rear brake problem

[lout207]

I'm in the process of upgradng to Disc brakes on the rear of my 1972 (Built 6/72) 240z. When trying to bleed the system, I have the pedal go down about half way and seems to hit something . Also not very much fluid flows out the caliper bleeders. I do get some fluid from both sides and did bleed the master. The calipers DO NOT move the pads!! NO REAR BRAKES!

The pedal will NOT go the floor when I open the bleeder on a caliper or on the master for the rear section. I have an aftermarket Master cylinder installed at this time.

I just bought a rebuild kit a master cylinder and will install it on my old original master.

I noticed the "ORIGINAL HAS TWO "STOP SCREWS" but the new has only ONE STOP SCREW. Is this telling me anything.

With the master removed the pedal moves all the way to the floor without any resistance. So I don't have any mechanical problem.

ANY ideas of what to checkout??

I'm pretty mechanical (retired Mechanical Engineer and longtime backyard mechanic)

Thanks,

LOU

[Zed Head]

Sounds like the piston in your master cylinder is bottoming out in the bore. If so, it might be starting at mid-stroke in the bore. This would not let the bore fill with fluid, so would not pump any through the lines. You might have the rod in to the master cylinder adjusted to be too long. Adjust it to as short as necessary to get play in the linkage. Make sure that master cylinder piston is coming all the way back. Just one possibility.

[lout207]

Thanks

I'll look into that. It may be that the aftermarket master is a problem, so I'm going to go to clean up my old OEM and see if it makes a difference. I don't remember making any changes when I put on the aftermarket master but that was a few years ago. Don't even remember why I changed it out. Maybe I've only had front brakes snice then and didn't know it. That's a scary thought!

[5thhorsemann]

Correct me if I'm wrong, but the stock master will not move enough volume to actuate a disk brake calliper. The pistons are like 10 times the area of the single drum piston. Don't you need to change the M.C. when upgrading the rear to disk.

[IdahoKidd]

Endless posts say you need the zx master, 15/16's bore. I have it installed but haven't done much else on that system. I do agree with Zed Head about it being mid stroke. The rod is adjustable and the piston in the cylinder may have a different face on it forcing it to start at a later point (the original piston has a dish in it for the plunger to set it. If it doesn't have that dish, it would start much later in the throw for example.)

Do let us know what you find to aid in future searches and solutions.

Leonard