Funny noise from back of bike

[colin444]

Hi there, bought my son a secondhand 17in frame hybrid bike 3 gears front and 8 at back with shimano tourney derailleur. It was working fine for three months but now making noise from the back but only when free wheeling.

It does a 'chu-chung' sound then does it again a few seconds later and repeats, i tried it and it happens occasionally and sounds like the bike chain, any ideas what going on? and how to solve it? thanks.

 

[Cycleops]

Hello Colin and to the forum.

Could be a few things. Check the derailleur, looking from the rear does it look straight? The hanger may be bent, if so replacements are available. May also be the freehub which is making noise, a good spraying of the internals with WD40 may sort it but could need replacing. The internals may be difficult to source so a complete hub assembly may be needed, lacing it to the existing rim may make a new wheel assembly more financially viable. Unlikely to be the chain as that would manifest itself as skipping but if the bike is used it may need replacing. Do the gears select smoothly? May be they need adjustment. Release the rear derailleur cable and move the mech across by hand, does it move freely?
For my money the freehub would be the best bet.
The first thing I do with a secondhand bike is replace all the cable inners and outers and apply grease.

 

[si_c]

Get a video of the rear cassette, derailleur and chain when it happens so we can see it properly.

My immediate suspicion is that the freehub needs replacing or cleaning - when the inside gets sticky and starts to seize up instead of free wheeling the cassette starts to turn a little with the wheel then frees up which causes that Chu-Chunk sound as the chain moves out of position and returns.

It may not be that but if it is it's worth getting sorted as if you're out of the saddle when it could cause you to pitch over the handlebars. DAMHIKT.

 

[raleighnut]

I'd say it sounded like a sticky freehub.

 

[colin444]

Could someone explain what the freehub is, and where it is, thanks.

 

[raleighnut]

Could someone explain what the freehub is, and where it is, thanks.

It's the bit that hold the rear cogs on and allows the back wheel to freewheel when you stop pedaling, it's in the centre of the back wheel on the drive side.

 

[Cycleops]

It's part of the hub hence you may need to replace the entire assembly if it fails and you can't get just the freehub to fit your existing.
I think the easiest simplest fix would be to get a new wheel if it is the freehub. Try some WD40 first though.

 

[colin444]

Thanks, I will try 3 in one oil on it and see if that stops the noise. The bike is only just over a year old according to sellers original receipt (but now out of warranty), I am amazed and not too happy if that part is gone already.

 

[ColinJ]

View attachment 539935
It's part of the hub hence you may need to replace the entire assembly if it fails and you can't get just the freehub to fit your existing.
I think the easiest simplest fix would be to get a new wheel if it is the freehub. Try some WD40 first though.

I've had that problem and fixed it by just removing the freehub, cleaning everything, giving it a light lube and reassembling it.

 

[gbb]

If it were mine...
Upturn the bike, slowly rotate the wheel slowly by hand. Does the tyre move side to side as it rotates, as if it's not centred. Look for any points where the tyre may be rubbing, mudguards, mudguard stays, frame, brake blocks etc.
Check the chain from both sides, make sure there isnt a damaged link make sure the side plates aren't sticking out and catching anything, just a general condition check of the chain.
Look for tight chain links, rotate the cranks slowly as the chain passes round the chainring, tight links will stick up slightly. These can catch in your derailleur jockey wheels at the back.
Rotate the cranks slowly, can you feel or hear anything from the transmission ?
Check the actual rims of the wheel, make sure they're sound, not cracked etc and catching the brake blocks.
Broken spokes ?

It's a good thing to do these kind of things once in a while anyway.

 

[colin444]

I will check all that, thanks. And report back.

 

[colin444]

Hi guys, can you tell me how much it is to get a bike repairer to replace the free hub as that seems to be the fault, as the cu-chung sound only operates during free wheeling, and if bike stopped right away, and try to turn the pedal up a quarter turn to start the bike again with foot down, the pedal just falls down under gravity, as though the chain is not there. Bike is a Halfords crossfire II Carerra,

 

[si_c]

The biggest cost is the freehub body itself, and that's variable. For Shimano hubs probably around £30-£40 depending on series plus say £20 to fit.

 

[colin444]

Thanks for the reply, that not to bad a price for a new freehub, considering I got the bike half price at just over a year old, Got a feeling as the fault is random, the guy that sold it to me had spotted the fault and just wanted to get rid of the bike. I will get a price from Halfords to replace hub, as I am not good at complex bike repairs (well complex for me LOL), and want to make sure the bike is safe for my Son to use.

 

[Big John]

Safety first especially where kids are involved. That said, depending on what type of freehub it is, the job isn't that complex but you do need the proper tools - that's always the problem. Youtube will show you how to do it (rather than all of us explaining on here how to do it) but if in doubt use your LBS. As I've discovered today, though, there are a multitude of freehubs out there