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  1. What causes a bicycle tube to leak where the metal meets the rubber on a Schrader valve stem? I've had three tubes fail the same way over the past year. I make sure the stems are perpendicular to the rim. I'm not sure what else to check for.

  2. Does this joint have a name?

  3. Am I correct that there really isn't a good way to patch/fix this type of leak?

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    I don't know for certain, but the metal part of the valve extends all the way down to the tube itself; the rubber there is glued to the metal, so if it's leaking there the rubber has likely delaminated from the metal core.
    – DavidW
    Feb 12, 2023 at 20:51
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    So, poorly made tube?
    – Zack
    Feb 12, 2023 at 20:53
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    These 3 tubes that failed on you, all the same brand purchased at the same time? maybe try a different brand. Maybe also check the inside of the rim for any burs around the valve stem hole. Are you putting caps on your valves?
    – Hursey
    Feb 12, 2023 at 22:24
  • I don't remember about the brand. I suspect 2 were bought at the same time. I'll check the rim for burrs.
    – Zack
    Feb 13, 2023 at 14:05
  • could something about your pump be denting or pinching the stem in some way? maybe a burr inside your pump's head? you say this picture is for reference, so is this not your wheel? Could you put a larger, more detailed photo up for us to see?
    – bradly
    Feb 13, 2023 at 18:32

2 Answers 2

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It is unlikely that the leak is coming from that spot, as David said that is a solid tube of metal. You could be feeling air escaping there due to either a poorly seated/loose valve core, or sometimes your leak is from the tube, maybe a pinch flat, and the air is escaping from the gap between the stem and the rim which makes it seem like the stem is leaking. Do as Hursey suggests and inspect your rim, but also look for and feel (carefully) around the entire inside of the rim for jagged and sharp spots, also inspect the inside of the tire for sharp objects that could be puncturing your tubes. sometimes even wire fragments from the tire casing itself can break free and put a hole in your tube. If you have a valve core tool maybe check that its firmly seated.

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    A good trick is to wipe cotton balls on the inside of the tire. They will catch on even the smallest snag and eliminate the risk of cutting your finger.
    – Paul H
    Feb 13, 2023 at 1:24
  • The photo is just for reference. I put the tube in water and it is clearly leaking from that joint.
    – Zack
    Feb 13, 2023 at 14:07
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Do you have access to a valve stem tool?

Could be the valve itself was loose in the stem, and air coming out there could have felt similar to a leak up the sides between the brass and rubber of the stem itself.

If the valve hole in the rim is ragged at all, it can slowly cut a hole in the tube. Swarf from drilling can be removed with a file or even a strong knife/scraper. Ideally you want that transition to be "soft" Also its okay for the rim-tape inside to overlap the hole's edges some.

You can get other styles of tube that have more metal and less rubber in that part of the stem. Some brands like schwalbe are even threaded like presta valves and have a similar retention nut.


As for the existing tube - you could try inflating it to about 5 psi ("firmish") outside of the tyre, then dunk the whole area in a bucket or basin of clean water.

The leak will show itself in a stream of little bubbles. By rotating the tube you can identify the exact source. If the air is leaking between brass and rubber then epoxy might help, but may not adhere to the butyl rubber. Possibly wrapping the stem with a couple of loops of wire then twisting them off may help, but I'd test overnight before relying on such a fix.

Otherwise, replace with another brand of tube.

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