74 Camaro brake issue

chevrolet
camaro

#1

I have a '74 Camaro that has disc brakes in front, drums in back. Before I restored the brakes it had little play in the pedal. I replaced the front brake lines, and the master cylinder, because they needed to be gone through and they were leaking. I properly bled the master cylinder, and all 4 brakes but now I can push the pedal about half way down before feeling resistance. I do have good solid brakes after the part of no resistance too. Also without power I have resistance right away, no problem. So my question is- How can I remove the play in my brake pedal before I get resistance?


#2

Some brake pads are softer than others, but not that much. Actually, I think your brakes maybe working properly now, when before you may have had sticking calipers. Did you do anything to the calipers such as greasing the bushings (caliper pins)? The calipers should float freely.

If the calipers are not floating now, they may not be pulling the outer pad in enough and it springs back each time you release the pedal. If they do float now and they didn’t before (I suspect this) then before, the outer pad did not back out as it should making the brakes feel tighter than they should have. You got used to this.

The big question is, do they work. Bed the pads according to the manufacturers recommendation, some of this excess play may go away when this is done. Then in a safe area, test them. Do they stop as fast as they should? If they plaster your face on the windshield, then I’d say you don’t have a problem.

One more thing, did you do anything to the back brakes? If you did, you have to adjust them. On some models, you back up and hit the brakes a few times. On others, you set the parking brakes a few times.


#3

First thing to check with an otherwise firm but low brake pedal in a disc/drum setup is your rear brake adjustment,you don’t mention checking this.


#4

Keith- That’s what I thought at first too, that they might be working properly. But the thing is the resistance doesn’t start till about half way down, and no brakes until then. Also the front calipers are both new, along with brake pads. They both float fine, so I don’t think the calipers are an issue. Also the brakes do work, they just start working “late” compared to what it was anyway. EDIT- Yes I adjusted the rear brakes correctly by letting it roll in reverse, that is how you set them in my car and they work just fine.

oldschool- I actually restored the rear brakes too, with a whole new spring assortment, new brake cylinders, ect. The rears are working fine I believe, sorry I did not mention it before.


#5

Hey I accidentally posted my reply to you below "oldschool"s post, just so you don’t miss it I wanted to let you know!


#6

Still want to check the rear brake…Make sure they’re adjusted properly. If they are way out of adjustment the pedal may have a lot of travel.

Adjust the brakes so you can feel some resistance when you turn the wheel…but not too much that you can’t turn it. If there’s no resistance at all then you’ll have a lot of pedal play.


#7

I think you will find the most disc/drum setups don’t have much resistance until the pedal is about halfway down. I suspect that your old calipers were “frozen”. I don’t mean stuck, only that they didn’t float properly. You got used to that and now you think something is wrong.


#8

I just checked the rear brakes and they are adjusted correctly. Also the calipers were replaced about 6 months ago, so they were replaced before the brake lines and master cyclinder. So I don’t believe the calipers are the problem. So is there any other ideas? Could this possibly be a problem with the proportioning valve?


#9

If you have air in the master cylinder, front part, go up and down some hills and it might take the air out. If the master cylinder isn’t level, jacking the car will do the same thing. Front calipers will gravity bleed, so open the bleed valve until you see no bubbles in the fluid. Or just have a shop pressure bleed the system.


#10

Are we working with a mismatch in regards to the master cylinder/power brake booster? Any chance the booster itself is bad or not correctly fitted the the master cyl? Are you sure you are working with the correct replacement parts? I see no reason yet to suspect a porportioning valve problem. Do some detective work and see if it is even possible to pick the wrong master cylinder,will your supplier let you try a second master cylinder? I am kinda grasping here.


#11

pleasedodgevan2- I don’t think there is any air in the master cylinder, as I bench bled that and there seemed to be no air in the system. Also all 4 brakes are bled correctly, with no air coming out.

oldschool- There could possibly be a mismatch, I am not for sure. I am almost positive the connections are all good, as there are no leaks or anything. Also the brake booster seems fine without leaks in air and the vacum seems good. Especially since again, the brakes have good resistance right away. As for the correct replacement part, I am pretty sure it is correct. It is a different shape and such, but seems to be correct and it fits right up to the brake booster and the brake lines fit up perfectly. The only reason I would think it could be the proportioning valve is because it is the one part I did not replace, but I have no idea if that would cause any problems or not. I will look into the wrong master cylinder problem. Any other ideas that anyone can think of?


#12

Is the piston in the power brake booster returning to its correct position upon release of the pedal? I am thnking something is keeping it from fully returning to its resting position.


#13

Something I remember fellow mechanics saying (but I never verified) is that your symptoms are possible when new brake shoes are mated with very worn drums. Verify that the arc of the brake shoes is close to the arc of the brake drum surface.


#14

What does “correctly” mean to you? The shoes should adjusted out until the drum cannot be turned and then loosened until the drum can be turned by hand but still hear the shoe scuffing.


#15

oldschool- While I was bench bleeding the master cylinder the piston had no problems returning to the original position. Maybe that could change since it is installed?

JoeMario- The arc matches up pretty well in the rear drum brakes, I also got them turned about 6 months ago so they are not warped or anything. So I don’t think that is the problem.


#16

This usually isn’t a problem, but in your case, it might be worth a look. If you remove the master cylinder (MC), you will see a rod sticking out of the brake booster. You may be able to slide the MC out without disconnecting the lines.

Measure how far this rod sticks out from the surface of the booster. If you have a gasket between the booster and the MC, measure from the surface of the gasket. Then measure from the mating surface of the MC to the end of the piston in the MC. They should be about the same.

The rod is adjustable. I still think that you don’t have a problem, but try this also. Get a ruler and measure from the floor to the brake pedal. Then push the brake pedal down with your hand (engine running). You should start feeling resistance at about 1" of depression. If it is significantly more, then something isn’t exactly right.

If you repeat the above test with the engine off and the booster bled down, that is you work the brakes a few time to vent the stored vacuum, you will get a better idea of any gap between the booster and the MC. When the pedal hardens up, there should be very little if any play.

You may have a little more with new brakes, some it may be taken up as the brakes get a little wear.

Other checks you should do is find a steep driveway or hill and check your parking brake. You can check on flat ground by setting the brake, put it in gear and give it a little gas if an automatic. If a manual, use a higher gear and don’t go overboard. Do the test in forward and reverse.

Then find an empty road and do a few panic stops and see if the brakes perform the way you want. Be careful not to overheat the brakes so allow some cooling between stops, its best if the car is moving while the brakes cool off so as to not create a hot spot on the rotors.


#17

Okay I will look into all of that when I can. I still am not sure that the piston in the master cylinder is an issue as when the car is off the pedal goes down about 1" or less then you feel the resistance (or the piston in the booster hitting the MC). Also when it is running there is significantly more than 1" of depression before resistance, so I am sure something isn’t right. My car is a manual, and I have done the parking brake test before and it will not move easily at all. Also we did test the brakes on a secluded road and they stop the car quickly if you quickly push down the brake pedal. But they just don’t start working as soon as I think they should. So once again, any other thoughts on what this could be? I just want to have all senarios thought through so I can fix this.


#18

With the engine off and vacuum bled from the booster, there should be almost no play in the pedal before feeling resistance. Look at the mechanical advantage the pedal has on the master cylinder. 1" free play would translate to about an 1/6" gap between the booster rod and the piston in the master cylinder.

EDIT: check this free play with the parking brake set and with it not set. There shouldn’t be much, if any difference.