I looked at a really old Schwinn 5 speed today. The seat post was one of the smallest I've seen.

The person was complaining that they tighten the seat, but with use, it comes loose. I haven't disassembled yet, but I'm thinking the teeth on the clamp may be worn.

I've never seen an alloy seatpost that size, so I think we would be stuck with the one they have.

Ideas to strengthen it?

I was thinking I could set the angle, then tig weld one half of the clamp adjustment, so that it couldn't move, say on the right side. The other side would still disassemble for installation.

Other ideas?

Oh, also, anybody know if the old Schwinn Messenger seats had standard rail spacing?

I gather you're talking about one of these


Buy some corundum in a fairly coarse grit, Mix into nail polish or other paint and coat one side of each clamp mating surface. Allow to cure and you've bought yourself another few years.

BTW- new ones are a few bucks and if you're lucky will come with the 1/8" thick curled insert for the 5/8" seat pin.

I've had good results freshening the knurled surfaces of saddle clamps with various methods. One like the pic FB posted, I'd disassemble, then touch up each groove with a Dremel and a cutting disc. If the surfaces are flat enough, I might try a metal cutting blade and a figure saw. Hacksaws leave a too wide groove.

Yep, that's the one.

I'll try to get to do some work on the bike in a couple of days and get a better idea of the condition, as well as taking some measurements.

Have you actually done the sandpaper idea? How well did it hold up?

Of course a new clamp would have the same weaknesses of the old one, but perhaps would be ok if tightened down properly.

Another option I was thinking. If the Inside diameter of a "modern" alloy post is similar to the outside diameter of the Schwinn post, then I could make a 6061 post that could be welded or epoxied inside of the alloy post.

As long as there are new saddle clamps with the right rail spacing to be had for little money, I wouldn't spend much effort on getting the old one to work.
If new clamps expect a bigger diameter seat post, it has to be easier to make a shim to line the clamp and make it fit the narrow post than to start making and grafting seat post stubs to things.

It might even be enough if you cannibalize a new clamp to get fresh teeth on half of the interfacing surfaces.

You could try making some washers out of coarse emery cloth to go between the serrated faces of the clamp.

Beat in deeper grooves with a Cold Chisel.

"If at First you don't Succeed, Try a Larger Hammer"

Not sandpaper but coarse SHARP biting grit, and it works fine if compressed between mating surfaces. The quality of the fit and size of the grit are key because it needs to be squashed tightly enough to be forced into both surfaces to do the job. But, yes, it can provide very strong hold.

Likewise a new clamp (if you can make or find a reducer). These depend on a "gear mesh" of the ridges, not some random fit. Once meshed and clamped they are very secure and can stay that way forever. They get a bad rap because people ride them loose, which allows movement and wear until the quality of engagement is totally compromised. Same issue as Sq. taper cranks, or using a sloppy wrench on hex nuts.

I suggest a new clamp because it's a cheap enough answer, but I suspect that the old one may not use a reducer you can transfer, so you'll need a 7/8" to 5/8" bushing (split) to use the original pin.