New freehub body causing chain slack and ghost pedaling

Question

I have replaced my freehub body like-for-like. Now when I freewheel, the top part of the chain goes slack and the pedals spin when I take my feet off them.

This usually occurs on old gunked-up freehubs, but this is a brand new one, so I'm at a loss as to why it's happening. When replacing it, I just pulled off the old one, wiped out the ratchet ring, spread some new grease inside the ratchet ring, slapped the new one on, and then put the cassette back on. The chain is brand new and correctly sized. The only thing that's been changed is the fhb. What am I doing wrong here?

--- EDIT ---

Upon further inspection, I've noticed that the freehub only exhibits this behaviour when the quick-release is engaged: - I turned the bike upside down, with the wheel sitting loose in the forks, and there was no ghost-pedaling until I engaged the quick release. I think I may simply need to adjust the cones.

Answer 1

In response to your update, I have encountered this once before where the shim that separates the freehub body bearing from the main hub was ground down over time by a seized bearing in the main hub body. This was on a high end wheel and the new freehub body provided by the manufacturer came with a new shim that was measurably taller than the original one.

While your problem is different, it's entirely possible that your defective freehub body has worn some aspect of the hub that would not normally be a problem. Check the bearing closest to the freehub body and all the shims and spacers. If you have the facility to add a very small shim, you may find you can resolve the problem.

Without having the wheel to hand it's impossible to say that this is your problem but you have exhausted the basics, so it's worth a check.

Answer 2

The most common causes are a seal (such as whatever is sealing around the drive ring) in need of more lubrication, or too much/too viscous of lubrication in the ratcheting mechanism.

Some freehubs are fine with light grease, especially in hot climates (or more like as long as they're not in a cold climate). Even then, it's important to not overdo it, because too much grease creates resistance against the freehub spinning. However, many do better with medium oil. That's the first thing I would try, providing the problem you describe is more along the lines of the freehub having a hard time "keeping up" than not moving at all.

Answer 3

It is possible that the cartridge bearings simply need a short time to break in. For cartridge bearings, I think this is mainly the grease getting distributed evenly throughout the bearing and on the rubber seals.

The fact that you only notice seal drag when the wheel is clamped in the dropouts illustrates the effect of preload. Preload basically means the bearing is getting clamped from the side. If you closed your QR with excessive strength, which I assume you didn’t, then that could cause the bearing to exhibit a lot of resistance. Some hubs require you to adjust the amount of preload. For example, the recommendation I’m familiar with for cup and cone hubs is to leave the preload loose enough that there’s a bit of side to side play when the hub is off the bike, and the play should disappear when you clamp the QR. Basically, you hold the ends of the hub with one hand and push side to side off the bike, and you try to wiggle the wheel side to side with the QR engaged.

The thing is, I believe this doesn’t apply to you. I believe that all Novatec hubs use cartridge bearings, and only some cartridge bearing hubs are designed to even have preload adjustment (e.g. White Industries and Chris King hubs have preload adjustment). In a design without preload adjustment, I believe they should be Ok under any reasonable amount of preload, I.e. you simply don’t tighten the QR with excessive force. If there’s some sort of obvious system to adjust the preload or the bike’s manual contained instructions for adjusting preload, that’s another story, but if the hub has cartridge bearings then I don’t think it does. Also consider, Novatec is an OEM hub manufacturer. It is, to my knowledge, a bit more of a mass market manufacturer, whereas the two manufacturers I named are more boutique ones. For mass market, you would want to make the system relatively simple. Given that most cartridge bearing hubs don’t require preload adjustment, it would be more likely that they’d choose this design.

As an aside, another example of preload adjustment is cranksets. The instructions for Shimano cranks say to tighten the top cap down to finger tightness, I.e. most likely below 2Nm, which I suspect is the minimum on most bike torque wrenches. The top cap imposes preload. On SRAM DUB cranksets, there’s a plastic collar inside the non-drive arm that you tighten with your fingers (actually you loosen it to increase preload, and you screw it tighter to decrease preload), then you fix its position with a small set screw.