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Discussion Starter #1
Someone.. please help...

so this is my first post. I have a 76 280 I bought last year and I’ve been working on it a little. Doesn’t need much honestly the whole thing is completely stock runs and drives nice. The only thing is that the front brakes lock up, I never drive the car a far distance so it hasn’t completely locked up yet, but it’s gotten super tight before. At first the brakes feel normal, not stiff at all, the brakes will engage after pressing on the pedal maybe about an inch or two, it feels normal honestly. But after a few miles, the pedal begins to rise slowly and become stiffer. There’s pressure being built up SOMEWHERE but I can’t find it. I know it’s only the front brakes because after driving it for awhile the front wheels get HOT and the smell of the brake pads is there. the rear wheels are just normal.

Naturally, since the car Probably has a lot of original parts, I went straight to the front calipers, master cylinder And brake hoses And replaced them. It didn’t fix the problem. So honestly, what’s left is my brake booster, the proportioning valve, and the lines. I’ve been reading adjustments on the pedal that maybe the pedal is adjusted incorrectly not allowing the pressure to relieve. I don’t think it’s the brake booster, I changed the check valve and there was a decent vacuum when I pulled it from the brake booster.

what are your thoughts?
 

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1983 280ZX Turbo
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Something is creating pressure and forcing the pads to contact the rotors. If you've eliminated the calipers as the problem, the booster is the best candidate.

Here's why I follow your logic: (pardon the long story, please...)

This actually happened to me with a Jeep Grand Cherokee on a 60-mile trip from Fort Collins to Denver. For a few days it had felt like the Jeep was losing power - which was actually the brake drag. On this trip, it got bad enough that I pulled off the road and did a walk-around. I could feel the heat coming off the right front wheel from two feet away. It wasn't hard to figure out that a dragging disc brake was causing it.

I found a couple of empty water bottles, filled them and baptized the rotor and wheel, cooling the brake enough to get another 15 miles. It took three water cooling stops to get to my destination in Denver, which was my daughter's place. I dropped it off at a mechanic and picked it up next afternoon with one replaced front caliper, new front rotors and pads.
 

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This happened to me when I put a new master cylinder in there. The brand I bought had its piston too long which covered the brake return hole in the cylinder so it just kept bringing up the pressure. So I returned it, got a different brand and was good to go.

Since you had this problem with the original and now new cylinder that SHOULDNT be the case. Try unplugging the big vacuum line that goes from the intake manifold to the brake booster and drive around again. If the brakes don't lock up its the booster.
 

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Well, you can eliminate the booster, since it acts only on the master.

It would be interesting to know if the rears are working normally or not.

There are only 3 places that both fronts share a common source; the master, the line to the NP valve, and in the valve itself.

In your place, I would carefully inspect the hard line from the master first, looking for a crimp. If nothing untoward, I would resign myself to pulling and disassembling the NP valve, looking for obstruction of the front inlet from the master..


The Exploding Head extrapolation would be this: the master on the car to begin with, was the wrong one, and it was replaced with an identical wrong one.

That's all I've got.
 

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Discussion Starter #5
Thank you guys for your wisdom lol all of you have pretty good things to check out. I really want to eliminate the brake booster from troubleshooting so I’m gonna try chaseincats thing first. Let’s see how that goes. I’ll definitely check out the master cylinder and NP valve also. I’ll keep you guys in touch
 

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I think chaseincats has it right. I saw this many many years ago on another z. Difference in length of the master cylinder and actuation rod. You may need to compare the lengths of old and new rods and adjust accordingly. Seal inside master cylinder doesn’t get back to where is should be and then acts like a check valve and does’t suck fluid back into cylinder. Then the pressure bleeds off through the seals just enough to let the system ‘relax’.
I think we ended up using like the old rod on the new master or something similar. It also was a Tokico to Nabco swap or vice versa.
 
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