Spouse has a 1980s vintage hybrid with twist shifters. For some time now the front derailleur will not shift it to the big ring and the twist shifter will not make the click. If I tug the cable by hand it will not shift either. I messed with the limit screws (which I am an amateur at and I am easily confused about which screw does what) but it does not help.

If this is relevant, I do think that I may need to put a new cable in anyway because the cable is broken off at the anchor point so there is no ability to adjust cable length.

Start with the most simple. pedal and shift by pressing directly on the cable arm of the FD. Does it move smoothly? Does it move far enough? If not, what's holding it back. It's easy enough to figure out which limit does what by noting how far the FD moves in each direction, then tightening one two turns and seeing which direction is now restricted. (the other limits the other direction).

Note the limits don't actually move anything, they just determine the end of the range of motion in that direction. While the cable is off, adjust the inner limit so the chain stays on the inner (innermost of 3) chainring when you let go, and shifts to and stays on the outer chainring when you press and hold the arm. You might need to fine tune later, but you now have the FDs range within reason. Now attach a new cable, and adjust it's length so the lever positions correspond properly to the various FD positions.

Usually you need to pull out all the slack while on the innermost chainring, but this can be difficult so use a pencil or something similar to jam the FD about 1/8" out from the inner ring. Pull up the cable, tighten the pinch bolt, and remove the pencil and the FD should drop back with the cable fairly tight.

BTW- if your bike does not have a barrel adjuster on the lever or frame, buy an in-line adjuster and install it when fitting the new cable. That will make fine tuning the FD cable length much easier.

"I may need to put a new cable in anyway because the cable is broken off". Fix what you know is wrong before you go about further troubleshooting. Then follow this procedure from beginning to end without skipping any steps. https://www.parktool.com/blog/repair-...ur-adjustments If one of the steps does not seem to be going right, stop and figure out why before proceeding because each step depends on the preceding one. Tweaking limit screws without understanding what you are trying to acomplish is pointless.

I agree with this, but still suggest you do a bit of diagnostics as I posted earlier, so you at least know if you have a working FD. You'll definitely want a new cable, since you can't work with yours, and given the age, should replace the housing as well (Buy a kit, and you'll have the rear for when you need it).

And look for adjusters, and if there aren't any, buy an inline adjuster while you're buying then cables. Then you can follow any tutorial and correctly set the FD up from beginning to end.

From the smallest ring to the middle I can push it over but it pushes with difficulty. From the middle ring to the largest at first I could not move it at all. Pushing hard I can get it to move over to the big ring. Not smoothly. Not really far enough.

So how do I figure out what is holding it back?

I know I need to replace my cable and tomorrow I am making the 60 mile drive to the LBS for the cable and housing. If there is something else I might need I'd like to figure it out.

I did clean and oil the derailleur FWIW. My spouse is not good about keeping a clean bike.

Good idea folks on the barrel adjuster. I'll add one when I do this project.

Use your eyes, follow the two limit screws down and you'll see what they touch on he moving derailleur. Different derailleurs use different sop points, but whatever they use, you'll see it if you look in the right place (the opposite end of each limit screw).

You might better off removing the FD, and working it in your hands. That will let you see the limit screws in action, and make it easier to massage out any rust or grit that may be interfering with the normal action. When you've got it working, oil everything, let it soak in and continue working until the action is nice and smooth. Now clean it dry with a rag, and it'll be ready to install when you get the cable.

At that point follow any of the tutorials on the net. I always suggest reading/watching a few until you have a good sense of the job before actually starting.

I have other work to do on this bike and in the course of doing the work discovered that the big chain ring is actually bent. The crank is a one piece job. I am going to replace it too. This may be a significant part of the shifting problem.

I really cleaned up the derailleur. Installed the new crank. Installed new cable. Installed a new shifting mechanism. Now it shifts to the big ring just fine. I do have to set the limit screws. Ick. I'm no good at that.

You've gotten this far, the limit screws are child's play!

Be sure that the derailer is free to move far enough to allow the 3rd click when you upshift to the big ring.
The cage should not be free to move more than a nudge past that point.
The cable should be virtually taut when in the lowest gear before setting up the limit screws.
If the shifter has only 3 detented positions, the cable tension should first be set so that the cage almost touches the left side of the chain when the shifter and the chain are both in the middle of 3 positions.
The cage should also barely clear the right side of the chain when the shifters and chain are in the highest (hardest to pedal) positions in front and in back.

See how easy that was?

Yeah, it wasn't too bad but it still makes me nervous. I imagine dropped chains into spokes. I first followed instructions from one book and wasn't happy. (I also put on a new rear derailleur so lots of variables here). I then did the Park Tool book routine and am happy with the result.

It isn't my bike, it belongs to my spouse who is much taller than I am. Nevertheless, I took it for a ride and it shifted just fine. Here is what I did to his old steel frame Bianchi hybrid:

Replaced crank
replaced front brakes, cables and housing
replaced rear brake pads, springs, cables and housing
replaced freewheel
replaced rear derailleur, cable and housing
clean front derailleur
replaced front derailleur cable and housing
replaced shifters
replaced chain
replaced pedals
replaced bottle cage with another old bottle cage

I thought about repacking bearings but everything rolls smoothly so why mess with it. Plus, I don't have the tools to remove her bottom bracket

I broke a spoke taking off the freewheel. I paid to have it replaced and the wheel trued. That is my next thing I want to learn to do.

Other than changing out pedals, putting on new brake pads and replacing the chain, everything else was a first time job for me.

That is an impressive list of repairs/accomplishments. Great work.