What causes zippers to fail?

I have a nice cycling top with a semi-busted zip. It’s progressively gotten stiffer to zip up over the past few weeks but still does so, but now has started to fail by the two sides separating once it’s zipped up.

Thing is, there’s no obvious signs of damage, no broken or missing teeth. Anyone know what causes zips to fail like this, and are there any fixes that can be attempted?

I can get it repaired, but would run me approx 50% of the cost of a new top.

No explanation but here’s a possible fix.

Wear in the slider, and wear in the teeth. Sometimes you can squeeze the sides of the slider together a tiny bit to make up for the wear, but I’ve found it a temporary fix at best. I’ve seen repair kits that have a new slider, but it takes some seamstressing to replace it.

I know it’s frustrating as the dickens to have a piece of expensive gear in otherwise great condition that has a faulty zipper.

worn teeth don’t have the grippage.

It’s not so much worn teeth or sliders, but the webbing, aka tape, that the teeth are bonded to starts to break down and the teeth are able to squirm and squish around. There’s very little tooth-to-tooth engagement surface to begin with, so just a little movement of one tooth can be enough to break the chain, so to speak.

I have fixed several zippers by replacing the slider alone. You can get packs of new sliders in a variety of sizes at sewing stores and such, and no doubt online. It helps a lot that most zippers are made by one company.

Sometimes, this will fix the teeth coming apart problem, but the OP’s description is not encouraging. If the “pinch the sides together” trick doesn’t work even temporarily, there’s something else going on (e.g., just worn out).

Another “trick” is to rub some bar soap on the teeth if the slider is hard to pull.

Thanks - v helpful. Squeezing the slider with some pliers and lubricating the zip has got it back working. Does still feel pretty rough, so may only be temporary, but we’ll see.

I know here there are shops that specialize in repairs to outdoor clothing, including replacing zippers. The fix may not be cosmetically perfect in that you can see the stitching for the replaced zipper is new, but other wise you get a new zipper for a pretty reasonable cost.