Common Shimano freehub replacement (Y3A398020) found unfit for purpose

[recordacefromnew]

I think it has been for over a year now, that one of the most common freehubs sold by Shimano is different to the original it is supposed to replace, and therefore incompatible to many hubs it is supposed to fit. The freehub in question is Y3A398020 - it is standard replacement part for the FH-M510, FH-M525, FH-MC18, FH-C500, FH-C501, and it also (should) fit numerous other Shimano rear hubs because these hubs have the same drive side cone, seal/spacer and dust cap adjacent to the cone. These include the FH-M756, FH-M755, FH-M752, FH-M570, FH-M555, FH-A416 etc. etc.

What is the problem with the part? The difference between the part and the original it is meant to replace is shown in the photo below. Essentially the integral dustcap of the freehub of the “replacement” (lower) is c2.5mm proud compared to that of the original freehub (on a brand new Deore FH-M510 hub).

In practice that means, that the drive side dust cap on the axle on top of the cone, spacer and rubber seal will clash with the lip of the “replacement” freehub’s integral dustcap.

What to do? If you are very lucky, you might find that you have a spacer of suitable thickness above the dustcap (on top of the cone) that can be shifted to below the dustcap. Unfortunately, that spacer is not of standard thickness between hubs – it varies e.g. based on the position of the drive side hub flange. Consequently, afaict it is nearly always either too thin or too thick. If it is too thin then the clash will persist, and if the spacer is too thick the seal against grit and weather will be poor.

Any sure fire solutions? Apart from finding a “new old stock” replacement freehub, I suppose one can machine a spacer of correct thickness/diameters and introduce it just above the cone, and then thin out the outer spacer/locknut to retain the 5.5mm of exposed axle beyond the driveside locknut to maintain the rim’s centred position. M10 spacers of particular diameters and thicknesses are not easy to find, afaik.

I think it is a surprising cock-up by Shimano. Hopefully Madison / Shimano will do something about it.

[Brucey]

I see what you mean but IIRC it may be a question of using a socket as a drift to nudge the dustcap further into the freehub body; as supplied the part is correct for many hubs that don't have the overhanging metal shield, and wouldn't be if the dustcap were set further in from the word go...?

BTW I am v cheesed off with Madison right now; I recent ordered a DH-3N72 cone and the cost (for one flippin' cone for a £50 hub....) has nearly doubled in the last month, to £7.99.... Are they on drugs or something? The same part in German online stores is six euros, i.e. just over five quid; that is bad enough but £7.99 is just ridiculous....

cheers

[mattsccm]

I keep a box full of freehubs and parts thereof. I just mix and match until they work. There seem to be millions of minor variations but they all can be made to work perfectly.