Cracked hub seal ring—will it be a problem?

Question

I just bought a mid-quality used wheelset for an excellent price, which came with the caveat that one of the seal rings on the front hub is cracked (see following images for context). The wheels are Shimano RX31. Is it okay to just leave it as is? Long-term, is the crack going to lead to water intrusion or damage the underlying rubber seal? I don't think a new axle unit would be expensive at all, but finding one would be a challenge. I'm just wondering whether it's worthwhile trying to find one.

(If the hub looks suspiciously oily, it's because I regreased the bearings right before discovering the crack and taking the photos.)

It is part #8 in the following image:

Answer 1

That seal does do work; the labyrinth seal concept will function much worse with it cracked like that. Water and grit will have a much easier path in.

This question has the nuance that the answer really depends on whether you would ever consider putting on a new rim when this one eventually meets its end. Most people wouldn't for the hub on a midrange Shimano prefab wheel, although there's nothing intrinsically unreasonable about it and in some cases (this is probably one of them) it's doable without jumping through too many technical hoops. The main one would be deciding whether to re-use the spokes and track down a replacement 24h rim that happens to be the exact right ERD, or finding a rim you want that matches with available Shimano spokes with the same head design, or making the determination that you don't mind using generic straightpull heads, which would then allow you to use whatever rim you want. I believe the nipples and rim hole on this wheel are standard or close to it.

If this were one of the standalone Dura-ace, Ultegra, or 105 hubs with similar contactless labyrinth seals and you wanted the hub to last through the highest number of rims possible, yes it would matter. If the goal is making it through just this one rim, and you're the type to even think about overhauling it when it doesn't feel so hot, it almost certainly doesn't matter. Maybe you wind up having to overhaul it a time or two more than you would otherwise. It does depend on your habits and climate; if you're riding in constant wet weather, it could be somewhat worse than that.

Answer 2

The rubberised seal obviously provides some degree of protection. Initially I was going to say "probably not a problem unless you ride in very wet weather" but it will also help to prevent the grease becoming soiled by dust etc, so it serves some function in a dry climate too.

It is hardly a deal breaker: the wheels could run for thousands of miles with the seal in that condition if you maintain them.

It is a shimano hub though, and there are plenty of those out in the world with a similar design, so you may eventually get the opportunity to salvage one from a scrap hub/wheel or even get a good deal on a new or used, similar shimano hub that you can cannibalise for parts, if that's preferable to asking a shimano dealer to order the part number in for you. I doubt you will find the part by doing a web search as it's not generally a stock item/big seller for most retailers even where they have access.

Answer 3

For me, if finding or making a replacement seal ring is not possible, the broken seal ring would be a dealbreaker.

The reason is that I expect my hubs to run for long durations with no maintenance required. I'm happy if I have worn 5-10 chains and 10-20 sets of brake pads and my hubs are still running strong. I would expect a hub with a cracked seal ring to require regreasing maintenance as often as you change your front brake pads (assuming disc brakes here, good rim brake pads in dry weather last practically forever; the hub looks like a disc brake hub so perhaps my assumption is good).

There's a reason why modern cars don't require regreasing anymore. Putting fresh grease in constantly to get dirty grease out wasn't a good tactic, far better was to seal the components in a car to never require regreasing. A bike with a broken seal ring in a hub would require constant regreasing. Maybe that's acceptable to someone but not for me.

All is not lost, however. You may glue the seal and it may work just fine. If you have access to rubber sheets of suitable thickness, you may also cut a seal of the same size from rubber.