Mchaz

So here's my conundrum. I have a vintage Reynold's 531 frame, and a forged aluminum seatpost. The seatpost does not want to stay where I put it. It will slip down until it hits the bracket for my tail-light. I know you might say, move the bracket down to keep the seatpost from slipping, but I would like to fix the problem legitimately. I have tried wiping the grease off as well as I could to no avail.

So what are some of your solutions to a slipping seatpost?

By the way, I tried a search and pretty much all of the threads had to do with slipping carbon posts.

Landgolier

are you sure the diameter is right? There are a lot of odd ones out there

late

There is a plumber's tool designed to burl pipe. It's an extreme solution, as the
tooth-like grooves will dig into the steel. But it does work.

CastIron

Scuff it up with a steel brush.

Mchaz

Yes. It is the original post. Though I have a theory that over the years the seatpost could have been ground down a little at a time, so now it is just slightly too small.

coelcanth

the quick and dirty way, without the special knurling tool, is just to rough it up with some coarse sandpaper

Grand Bois

knurling raises the surface and increases diameter. Brushes and sandpaper can only remove material. Roughing up the surface doesn't help much, in my experience.

I had a cheap Kalloy laprade seatpost that was a loose fit, even though it was the correct size. When I loosened the clamp, it would drop until it hit a water bottle bolt. The Control Tech I replaced it with is supposed to be the same size, but is a snug fit.

operator

Take a heneiken can, cut it out, wrap seatpost and reinsert. Enjoy.

iNewton

I heard bud light works as well, and it's cheaper.

You do have to drink it, though, so I'd go ahead and recommend heneiken as well.

Mchaz

Hmm, a shim, novel idea. Though getting my hands on either Heniken or Bud Light might prove to be somewhat of a difficulty. A can would be easy, but since I have to drink it, maybe not so much. However, I know some college guys that might get me some.

Anways, I'll keep the aluminum can shim in mind. I have tossed around the idea of trying another post, but this bike is all original. I don't know if I want to break that. Haha.

coelcanth

knurling can only remove material as well
but it also 'moves' it

it's the same idea with sandpaper
it raises the surface like the knurling tool but on a much smaller scale
in my experience it works quite well if the initial fit is not tooo loose
(forgo the grease too, in a pinch)

the knurling tool comes in handy in extreme or expensive last resort type cases, like increasing the fit on a fork crown seat rather than throw it out

a shim is sometimes useful when the seatpost is not the correct size,
but in this case it will probably be too thick
the seatpost is designed to be about .2mm smaller than the tube
i reckon a can will be around .4mm thick

no harm in experimenting

MrB

If you definitely want to keep stock and the can is too thick, you may want to get your hands on a set of feeler gauges. You can buy a really cheap(2-3$) set at a place like Harbor Freight I'm sure. I think Sears has a set for 6$ though. Or if you are like me and have blacklisted the new Sears tool departments, any automotive parts place will have them.

Grand Bois

Do you really believe that nonsense?
Knurling removes no material, it displaces it. Sanding does nothing but remove material.

coelcanth

wel you can stubbornly believe it's impossible
but i'll i sit on my seatpost.. cured from slipping because i scratched it wit some sandpaper

Al.canoe

I had the same problem with my Stumpjumper FSR. The original seatpost could no longer hold the saddle properly. The only Specialized replacement did not have enough set-back, nor did any after market post of the correct diameter. So I bought a smaller diameter seatpost with a sleeve. I could not keep the seatpost from slipping in the sleeve. So I clamped on one of those clamp-on water-bottle-cage attachemnts which I had for the original diamater seatpost. Now it never slips and the seat height is self adjusting when ever the post is removed.

Al

digger

I had that problem last year on my road bike that I had owned for 7 years up to that point. Never slipped until then.

The problem? Too much grease on the post, took the stuff off, never slips now. Yes, there is just enough there to prevent a rusted on post, I guess I had put too much on before....

operator

Bud light? WITCH!!

Mchaz

Well, to rule that problem out, yesterday I degreased the post and inside of the seat tube. I used denatured alcohol on a rag. There was only a slight sticky residue in the seat tube, but otherwise the grease was gone. It still slips, not nearly as bad as before, but it still slips. Argh. Time to start scouring Ebay for a cheap Thomson, or find a plumber with a knurling tool.

erader

get a different seat post. that's what i've done in the past. lightweight posts are especially notorious for slipping and sometimes creaking.

erader

Brian Ratliff

A third vote for the Al can shim, it doesn't have to be beer, I used a Mountain Dew can; works just as well. I had this problem on a brand new bike, cut a shim and problem is gone.

The problem with simply roughing up the seatpost is that, while it doesn't slip, it still isn't secure. The seatpost is supposed to fit tightly into the seat tube so that only a little clamping force is necessary to keep it from slipping and the seat tube doesn't deform. When you rough up the post to solve the problem, what happens is that you end up using a lot of clamping force over a small, pinched area and run the risk of putting a crack in your seat tube because the tube is now pinched and the seatpost is only held in by the very top of tube; the bottom is unsupported.

So, either cut a shim or get a new seatpost. Don't try to overtighten the seat post bolt.

roadfix

Some rubber cement worked for me. It created just enough friction for the seatpost to stay put.

Mchaz

Interesting. Did you apply grease surrounding the cemented area to prevent rust/corrosion?