Cycling UK Forum

Hi,

I have an old bike with the standard setup of 12-28 but I would like to have a little closer spacing (maybe 13-24).
I have been Googling to see if I can just get a new block but, not surprisingly there are not many 7 speed blocks around !!

I saw an exploded diagram of the 3*7 that shows it uses separate splined sprockets "Power Glide", presumably Sachs/SRAM specific. They look identical apart from the smallest that has built-in spacer so I guess I only need to find the 'missing' sprockets and can shift the others around (with the spacers kept in the correct places ?)

Does anyone know where I can get these 7-speed sprockets ? Can I use "Power Glide 2" sprockets ? Can I use 8- or 9- speed sprockets ?

TIA, Simon

Earlier Sachs 3×7 hubs (now called Dual-Drive by Sram) used a special cassette with a dished biggest sprocket and no spacer between that and the rest of the sprockets, which were just the same as normal Sachs/Sram, or Shimano, or Sunrace etc. cassette sprockets.

Later models were redesigned to accept completely standard cassettes, so provided the back of yours is flat, you can use any Shimano-compatible 7-speed cassette (and if it aint, you can use all the rest of such a cassette except for the biggest sprocket and its spacer).

You cannot use an 8 or 9-speed cassette as it is, because the 7-speed freehub body will not be long enough for that many sprockets. But you could use individual sprockets extracted from such cassettes, or a cassette omitting the biggest sprocket or two and making up any difference between the overall width of the original cassette and what you now have, with sundry spacers fitted onto the body behind it.

If you want your alternative sprockets to index with a 7-speed shifter you'll need to put 7-speed spacers (3.2mm thick) between all the middling-to-big sprockets. You'll find that the smallest ones, which have integral spacing (plus perhaps a thin washer) are already spaced enough for 7-speed, even though they come off an 8 or 9-speed cassette.

Rose sell individual sprockets, so it is feasible to make up your own cassette to suit yourself.
http://www.rosebikes.co.uk/products/tec ... r_products

The sprockets come in defferent versions with code letters. Which you should use in any position will depend on what the adjacent sprockets are. If you get it wrong the shifting won't be as good as usual. Some googling is in order.

Hi Chris,

Thanks for the fast and detailed reply. (I thought the CTC Forum might be a good place to start with a question on "older" equipment !)

CJ wrote:Earlier Sachs 3×7 hubs (now called Dual-Drive by Sram) used a special cassette with a dished biggest sprocket and no spacer between that and the rest of the sprockets, which were just the same as normal Sachs/Sram, or Shimano, or Sunrace etc. cassette sprockets.

Later models were redesigned to accept completely standard cassettes, so provided the back of yours is flat, you can use any Shimano-compatible 7-speed cassette (and if it aint, you can use all the rest of such a cassette except for the biggest sprocket and its spacer).[/quote]

I guess I must be too cynical: I had assumed that Sachs/SRAM would not be compatible with Shimano !! So the cassettes and sprockets *are* compatible (assuming 7-speed), and also the spacing is the same (i.e. I can use the same dérailleur and shifter ?).

As I am home now I looked at the bike (a PDQ) and as far as I can see the largest sprocket has a flat back so I guess I am lucky and have a newer one. In that case I would just buy a new cassette (Eur 14 at Rose !) to save fiddling (and maybe quick swapping). I think the chain should be OK as it is very long (recumbent) and has relatively few summer miles on it (I have a different recumbent for commuting).

andrew_s wrote:Rose sell individual sprockets...

Thanks: as I live in Germany I have used Rose often but I had not realised till Chris's reply that I could use Shimano on a Sachs/SRAM hub !!

At the moment Rose have complete 7 speed cassettes in various sizes for only Eur 14, so I think I will just get a complete one to ensure compatibility !!
http://www.roseversand.com/products/tec ... ed/7-speed