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Hey guys so I’ve just got my rear disc conversion done and so now I’m all wheel disc and I’m wondering what size master cylinder you guys used and the brand because I’m not getting any petal and there’s no air in the system. I’m pretty sure I’ve got the 1” bore so I’m wonder if the 1 1/8 inch bore worked for you guy? Thanks!
 

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The correct master cylinder bore is determined by your front discs and whether you have power assist. In general if you are using GM calipers on the front, you should be using a 1" bore with no assist, or 1-1/8" with assist. An exception would be a 62-67 with factory booster, you could use a factory 1" master cylinder.

If you have a rear disc conversion with the Caddy calipers, your problem is possibly that they haven't been pre-adjusted so that the caliper pads are all the way out on the rotors prior to attempting to bleed the brakes.

The other possible source of your problem is that the master cylinder (or booster if you have one) pushrod has preload. The pushrod between the booster and master cylinder should have .015-.030" clearance. The pushrod between the booster and pedal arm should have no preload - the clevis pin should go in by hand. Same if you don't have a booster. Preload keeps you from being able to fully bleed the brakes.
 

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I did a Wilwood front disc conversion on mine along with their master cylinder. I went with a 1" bore as my car has manual brakes. For power brakes Wilwood recommended 1 1/8" bore.

You can go with a 3/4" or 15/16" bore as well on manual brakes, it makes for longer pedal travel but less effort. I think 15/16" to 1" is probably perfect. Mine stops much better than with the stock drums before, but they're still manual brakes that require more effort than power brakes.
 

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I have 4 wheel manual disc on my car. LS Camaro on the rear and CPP zero off set on the front. I used a 69 Corvette 1 inch master. I had trouble bleeding the brakes at first. I had people pump and pump, opening and closing the rear bleeders. Soft pedal almost to the floor. I went to Napa and bought a reverse bleeder tool that pumped the fluid from the bleeders to the master. First try and I had a rock hard pedal Some how there was still air in the rear line.
 
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