Bleed clutch with master cylinder cap on or off?

I'm planning on replacing my master cylinder today. I've got no pedal pressure, the slave cylinder was replaced recently, and I don't see any leaks on the line. Does the cap on the master cylinder need to be off when I bleed the system? I was thinking about when you hold your thumb on top of a drinking straw.

The cap can be on or off on the bleed process.If your having issues still after bleeding with the clutch not working correctly you might want to replace the master cylinder for the clutch itself.Keep in mind the 2 hydraulic hoses for the clutch slave could be deteriorated and or collapsing internally and causing the problem as well.Both hoses are at the firewall area and available from various auto stores and rock auto.In short my clutch master leaked at the rubber orings for the res,but cost wise cheaper to just replace the whole unit over buying the orings and yet still have to bleed the system.Just way to much rambling from me with over info.

Cap on or off doesn't matter, should have a small bleed hole in it anyway.

Bench-bleed the clutch master before installation. Then bleed out ALL the old fluid so that only new fluid is in there.

87 & Cusser, thanks very much. I'm trying to bench bleed it but I'm doing something wrong. I've been attempting to research bench bleeding for the last hour online but I'm still not sure how to do it.

This video seemed the most understandable to me although he didn't start from the beginning:
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I put the mc in a vise, filled the reservoir and connected a tube from the exit hole to the reservoir.

Where is the plunger? Is it in there and needs to be pulled out somehow?

I've also got to get a better connection for the tube. I just got done with biking to town and back to the auto parts store for wrenches, and didn't want to do it again to get a bleeder kit. I drilled a hole in the grommet that came with the mc and stuck some aquarium tubing in it, but it looks like fluid is already oozing from under the grommet.

That looks pretty good. Use a #2 Phillips screwdriver as the "push rod" in the recess of the MC plunger, and press the plunger of the clutch master cylinder slowly in. You should see air bubbles in the plastic bleed tube. Now, when you release that screwdriver, fluid should be sucked back in through the tube instead of air. Keep doing this a few times until it's all or mostly fluid being pumped out and sucked back in. That's bench-bleeding.

I clicked on that video link, but all I heard was his words.

Re-post if you have issues, I'll be home tonight.

Cool, thanks! I think I did it.

On the truck, I mangled the bolt connecting the line to the mc while undoing it. I thought I'd be able to replace the bolt, but the line has that little flare at the end of it, so the bolt won't slip over. Is the only way to replace the whole line?

I'd replace the entire line, not that long, and not that expensive. The trick is to use a metric flare wrench for initial loosening and final tightening, important. And the other trick is to get it threaded in several turns by hand, so when one loosens/removes the fitting, leave the tubing there, has to line up exactly or will cross-thread.

If you can still thread that in, I'd try open end, flare wrench, or vise-grips to tighten it.

If you do go "universal metric brake/clutch flare" tubing, longer piece is OK, just coil it around a jar so it doesn't kink. The ends are flared, that's what makes the seal, not the nut.

F**k yeah! Got pressure back and she's rollen. I will look up the lines tonight when I get back. Thanks so much for the help, really.

Just a little follow-up to this. I drove to work patting myself on the back for getting the truck going again. When I arrived, I noticed a gasoline smell and looked under the truck to discover gas on the side of the tank. I happened to be close by a mechanic friend's house, and took the truck over there. Fuel was spewing out when I started the truck. We dropped the tank. It turned out one of the metal lines on the sender had a hole in it. I haven't been really able to deal with the truck the last couple of weeks but now am going to order a new fuel sender. Hopefully my friend will have time soon to work on it. It's funny how right on cue the next issue surfaced. Fortunately it happened at the right place as well as not sooner. Today I put something in the bed of the truck and the handle of the lift gate broke. Aye ay aye. I guess she's just asking for some TLC.

I see you've got a fuel sender thread, nice. Checking it out.