can I use an old 126mm wheel on my new bike?

Bob Haase said:

diamondback that I'd really like to use on my new 9-speed Shimano.
I've read that I may be able to swap the freewheel body with a new
9-speed one.

Yes, if it's not a 7x DuraAce which features a different freehub.
Alternative is to install 8 cogs of a 9x cassette.

Quoted message said:

Can I use a shim (or a pair of shims) on my 126mm old hub (with a
new 9-speed freehub body)?

Yes, the axle is long enough to respace the hub to 130mm.

Quoted message said:

Also, if I use my old front wheel (126mm) on my new bike, do I
need to put some spacers inside the dropouts?

Front width is 100mm for quite some time already...what's your old
wheel's?

--
MfG/Best regards
helmut springer

Bob Haase said:

Hi,

I upgraded my bike from an old diamondback to a Trek 5200. I have a set of
tubular race wheels for my old (1991) 7-speed Shimano diamondback that I'd
really like to use on my new 9-speed Shimano. I've read that I may be able
to swap the freewheel body with a new 9-speed one. I've also read that you
shouldn't try to use a 130mm hub on a 126mm bike. what about going the
other way? Can I use a shim (or a pair of shims) on my 126mm old hub (with
a new 9-speed freehub body)?

Also, if I use my old front wheel (126mm) on my new bike, do I need to put
some spacers inside the dropouts?

You can put 8 of the 9 cogs onto the 7sp hub body. Add just 2 mm of
spacers to the non drive side of the hub. Put the wheel onto the
bicycle and either adjust the brake arch so that it is centered over
the rim or turn the spokes on the NDS about ½ turn each. Get a loose
cog cassette like a 105 or LX. The 2 mm spacer costs <$1.

Your front wheel is 100 mm spacing on both 7 and 9 sp wheels.