Peugeot 531P weird expander-bolt seatpin: clamp grips and clamp bolts have broken. Any fix or replace advice.

Question

The frame cannot be adapted for standard pinch-bolt seatpins....26.4mm pin, anyway!

Answer 1

If the seatpost itself has broken, I suggest that you purchase a regular STEEL seatpost that fits correctly, then split the bottom of it with a hacksaw about 1 1/2" (40mm). Braze a washer on the top of the post, install a sufficiently long bolt through the washer and add a correctly sized binder nut that came from a quill stem. If necessary, before you split the seatpost you could cut it down to match the bolt. You will probably need to cannibalize a stem that has a 1 1/8" diameter. Peugeot, Kabuki, Bridgestone, Itoh all had these types of seatpin.

Tightening the bolt will pull the nut through the seatpin and expand it to secure in the frame.

You will need to also get a saddle clamp that will attach your saddle to the post... bike shops have all these parts.

Answer 2

Peugeot had some pretty stupid ideas over the years. One of my friends had a Peugeot like that. The seat-post itself went bad. NO expander bolt replacement seat-posts like that were available anywhere. As a temporary fix, he ended up setting the seat position where it would work for him and drilled a hole in the frame and seat-post and stuck a screw and nut through it to hold it in place. I didn't think very much of this fix, but he proved that it would work until he could "junk" the bike (which is what I meant by the temporary fix). Hey, what else could he do?