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Peugeot Seatpost Size/ Rehab(?)

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Peugeot Seatpost Size/ Rehab(?)

Old 08-31-18, 09:53 PM
  #1  
agnewton
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Peugeot Seatpost Size/ Rehab(?)

I've moved my 66cm Peugeot back to North America from NE Asia. Based on S/N and the badges/ decals on the bike, I am assuming that it is a 1978 UO-10. The saddle and seat post (along with the bike wheel set and drivetrain) were assembled for me back in 2010 by an older Japanese man who owned the LBS in Tsukuba-- I spoke no Japanese, so I had no input and paid a pretty generous foreigner tax for the completed bike but he did provide me with some '80s era Suntour derailleurs. When preparing the bike for shipping, I discovered that the seat post was "seized"; so the bike was packed as is and fingers were crossed. Aboard the container ship, something flattened one of the seat rails. The seat tube collar was a bit distorted from round toward the side of the flattened seat rail. I checked the seat tube and it's still straight and I also strung up the frame and that's straight, too. I've bought a replacement for the seat and extracted the seat post with a pipe wrench this week.

In pulling the seat post out, I discovered that the seat post bolt was bent, as it had been overtightened. The seat post I pulled out is marked 25.0mm and is "pinched" where the seat lug collar was overtightened in three separate locations on the seat post (no attempt will be made to assign blame for the over tightening-- I was a noob in a strange land and how common could French bike parts be in Japan). For a pound of flesh, I bought a replacement seat post bolt on eBay. I've now got the seat lug collar "opened" enough to pass the new (straight) bolt through with just a final, gentle tap, but I realize that any measurement of the seat post opening will be exactly whatever I open it up to. The "roundness" of the seat tube opening is also much improved.

I'd like to replace the seat post with the correct size (best practice), but I can't figure out what that may be. Previous threads on the forum (see below; add prefix www.bikeforums.net/classic-vintage/ to URLs) give three different diameters: 24.0, 25.0, 25.4mm; the Sheldon Brown database says 25.5mm for 70s Peugeot UO-8s (w/o shim). The bike frame is "Peugeot Lightweight Tubing" according to the specs on bikeboompeugeot.com and the bike has the decal "Cadre Allege" on the frame (I think that may be French for "gas pipe"). I measured the O.D. for the seat tube, it's 128.14mm. I can eliminate the 24.0mm size from consideration, but that still leaves the two other possibilities. With the seat lug collar still a bit compromised, it's a bottleneck to checking the fit of either the 25.0 or 25.4 mm seat posts. The tubing seems to be the same as the UO-8 and UO-9 from that year. Does anyone have any experience with Peugeots of that vintage ('78) or can anyone provide any guidance on how to determine the correct size other than buy both post sizes and see which fits?

Thanks for reading and thanks to previous forum participants for sharing their knowledge.

Old Posts on Peugeot seat posts (sorry no links until 10 posts):
793602-24mm-peugeot-seat-post.html
352534-peugeot-seatpost-database.html
472048-peugeot-seat-post-odd-size.html
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Old 09-01-18, 10:29 AM
  #2  
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You need a caliper that can measure inside the seat tube, agnewton. The “Cadre Allege” (“light frame”) tubing can have some differences, so you can’t assume that all of those seat tubes take the same post size.

That said, my mid-70s AO-8 took a 25.5 mm post without the shim. That was unobtainable, so I used a 25.4 post with a thin aluminum shim along half the diameter. If I were to build it up again, I probably would let a machinist turn down a 25.6 post so I would not need a shim.

There are a lot of fans of the 70s Peugeots here. The bikes ride exceptionally well, and having tubes that are a bit heavier is no issue at all.
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Old 09-01-18, 10:48 PM
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Thank you for your reply Aubergine. Sorry, I didn't mean to malign the Peugeot lightweight tubing. I just thought it might help to identify the seat post diameter. I have seen many riders comment favorably on the old Peugeots and I'm grateful for what I've got.

I was a bit distracted by the thought that vernier calipers and any tapered rod to measure the seat post diameter would be off. You're definitely right about the tool. A pair of inside calipers were acquired this afternoon at the hardware store. The average I.D. for the seat post from ten measurements was 25.65 +/- 0.13mm. So, it seems the extracted post (25.0mm diameter) was definitely too small and maybe was the reason for the overtightened/ bent seat tube bolt(?). The 25.5mm size seems to be within the tolerance and the best potential fit. Thanks for laying out the two options for acquiring this unique size. I'm a bit impatient to get my bike back on the road, so I guess I'll shim the smaller post for now and look into having a post machined down this winter. Thanks again.
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Old 10-17-18, 07:59 PM
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Thanks again for your reply Aubergine. I got the seat tube collar opened up to the right size and the new seat post installed. I added a Stronglight 93 crankset, some Lyotard pedals, and the correctly threaded adjustable BB cup (French). My UO-10 is on the way to recovering its French-ness. Next task, a set of 70s era French derailleurs.
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Old 10-17-18, 10:17 PM
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Very nice! I use a Huret DuoPar rear derailleur on my AO-8, and the Huret front derailleurs also work well. But a Simplex pairing would be more in character for Peugeots of that vintage, I admit.
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Old 10-18-18, 04:11 AM
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Originally Posted by agnewton View Post
Sorry, I didn't mean to malign the Peugeot lightweight tubing. I just thought it might help to identify the seat post diameter. I have seen many riders comment favorably on the old Peugeots and I'm grateful for what I've got.
Nothing wrong with your UO-10. From the catalog specs, it was the top-of-the-line "Peugeot Lightweight Tubing" or Cadre Allege tubing model, just below the 531c frame models. The difference between yours and the low-end models, even though the frame materials are the same, was in having an alloy wheelset, and a higher level of components. It should end up as a very nice rider.
https://www.bikeboompeugeot.com/Broc...RN10E_UO10.jpg
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Old 10-18-18, 05:26 PM
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I do still have the Simplex D/T shifters, so I agree, the Simplex derailleur set would be consistent. I've read some of the thread that started 10 yrs ago on a Simplex v. Huret theme and it seems to boil down to personal preference. The delrin parts on the Simplex derailleur are often mentioned as a disadvantage, but I guess I'll only know if I give it a try. The Suntour Honor on the rear and the Suntour Ole on the front provide smooth and sturdy shifting for now.

I've downloaded the '78 Peugeot catalog from the bikeboompeugeot site. It's what I used to help ID the bike as a UO-10 (D/T shifters and the decals). I'm using the spec table to figure out where it started and looking to replace things at a level slightly above the original. I think the original frame already included one upgrade-- the handlebar is "Guidon Phillipe; Atax Franco Italia D352", so I am assuming that those are the "Atax 'Phillipe'" bars in the table.
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Old 10-19-18, 03:26 AM
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Originally Posted by agnewton View Post
I do still have the Simplex D/T shifters, so I agree, the Simplex derailleur set would be consistent. I've read some of the thread that started 10 yrs ago on a Simplex v. Huret theme and it seems to boil down to personal preference. The delrin parts on the Simplex derailleur are often mentioned as a disadvantage, but I guess I'll only know if I give it a try. The Suntour Honor on the rear and the Suntour Ole on the front provide smooth and sturdy shifting for now.
The Delrin is more of an issue with the front derailleur, which cracks when it is overtightened on the seat tube. Being a rod-operated derailleur, also, it does not work as well as a modern front derailleur with a parallelogram. The rear derailleur on the other hand works quite well.
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Old 10-19-18, 08:35 AM
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...just as a point of information, it's not a big deal to take down an alloy seat post with sandpaper by the amounts you are talking about in this thread.
You mark an approximate height line, and then sand down the part below that, checking every so often for fit so you don't go too far. You can polish the results with finer grades if you are so inclined. Just go slowly, check fit often, and exercise some caution and restraint. Machining gives a nice result, but many people are reluctant to go to that much trouble.

Seat post size on older bicycles is one of those black arts things.

Just one man's experience, but your bicycle will shift better and work longer if you leave those Suntour pieces on there. If it helps you to rationalize, Motobecane started using Asian derailleurs long before the other two big French manufacturers, and no body I know has ever questioned the Frenchness of any of my Motobecane bicycles.

Last edited by 3alarmer; 10-19-18 at 08:40 AM.
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Old 10-20-18, 03:48 PM
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My 1980 UO 10 used a 24mm seatpost.

https://www.bikeforums.net/17163738-post2072.html
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Old 10-21-18, 01:43 AM
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Originally Posted by Rocky Gravol View Post
My 1980 UO 10 used a 24mm seatpost.

What came in the post for you today?
Did your seatpost come with a shim? I have a few French bikes that came with 24 mm posts, and they all had a shim between the post and the seat tube.
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Old 10-23-18, 08:04 AM
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Originally Posted by 3alarmer View Post
...just as a point of information, it's not a big deal to take down an alloy seat post with sandpaper by the amounts you are talking about in this thread.
Seat post size on older bicycles is one of those black arts things.

Just one man's experience, but your bicycle will shift better and work longer if you leave those Suntour pieces on there. If it helps you to rationalize, Motobecane started using Asian derailleurs long before the other two big French manufacturers, and no body I know has ever questioned the Frenchness of any of my Motobecane bicycles.
Thanks for the points of information. Machining the seat post down is outside my skill set (and toolbox) right now, but sanding should be OK for future bikes.

I haven't had a bike with non-index shifting since the pre-index era, but I have been pleased with the smoothness of these Suntour derailleurs-- no complaints at all and a very solid reputation, too. My search for a French set is a self-imposed constraint (irrationalized?) as I have a parallel project bike in a '73 Fuji S10 that I'm constraining to Japanese-ness in my build/ cleanup. Admittedly, these may just be a noble experiments, but with the derailleurs I'll get a chance to compare the SunTour derailleurs to their contemporaries.
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