Brakes Help?

[bhermes]

I have recently purchased a 1976 280Z and have been trying to get the brakes to work ever since. I will give a little background on the situation. The brakes were very noisy. They had new pads but cheap ones. I added shims and some lubricant and the noise stopped. The next issue was that one of the rear lines was leaking. I replaced the line. Through this entire process when ever I applied the brakes the care would pull badly to the left. I assumed that the front right brake was not working. I replaced both front calipers and purchased Thermo Quite brake pads. I have bleed the front brakes a few times now. Not and expert at brake work. Here is the issue. When the car is off I seem to have good pressure on the pedal. When I turn the car on I basically have no front brakes.

Any thoughts?

This has the tandem master and I believe that one is for the front and one for the back. Is this correct? I am thinking about replacing the master cylinder but just curious why the brake pedal seems good when the car is off but not on.

[Walter Moore]

When the engine isn't running you have no vacuum assist, so the pedal is hard to press regardless of how well the overall system works.

When you bleed the brakes, do you actually get fluid? How do you know that you have no front brakes? Have you tried to spin the wheels with the car on jack stands, or are you just assuming that you have no brakes because the pedal goes to the floor? The later symptom could mean that you have air trapped in the rear brake circuit too by the way.

My guess is that you still have air trapped in the system somewhere, and that is causing the true problem. How are you bleeding the brakes? I have had the best luck with a vacuum bleeder, but I know people who hate those things.

I will let one of the professional mechanics on the board give you more accurate information, but of all the cars I have ever owned, the Z has been the one that I had the most difficulty getting the braking system to work. I cannot explain WHY that was the case, because it isn't that different than other cars of the era, but it took me many tries to get it working.

Check for leaks in the rear braking system where you replaced the line. Even a really small leak will cause the soft pedal you describe.

[Reverend]

I had the same kind of problem and it went away after thorough bleeding. Use search and you'll find tons of info about that.

[bhermes]

Thanks for the replies.

After replacing the calipers in the front I only bleed the front brakes. Are the systems separate or do I need to bleed the back brakes again?

I thought that the front brakes would provide enough braking even if the bakes were not working properly.

When bleeding the front I did get fluid out of the bleeder fitting and no air bubbles. The brake pedal when the car is running does go to the floor with little pressure but will stiffen up if I pump it quickly several times. When trying to pull out of my driveway which has a slight downward slope I had trouble stopping the car.

I think I will try and bleed all four brakes and see what happens.

Any further thoughts would be appreciated.

[Zed Head]

Are the bleed valves at the top of the calipers? It is possible (and easy) to install the calipers on the wrong sides of the car. This puts the bleed valve at the bottom, leaving a big air bubble that can not be removed by normal bleeding procedures.

I've also seen similar symptoms from people who had the reaction disc in the brake booster fall out, but I don't know much about that problem.

[conedodger]

Without an answer to that question, the easiest way to handle this is to pretend they're not. Separate that is. Bleed the right rear first then the left rear, then the right front, and last the left front. You want to move from farthest away from the master cylinder to closest. Have whoever you have inside the car give that pedal a good stomp. You are trying to dislodge air bubbles and they like to hide in the most secure places where they're hard to move.

As for your pull to the left. That is kind of unusual. Because of road crown, cars *can* pull to the right and have perfectly serviced brakes. When you replaced your pads originally, was there unusual wear? Like for instance, one side have pads that looked nearly new while the other had a completely worn out pad? If your caliper pistons aren't moving freely, you may need your calipers rebuilt.

[bhermes]

I am bleeding the brakes, all 4, again tonight. The pulling to the left was prior to putting on the new calipers. Have not been able to drive since they were installed. Not sure on the bleeder fitting but think they are at the bottom. Will check when I get to the car.

Just to be clear, if they are at the bottom should I remount them?

I was told that if it was a brake booster problem the pedal would be stiff. This was from a local import repair shop. I am not sure.

Thanks for all the help and guidance.

[Zed Head]

The bleed valves should be at the top. If not, swap them, you'll never get the air out otherwise, no matter how many times you try.

I would do this first, if they are on the bottom, and then bleed just the fronts. You might already have all of the air bled out except for the two air pockets in the calipers.

Edited June 14, 2011 by Zed Head

[Jeff G 78]

After verifying that the front calipers are on the proper sides (bleeders up), bleed the master cylinder. Use a 6" long hose. With the hose on the front MC bleeder port, insert the other end of the hose into the MC reservoir below the fluid line. Open the bleeder slightly and slowly pump the brake pedal up and down until no air bubbles come up through the fluid. When the bubbles are gone, close the bleeder and repeat for the rear port. You MUST bleed the MC prior to bleeding the calipers and wheel cylinders. Once the MC is bled, start at the LEFT rear. On a Z, it is actually the furthest from the MC since the lines travel down the RH side of the car. Continue to the right rear and then the right front and left front. Don't forget to keep adding fluid to the reservoirs. If they run dry, you will have to start over with the MC bleeding.

[bhermes]

Ok. Calipers have been moved to the correct side. I will bleed the master cylinder and then the brakes and see if that fixes the issue.

Keep your fingers crossed.

[bhermes]

So far so good. Brakes appear to be working well.

Just to summarize for future reference.

Calipers were put on the wrong side and bleeder fittings were at the bottom. Reversed calipers so that the fittings were at the top. Bleed master cylinder and then the brakes.

I will test them more when the rain stops and I can get on the highway.

I want to thank everyone who responded to my post and for all of the help.