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1972 Brake issues

 
Old 02-12-2019, 10:23 AM
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grumman41
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Default 1972 Brake issues

I took a hiatus from my 72 for over a year and I'm now looking to get it back on the road. All of the brake components at the axles have been replaced prior. I currently cant get any brake pressure at the pedal to bleed the brakes. Can you help me with advice as to what component to replace next? The master cylinder looks very clean but probably pretty old. Is this something you can get a rebuild kit for? Would the booster cause issues?

Thanks in advance, Kevin
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Old 02-12-2019, 10:41 AM
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The booster only comes in to play with engine running and is a pedal pressure assist only. In your case with "no pedal," with engine off sitting in the garage, you have other issues.
If I had to guess, I would say the old brakefluid in the master has deteriorated the MC piston seals. The seals can snag on rusty bores and actually roll over on the piston making the unit worthless. To test the MC you simply remove the two brakelines and plug the ports. If you can stand on the pedal, the MC is ok. If it goes to the floor, well, then, . . . . . . . . .

There are kits to rebuild the MC. But they require a good honing and if not done correctly could put somebodys life in jeopardy. Much safer, easier, wiser to get a correct rebuilt unit from a Vette vendor.

Its not a bad job removing the MC. Two lines, two nuts, its off. Bench bleed your new unit, then try bleeding the entire system again. Should be good to go.

Last edited by HeadsU.P.; 02-12-2019 at 10:43 AM.
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Old 02-12-2019, 10:44 AM
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Thanks for the input. I would like to keep as many original components as possible, may check with Baur maybe they can rebuild.
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Old 02-12-2019, 10:53 AM
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Some vendors will want your old core, some don't. From past posts, the C3 master cylinder fitment issue has been hit or miss in the past. Having said that, I would shy away from local counter part employees and contact a Vette vendor. The MC design has changed over the years so it is imperative to get the correct year unit. Ones for manual brakes are different than P.B. Some have bleeder screws on the MC, some do not. Again, they kept changing. Bore sizes can be different too. This gets back to the counter person at the local parts store. Their computer says "fits all Vettes" . . . . . . . . .
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Old 02-12-2019, 11:15 AM
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Thanks for the heads up!
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Old 02-12-2019, 01:09 PM
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2 different combos of the m/cyl and the boosters in the C3.....I THINK it was '77 when they went to the shallow divot on input to the m/cyl and a short nub outta the m/cyl to mate with it.....but in a '72 the booster has a long dick hanging out and it goes into a deep hole in the m/cyl piston......

another problem area is the rear main line along the frame rail to the splitter, another is that pressure switch that has a brown wire to it, telling the driver the front OR rear brakes have failed....it's prone to leaking /etc....

so look for brake fluid in that area, forward of the m/cyl and down lo on the frame.....I would eliminate it like I did on my '72......

the car should by now have stainless lined calipers, and so to do an O ring conversion on them....
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Old 02-12-2019, 01:24 PM
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It looks like I have the correct casting number....any recommendations for an overhaul?
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Old 02-12-2019, 01:48 PM
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Before even thinking about a rebuild, you need to test the MC. It may be fine. How would you know w/o testing?

Remove both lines , plug ports, step on the brakes. Firm pedal or not?

Last edited by HeadsU.P.; 02-12-2019 at 09:18 PM.
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Old 02-12-2019, 02:22 PM
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The car has been sitting for years and the fluid is dark, rusty and looks like debris in the MC.
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