Strange brake problem, '68 Z-28 - Team Camaro Tech
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post #1 of 8 (permalink) Old Jul 3rd, 10, 09:35 PM Thread Starter
Lou
 
Join Date: Jul 2008
Location: Sacramento, CA
Posts: 27
Strange brake problem, '68 Z-28

I have a Ď68 Camaro, Z-28 that I bought in Ď70. The brakes are stock front disc, rear drum. Last weekend I pulled off the freeway and the brake pedal went to the floor with minimal resistance or stopping power. The brakes had worked perfectly prior to that. I was at a motel full of car guys for a show and our best diagnosis was a master cylinder failure. I bought a new NAPA M/C and after bleeding and installation I had the same problem, the pedal went to the floor. Needless to say I came home on the back of a AAA truck.
Today I removed the line to the front brakes and plugged the M/C port. The pedal moved less than an inch and was hard. I reinstalled the front line and the pedal was again soft. Iíve pulled all four wheels and inspected the brakes. All appears intact and there are no signs of leakage. The front flex lines are Russell steel and the rear flex line is stock rubber, both are about five years old. Tomorrow Iíll bleed the entire system but even if I do find air in the front system, how in the world would it have entered? What other places might absorb the pressure/fluid. The hold off valve?
I look forward to the wisdom of the guys that know!

Lou
If you can't fix it with a hammer, you've got an electrical problem.

1968 Z-28 Camaro
1965 Malibu SS
1975 IH Scout II
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post #2 of 8 (permalink) Old Jul 3rd, 10, 11:55 PM
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john
 
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Location: northern california
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Re: Strange brake problem, '68 Z-28

You may have alot of movement in the rotor or caliper.

Bending or bent caliper bracket?
Misaligned bracket,rotor or caliper?

In other words...you may be solid hydraulically but loose in other ways mechanically.

Remember,I'm not making this stuff up!

1969 rs/ss 396 350hp/4spd conv a/c,pw,ps,foldown
1968 Z/28 crossram- j/l8 conv pw,ps,foldown
1963 nova ss 350/4spd conv a/c,ps,pt
1963 nova 400 4dr 6cyl/700r4 a/c
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post #3 of 8 (permalink) Old Jul 4th, 10, 12:16 AM
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Robert
 
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Re: Strange brake problem, '68 Z-28

Four piston calipers can suck in air if the rotors have more then .011" runout. They will suck air without displacing any fluid, in other words no leaks. Bleed and if the brakes are ok, then after driving a few miles the problem comes back, you have a wheel with excessive runout. This may or may not be your problem but it is one of the oddities of 4 piston calipers. Early Corvette owners know all about this!
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post #4 of 8 (permalink) Old Jul 4th, 10, 04:11 PM Thread Starter
Lou
 
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Re: Strange brake problem, '68 Z-28

I certainly appreciate the help here. I rebuilt my original master cylinder and carefully bleed it in a vice. Itís amazing how long they spout bubbles. I bolted the M/C back on and pressure bled each wheel. The right front had some minor bubbles and the left front gave quite a bit more. I checked the pedal and it was high and hard. Oh happy days. Then I found I could not make either front rotor turn. After some minutes I realized Iíd left the pressure bleeder on with 10 psi. Once I removed that I put the wheels back on and went for a spin. Excellent brakes.
Now Iím left with how the air got into the front system in the first place. I took what you said here Robert regarding the 67/68 four piston calipers and did some looking around. It seems the hold off valve can also allow air into the system. I really donít want to go through this again and having a numbers correct car is not important. Iíd like to look into converting to a í69 and later single piston rotor/caliper. From what Iíve seen thus far itís as simple as a caliper, rotor and proportioning valve. Thanks again for your thoughts.

Lou
If you can't fix it with a hammer, you've got an electrical problem.

1968 Z-28 Camaro
1965 Malibu SS
1975 IH Scout II
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post #5 of 8 (permalink) Old Apr 2nd, 12, 10:05 AM Thread Starter
Lou
 
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Re: Strange brake problem, '68 Z-28

Robert, I'm doing some housekeeping here and wanted to update you on what happened next. Shortly after my last post I was on the freeway when I had the same loss of brakes. I again bled the front calipers and they did have air again. I then did further research based on your comment that Corvette owners know all about this. You're right. Corvettes from '62 to '85 used these four piston brakes and they can suck air. I bought a kit that replaces the pistons and seals with a different design and the problem is gone.
Thanks Robert, you helped fix my problem and I've helped two others that had this odd problem.

Lou
If you can't fix it with a hammer, you've got an electrical problem.

1968 Z-28 Camaro
1965 Malibu SS
1975 IH Scout II
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post #6 of 8 (permalink) Old Apr 15th, 12, 12:25 AM
Mario
 
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Re: Strange brake problem, '68 Z-28

MalibuLou, I'm having a similar problem with my '68 Z28. What was the kit you used to fix the calipers? I have a feeling my own problems are related.

Thanks ahead of time.
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post #7 of 8 (permalink) Old Apr 15th, 12, 09:44 AM Thread Starter
Lou
 
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Re: Strange brake problem, '68 Z-28

Mario, I'm sure I got the "O" ring/piston kit from Vette Brakes in Florida but they are available from many companies. If you haven't yet had stainless steel sleeves installed in your calipers, this would be the time to do it as the stock bores are prone to pitting. Vette Brakes installed mine some 20 years ago. I've also seen that Rockauto offers rebuilt calipers and a rebuild of your own calipers. There are lots of options available. As I recall the bore size for these calipers is 1-7/8" though some (A body I think) may have used a 2-1/16". Just something to be aware of.
Since I installed my O ring kit in my calipers I've had no further problems with the brakes on my Camaro. My Chevelle however???

Lou
If you can't fix it with a hammer, you've got an electrical problem.

1968 Z-28 Camaro
1965 Malibu SS
1975 IH Scout II
MalibuLou is offline  
post #8 of 8 (permalink) Old Apr 15th, 12, 05:10 PM
Mario
 
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Location: San Luis Obispo, CA
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Re: Strange brake problem, '68 Z-28

Thanks for tip! And good luck with the Chevelle.
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