I have an 80 and this brake problem is driving me crazy. A few months ago I installed a new rear-end on the car. but now I put everything back together and the brakes are not working. I already rebuilt all the calipers and got a new master cylinder. The problem seems like there is no pressure in the brake lines. Could this be that is clogged up somewhere? What would be the best way to do this? or could this be some other problem?
Things I tried:
Bleeding the calipers does not help, done this numerous times.
New master cylinder, did nothing.
Rebuilt all the calipers, doesnt seem to help any.
I had the brake line on one of the back calipers off and looks like only a little brake fluid is coming out.

This is the only thing holding me back right now. I'm ready to start working on the body and paint the car. I have the paint already to go.

 

Have you checked the line for any kinks?

 

yes, I put the car on blocks so I could be easier to check and nothing

 

the inside of the flex line could have been further damaged during the rebuild causing it to "collapse inward" (one way to look at it).
taking a line off the caliper and bleeding, you won't see much fluid.
if the flex lines check okay, i'd get a pressure bleeder on it next.
did you install lip seals or o-ring seals?
if you are pedal bleeding, make sure that you watch each piston as the pedal is lifted after bleeding. the piston may be retracting.
with a pressure bleeder, push the pistons back into the bores while bleeding to help expel air trapped behind the seals.

 

Although this might be messy........ Can you remove a rear line (right rear), get someong in the car to press the pedal to see if you get a strong stream out?

Other question. What are you using for the bleeding, the manual way, or possibly using a Motive style pressure feed, or, MiteyVac?

 

I'm guessing lines could be bad. if they were sitting for awhile.
I installed the lip seals on all of them. I'll try to check the pistons today to see what its doing. thanks

 

This was the last thing I tried, i removed the rear line and only got a little bit of brake fluid. I'm doing it the manual way.

 

What about the Proportional valve...on some GM cars you have to hold a button on the valve to bleed the rear...

 

No, the "push to bleed" function is for cars that have a front "metering valve". It is only used with front disc, rear drum brake systems. Vettes have 4 wheel disc so that function is not there. Did you "bench bleed" the M/C before installation? If not, it is almost impossible to get all the air out of the system. Check this thread for bench bleeding.

http://forums.corvetteforum.com/show....php?t=1449975

 

The problem could be in the combination valve. Part of it’s function is to block off the flow to the side loosing pressure.

 

No, it is always open to flow even when one side fails. If it didn't, you would never be able to bleed the brakes to get the light to turn off after fixing the problem.

 

Thanks Duke, for the correction. I was sure that the combination valve had a restrictor circuit.

 

OK...give us some details on how you are bleeding and on your brake system. I suspect an OEM system. Is it power or standard? Are you bleeding BOTH rear bleeders? Are you watching for air bubbles when you bleed?

Here's what I do. Buy a one-man bleeder kit at your local parts store. It will include the plastic bottle with a magnet attached which Tom454 spoke of, and a foot or so of tubing...it's like $5.00 or something like that. Buy a Quart of brake fluid. It shouldn't make any difference which kind you have since they are compatible per Department Of Transportation (DOT) specifications. Though DOT does recommend using DOT-5 for any new systems, it is more likely that your system still has DOT-4. I suppose it really does not matter what you use, and I've never seen any reason to buy anything but the cheapest and have never had brake problems.

The only other tools you will need is a 1/4" and/or 5/16" box end wrench(s). Also, if you are going to do the job yourself then you will need a 2' 2x4 and a towel...the 2x4 will be used to pump the brake pedal and then wedge it between the pedal and the driver seat while the towel will be placed in front of the seat between the 2x4 to protect the seat.

Slide the box end of a combination wrench onto a bleeder, attach the clear hose to the bleeder valve and the other end into the small clear bottle. Attach the bottle magnet to the brake disk and position it so you can see it while squatting under the driver side door, cause you will be reaching in with the 2x4 to pump the brake pedal while looking under the car at the bottle.

Open the bleeder valve about 1/8 to 1/4 turn (if you open it too far you will get air through the screw threads), (run the engine at idle for power brakes) pump brakes using the 2x4 while watching the tube until clear bubble-free fluid exits then wedge the 2x4 between the pedal and seat to keep the pedal depressed and tighten the bleeder. If you get to 20 pumps and you still don't see clear fluid then refill the master cylinder and keep pumping until you see clean bubble free fluid come out of the bleeder. Don't let the master cylinder reservoir run out of fluid.

This in the order to bleed in order to conform to the Bureau of Automotive Repair (BAR) requirement to bleed hydraulic systems beginning with the bleeder furthest from the master cylinder (you can use others…it’s just that this one may be required as an answer to test knowledge of brake systems before a license can be issued):

Passenger Rear Outer
Passenger Rear Inner
Driver Rear Outer
Driver Rear Inner
Passenger Front
Driver Front

Yes, there are two bleeders at the top of the rear calipers...one on each side of the brake disk and need to be bleed separately. If there are bleeders at the bottom of the calipers then ignore them...those should just be plugs, but bleeders are cheaper than plugs so if someone has worked on the brakes and didn't care what they used then there will probably be bleeders in the bottom holes instead of plugs.

Repeat this cycle once to be sure all air is out of the system and that no air is getting in and that the entire system has fresh fluid.

If you keep getting air bubbles out of a bleeder then there is a leak somewhere, usually it's the caliper and replacing (recommended) or rebuilding (cheaper, but not for the timid) fixes it. Keep in mind that holes in the system can be small enough to let air in, but not leak fluid which means that there can be a hole in the system letting air in, but you won't see any fluid leaking out. It is also why pumping is best (over other bleeding methods) because it will cause a vacuum in the system when letting up off the brakes, while providing the desired pressure to properly bleed the system.

This method is best because it activates the system the way it will be used thus detecting any problems that may occur while using the brakes on the road (except warped rotors which you find out upon test driving).

I think brakes are important, and if you can't get them bled properly then try to find a mechanic that will talk to you in person...see if they will let you read their Bureau of Automotive Repair brake inspection & repair manual...they are required to have it at their site if they have the BAR Brake Inspection Station sign out front. Sometimes visiting them with a 6-pack when they are just getting off work helps loosen their tongue...when I was the on-duty mechanic at a Chevron station I would-ah spilled my guts for a beer...or was that spilling my guts after too many beers? Oh well, I hope you get my point.

 

You mentioned that you put on a new Master cylinder. Did you bench bleed the maser cylinder? If not you can bleed the brakes forever and you won't get any pedal pressure. The above post mentions a bleeding sequence. There has been some discussion lately about bleeding sequence for Corvettes and the recommended sequence is different from the above post. The sequence is: Left rear inner, Left rear outer, Right rear inner, Right rear outer, Left front, Right front.

I followed this sequence when I bled my brakes a few weeks ago and it worked fine.

BTW, I posted something earlier today about a bench bleeding procedure that I performed with the Master cylinder on the car that might be helpful.



Rick B.

 

I've had a ton of problems with my brakes untill I found a great way to bleed. Gravity bleeding!!! I was actually doing this today, and forgot to watch the master cylinder and it went dry...ummm. Anyway, I removed the master (as I knew it had air in it) Bench bled the master, reinstalled then gravity bleed. I use rock&rolls sequence and just crack the bleeder screw open (maybe 3/4 turn) and let gravity do it's thing, (catch in a clean cup) Bleed approx. 20 min. each bleeder. On the rear inners and front I use a plastic tubing for a return to a clean container. For my hard effort (standing there watching), I get the hardest peddle you can imagine and I use Dot 5!!!!!

As indicated: keep a close eye on the master... don't let it run dry as I did . Muddy

 

ok this is what i'm doing. I did the bench bleeding. Made sure no air came out. closed the MC and installed it. I had someone pump the brakes like 10 to 15 times with the car on. Then hold the pedel down, the I open the rear passenger caliper valve and nothing happens. Close it, pump it some more and hold it down and open the valve again and nothing. There should be some kind of pressure. I'll try bench bleeding the MC again this afternoon. Start all over maybe i missed something.
I was going to do it yesterday but got furstrated and started doing some fiberglass work on the hood.

 

Try this: Open the bleeder then pump like 10 to 15 times. You need to get fluid in the lines and the only way to do that is to pump it through. After you get fluid in all the lines then go back around and open each bleeder and pump until you get no bubbles...do this twice to make sure you have no bubbles.

If all you are doing is pumping up air then air is all you are going to get out of your bleeder...you need to pump fluid into your lines.

 

When you did this, did the brake pedal go down? If it went down when you opened the bleeder, then you are building some pressure. If it didn't go down, then I would say there is a clogged in the line somewhere.

 

blow fluid through..

 

You need to crack open the bleeder and then pump the pedal, not pump and then crack.