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Convert bike from 7 speed cassette to 8 speed cassette



 
 
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  #1  
Old November 26th 04, 01:54 AM
Russell Seaton
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Default Convert bike from 7 speed cassette to 8 speed cassette

I have a 1991 Shimano Deore DX rear hub. 7 speed cassette. I want to
convert the bike to 8 speed cassette. Will an 8 speed cassette fit
onto the same hub as a 7 speed cassette?

I know I will also have to get new 8 speed bar end shifters and a new
chain.
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  #2  
Old November 26th 04, 02:13 AM
James Thomson
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"Russell Seaton" wrote:

I have a 1991 Shimano Deore DX rear hub. 7 speed cassette. I
want to convert the bike to 8 speed cassette. Will an 8 speed
cassette fit onto the same hub as a 7 speed cassette?


I know I will also have to get new 8 speed bar end shifters and
a new chain.


An 8-speed cassette is a few mm broader than a 7-speed one, so you can't
put an 8-speed cassette on your current freehub. You would need to replace
the freehub body with an appropriate 8/9 speed model.

http://www.sheldonbrown.com/k7.html#transplant

Another option would be to make use of the fact that eight ninths of a
9-speed cassette will fit perfectly on a 7-speed freehub. You'll need
9-speed shifters of course. When the time comes to replace your rear hub,
you can then make the transition to 9-speed.

http://www.sheldonbrown.com/k7.html#up7

HTH

James Thomson


  #4  
Old November 26th 04, 04:39 PM
Qui si parla Campagnolo
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russel- I have a 1991 Shimano Deore DX rear hub. 7 speed cassette. I want
to
convert the bike to 8 speed cassette. Will an 8 speed cassette fit
onto the same hub as a 7 speed cassette? BRBR

I answer-yes it will. A LX or XT freehub from the early 90s, before 'parallax'.


Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
  #7  
Old November 27th 04, 10:13 AM
James Thomson
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"Paul Kopit" wrote:

You would need to put on a hub body, which costs $25-35.
You can get by with the existing axel if you can add 2 mm
of spacers to the non drive side of the hub and center the
axel between the axel nuts.


Since an 8/9 speed freehub body is wider than a 7-speed one, it's usually
necessary to remove some spacers to compensate for the extra width.

You'll need to redish the wheel slightly.


That hub will go into 126 mm spaced rear dropouts.


In 1991, the DX hub came in both 130mm and 135mm versions. The 135mm model
is the simpler conversion for two reasons. First, it has a broad spacer on
the left that can be removed to compensate for the wider freehub body.
Second, these hubs had slightly wider flange spacing than more modern hubs:
a 130mm 1991 DX hub with an 8-speed freehub body transplant ends up with a
very large left-right spoke tension disparity.

If the dropouts are already 130 mm, you can skip the fooling
with spacers.


If the dropouts are already 130mm, it probably makes sense to spread them
to 135 and respace the hub to suit.

I'd recommend that you get 9sp barend shifters and just 8 of 9 of the
9sp cassette cogs on the 7sp hub body.


That seems like the best plan to me.

James Thomson


  #8  
Old November 27th 04, 03:56 PM
Qui si parla Campagnolo
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rinwa- Hi Peter, I have a 1991 LX freehub (FH-M550)which came with a 7 speed
cassette. Are you saying that an 8 speed cassette will fit this hub
without changing the freehub body? That would be good news indeed!! BRBR

I answer-Nope, if you want a 8s cogset to fit, you need a taller, 8s freehub
body, of which there are many that will bolt right on.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
  #9  
Old November 27th 04, 03:58 PM
Qui si parla Campagnolo
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James writes- I'm not sure what Peter's saying, BRBR

After I wrote- yes it will. A LX or XT freehub from the early 90s,
before 'parallax'. BRBR


That is, replace the freehub with an 8s one from the early 90s..

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
  #10  
Old November 27th 04, 04:36 PM
g.daniels
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try harris cyclery-special order parts section. buy a 7 via nashbar
and add an extra gear. sheldon brown hasa chart for it!
 




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