I know it says in the manual when changing a set of brake pads on the front of my FLHTCi that you should change all pads up front at the same time. How important is this issue? What could happen if I only changed the most worn set being the other set has quite a bit of wear left?

The reason to change all the pads at once is mostly because they all should wear at about the same rate. So if one is worn then the rest won't be far behind. It is best to change them out at the same time so they wear at the same and have the same amount of grab & life. Also to keep the calipers equally pressured.

If one side is wearing faster than the other - you might have a problem with the calipers not having equal pressure on the rotors - which is less braking efficiency.

The one thing you should never cheap out on is your safety. Skip something else and pony up and get all fresh pads. IMHO!!

Yeh, especially since I haul a camper along with having my wife on the back. I need all the stopping power I can get.
Thanks.

I've been thinking about what you said, that one side wears faster than the other...
I don't know but maybe you might need to bleed them and make sure you're getting all the same binding on both sides. Just a thought. Anyway, happy to help. Stay safe.

I'm gonna now be completely honest here. I did change out only one side. The difference in wear from one side to the other is very minimal. However just by changing out the worst side my breaking is a surging. I better understand what's going on now cause running off one master cylinder the pressure on the pads isn't the same as it should be. I will immediately be matching up both sides with two bran new sets & never do this test again.

Thanks for the help & info.

Surging can be a sign of warped/worn discs. Once you get the new pads in if it still is surging you can try to wear in the new pads by riding then for a mile. This will get everything hot so be careful. Once they get good and hot let them cool completely and then do a brake check. If they still surge you might need to get a set of discs. My bike does this once and a while but not really bad enough to be a problem. A little bit of surge might even be normal. IF it's a safety issue - don't mess around. It's always cheaper to buy parts for a bike than a hospital bill.

I"m thinking the unevenness that was causing some surging is slowly going away. It seems the surging is less and less every day, almost smooth again not quite there yet. I know my discs aren't warped because I put an indicator on them....only .005" difference.

Even if all continues to break in well, NEXT time I'm replacing BOTH sets up front at the same time so I don't have to go through such a break-in period.

Appreciate the help through this.

Yeah the break in I described was the fast way to do it. If the discs are straight then the only thing to do is ride it and enjoy it.
Happy to help a fellow rider.