Shimano freehub oddity

My rear hub was self-tightening while riding. Taking it apart i noticed that the freehub was loose. On removal I see that the freehub retaining bolt appears to have a bearing surface on it. It is the one on the left in the pic below. I've not seen one like that before. That bearing surface is knackered - the outer edge has totally worn away.

The freehub has no part number on it. It is off an Parallax XT M737 hub. Freehub is 7-speed and may be the original.

Are these bolts with a bearing surface available (can't find any). Can I replace it with a standard retaining bolt - the rest of the freehub looks similar (though shorter) than a more modern one? Or do I need to replace the freehub (cup surface looks ok)?

Any advice appreciated.

Just use the standard bolt as the one on the left doesn't look original and as M737 was 8speed IIRC the freehub may have been change so actually the bolt might be too big ? bolt it up if its ok you're good to go.

Thanks kingbling. I'll try that. The drive side cone needs replaced too so I'll need to see if i have one. Off for a dig through the boxes....

Sounds about right. Found a couple of links to exploded diagrams which don't suggest a bearing surface:

viewtopic.php?t=28643

Nice one Ian. Those exploded diagrams are very handy as there seem to be various non-standard bits and missing spacers too (might explain the self-tightening). By the way, the freewheel bolt requires a 3/8" allen key to remove. I thought the Shimano standard was 10mm? Maybe not the right bolt as you and kinbling suggest.

To be honest i can't entirely decide if that bearing surface actually belongs to the bolt. It looks pressed on. My initial thought was that it had been 'picked up' somehow but there's no mechanical carnage elsewhere so must always have been there.

Have you got a picture of everything ?

Here you go. The drive side has two outer 17mm hex nuts. Looks like there is a spacer/washer missing on that side and maybe wrong locknut?

Prior to the recent self-tightening issues I'd been running two years without problems. I had it apart for a grease and rebuilt it same way as it came apart about a year ago.

If it was self tightening the bearings in the freehub body have probably given up & the freehub body begins to oscillate rather than rotate. This then causes the interior of the freehub body to rub on the axle & retaining bolt, rolling the end of the bolt over. Should still be a 10mm hex for the Allen key but the rolled edge has made a lip reducing the space to get the Allen key in.

Are the bearing races still good in the hub body?

Ta Fettler. You're right - the bolt is actually 10mm and the tops of the internal splines were flattened off creating a lip internally (see pic - pointer showing flat top on spline). Top marks!

However, the freehub bearings feel very smooth and once bolted up to the hub there is no lateral play. It feels good.

I'm wondering if the worn drive side cone coupled with dodgy/poorly fitted lock nuts might have allowed the freehub to unwind itself, causing self-tightening? That said, peddling should presumably wind the retaining bolt it in, not out

I've not had chance to eye one up in the garage but from memory if you say the freehub was loose, I'm guessing it was the hollow retaining bolt that has worked it's way out. All has been goodish for a while as the bearing & cups will hold everything together until the retaining bolt starts to rub against the ball bearings creating a third contact point on the balls (not good) causing the friction/damage to the bolt head & causing the locking.

Micro destruction nanobots at large!