I am currently building a bike for my wife and have run into a problem with the rear wheel. We want to put a coaster brake on it but we are having a problem with the rear spacing. We need a 175mm axle for the hub and I cannot find a prebuilt wheelset that has that. I have found some replacement axles that length and I am thinking of switching them out. I have never messed with anything involving hubs. Would I be opening a huge can of worms or can it be done relatively easy?

Shoul be easy. Just match the diameter and thread patch. For example rear = 10x1 etc. And you already know the other measurement, length.

Thread pitch wil lbe the catch here. Most coaster brake hubs I've dealt with were 3/8 x 24 tpi. Standard is 3/8 x 26.

What, exactly, are you trying to accomplish? Just a couple of thoughts.

It sounds to me like you are trying to retro fit a coaster brake onto a geared bike frame. Does it have horizontal dropouts? You are going to need them so that you'll be able to djust the chain tension. I'm also thinking that resetting the rear triangls spacing might be easier than rebuilding the rear hub.

So if I am looking to buy a solid axle specified as SOLID AXLE SET, 3/8''x26x175mm, 26 would be the thread pitch ?

https://www.biketoolsetc.com/index.cg...id=AP-3826175S

Correct.

Assuming the OP knows what he's doing the only reason I can think of is that his current axle was designed for 126/120 or something in that neighbourhood and fitting it onto a 130 frame would mean not enough axle length.

It is a geared bike frame. It has track ends so it can also be a single speed. The only brake mounts on the frame are for disc brakes. Which she doesn't want because she really wants a streamed line look for the bike. It could be run as a fixed gear but she doesn't feel comfortable with the stopping methods with those. I have found a few wheelsets that would work but they are quick release. You really can't get good chain tension with them as compared to bolt ons. I know it sounds goofy but if you have ridden a bike with a coaster brake lately they are fun.

You put one of the worst braking systems on the face of the planet on that bike FYI. And you're also wrong about the quick release on horizontal dropouts (I really doubt it has disc mounts, a derailleur tab AND track ends). Plenty of people run QR's with horizontal dropouts, either with gears or with fixed/ss with no problems.

High quality shimano QR helps immensely. Trying to save you from solving a problem which doesn't exist.