driveway when this happened and wasn't on the road. It turns out the right rear steel brake line broke off near the caliper I think due to corrosion.

My question is, I thought the C3 has a seperate front/rear system so that if there's a loss of hydraulic pressure in one circuit, the other still works. In my case, all of the hydraulic pressure was lost and I had no brakes, even though the front brakes were fine. My master cylinder has two seperate fluid chambers and I could see the rear chamber was losing fluid, and the front was full and didn't lose any. I know there is a proportion valve or combination valve - if this failed would that cause the problem I got? I see MidAmerica sells rebuilt combination valves and takes core changes, so is this something that is common to break or wear out?

 

I have found that at best the system gives a modest degree of braking ability when one of the sub-systems fails, but you should not expect to have a hard pedal when it does. You might get some braking but the pedal will go to the floor.
More importantly, if your lines are so corroded that they would break, you might want to take a hard look at your car's entire brake system - I have had wheel cylinders fail that way on old cars but never a brake line. :eek:

 

I test drove a vette that had the brakes fail like that. It was also a 70, but that doesn't matter. In that case the front were shot and leaking and the brakes pedal when right to the floor and the brake light came on indicating the piston was pushed off center in the valve.
A couple of questions since the line rusted away. Was any work done to the car brake system lately? If not I would check the entire system which would enclude:

1. checking each caliper for leaks, are they SS lined ?
2. replace the rear hoses and the caliper line.
3. replace the front hoses-don't forget to change the copper washer too.
4. Bleed the M/C, if it ran down then it probably sucked in air.
5. Check the runout in the rotors front and back- anything over .003' and you have to fix it. I know the book calls for .005" but I just turned rear rotors/spindles that had .004"
6 If you have rivets in the rear rotors then they probably are theoriginal unless someone went NCRS with it, if you don't have rivets then someone was in there- not unusual for a 32 year car. You don't want to take the rear rotors off and have them turned separate from the spindles- they won't be concentric and still may have runout, but they will look nice :rolleyes:
Check it out and post here for more answers, there are a lot of informed people here and brakes are a common topic.
Gary

 

Thanks for the info. I guess my combination valve is OK then? I would rather not spend $100 for a rebuilt one if I don't have to.

I purchased and installed new stainless steel brake lines for both sides of the rear from Mid America. The new lines look MUCH better than what was on there. The stainless steel makes a big difference. Plus the new lines have some armor shielding on the rear part to prevent stone damage kicked up the tires - the ones on there didn't have this. Even though it was just the right rear line that broke, I replaced the other side too. Looking at closely, it had a bit of corrosion under the flare nut that hooked into the caliper - this is where the other line broke - right behind where the line attaches to the caliper with the flare nut.

I installed the new lines and bled the rear brakes, and it works great now. The only odd thing that may have contributed to the brake line failure somehow, is I just experienced a flat tire driving on the highway on that same wheel. I drove home with the spare tire on without any problems. After I got the tire repaired and replaced the spare with the repaired tire is when the brake line broke. I don't see how this could effect the brake line though, because even flat the tire doesn't come near the brake line. Probably just coincidence.

The brake system in the car overall is very good. I bought the car 7 years ago, and it had newly rebuilt calipers with SS and new front brake lines (the rubber ones). I put a new master cylinder in the day after I bought it as the original just happened to fail then. Last year after the car was in storage for 8 months, I noticed the left front brake caliper was leaking so I replaced it. It shouldn't have failed like that being SS like the previous owner told me. But the other 3 calipers seem to be holding up fine so far.