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Bottom Brackets
This issue has the potential to be a real showstopper. This is where the French heritage really starts to be a problem. New parts are no longer available so you will need to upgrade. Find out how...

 

Bottom Bracket details
 
The bottom bracket is the cylindrical shell that hold the axle/spindle and bearing for the crank arms. It may surprise you to know that there are many different sizes. For full explanation see Sheldon Brown. The vast majority of modern bikes are "BSA" = British (1.37" x 24 threads per inch) with the right hand side (fixed) having LEFT HAND thread and a 68mm shell width (mountain bikes have a 70,mm shell width). The Peugeot being French is different. It has a different thread 35 mm X 1mm (25.4 tpi) and both sides are RIGHT HAND threaded. This means that the right hand cup is prone to come unscrewed. It has only happened once on my bike, but some people have regular problem with it. However this isn't the main problem. French BBs are long obsolete, so if your BB cups are worn out, then you can't get new ones. Neither are modern "cartridge" BBs readily available in French threading. Also many people (including me) have found that the threads are damaged anyway. If the cups are OK, it is just the spindle you need to change. These are getting harder to find although there is plenty of old stock still around. Measure your spindle length and try and get one of the same length. Remember that the original TA and Stronglight cranksets were ISO and the majority of replacement spindles are the Japanese JIS standard. This means your original crankset will sit approx 3mm further out than on the original axle so you can go for a slightly shorter one. The shell width is the "road" 68mm standard, but I have found some (not all) 68mm replacement spindles allow the cups to screw in slightly too far and there are not really enough threads to get the lock ring securely on with at least 1 thread protruding. I am not sure why this is, but it might be due to the design of the French cups. So, you might be better off getting an MTB standard 71mm replacement spindle. If it is too long, you can can place a Sturmey Archer sprocket spacer, which is exactly the right size, between the fixed cup and the bottom bracket shell.
Measuring spindles is a bit of a nightmare! Some are made symmetrical (the more modern ones) and some are asymmetrical i.e. the spindle is longer the chainset side (which is logical). The originals are asymmetrical, so if you buy a modern symmetrical spindle, you will need to get a longer one. This is exacerbated by the fact that the TA and Stronglight chainsets need to sit further out from the BB shell than modern ones, to avoid contacting the chainstay, so you need a very long exle by modern standards, particularly if you have a triple. I used a 5R 132mm (asymmetric) spindle for my TA triple, which worked out fine. By contrast a modern triple specifies 123mm. The best solution is if you can find a nice old fashioined bike shop which has a drawer full of spindles to try a couple to find out what fits best. At the time of writing SJS Cycles are selling off their old stock at £4.99 each, so its economical to order 2 or 3 and find which fits best. There are dimensioned drawings of each on their web site which helps. You can always sell off the unwanted ones on ebay!
 

How to fix it!
 
There are two "easy" solutions that I know of.
1. Velo Orange in the USA now make
French threaded cartridge BBs not cheap at $48 +P&P. I imported a pair of them to the UK and with shipping tax etc they came to well over £100 for the pair. They are vey nice quality items, but require a little fettling before they fit. The original French cups are quite shallow whereas the V-O ones are about 3mm deeper. The threading in the BB shells is only as deep as the original cups, so you need to remove about 3mm of thread from the inner end of the cups. This takes a couple of minutes or less on a bench mounted belt sander, but you can use a small hand file. Once this mod is done they fit just fine. PLEASE NOTE: The maximum length they have is 122mm, which is shorter than the 126mm that comes as standard. You might be able to use this with a double TA Cyclotouriste or Stonglight 49D chainset if you add a spacer. On the other hand 122mm works fine with a modern triple chainset.

2. SJS Cycles stock thePrestine "threadless" bottom bracket," which some Peugeot Tandemists are using, a little cheaper at £19.99. I have heard mixed reviews of these.

Obviously a tandem requires 2 bottom brackets, so that means double trouble. If it is just the front "Captain's" BB that you need to replace then I have found a simpler solution a
replacement eccentric which takes a standard British BB fits our bikes perfectly. This what I have on my bike and it's a plug-in replacement. I am told that other "generic" eccentrics fit too.

A permanent solution to consider, if you are have the bike repainted is to get a frame builder to fill the old threads with braze and re-tap the BB shells to standard British threads then you can use a standard cartridge BB. This is also the solution to adopt if you are considering moving away from "traditional" square drive cranks to one of the more modern systems.