So a while back I broke a spoke on my mtb, I replaced it and it seemed like no big deal. However, since then every 3 or four rides I get a broken spoke. I initially thought that maybe I didn't know what I was doing and took it to a shop and had them replace the spoke and true the wheel. The result is the same (broken spokes).

The spokes are breaking right at the nipple which means I've been having to junk them. I've also that they seem to be on the non-drive side with the disc brake. Finally, the rim has faint, small lines (possibly stress lines?) that run perpendicular to the edge of the rim. I showed these to a mechanic and he said to monitor them but not to worry too much.

I've heard some people suggest that when this happens you should think about rebuilding the wheel? Is this just a tensioning issue or is this something that I'm going to have to replace? It's putting a real hamper on my ability to go ride.

If it was mine,I would rebuild the wheel with new spokes.As far as the rim goes,depends on where the little lines are and if it's the front or back.If the lines are around the spoke hole,I'd put a new rim on also.If they are where the braking surface would be,I might run it if I was broke and it was the back wheel.I don't second guess with the front wheel,you could have a real bad day if it fails.Normally,I would put a rim and spokes on and call it a day.

Some times when you break a spoke others will follow unless the entire wheel is re-tensioned. Most shops will not spend the time needed.
HOWEVER, Faint hairline cracks at the spoke hole are IMHO cracks. Wheels and cracks do not go well. I bet it's where the spokes were replaced.
I think the rim is on it's way out and time for a new wheel.

Have another shop check the wheel and if I am correct then lose the other shop.

U need to relace the whole wheel with descent spokes.

That's what I think too.

1. I suspect that the spokes breaking at the nipple is the result of inadequate tension allowing the spokes to move back and forth as you go from powering the bike to brakeing.

2. A hairline crack is still a crack. Rims never heal themselves. The cracks can only get bigger.

If the wheel has a lot of miles and breaks a spoke then you will probably see an increasing number of broken spokes occur with some regularity. Best to relace the wheel with all new spokes and nipples. If you are seeing cracks check closely with a magnifying glass. Sometimes you can get a crazing of the anodization which may not be a problem. BUT if the cracks are around the spoke hole then go for a new rim...insurance. Medical bills from a crash are very costly. If you have gotten a lot of miles of hard riding with those wheels then retire the rims, spokes, and nipples...rebuild the hubs...check the cones for pitting and build up new wheels. I would go for a wheel with a stamped eyelet. This will takeup and distribute the spoke stress over a larger area and prevent stress risers and cracking.

I will check it out tomorrow morning and report back to you. Hopefully I'll be able to take some pictures of the lines that I'm reporting that will show them. They're not really around the nipple.

Having to replace the rim makes me cringe. Poor student and all. I actually haven't gotten what I think are decent number of miles out of the rims but the bike was crashed which I suspect is contributing to my problems.

Your breakage problem sounds like something I went through recently:

https://www.bikeforums.net/showthread...or-Explainable

Replacing the spokes, because I could do it myself, was the way to go in this case.

In your case, if the rim is even questionable, consider buying a new factory wheel. It'll be as cost effective or cheaper than building a wheel on an old hub and you'll have little reason to worry about future failure, especially if there's a chance that the hub design was contributing to the breakage.

One broken spoke could be a fluke.

Two broken spokes is marginal.

Three or more means it's time to replace all the spokes or the entire wheel, whichever makes more sense for your situation.

Riding stresses the spokes but not to the point where they break. But the greater the stress, the more you weaken a spoke. You increase stress if your spokes aren't adequately tight to begin with.

So this happens: you ride, thereby weakening your spokes. Then you ride again, with weaker spokes. At this point, the stress is too great for the newly weakened (fatigued) spokes.

Once your spokes are fatigued, replacing them one by one does no good.