Why is my free hub making loud bangs?

Hi,

My rear hub has had pretty much a full rebuild over the last 6 months.

New freehub ( gouged by cassette, worn out bearing)
New axel ( snapped just where the freehub stops and hub bearings start)
New teeth in the hub body( smashed when the axel was replaced)

Pedal, pedal, Bang!
Pedal, stop, bang!
Pedal, pedal hard, Bang!

It’s intermittent. On the road for 5 min back from the trails yesterday it did it twice.

On a 2h ride it did it 20 ISH times

The hub is a novatec d792sb if that helps.

http://www.nguide.eu/hubs/d792sb-11s

I can’t work it out?
The free hub slipping before the teeth catch?

I would guess pawls are not engaging consistently with ratchet ring teeth – therefore either pawls are becoming knackered or the teeth are.

Take the freehub off and have a look?

The causes behind this could be multiple, but at least confirm this bit first

Worn cassette can cause this, but will only be in specific gears. Check the hub’s ratchet ring as mentioned above.  TBH, if you’ve not pulled the freehub off in a number of months (and it’s winter) there could be crud between the hub ratchet and the pawls causing engagement issues.

Sounds more like symptoms of a chain skipping on the cassette, have you checked for chain wear? If it is the hub take it apart and check the pawls are free and clean, check for any broken teeth on the ratchet and replace the hub if any are damaged.

Sounds like the hub has done its time if it is problematic six months after a full rebuild.

This happens to me a reasonable amount – I don’t know if I’m Chris Hoy or something but I’ve blown up a lot of freehub ratchet rings and pawls.

Some options at the simpler end of the scale might be-

– Too much grease around the pawls which will stop them springing back and biting the ratchet ring properly

– The ratchet ring is about to strip out (which will happen suddenly, leaving you stranded in the middle of nowhere. This has happened to me three times now)

– Cassette’s knackered

– The ratchet ring is bedding in, if you’ve replaced it recently, but that should only happen for a ride or so then stop.

Sounds more like symptoms of a chain skipping on the cassette,

OR maybe chain skipping on chainring.

Had that on my old road bike and it was really foxing me and the LBS until one of the mechanics sussed it.

Possibly not that if it’s an MTB with narrow wide, but worth eliminating that and the cassette.

Do you feel it “give” for a second as it bangs?

Thanks!

I have not done many miles on the bike since all the internals have been replaced.

The cassette has been on for ages. The chain is the second. The chain ring has been on for ages. I’ll give that lot a check.

The ratchet ring teeth and pawls were perfect 20 miles ago. Everything was spotlessly cleaned and oiled when putting the new axel in.

The hub only likes oil. Grease gave poor results the first time I cleaned it up.

The bike does feel like it has a bit of give. I put that down to the rest of my bikes not having rear suspension, and comparing it to that.

I would think (based on ym chasing similar things around my bikes!), it could be, as you suspect:

axle flex causing the pawls to mis-engage with ratchet teeth – the previous broken axle at the classic highest flex load point suggests this is likely, is there any tell take scaring of the teeth marking the freehub body between then pawls?

Chain skipping on cassette (but you would only really see on smallest cogs), or slipping on chainring if it is super worn. If the chain is new/ish and not stretched, that could be what is causing that. New chains on old worn cogs/rings is not a happy combo.

Maybe just check the pawls ‘flick/return’ freely on their springs as well, you could maybe have a dodgy spring that is causing issues?

The bike does feel like it has a bit of give.

I meant do you feel the cranks slip suddenly as it bangs?

Does it just happen under heavy load?

If you have an old cassette and chain has been replaced, my first guess would be that the chain skips on the cassette on certain – the most worn, not necessarily only the smallest  – cogs when you put in enough power. This is the most common cause.

Dear OP Tall Martin

Sounds very similar to what happened to me a few years ago on my road bike.  I had Miche Primato hubs.  It was caused by the place the pawls sit getting deformed….so the pawl could move more than it was supposed to, and under high load it went bang, horribly, as well as damaging the steel ratchet ring.  Supposed to be a fairly burly hub, but I guess a lot of climbing (Peak District) and my weight 86kg and the design didn’t work well.  First time it happened was on slippy, very steep cobbles. Rear wheel slipped, then suddenly got grip…and all my not particularly immense power suddenly re-engaged causing damage.

Anyway, the seller of the Miche hubs couldn’t believe it until I showed them pics…they sent me the spare parts out (new ratchet ring and freehub)..got them fitted, and it happened again, same kind of damage.  Switched to DT Swiss 350 hubs that don’t use pawls, and feels solid as a rock.

The chain is well past 1 on the chain checker. So it’s new chain and cassette time.

I did a (cautious) 25 mile ride in the peaks.

It banged a few times at the start just getting to the off road.

Under steady pressure it was fine.

There were definitely some inconsistencies in shifting and sponginess in different gearing. 3rd from bottom was worst by a long way.

Axel flex. No idea how to check for that inside the hub. It’s been fine for ~1,500 miles over 4 years before all the internals got replaced.

any tell take scaring of the teeth marking the freehub body between then pawls?

None I can see

check the pawls ‘flick/return’ freely on their springs as well, you could maybe have a dodgy spring that is causing issues

I thought that and tried the old frehubs spring- it was the same.

I meant do you feel the cranks slip suddenly as it bangs?

Does it just happen under heavy load?

The slipping and bangs don’t happen at the same time.
The slipping is, change gear pedal off and it feels like all the power isn’t getting transferred. If I pedal x hard tit’s only getting x-a bit to the bike.

It was caused by the place the pawls sit getting deformed…

I’ll have a look. A close look!

I destroyed a SunRingle where the actual hub shell deformed around the ratchet ring, which was also egg shaped. There was no coming back from that. I have moved to DTSwiss Ratchet drive hubs now. I blame singlespeeding in my younger days….

Sure I had a similar problem once and there was a spacer missing/broken on the hub somewhere. Just check everything is lined up correctly inside the hub + as above, nothing is deformed.

A couple of wet and muddy days in morzine killed a sunRingle hub for me.

The mud wore out the internals!in two days! The bike was 2 months old and fine before Morzine. I was unimpressed to have to buy a whole wheel to keep on riding the remaining 5 days.

Replaced under warranty ( thanks canyon) and promptly sold (cheaply). Maybe it was that particular hub, I didn’t want to take the chance.

I blame sunRingle!

the symptoms sounds really weird and disconcerting. Hope you find what it is, and tell us about it – I am intrigued!

Thanks again for all the suggestions ! 😃

Well I think I’ve found the culprit. Looks like the ratchet ring that the pawls catch has cracked in a couple of places.

Even by hand there is an inconsistency to how the hub engages when you turn it. Sometimes it engages straight away. Sometimes there is a significantly larger turn to get it to engage. I guess that was the mushiness.

It’s £12 for the ratchet ring so I might replace it. But I’ve spent more that a new hub on all the bits.

A replacement hubs a possibility, it’s got a light carbon rim which is in decent nick.

I’ve stuck a spare wheel on, new cassette and chain, then looked at the chainring and jockey wheels. All knackered.

At least it hasn’t broken somewhere out on a ride.

Well

#yourbikehatesyou

It’s probably those red rings rolling about inside that caused it to crack. 😉

Looks expensive 😬

FWIW I had a Novatec singlespeed hub on a nigh on new Rose jump bike a few years ago which did the same. Had it apart, grease inside still fresh, no cracks or corrosion to be found, put it all back together, and no improvement. Drove me nuts, so I replaced it with an ever so nice Hope trials hub, and put it down to a QC issue. (Bought the bike secondhand, so a warranty claim wasn’t possible.)