I have a thru-crack on the driveside dropout near where it meets the chain stay. The bike is an early 1980's steel frame Trek mountain bike.

See pics.

Bike rides fine otherwise and I have invested a lot of love (and sweat) in cleaning it up...

If it can be welded simply and securely (at minimal cost), I will keep it -- otherwise I guess I have no choice but to throw it out.

(Note that I don't think Trek had a lifetime frame warranty in those days, plus I no longer have the receipt — it was a present from my parents).

chainstay crack

crack alt

  • 3
    A frame builder could replace the drop-out but on the other hand would it be worth the cost. Welding my not work because the drop-out is brazed and the heat from the weld will undo it.
    – Carel
    Commented Dec 18, 2019 at 8:27
  • 3
    Side thought - I suggest you have a good super close look at all welds on the frame. Specifically the other rear dropout in case its happening there too, but look at all welds with a bright light and a magnifying glass or similar. There may be horrors lurking elsewhere.
    – Criggie
    Commented Dec 18, 2019 at 12:43
  • TIG welding would probably be the best method of welding for this case. I believe it can be welded but as suggested by others you have to decide if the cost (it might be a bit less than 100$ that was charged for the cracked seat tube, since the seat tube is thinner material, round surface, harder to reach potentially and if it's on the top part of the seat tube it needs to be flat on the inside in order for the seat post to fit) is worth it for you. My guess is 50-70 USD should do it. Commented Dec 18, 2019 at 13:54
  • Have a professional replace it those parts are furnace brazed from what I've seen Commented Dec 19, 2019 at 3:48
  • @Criggie, this frame is brazed, not welded, but yes, worth an inspection 👍 Commented Dec 19, 2019 at 8:12

7 Answers 7


You need to consult in person with someone local to you who can make a qualified recommendation.

"It is Steel so can be welded" is mostly true, but there are always exceptions. A good welder will give you their professional advice. Don't bother asking someone with a stick welder in their garage.

I've personally just got a quote on welding a crack in a seat tube, and that came in at $100 NZ. The bike cost me half that to buy, but I can't replace the frame for anything like that.

When you do find someone local, prepare the frame by stripping everything off the bike. Everything that is not frame needs to be removed, and you should cover and protect all the threads/bearing surfaces with rags and tape.

Yes, I would remove the fork and headset, and the bottom bracket, leaving just Frame and Paint.

The only non-frame thing I might leave in there would be an old scrap axle bolted into the dropouts, to help keep everything in line and not getting extra-stressed while manhandled.

Also, clean the bike. Noone likes getting dirty, and your welder is more likely to agree if its not filthy.

If the welder suggests unbrazing and replacing the dropout instead of welding, then you should take that advice. They may suggest a sleeve or fishplate for strength — take that advice. Figure out if it will interfere with your chain/cassette or fitting of the rear wheel.

And lastly, if its not safe to fix, or if its super expensive, consider retiring the frame and put those costs toward another bike.

  • 1
    I don't see why he needs to remove the headset, but taking both wheels off and ideally the chain is probably a good idea just to make it easier to move the thing around.
    – user68014
    Commented Dec 18, 2019 at 14:24
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    I'm someone with a stick welder in my garage and 100% I could weld that back together in like 10 minutes.
    – jesse_b
    Commented Dec 18, 2019 at 14:28
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    @user68014: I can see the picture and I can tell you that is incorrect. That metal is probably closer to 8mm thick. A piece of heavy stock paper is about 0.8mm thick. The paint is probably closer to 0.8mm thick
    – jesse_b
    Commented Dec 18, 2019 at 16:54
  • 1
    Dropout thickness, counting both sides, ranges from 8mm for stamped steel dropouts to 20mm for aluminum dropouts.. You can stick weld steel as thin as 1.5mm
    – jesse_b
    Commented Dec 18, 2019 at 16:59
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    @Michael, having less weight on the bike as well as fewer things to manage while holding the bike in place is a good thing. They are likely going to have to reposition the piece to access all sides to weld. I've done some welding and the fewer complications the better. What I don't get is a welder having a problem getting dirty. Welding is messy/dirty work. Someone seeing a spotless welding area could make the mistake of not noticing it takes a lot of work to keep it that way. I can definitely understand not wanting flammable grease in the area, though. Commented Dec 18, 2019 at 18:59

A lifetime frame warranty may not require that you have the receipt.
Take it to a Trek dealer and see what they say.

Several of the shops I worked at did frame warranty work with no receipt.

  • 5
    Agreed, worst they could say is no. It seems very likely Trek could look up the serial number and see if they offered a lifetime warranty for that frame or not.
    – Weiwen Ng
    Commented Dec 18, 2019 at 17:16
  • Typically 'lifetime' refers to the expected life of the product. I looked it up and Trek's is actually based on the lifetime of the original owner. Subsequent owners get 3 years. Proving you are the original owner might be required.
    – JimmyJames
    Commented Dec 20, 2019 at 17:08

Yes I think it can be repaired as the failure is of the dropout itself which is quite thick steel (about 4 or 5mm).

It needs the paint removing an inch or so out, to be cleaned up, beveled and carefully TIG welded. I have repaired a very similar failure like this before although that was a little bit easier as the break was a bit further away from the end of the chainstay.

The chainstay is brazed into the dropout so we don't know for sure if it is a weldable alloy. But it probably is (it is most likely 4130 cromoly). If it's welded at the BB end that proves it is. There's therefore no harm in the repair tying in to the end of the chainstay a bit.

As Carel said there is a risk of the existing braze melting out and ruining your day as it's so close. But still worth a try I'd say.

Replacing the whole dropout is quite tricky because you'd need to find one the same size and then try and unbraze the existing one without damaging the ends of the stays. Or you could make a slightly bigger one so you can cut the stays back a bit. Either way you also need a jig or fixture to hold the dropout in the right place. All this would be quite a bit more work so probably would not be economical.

Having said all this I can't guarantee that whoever you take it to will want to have anything to do with it or how much he would charge. It wouldn't take more than about 20 minutes to do.


As a welder who has extensive experience with thin wall tubing. This could easily be welded with TIG. Depending on the metals just a little Beveling and alignment of the stay in a jig and you’ll be all set.

  • It's not whether that thin wall tubing is weldable-- often the whole bike is welded and the other end of that chainstay probably is. It's just whether you melt the braze out (because this end happens to have been brazed). But the heat with TIG is very focussed and I think it would be OK so long as one was careful not to cook it. As for alignment it's a little bit less critical with this style of dropout since the wheel has a big slot it can be moved around in, although obviously you'd want to get it as close as you can.
    – user68014
    Commented Dec 19, 2019 at 10:50

I'm a TIG welder.

The break is thru the drop out not the brazed joint The dropout could welded and re-brazed into the frame, but better to make or get a new dropout and braze that in. Best option is see a framebuilder in your area or cheaper option would be a engineering shop that does brazing and welding..


Yes, I would TIG weld it but insert a small piece of flat steel that would go into the tube and lay flat on the rear wheel yoke by about 25mm then weld all round.


I'm also a combination welder, MIG or TIG would be a good choice as long as the parent metals are throughly cleaned and free of paint and dirt. As for the inspection of all other welds the use of die penatrant and developer is the easiest and fastest way to check for cracks. I use this method or race car chassis's after drivers have had a hard impact.

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