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1961Chevrolet c 10. replaced main reservoir with main reservoir off 1967 Chevrolet c 10. Did this to get power boost and safer master cylinder. Can't seem to get brakes to bleed. Does the engine need to be running to bleed? Seems to have me stumped. Thanks for help in advance.

explain in more detail what you did. did you install a power brake setup? is this a stock 67 setup and did you install a new mastercyl with it or the one that was with it. so what are you using for a clutch master?. why is the 67 a safer master cyl?
ron

Did you bench bleed the master cylinder before you installed it?

Yes I installed a power brake set up. the clutch master was split off, Captain fab bracket. Did not bleed the master. how hard is it to bleed and does it have to come out to bleed?

Like Ron said, more details are needed. How much of the system did you replace/overhaul? Dry system? 32vld already covered one question, bench bleeding the master cylinder? Using proper bleeding procedure (which may be different from the '61 procedure due the change in parts)? How are you bleeding the system? Pumping the pedal? Speed bleeders? Vacuum bleeding? Pressure bleeding? Have the system been checked for leaks? Brake shoes properly adjusted?
That said, if you have bench bleed the master cylinder, along with at least the line that would need changed to make the dual circuit system work, you have at least a 50% dry system. That is going to take longer to get all the air out, especially if you are manually bleeding the system. Without seeing just how the lines are routed, here's what I would suggest; With the engine off, rebleed the master cylinder. That can be done with it on the truck, no need to remove it, just disconnect the lines, install the bench bleed kit back up, and have a helper pump the pedal. Reconnect the lines and tighten until the are almost seated, then have the helper push the pedal down, then tighten the lines. Next, start at the wheel with the LONGEST line (you'll have to figure it out according to how the lines are routed), bleed that wheel first. Bleed it as many times as needed, checking the master cylinder after about every 3 times to make sure it is full, until no air comes out. Repeat on the next longest line until all 4 wheels are done. Check for pedal feel, both with the engine off and started, then go around them again bleeding at least 2-3 times per wheel. Recheck pedal feel again, bot with the engine off and started. That procedure should get you a good pedal.

with some of these changes you have to also check the pushrod length. are you using the orig p/rod or the one from the 67?
bleeding sequence on these trucks is l/rear, r/rear, r/front and l/front if it is plumbed in accordingly
ron

Thank all for the help. I said the new master was 1967, was a 1976 instead. Sorry about that. After trying to bleed by myself all the ways mentioned, found bench bleeding master seemed to do the trick. This site is the best tool in the shop. Thank each and everyone again...

Master cylinder needs to be bench bleed because all the air in the MC just gets pumped into the brake lines.

Many people do not make that connection mainly because, first the MC is not being replaced and second they associate bleeding the brakes as someone sitting in the car/truck pumping the pedal while someone else is underneath opening and closing the bleeder screws. Jeffrey

sitting in the car pumping the pedal was about the only way to bleed them a while back.
ron