Chain skip after freewheeling

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mark a.
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Joined: 8 Jan 2007, 2:47pm
Location: Surrey

Chain skip after freewheeling

Postby mark a. » 16 Nov 2018, 2:48pm

My Surly Cross Check pedals just fine and the gears change nicely both up and down. However, if I freewheel for a bit (or, worse backpedal) then there's a good chance the chain will slip when I try to pedal again.

I can replicate the problem on the bike stand, but it happens too quickly for me to see where the issue is, although I'm pretty sure it's in the sprocket region. The obvious answer is chain stretch and / or worn sprockets, but I'm not sure. I have a Tiagra STI / 9-speed / triple front setup.

- My chain checker tool (Park Tool) suggests it's not even stretched to 0.5%
- The sprockets look ok to me (I've seen much worse)
- Everything's clean* and oiled

What else should I be looking for? We've just moved house so the bike might have got knocked. The derailleur / hanger seem ok but perhaps they're bent? How would I know?

I've attached some photos of my messy garage - I mean gears.

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* To a normal person's definition of clean for a drivetrain, not MickF's.

the snail
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Joined: 5 Aug 2011, 3:11pm

Re: Chain skip after freewheeling

Postby the snail » 16 Nov 2018, 2:53pm

Could be the freewheel pawls are sticking and not re-engaging when you start pedalling?

mark a.
Posts: 1349
Joined: 8 Jan 2007, 2:47pm
Location: Surrey

Re: Chain skip after freewheeling

Postby mark a. » 16 Nov 2018, 3:01pm

Ah, yes. It just occurred to me that it could be the pawls. Hence why it's a problem when the freewheeling - the difference in speed between the sprocket and the hub is too high for the pawls to engage.

OK, now to take off the cassette and see if I can remember how to access & fix the pawls.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Chain skip after freewheeling

Postby Brucey » 16 Nov 2018, 3:17pm

to test for the problem test the pickup of the pawls with the wheel off the bike. If the freewheel 'misses' on a quick pickup, it won't work right on the bike.

To fix the problem (nine times out of ten)

- remove the cassette
- loosen the LH cone and locknut
- hold the LH cone against the hub and unscrew the axle from the RH side
- when there is a gap on the RHS that is large enough, add a fair quantity of oil to the RH bearing
- screw the axle back into position
- with the wheel set so that the axle is horizontal, and holding the freehub body in your left hand, spin the wheel for a couple of minutes

normally this will allow the oil to penetrate the freewheel mechanism and it will (usually) free off. Test for a good pickup.
Adjust the bearings and run the hub like that for a few weeks. Then go back into it and lubricate the bearings properly. I recommend using a semi-fluid grease in the rear hub (provided the seals are in good condition). If of the correct consistency ( about that of tomato ketchup) it will keep the freewheel mechanism happy as well as the hub bearings.

If the oil doesn't help, leave it overnight and repeat the treatment the next day. If this doesn't work try something thinner (a penetrant). If you draw a blank then the freehub will either need overhauling or replacing.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mark a.
Posts: 1349
Joined: 8 Jan 2007, 2:47pm
Location: Surrey

Re: Chain skip after freewheeling

Postby mark a. » 16 Nov 2018, 9:56pm

Thanks for that Brucey. I'll take the wheel off and give it a go this weekend.

Mark

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LinusR
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Re: Chain skip after freewheeling

Postby LinusR » 16 Nov 2018, 10:19pm

Brucey wrote:- with the wheel set so that the axle is horizontal, and holding the freehub body in your left hand, spin the wheel for a couple of minutes


Can I ask why hold it so the axle is horizontal? Why not vertical (or diagonal) with the freehub body uppermost so that the oil runs downwards?

peetee
Posts: 1334
Joined: 4 May 2010, 10:20pm

Re: Chain skip after freewheeling

Postby peetee » 16 Nov 2018, 11:36pm

There is a square cut-out in the internal face of the freehub body. Holding horizontal allows the oil to fall in. If you held it axle upright the oil would drop into the axle bearings.
Current status report:
Latter side of fifty and feeling less than nifty.
Too many bikes on pegs and too few miles in the legs.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Chain skip after freewheeling

Postby Brucey » 17 Nov 2018, 8:11am

LinusR wrote:
Brucey wrote:- with the wheel set so that the axle is horizontal, and holding the freehub body in your left hand, spin the wheel for a couple of minutes


Can I ask why hold it so the axle is horizontal? Why not vertical (or diagonal) with the freehub body uppermost so that the oil runs downwards?


The oil is centrifuged outwards and dragged round by the turning parts and should soon work its way into the freewheel mechanism. If you tip the axle very far past horizontal the oil may drain into the hubshell via the hollow bolt instead. Once tipped away from horizontal, any oil that hasn't yet made it's way around the outside of the RH hub bearing cup is unlikely to do so now, no matter how long you spend twirling the wheel round.

BTW because you are holding the freehub body in your left hand, you can feel any changes in the state of the bearings/pawls as the oil penetrates. The RH ballrace in the freehub body may be full of dried grease and this will at frist inhibit penetration of any lubricant.

Because the seal is still in the RH end of the freehub body, even with the axle removed, you can have a puddle of oil at least 5mm deep in the space that is ordinarily occupied by the 1/4" hub bearings. This is deep enough to penetrate the freewheel mechanism. Provided the wheel is kept turning, you can add even more oil than that, and it won't spill out until the wheel is stopped.

If the freehub body has no seal in the LHS, you will know when the oil has fully penetrated the workings because it will start emerging from the LH end of the freehub body. If the oil is rust-coloured then you know that water has penetrated the mechanism. If there is a seal in the LH end of the freehub body then there will usually be a slight oozing instead.

A little corrosion in the freewheel mechanism is not the end of the world (under normal circumstances the bearing only moves during freewwheeling, i.e. when it isn't loaded), but it is potentially problematic in that

a) if the bearings develop slack in them then this will only get worse; the bearing increasingly starts to scuff around when it isn't meant to be moving, i.e. during pedalling
b) the prevailing conditions inside the freehub body will tend to turn acidic whenever there is any rust present, which just encourages more corrosion; a vicious circle. Only removing all the rust or adding a lubricant with lots of corrosion inhibitors will stifle further corrosion.
c) the pawls are usually worked by a single spring that is typically made from steel piano wire that is in the range 0.25 to 0.5mm diameter. This can easily be seriously weakened or even broken by the effects of corrosion.

It appears obvious that if the lubricant is contaminated with particles of rust, it won't work properly any more. However it usually isn't the abrasive wear rising from the particles (polishing is a likely outcome from this....) that is the main concern here; it is the chemical effect of the rust particles; this turns conditions acidic and this both promotes further corrosion and further degrades the lubricant; most oils and greases are designed to be slightly alkaline and when conditions change away from this, problems ensue.

Thus I recommend that a lubricant is used for this part which has got plenty of corrosion inhibitors in it; most lubricants (even some that say they do) have nowhere near enough of this kind of additive in them.

An alternative to this is to use oil and allow it to operate as a 'total loss' system, i.e. oil leaks out of the hub all the time and carries rust particles, dirt, water etc with it. This is how many bicycle bearings used to work, including SA hubs (when they were still fitted with an oiling port). This makes a mess but is usually effective at keeping the bearings in good working order.

A rough-running freehub bearing is genuinely not a big problem per se, but the free play in the bearing and the other things like the effects of corrosion on the pawl spring can be.
cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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LinusR
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Re: Chain skip after freewheeling

Postby LinusR » 17 Nov 2018, 12:57pm

Brucey wrote:
The oil is centrifuged outwards... [snip]


Thanks Brucey for taking the time to explain that very concisely yet comprehensively. Thanks also to PeeTee.

Linus

mark a.
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Re: Chain skip after freewheeling

Postby mark a. » 17 Nov 2018, 5:58pm

Thanks again. I've returned from the garage and have caught up with the rest of the comments. It's definitely the freehub and not the chain skipping.

I haven't had much success in fixing it, since the freehub is still slipping, so I'll try again tomorrow to see if the oil has penetrated. I was discouraged by the lack of initial success so I've taken things to the next step and removed the freehub. Now I understand much better how it all fits together, what's happening and how the oil would get into the freehub (once the bearing are removed the cutout becomes clear, and what would happen if the axle was tilted).

I haven't serviced the freehub (the seal seems pretty, well, sealed and I didn't want to hurt it) so the internals are still a mystery at the moment. I'll try more oil tomorrow and see if that helps. Otherwise I'll get into the freehub to see what the pawls are doing.

I've serviced a Hope hub (Pro II I think) in the past and that was lovely and easy, with giant (and very clicky) pawls. The Shimano is much more mysterious so far.

I'm sure I've got the wrong oil (just using Finish Line green) and will use the wrong grease (Finish Line white stuff) but that's what I've got to hand while my garage, tools and budgets for more bike stuff are still in a state of disarray following the house move.

Thanks again for your help. Hopefully my tomorrow I'll have a working freehub or I've ruined it - in either case I'll be better informed :D

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LinusR
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Re: Chain skip after freewheeling

Postby LinusR » 17 Nov 2018, 6:05pm

mark a. wrote:
I'm sure I've got the wrong oil (just using Finish Line green)


Yes, you'll get a telling off for that. I'm sure a reprimand is on its way... :wink:

Brucey
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Re: Chain skip after freewheeling

Postby Brucey » 17 Nov 2018, 7:26pm

if you have removed the freehub body from a Deore hub like yours, then you can pick the seal out of the left side of the freehub body, and add oil (and/or penetrant if the pawls are still sticky) that way. The LH seal is just soft rubber and will come out fairly easily if (say) a cocktail stick is used on it.

FL grease is good stuff but I remain unconvinced by that chain lube when it comes to freehub bodies; chain lube is basically designed to be sticky enough that it doesn't fly off chains easily. It can cause pawls to be sticky too.

For freeing off sticky pawls and providing lubrication for a few weeks, ATF is quite a good thing to use. Some folk leave the freehub body soaking in a bath of the stuff overnight.

BTW if the freehub is to be disassembled note that

a) you need a special tool to undo the RH ball cup (which is on a LH thread)

b) you need to improvise a special tool to reshape the dustcap that presses into the freehub body (otherwise it is liable to be a loose fit which is not acceptable) and

c) there is no point in removing the freehub body from the wheel if you are going to disassemble the thing; IMHO it is both easier and better to leave it in situ.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mark a.
Posts: 1349
Joined: 8 Jan 2007, 2:47pm
Location: Surrey

Re: Chain skip after freewheeling

Postby mark a. » 17 Nov 2018, 9:41pm

I'm glad the seal is easily removable. I'll see what's inside tomorrow.

I'll see if I have anything better than FL green lube for the pawls. I think I probably have some super-light stuff (teflon spray, sewing machine oil etc) which would probably wrong in the other direction to too-sticky grease.

I suppose I our to get some ATF. IIRC it works in hub gears too? Or was that differential oil? I get so confused. I'd have to check your post history to remind myself. It probably won't be worth me getting official Shimano freehub grease since I imagine I'll do this approximately never again in my life.

If I ever get to the stage of dismantling the freehub, someone either shoot me or tell me to just buy a new one.

Thanks again,

Mark

Brucey
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Re: Chain skip after freewheeling

Postby Brucey » 17 Nov 2018, 10:00pm

I recommend using Hypoid gear oil in IGHs. Mixing either that or ATF with a #2 grease can make a half-decent Semi-Fluid Grease (SFG).

Basically you can use almost anything to free up sticky pawls but some lubes are thin enough that they won't provide good long-term lubrication.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Rossco8854
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Re: Chain skip after freewheeling

Postby Rossco8854 » 17 Nov 2018, 11:06pm

I just fixed the same problem on an 11speed ultegra which was a dirty rear hub, stripped cleaned and 150 miles later no more chain skip. Thought initially it needed a new hub, chain, rear deraileur spring or anything else that Google search brought up as after the first strip and decrease (also my first time removing a cassette etc) it done it after 60 miles. Turned out the regrease was too heavy so be weary of that if your a novice like myself.