hi all

I have a bit of a perplexing problem and would appreciate your insights-
I have an old peugeot (i think uo8) frame which I've built up with modern (duraace 10 speed) running gear.

I bough a 1in aluminium seatpost which was a very snug fit into the frame, but the problem is that even with the seat-tube bolt cranked VERY tight, I can still move the post side to side (rotational). Strangely, it takes my weight and doesn't drop down at all during a ride, but can be easily moved side to side.

the bolt wont go any tighter and the slot in the seattube is completely closed. i did put some grease on the post- was that a mistake??

any thoughts?


poggor

poggor - When you say it is a 1” post is that then marked as a 25.4 mm? I know French frames used smaller than the 27.2 standard seatposts but you might want to search some for the correct size for your Peugeot. It must be in the 26.** mm range. That slot closing up, the bolt fully tightened and the side to side movement are all clues that you have correctly identified as not OK.

Continuing to run it as-is, even though it isn’t slipping down is not advised as you probably anticipated folks wold say. With my luck, if it were my bike set up like that, I would hit a bump and it would slide down 2” gouging itself all the way down, then the seatpost bolt would snap off and leave half of the broken bolt stuck in the frame. There were some nice 26.4 and 26.6mm Shimano Deore XT seatposts sold through eBay and a vintage parts guy in Colorado, but first - knowing the correct size.

Thanks a lot for this Masi. yes its 25.4mm. It's just strange because I measure the seat-tube ID with calipers prior to purchase and the seatpost is definitely snug- quite hard to get it in the tube even with bolt out. I'm not sure a 26.4mm post will fit but it's the obvious thing to try- I'll get one!

poggor

-----

the U08 model did not have a constant internal diameter seat tube

it is larger up at the top, i.e. counterbored

this is because a thick shim was employed by the manufacturer which was about 25mm or so in length/height

the OEM saddle pillar was a constant diameter 22.0mm (un stepped)

it may be necessary to ream and go to a larger diameter pillar in order to solve the wobble symptom...

-----

I went to look for my spacer to measure it, but alas I have lost it.....but I did measure my seatpost on my AO-8 and its 25.4mm; my frame is older with Aztec lugs so YMMV. The slot is not completely closed up and the post is an SR LaPrade.

Oh, and to juvela 's comment, the original seat post was indeed not stepped and I suffered the dreaded seat slip due to the missing step....luckily no injury but there was a circular dent in the bottom of the leather as the saddle bottomed on the top of the seat post.

You could cheaply solve your problem with a pair of scissors and a nice cold can of beer.
Also, I have a question about your 10 speed setup. I see that you're running an older Dura-Ace crankset. Do you have problems with the narrow chain dropping between the chainrings? I've been wanting to go up to 10 speed, but I'm not sure if I should buy a new crankset.

krakhaus

I have been considering the aluminium can shim- it may come to that. I have a lathe so turning down an oversized seatpost is also a (possibly more elegant) solution.
regarding the build-

crank is DA 7400 which I wanted for the square taper bottom bracket and for the overall slightly retro look. I also wondered about the 10sp/9 sp thing but it's fine. shifts normally from big to small chainring.
overall the setup is very smooth and the indexing is spot on.

Right on. Yeah, the lathe sounds like the way to go. And thank you, that helps a lot.