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Slack chain.... derailleur or freehub?

11K views 13 replies 5 participants last post by  FBinNY 
#1 ·
Hi All,

When i stop pedalling in a fast gear (ie back pedal slightly) the chain betweeen the casette and cranks goes slack because it doesnt move back through the derailleur, as you can imagine it aint good having a chain bangin round near the spokes and it takes a turn to engage the drive again.

I serviced the derailleur and made sure the cogs were turning easily but it is very old (ten years) so the spring in it might not be good.

Is it likely to be that the freehub needs servicing? I ask because i think its weird that it only happens in the fast gears, and the cassette seems to turn freely when i spin it with my hands.

It would be great if someone could help!

Cheers
 
#3 ·
If it only goes slack when you back pedal, it could be either freehub, derailleur or chain, since you're using the crank to wind the lower loop up to the top, and any cause of resistance will cause slack. As Jeffscott crosschaining alone can often cause it.

OTOH, if coasting alone without backpedling causes the upper loop to slacken, then it's a freehub problem. The wheel isn't totally free and is trying to turn the cassette with it.

Test by shifting to high, lifting the bike and spinning the cranks till the rear wheel is spinning then hold the cranks and see if the upper loop is slackening more than the little bit which is normal.

If you suspect the freehub, first remove the cassette and see if crud (string, twigs, leaves, etc) .is packed between the cassette and hub. This is often the cause, and simply clearing it out the cure.
 
#5 ·
Thanks for the input guys.

The derailleur was bent so i replaced it with an XT one but it still happens, i was out on a ride earlier and had a eureka moment! I should have noticed earlier but when im in a high gear and stop pedalling the cassette carries on turning a bit, which i guess shows that the freehubs binding. Il give it a service tomorrow and hopefully it will sort it out.

It caused an almighty stack earlier! :)
 
#6 ·
I know this threads a couple years old, but I recently started having this problem with my giant rincon. When I go to coast I get slack in the top of the chain and when I'm walking with my bike it will "ghost pedal".
So I went through and cleaned the hub and regreased it but it's still doing it. What's the next step?
Do I need to pull my cassette off and clean it real good?
Also on my bike it has a SRAM PG-820 cassette also is the free hub part of the cassette or is it a totally different piece?
Sorry for all the dumb questions I'm just trying to figure all this stuff out lol
 
#7 ·
Neither the hub no the cassette is causing your problem. The ability to freewheel is in the ratchet mechanism of the freehub body itself, which is sticking. The cassette has no moving parts, but you will need to remove it to do the repait.

While you greased the hub bearings, that didn't do anything for the ratchet. The key is to flush the freehub body, wash out any dried grease, dirt or rust.

On some you might be able to inject solvent through a lube port, in which case you'd flush with solvent, dry it, then inject some sticky oil like Phils or my stuff. Others are less friendly and need to be removed to service if possible, or replaced.

So the details vary according to the specifics of your hub, but the basics are the same, the ratchet mechanism and/or the bearings of the freehub itself need to be cleaned and lubed.
 
#9 ·
That makes things a lot clearer now thank you!

But I'm still confused on what the part is called that is messed up on my bike a free hub, free wheel?
Thanks
A bit of nomenclature. Freewheel in general refers to the ability to coast, and is achieved by using an overrunning clutch, which on most bikes is a ratchet system. So we'd call that the freewheel mechanism. Until roughly 25 years ago ratchet was built into a separate unit which inclided the sprocket(s) and threaded onto a simple hub, hence the term freewheel to refer to the whole thing.

When they later mover to the current cassette systems, the freewheel mechanism was removed from the sprocket assembly, now called a cassette, and made part of the hub, which became a freehub. To avoid confusion, most people refer to the old freewheel units as spin-on freewheels.

For technical writing I'd prefer to call the part that allows coasting the clutch, but I don't because most wouldn't know what I was talking about. So like others I describe the ratchet or freewheel mechanism, which can be part of a spin-on freewheel or a freehub.
 
#11 ·
Haha I just learned a lot more then I had planned on learning!

Ok so one more quick question. Got home last night and went to mess with it and the free wheel is completely locked up.

I'm torn on should I try to clean it up (Does this usually fix the problem) or because it's a 2010 bike should I just invest in a new free wheel?
I have no clue how much they are or anything else so don't flame to hard on this question lol


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#12 ·
Can't answer on the best remedy without knowing particulars. The ease and cost of service will depend on whether it's a spin-on freewheel or cassette/freehub system. Freewheels are all similar, can be unscrewed with a freewheel remover, and respond well to to soaking and re-oiling.

Freehub systems are more involved, but there are many versions out there so I can't offer advice.

Either way, before going to the bike shop, you can try removing the wheel and spinning the sprockets backward to see if they'll move at all. If so, try continuing to turn the sprockets while running solvent into the space between the turning and stationary part, and flushing it out (warning- this will be messy on the wheel). If you can get it loosened and spinning fairly easily, set it aside to dry, then run oil in the same way, and you'll be OK as long as it holds up. (anytime from a month to forever).

BTW- this isn't usually expensive work if you bring just the wheel (and sprockets) to a bike shop.
 
#13 ·
I have one more question about this part of my bike. If I take it to a bike shop so they can remove my cassette and the other bolt that you need a special tool for. Can I reassemble this hub without those tools? Or will I have to take it to the bike shop again to have them reassemble it for me?


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#14 ·
I have one more question about this part of my bike. If I take it to a bike shop so they can remove my cassette and the other bolt that you need a special tool for. Can I reassemble this hub without those tools? Or will I have to take it to the bike shop again to have them reassemble it for me?

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Freehub mounting systems vary by brand. The most common arrangment uses a large hex key (12 or 13mm) to turn a mounting bolt holding the freehub body to the hub shell. Then there's the cassette lockring.

In your shoes I'd bring the wheel to the shop, let them service or replace the freehub, then reinstall the cassette. There's no reason for you to buy the large hex key since you're not likely to need one later, but you should consider buying a cassette lockring tool for between 6 and 10 dollars, so you can change or clean cassettes in the future.
 
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