Why are M738 hubs different?

[Anthony]

Not having had an M738 before I assumed it was a standard mtb hub, but I've just received a wheel with an M738 and the axle is shorter than standard with the cones only 94mm apart instead of 100mm. I don't understand that. I know it's only 6mm less, but was it intended for some special kind of fork or were you supposed to force the fork legs closer together with the skewer?

On the other hand, the actual hub body itself looks just like an M737 and has the same flange spacing, so I'm wondering whether you can fit a standard axle/cones assembly to these hubs? (especially as the cones on this one are shot)

Just to complicate the issue even further, the Shimano drawings make it out to be a full half inch shorter than an M737, not just 6mm. Were there different variants of M738?

http://www.paul-lange.de/fileadmin/paul ... 738-94.PDF
http://www.paul-lange.de/fileadmin/paul ... 737-94.PDF

 

[LTS Biker]

The only thing I know is that the M738 is the suspension version of the M737.
Wider diameter so stiffer for suspension forks.

 

[one-eyed_jim]

The M738 should be a standard 100mm front hub with the fat aluminium axle that's common to the XTR HB-M950.

The 13mm discrepancy between the 737 and 738 axle lengths in the pdf files above is correct: it refers to the total length of the axle, not the physical over-locknut width of the hub. You'll note that both pdf files specify an OLN width (Gesamtlänge) of 100mm.

The steel axle of the 737 extends 4mm beyond the locknut into each dropout, giving a total width of 108mm. The 738 axle stops short of the full width of the dropouts. The locknut/endcaps increase the effective width to 100mm, and each endcap has an extension that locates in the dropout as the axle end of the 737 would.

I suspect your hub has incorrect end caps, missing spacers, or possibly undersized bearings.

Which version (if either) of part 4 from this diagram do you have?

http://bernd.sluka.de/Fahrrad/Shimano/T ... 8_1994.gif

 

[RockiMtn]

are you referring to the "gold" label m738 front hub? i was told it had a thicker axle for suspension or something like that. I recently got a wheelset with the m738 front and it fit fine compared to a m737.

 

[Anthony]

Ah, apologies, that'll teach me to take measurements late at night!

Reverting to the less silly part of my question, the oldest standard XT axle assembly I can find on Petra Cycles (which seems to use the Madison database) is Y25S 98010 off a HB-M760. It looks fairly similar, but do you know if it would fit?
http://www.paul-lange.de/fileadmin/paul ... B-M760.PDF
Or would an axle assembly scavenged off a lesser period hub be a better fit?

I'm assuming this cone is a write off, is it? I must confess I've never actually tried persevering with a cone like this, but it does seem a bit of a shame chucking this piece of aluminium art work (the other cone's surface is actually fine, although the outer casing is distorted as you can see).

 

[andrewl]

I'm assuming this cone is a write off, is it? I must confess I've never actually tried persevering with a cone like this, but it does seem a bit of a shame chucking this piece of aluminium art work (the other cone's surface is actually fine, although the outer casing is distorted as you can see).

I've run a cone like that for over 5 years now and it still runs amazingly smoothly, so while it may look bad it should be fine with some new grease.

 

[Anthony]

Would you believe it?

http://www.petracycles.co.uk/hbm738-con ... -5680.html