Soft Brakes No Leak

[eoseitz]

Hey everyone. I have kind of a strange issue. I have a 1974 Corvette that the prior owner had switched over to 4 wheel disk. I had the car sitting outside for a few weeks while I changed out my carpet. I finally got it back together and was going to take it out for the first time this year and noticed the brakes didn't feel right. They pretty much hit the floor. I checked the master cylinder and found the front compartment empty. The back one was still full of brake fluid. I assumed I hit a brake line while cutting a stuburn bolt off of my seat mounts. However, I haven't found any leaks. I noticed my gasket was shot in the master cylinder so I replaced it. The brakes still hit the floor. I've tried pumping them and get nothing. Could it be as simple as air in the lines from where my master cylinder went dry? I haven't pulled the tires yet, but from behind I didn't see any fluid leaking from the calipers. It just seems odd that last fall the master cylinder was full and now it's empty. Feels like a leak, but that's a lot of fluid to lose not to see any dripping anywhere. I believe the back disk breaks are off of an 80's model corvette.

 

[Hib Halverson]

first...your car came from the factory with four wheel disc brakes like every Corvette since 1965.

second...I would not drive the car with one side of the brake system dry.

third...have the car towed to a service shop and get them to troubleshoot the brakes for you.

 

[Chas]

As already stated.....

Take it to a pro who knows Corvette brakes, do not drive it like it is now. Yours came with 4 wheel disc brakes. There are quite a few folks here from your area of Ohio and if you ask they may be able to help you find the right place to go.
Chas

 

[eoseitz]

first...your car came from the factory with four wheel disc brakes like every Corvette since 1965.

second...I would not drive the car with one side of the brake system dry.

third...have the car towed to a service shop and get them to troubleshoot the brakes for you.

My father works at an accredited break/muffler shop for a living. I wasn't aware they all had 4 wheel disc brakes though. I could have sworen the previous owner said he converted them over. Thanks for the info. That will definitely help if I need to replace any parts. I didn't know what year to ask for. I haven't drove it with the brake system dry. I was going to take it out for the first time this year and realized there was something wrong with the brakes. My fluids are always topped off. This is what has me baffled. I don't know where the fluid could have went if there are no leaks. The gasket over the portion of the resovoire that was empty was shot. Maybe it drained out, however, I don't think it did from there. I would think I would see signs of it somewhere. Unless the heat from the engine burned it off.

 

[GTR1999]

As noted the brakes on 65-82 vettes were all the same, with some exceptions of HP road racing calipers. The system is pretty basic, you have a 2 chamber m/c. The front chamber supplies the front brakes, the rear supplies the rear. Follow the 2 lines out of the m/c and they go to brass block, either on the top of the frame or the side, depending on the year. There will be or should be a brown wire going to the block which houses a spool. If the system has a leak, like in the front, the fluid will leak out and the spool in the block will shift and activate the red dash board "BRAKE" light that also lights up with parking brake handle in the up position.

You have major leak in the front system, most likely a caliper but it could be a rotted line or split hose. You need to find it and correct it. Then you may have to bench bleed the m/c and then the system. The best tool is the Motive bleeder it will work great on vettes. If you have SS lined calipers you can rebuild them with a seal kit as long as the bore is still good. If you have untouched original brakes the bores are cast iron and will pit from old brake fluid absobing moisture turning into an acid fluid, pittind the bores. This has been a common issue with C2 & C3's and started a whole cottage industry in brakes that expanded to some of the vendors you see today.

Not a big deal but you have to fix it. Also you have to get the rotor runout under 003", your Dad probably has a good brake lathe for the front and maybe an on the car for the rears but DON'T turn them if they are not grooved. Most times all you need to do is D/A them to break the glaze and then dial in the rotors with some small ss shims. Rotor thickness is only 1.250 down to 1.215 so 035 is all you get for both sides.

 

[eoseitz]

Hopefully the roter isn't cut into. I didn't have any problems last fall when I parked it, so hopefully, whatever broke, happened in the drive way. I didn't even think about the brake light. It comes on when I pull the ebrake, but it isn't lit up right now.

 

[eoseitz]

Well I got a chance to tear into the brakes yesterday. We inspected all of the lines and couldn't find any breaks in them or leaking fluid. Actuall, the line going to the back right caliper was a new line. We went ahead and bled all four break lines to make sure there was no air in the lines. There was actuall a bit. After bleeding them all until the air was out I still have no brakes. I went ahead and changed the master cylinder. I bled it when I installed it. Still no brakes. We followed the lines from the master cylinder down to the metal box that splits the lines. No leaks there. My father, who was helping me work on it and works for a brake shop, said most brake systems has a type of reset button on the splitter box. We couldn't find one on the corvette. Is this normal? Does anyone have any other ideas? Vacuum hoses are all connected to the brake booster and it appears to be working (The brakes hit the floor even easier when the car is running). The only thing I can think is that we didn't get all the air out of the lines. If it's not that I'm completely stumped.

Oh I should also mention we checked the pistons on each caliper and they also weren't leaking. I was surprised to see the calipers have four pistons. Did the previous owner upgrade these or were they stock. They were marked delco. I thought he said he switched the back "drums" for calipers. Maybe he said he upgraded the calipers.

 

[JohnZ]

I was surprised to see the calipers have four pistons. Did the previous owner upgrade these or were they stock. They were marked delco. I thought he said he switched the back "drums" for calipers. Maybe he said he upgraded the calipers.

All '65-'82 Corvettes used exactly the same 4-wheel disc brakes with 4-piston Delco calipers; there were no "drum" brakes. There's no "reset button" on the combination valve. If there are no visible fluid leaks and the pedal goes to the floor, there are only two causes - you still have air in the system, or the seals on the master cylinder pistons have failed and are bypassing internally.

 

[eoseitz]

You were right JohnZ. I changed out the master cylinder and bled the brakes again. Brakes are working perfectly now. I was able to take it to the electrician yesterday. $250 to wire everything from the firewall up. He had it done in two days. I was very satisfied with his work. I bought the susension rebuild kit a few months ago; This weekend I can finally put it on.