slipping seatpost

[glocal]

I have been riding my Brompton for six months. My seatpost has been slipping since the beginning but now the saddle sinks about an inch every 2 miles or so. Carrying bags and everything on my body I should be close to the 120 kg limit, but it still doesn't sound right. More recently I noticed white powdery residue on the seatpost, which probably suggests some plastic collar disintegrating because of the friction. More peculiarly, when I lift the folded bike from the saddle the post slips slightly in the other direction, and when I just wheel it the saddle rotates. All this probably suggests the quick release nut was simply not tightened properly in the first place, but before I over-tighten it, is any of this common?

 

[shouldbeinbed]

No it's not. Particularly if it slips up when picking the bike up.

There should be an element of resistance to the seatpost QR as opposed to having to force it closed and lever it open again.

Tighten it incrementally at least until you can pick the bike up without slippage and go from there.

For belt and braces you could take the seatpost out and thoroughly clean the surfaces and investigate the white residue. I've never had my post assembly apart but I don't think there is a shim or insert that could be disintegrating.

 

[raleighnut]

The 'white residue' is oxidised Aluminium, I'd also go for tightening the seatpost QR nut up a bit.

 

[TheDoctor]

I doubt it is oxidised aluminium on a Brommie. Don't they have a steel seat post?

 

[glocal]

OK, I tightened the nut. The QR lever feels firmer now and the saddle doesn't rotate. I think that should sort the problem. I will report back if it doesn't. Many thanks everyone.

 

[Kell]

There was a long thread on this a while back. My response in that thread was that I just roughened the surface of the seat post with some sandpaper - just enough so that it wasn't perfectly smooth, and only where it clamps in.

It sorted mine out immediately. But then mine was less than a week old at that point, surprised yours is still doing it after 6 months. Which suggests that, as mentioned above, the QR wasn't tight enough.

 

[Bill]

Try fitting a Jubilee clip fitted with a butterfly nut like I did! Works as well....

 

[Brommyboy]

When mine slips I degrease it. It is amazing how much road dirt collects on the seat post, and this can sometimes also affect the sleeve. Over-tightening the nut can deform the seat post.