Bleeding my rear brake. What am I doing wrong?

When I got my 79 the rear brakes did not work at all. Rather than bothering to diagnose and fix it, I simply removed the entire working rear brake system from my 81 and put it on, line and all.

Now I can't get them to work at all. I can pump the brakes till my arm falls off and I get nothing at the bleeder screw. Once in a while I get a small puff of air. Tried a vacuum pump and still nothing. I get not pressure build up on the pedal no matter how many times I pump it. The 79 had a SS line which looked good so I tried that and still nothing. When I pop off the banjo bolt at the master cylinder there is no brake fluid getting up into the line at all.

The only thing not from my perfectly working 81 rear brakes are the reservoir screws. I had to drill the heads off and replace them with bolts because both sets on both bikes were stripped. Tried using an impact driver and still they wouldn't turn.

What am I doing wrong? Or did this master cylinder die on me during the move from one bike to the other? It was 4 bolts. I am beyond frustrated with this.

when bleeding brakes you need to be patient, you push down on the pedal and hold it down, open the bleed valve, close the bleed valve then let the pedal back up, if you let the pedal move while bleeding you will suck air back into the line, slow and steady, pump a few times, hold down, bleed, tighten, pump hold bleed tighten

I lost count at 30 times before I switched lines and did it 20 or so more times. I'd pump slowly 5 times, hold, crack the bleed screw, close it then back to pumping. I have zero pressure buildup after all of that and no fluid in the line at all.

My thought is that somehow you have managed to get a blockage or the mastercylinder has packed up for some reason. This can happen if the cylinder, which has been operational, starts working in an area of the bore which is not normally used, ie bleeding the system.
Over time crap can build up in these non used areas and when you bleed the brakes this crap can score the rubber seal of cup allowing fluid to bypass. Not saying that this is the problem, just a thought.

Another trick I have used successfully is to get a syringe and attach a plastic tube to it and reverse flush tbe system. Attach the tube from the syringe to the bleed nipple of the brake. Open the bleed nipple and apply pressure to the syringe forcing fluid back into the system. If the is an airlock or a bit of crap blocking it this may dislodge it and get it working again. Again not saying it will fix it but worth a try.

Thanks Torque.

What would the the obvious symptoms of a failed master cylinder? Would it be leaking anywhere?

When I press the lever with the banjo bolt out I can see the fluid moving in the hole but it doesn't squirt out or anything. I can't get a single drop of fluid down the lines.

The master cylinder was working fine before I switched it. When I took it off and opened it, it was full of thick yellow goop. I used a whole can of brake cleaner trying to get all the crap out of there.

I used air to blow out all the banjo bolts after using brake cleaner. I also blew out the lines with air because my first through they were blocked.

I'll bet the other master cylinder is baked as well.. which is why it didn't work in the first place. Seems every damn part I swap is no better than the one that I was replacing. I'm almost ready to break out the flamethrower. This has been the single most frustrating motorcycle "adventure" in my life. Two bikes... both junk.

I hear what you are saying Ledkz1300, I think we have all been where you are now, this bike can be vey frustrating but when it's all sorted is well worth the effort. Don't be disheartened.

If your master cylinder has failed and fluid is bypassing the rubber seal then eventually fluid would leak from around the top of the cylinder ( where the push rod fits ).
Depending on the severity of the leak depends on the amount of fluid.

My suggestion would be that if you have stripped out the master cylinder and you know it's nice and clean, I would give the bore a careful hone and fit a new kit and reassemble it. Before you fit new seals check to make sure there are no pits or scale still in the bore. If so you may have to have a stainless steel sleeve fitted. That is what I had to do on my bike to both front and rear mastercylinders. Make sure you use a little rubber grease when you do, or some brake fluid.
Once you have done that you can bench test it. Fill the reservoir with brake fluid and then seal your thumb over the banjo end of the cykinder to keep pressure. Gently pump the master cylinder until you feel the pressure build behind your finger. Once you know the master cylinder is working ok and is kind of primed refit it to the bike and reconnect everything. Then go through your normal bleeding sequence.

Don't try to use your old seal in the master cylinder if it is scored or has failed you won't be able to resurrect it.