Rtmackeil

Hey All,

this is my first post. I recently bought a Peugeot St. Laurent in hopes of learning the ins and outs of bike mechanics. I intend to pull it all apart, clean and reuse (what’s worth reusing) crank and headset bearings.

I would like to update the shifters (currently original thumb shifter), cassette (currently 3x6 would like to maybe go 3x8?), and derailleurs to some more modern and smoother operating components.

I am intimidated by picking new components and making sure they are all compatible (I will likely need a new chain too).

Any advice on choosing components that will be compatible with each other? Also can I just take off the old cassette and put in a newer one with more gears without getting a whole new hub/free wheel assembly?

thanks I’m advance! I will try to take some pictures soon to make this process a little more gratifying for everyone involved (including myself)

Ross

Andrew R Stewart 

One of the early steps will be to discover all the interfacing dimensions that the new parts need to fit with. Tubing diameters, BB shell specs, rear drop out spread, Brake reach and mounting bolt/nut options. Seat post and stem specs. Rear der hanger tab specs.

Your Peugeot might have common English/ISO based fittings. Or be old enough to still have been French dimensions. Knowing which and what the specs are will go a long ways to reduce buying twice (after the first assumptions prove wrong) Andy

Rtmackeil

How do I go about getting these measurements? Calipers?

Bill Kapaun

Look at the fixed cup of the BB.
French is 35mm x 1mm and RH threading.
BSA is 1.375" x 24 TPI and is LH threaded.

IF French, it can be a real PITA can of worms with the odd threading. Else, it's a can of worms converting a 6 speed Free Wheel to an 8 speed Free Hub.
You have to cold set the stays for the increased width of the hub amongst others.
Freewheel or Cassette?

Best to look for an early 90's bike with the proper spacing.

Geepig

The first task is to take pictures of everything, then remove all the minor items and then begin to work toward the more difficult ones. This not only helps build confidence but also gives you a bit of time to notice stuff that we can often miss in the glow of a new purchase. I have rebuilt many bikes, but I am still surprised - only last week I discovered that some cranks do not need a puller, just a suitably sized bolt from my local DIY store. Anyway, the more that you remove, the easier it can be to work on.

Rtmackeil

sounds like a great start, thanks for the advice!

2old

Also, don't be surprised if some of the parts like headsets, bottom brackets (who knows) are reusable with a little cleaning/polishing and grease. I just put together a 1984 Schwinn for my granddaughter and was able to use every metal part from the original bike.

SJX426 

@Rtmackeil - So you have a 6x3? So your rear hub is likely a freewheel. Can you go to 8? Well yes but it is not advised as 8V rear freewheel configurations tend to bend axles. This implies a new rear hub or wheel. Then there is the issue of the spread between the drop outs. 6 V typically is 120 8speed needs 130. You can spread the frame but.... Do a google search on that topic.
8V chains are readily available. You should check that your chain rings will work, likely.
Picking an RD must include if it will span the the number of sprockets and will work with the largest you want.

Bottom line is that a lot of research and decision need to be make, including where are you going with this and to what benefit.

icemilkcoffee 

120mm was for 5 speed freewheels and occasionally 6 speed 'Ultra' freewheels (it's a 6sp freewheel designed to fit in the same space as a 5sp freewheel). Regular 6 speed freewheels typically went with 126mm drop outs. If the freewheel is a british threaded spin-on, you can replace it with a modern 7 speed freewheel with HG style cogs. If it's a Maillard type then you are out of luck.

But to the OP, the best way to learn about older bikes, is to read Sheldon Brown's website end to end:
https://www.sheldonbrown.com/

Rtmackeil

Your bottom line statement is valid, it may be that I end up just keeping it a 3x6. I see now to go 8 would be a little more involved than I care to go. As long as it shifts well and can handle the incredible amount of torque I’ll be putting on it 😏

Rtmackeil

Awesome! The external resource is much appreciated. I hadn’t realized all the nuances of different part sizes between makes/countries. It’s amazing how much I’ve already learned without yet getting my hands too dirty!

What a wonderful community this is, all the help and suggestions are much appreciated!

alcjphil

It is very likely that your Peugeot was built in Canada

Ironfish653

It looks like your Pug is an early 80's style 'ATB', so it's likely to have a lot of BSA/ISO standard parts, rather than the more isoteric French stuff. Depending on what kind of shape it's in, many of the ' greasy parts' like the BB, headset and even wheel hubs can be cleaned, repacked and put back into service.

Like it's been said above, converting to 8-sp indexed shifting might be more trouble than it's worth, unless you've already got a bunch of parts on hand.
If the derailleurs and shifters are in good shape, an easy bang-for-the-buck upgrade is a modern freewheel and chain; the ramps and bevels designed into the cogs and chain profiles that make SIS-indexed shifting work, also improves shifting performance with friction shifters and vintage derailleurs.
Shimano MF-TZ 6-sp freewheels are inexpensive and will fit the wheels and frame as-is. Any "8-speed" labeled chain will work; I like the KMC Z-series, as they're (also inexpensive, lol) and play well with the mix-n-match drivetrains you find on vintage bikes.