Choosing new components for a retro MTB project

[Cleatus]

I am fairly new to all of this. I recently picked up an old Trek 850 which I stripped and rebuilt replacing most of the consumables and got it back out on the road. I have now bought not one but two specialized Hardrocks. One 1991 pink hardrock that is mueseum condition and an knocked about 92 (I think) version.

I am going to start taking apart the knocked about one first and hope to rebuild but this time with new compenents. What do I need to consider to entirely swap out the drive train? I am happy to purchase second hand or buy from new but just need an idea of where to start.

I am sorry if this is a simple question.

Thanks for your help.

 

[CassidyAce]

Re:

The first thing you need to consider is what you want from the finished result. Is it just replacing, say, an old 21 speed system with a new one? Are you aiming to lower the weight of the bike? Do you want higher gearing for higher speed? What you want from the bike determines the components you look for. After that, compatibility is the key - both with the bike and the other components you choose. And after that, you look for colours - basically, silver or black - to suit the look you want. Last but not least, there's your budget.

What is it that you do want from the bike?

 

[Cleatus]

I need a range of gears. Something that can handle hills but still go to the higher gears on the road. I have a Kona Sutra and am happy with a bike that has versatility. I will be likely replacing and old 21 speed for a new one. Particularly on the beat up hardrock as it has a mixture of parts on there (I think just to get it sold) and they just don't work well together.

How do I work out what is compatible? I suppose that's the key question. If I can narrow my options down to what I can get on there then I can decide what I want.

Budget is not a big deal. Obviously I won't be spending the big bucks for an old bike but will scale up or down the budget depending on what's available.

 

[CassidyAce]

Re:

Because it's old and beaten up, you might want to look for good condition used parts. However, if you want to buy new (or used for that matter) there are some things to remember, including:

1) The crankset determines the bottom bracket spindle length so choose a crankset and then choose a bottom bracket of the right length.
2) Shimano use a 2:1 actuation ratio for their shifters/derailleurs; SRAM use 1:1 (except on a few parts designed to be Shimano compatible) so, in general, Shimano shifters are not compatible with SRAM rear mechs and SRAM shifters are not compatible with Shimano rear mechs.
3) V brake levers are not designed to be used with cantilever brakes and vice versa.

Aside from those considerations, just look for parts labelled as 7 speed or 21 speed. However, 8 or 9 speed cranksets can be used with a 7 speed system. (But front mechs labelled as 9 speed can be a pain on a 7 speed system: the narrower cage means chain rub is more likely.)

FWIW, if I were you, I would avoid SRAM X3 and Shimano Tourney: too cheap and nasty. Modern Shimano Altus is solid and functional, though. However, good condition, used STX or LX might offer a better price-quality ratio and suit the bike better.

Edit: I forgot to mention, your seat tube is probably 28.6 mm in diameter; if you get a brand new front derailleur, it will probably be designed to fit a wider diameter seat tube and you will need a shim/adaptor thingummy to make it fit. First step: measure the diameter of your seat tube.

 

[ishaw]

Re:

My advice is decide what you want the end result to be and go from there. Are you looking to build a catalogue spec garage queen, a period correct rider, a functional bike, or even a retro mod (old bike, newer parts).

Once that decision is made, you can start your search for parts.

As mentioned above, picking parts is not always that simple, certain things need to be the right size for your frame, such as headset, bottom bracket shell width, seat post, stem etc. Some parts need to work together, such as bb spindle length (and type of axle) and crank.

Cassette range is personal choice, as is number of cogs, but depending on hubs, you might not be able to fit say a 9 speed cassette on older hubs designed for 7 speed.

Mixing sram and shimano gearing (aside from cassette) doesn't work.

Sounds daunting and a lot to think about, but it's pretty simple once you get your head around it.

If in doubt, ask on here, plenty of helpful folk will be willing to help, advise and sell you what you need.

Good luck.

 

[legrandefromage]

A lot of original parts can be recycled

older Shimano 7spd mechs will happily shift 9spd

older 7spd wheels can have their freewheels replaced so they can be redished and used with 8/9 or even 10spd cassettes

older front mechs are a little more tricky to mate up with later shift systems but it can be done

there are plenty of very wide range cassettes available too

just one example https://www.ebay.co.uk/itm/SR-MTB-BIKE- ... mbjghiIyiA