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The Grind


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So, here's my situation...

I have a 71Z, stock brake set-up, no idea how old the components are. My MasterVac is disconnected b/c lack of funds/credit to fix, so it's blocked off with caps until I can replace it. No brake problems to speak of.

So the other day I have to make an emergency stop in traffic, I'd say from 30-35 mph to stop as fast as I could. At the first stoplight after that, a faint grinding comes from the rear passenger side. It's a little worse at the next stoplight, a good bit worse at the next, and at the fourth stop, its a horrible, loud metal on metal grinding that makes my heart stop, and I drive home (through the neighborhoods, thank god) with good downshifting and the e-brake.

The grinding is only on one side, and only when the brakes are applied in motion. No noise when rolling, none when pressing the brakes sitting still.

Stripped a shoe? Whacked out something else? What do you guys think?


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Yeah, I'd guess that the lining came loose on one shoe. Easy enough to find out, jack it up and pull the drum and look.

Easier said then done on some Z's. I had to destroy the drum on the 260Z to get it off. But you're right, sounds like a shoe slipped off or something.


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The master vac does not have 14.7 psi of vacuum. At best it is 22 to 24 in. Hg. or around 11 to 12 psi of vacuum. Just saying. :) Your master vac only has teh vacuum it pulls from the balance tube or intake manifold. The most vacuum it sees is from high RPM deceleration with your foot completely off the gas. At that point you'll pull around 22 to 24 in. Hg.

This is why large cam'd vehicles have brake booster issues.

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It is not the pressure of the atmosphere but rather the differential pressure across the diaphragm. Now stay with me here. The engine applies a vacuum that is not a true full vacuum, therefore the differential pressure across the diaphragm is not going to be 14.7 psi but rather 11 or so psi.


If the engine did not create a vacuum, or creates a low vacuum at idle like on a radically cam'd engine, then the differential pressure is going to be minute.

Edited by ktm
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  • 3 weeks later...

Man was I off...

I went back and tried to pinpoint the origin of the noise, and find that it is not the back at all, but the front brakes! I pull the wheel and do a quick visual, and find that the passenger caliper is very screwy. Somehow, the outer half (toward the wheel) is dragging on the rotor. So the caliper itself is grinding down the upper 1/4 inche of the rotor! Anyone else had this happen?

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The only way for that to happen is for the caliper itself to be loose. The 240z/280z caliper is a one-piece unit that is attached via two bolts. Maybe one of the bolts snapped/backed out and the caliper rotated forward/backward?

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