Traction981

Hi, I been having brake problems for about 17 years and need some advice. Every year I change something and try and get the spoungy feel out of the brakes. I have changed master cyclinders twice, brake booster once. In the last couple years I have changed all the rotors, calipers, brake pads, steel braided whip lines to calipers, and the porportioning valve. I have changed everything exept the steel lines on the frame and the blocks that tie in the other calipers. I have a new engine and the cam is bigger so I do lose some vaccum at the idle but this car always has been like this. This year I bought a power bleeder that attaches to the master cylinder top and pushs brake fluid under pressure into the calipers. I bleed from farthest caliper away to closest. Still doesn't seem to help. Brake fluid comes out at all calipers. Car still wants to lock up on front end. If there is a little gravel on the road it really wants to lock up the front. I also tried to set the pushrod in the master up to do a better job. It just seems like my only option is a hydro boost kit. Why not spend some more cash on this dam thing. Any help would be great. I don't know what else to do. Thanks for any help

CA-Legal-Vette

So just to be clear, is the problem that the brakes are spongey or that the fronts lock up?

Steve COSD

I had almost the same problem and tried everything. Finally I tried a different brand of pad and gravity bled the system and now they work great. I went to the Raybestos brand.
Good Luck

Oldguard 7

OK lets start at the brake booster. As you probably already know when you start the vehicle the brake pedal should drop slightly. Once you shut off the vehicle the pedal should be hard to push. Do that test to rule out the brake booster. You may have air in your system. What type of brake bleeders do you have? Regular or the bleeders you that have a check ball in them... also known as speed bleeders. The check ball in the speed bleeders prevents air from being sucked back into the caliper when bleeding. They are pretty cheap and are found at most auto parts stores in the Help! section. Purchase some and then try bleeding them again. This is the cheapest most simple route to go first. You also mentioned that your front brakes want to lock up... during light or heavy applacation? Is or does your brake light come on? When you installed your rotors, did you check for run out? That also could be a cause for air in your system. I would first try replacing the bleeders and bleeding the system again first. Let us know what is going on after you try this.

Traction981

I have the motive bleeder. The problem is I don't think the rear brakes are grabing as good as they should plus the pedal just doesn't seem right to me. I haven't driven any other vette besides mine but I compair it to my old 81 camaro with drums on the back. It felt like hard and pedal doesn't sink all the way to the floor like this vette. The brakes pads are hawk. I bought the complete brake set up from VB&P. I for the helphave to get the car on the road here to try out the brakes again. But just starting it in the gargage the pedal feels like I have to go almost right to the floor. I've never had an issue that causes me such a headache. I thought when I put all this new stuff on my issue would be gone. Maybe thats the way the brakes should feel on this car, but I can't see it. Thanks

Traction981

Sorry I never answered the other couple questions. I think I just have the standard bleeders. I will have to check. I don't have the light hooked up to the porportioning valve. I think I disconnected it long time ago.

HamadUP

I had the same problem before, it turned to be that I missed the other bleeding nipple on the rear calipers, I didnt know that there are actually two bleeding nipples (one on the back and one on the front), now my brake paddle is hard like a rock and the car will stop on a dime.

Did you bench bled your M/Cs before installations? , there may be some air still trapped in the rear calipers reservoir.

Peterbuilt

I agree, brakes on a 74 Vette can lead to pulling ones hair out! With power brakes you only have 4.6 inches of pedal travel so it seems to be low seems compared to our daily drivers.
Ad to that there is 1.8 inches of free play, and the pedal seems to be way to close to the floor before the car stops. (Consider your padding, carpet and mat and there is less room).
If your pedal seems spongy then you still have air in the system. You might try bleedeing again this time from closest to the M/C and see if that helps.
If your front brakes lock up before the rears, then you may have a bad porportioning valve.

...Roger...

Sounds like the classic air left in the system.
bench bleed the master.
with motive hooked up and 1 of the bleeders on the LR open tap on the rear line coming out of master,then tap on combination/proportioning valve , lines going to rear and all junctions, tap on caliper,open the other bleeder,tap on caliper.
do the RR the same way tapping all connections between the LR and RR.
Idea being that air can get stuck in the lines , connections and threads.
When air gets stuck in the proportioning valve it can be tough to get out.
When bench bleeding work hard on the rear cylinder until you have absolutely NO bubbles , I spend no less than 10 minutes on a bench bleed,very important. I tap pretty hard on the master while bleeding. Use the tubes to bleed not the plugs.

Traction981

Thanks for all the help. I will try and tap the lines all the way back. Thanks once again.

7T1vette

Is the brake booster being 'fed' directly from the rear fitting on the carb base plate? Have you checked to see that the base plate orifice and the fitting/tubing do not have any obstruction in them? Is the rubber hose connecting that pipe to the brake booster collapsing at idle?

Traction981

well I tried to bench bleed my master. It did have some air in it. I can't seem to get the bubbles out of the hoses. When I release the plunger the air bubbles just go back into the master. I can't seem to get them out. Any suggestions. Thanks

Traction981

Ok here is what I did. I couldn't seems to get the newer master cyclinder to bench bleed proper. So I gabbed my old one. Had no trouble bleeding it and getting all the air out. Installed it on the car and bleed the entire system with the motive bleeder and tapping on the lines. I'm sure I got it all out. I even left the motive bleeder on all night and cracked the calipers again this morning. The master feels tight when I push the pedal. When I start the car its almost to the floor. By what you are saying it looks like thats they way they are for the travel of the pedal. I guess know I just will have to get it ready and drive it a bit to see how it is. They just seem wrong to me. Maybe thats the way they are. Thanks for all the help.

...Roger...

To the floor is wrong. Did the old one "ever" work right ? Does the depression in the master piston where the push rod goes look the same on both cylinders ?

Traction981

Yes they measure the same. I use to have an adjustable pushrod in it. I played with different settings. The new booster cyclinder combo came with a fixed push rod. Its been the same on orginal booster, orginal m/c. Its been the same with 2 other m/c I have tried and the new booster. Its not quite to the floor but its close. As long as those rear brakes grab, thats good enough for me. Nothing ever has been easy with this car. i don't know why i spent so much money on it. I will have to wait to drive it till I find out if the back brakes work proper. I still want to go over it a bit more, with the new suspension, rear end and brakes. Thanks

...Roger...

If you have stock rubber type rear brake hoses,have you ever tried clamping them and then seeing how the brakes feel ? This would rule out the rear calipers. I wouldn't do this with SS braid lines as it will leave a dent in the outer mesh (not sure if it leaves a dent on the inside of the stock type).

Traction981

I do have the ss brake whip lines. I will hopefully take it for a drive later today or maybe tomorrow.

Rockn-Roll

If you use the pedal to pump fluid through while bleeding then this won't happen...you will be able to diagnose brake system problems and solve them without spending a lot of money.