Identifying cause of Skipping Gears under power.

wolfsbane2k

Hey.

I've got a 3 year old Triban 540 that's at the point that the chain is skipping when applying power across all gear range, and it's getting dangerous.

Chain is 700 KM old, with <0.25% chain wear ( checked with 2 wear tools)
Cassette is 2500 KM old, into it's 2nd chain, previous chain changed at 0.75% with 1800km on it.
Front chainrings are 2000 KM old.
Rear Derailleur and jockeys are original, and done 10,000 Km, jockeys still look ok, and bearings in the jockeys feel ok.

In the workstand, I've given it all a clean , and the shifting is perfectly crisp, and I can't mimick the issue.

I almost want to sit and stick a gopro on a the RD area to try and mimic it on the move to understand what's causing it.

Any think else to try out, other than replacing the damn lot again would be greatly appreciated.

Ta!

keef66

Given your description I'd normally say worn chainrings, but at 2000 km unless you ride the thing on the beach it sounds unlikely. Is it happening in all gears, ie all chainring / sprocket combinations?

Other possibility is a stiff link or one that's on the verge of failing?

Next most likely is the cassette, but it would be unusual if all the sprockets were worn after such a mileage

Killerclown

Skipping ( changing up and down the cassette unexpectedly ) or slipping ( chain slipping on a given ratio). If it’s skipping, I’d replace the cables ( inners and outers) and see if that helps, If it’s slipping, look for a bent / missing tooth / teeth on sprockets and rings. If it’s not that obvious, look for any deep gouges on the freehub splines, or stiff chain links as a start.

Vino'sGhost

Killerclown wrote:

Skipping ( changing up and down the cassette unexpectedly ) or slipping ( chain slipping on a given ratio). If it’s skipping, I’d replace the cables ( inners and outers) and see if that helps, If it’s slipping, look for a bent / missing tooth / teeth on sprockets and rings. If it’s not that obvious, look for any deep gouges on the freehub splines, or stiff chain links as a start.

Why not suggest he changes his bottom bracket and handlebars too? Idiot

Killerclown

Vino'sGhost wrote:

Killerclown wrote:

Skipping ( changing up and down the cassette unexpectedly ) or slipping ( chain slipping on a given ratio). If it’s skipping, I’d replace the cables ( inners and outers) and see if that helps, If it’s slipping, look for a bent / missing tooth / teeth on sprockets and rings. If it’s not that obvious, look for any deep gouges on the freehub splines, or stiff chain links as a start.

Why not suggest he changes his bottom bracket and handlebars too? Idiot

Having ownership experience of the actual bike the OP is asking about, I prefer to share the things that helped, when mine did something similar, but I guess you wouldn’t know that, because you haven’t actually experienced these things, and sorted them, on an actual T540. Sorry, about that.

phil485

just replaced chain and then cassette but still getting skipping on power ( standing power) on large chain ring . just replaced chain rings and all good. That may be a good step.for you

cycleclinic

You can identify worn chain ring teethm they look all sharp.

photonic69

If you are getting skipping on the rear cassette (moving between cogs) and as you say the chain and cassette are not very old and are perfectly indexed on the stand then it can only be one of two things:

1/ rear hanger is slightly bent

2/ the linkages/springs in the rear derailleur are worn/tired causing movement under strain

Sticky cables can cause an issue if you have been in a bigger cog and have changed to a smaller one before the skipping starts as the rear mech hasn't moved out enough. This won't happen if you go from a smaller cog to a bigger one before putting the power down. Easy to check so try and then report back

jermas

It could be the freehub that's skipping under load rather than the chain (it gives a very similar feel). The freehub pawls might need a clean / lubing.

Bumo_b

I changed by sons cassette on his BTwin due to rubbish shifting and had the the issue above. My experience or rather his was that if wear on any of the drive train components was on the limit, the other components play up very quickly when one is replaced. What condition were they in when you started replacing the items? I note you said the derailleur is 10000km old? Although there might not be noticeable wear by inspection, there was enough wear in my sons under strain with the linkages as mentioned above to cause slight movement and issues with jumping when peddling on my turbo.

Vino'sGhost

Killerclown wrote:

Vino'sGhost wrote:

Killerclown wrote:

Skipping ( changing up and down the cassette unexpectedly ) or slipping ( chain slipping on a given ratio). If it’s skipping, I’d replace the cables ( inners and outers) and see if that helps, If it’s slipping, look for a bent / missing tooth / teeth on sprockets and rings. If it’s not that obvious, look for any deep gouges on the freehub splines, or stiff chain links as a start.

Why not suggest he changes his bottom bracket and handlebars too? Idiot

Having ownership experience of the actual bike the OP is asking about, I prefer to share the things that helped, when mine did something similar, but I guess you wouldn’t know that, because you haven’t actually experienced these things, and sorted them, on an actual T540. Sorry, about that.

Ah yes is this the bike you tool around on with a 40kg pack on your back? Plank.

drlodge

Stretched rear derailleur cable can cause skipping under load, just needs a wee adjustment.

keef66

jermas wrote:

It could be the freehub that's skipping under load rather than the chain (it gives a very similar feel). The freehub pawls might need a clean / lubing.

That's a good point I hadn't considered. Is the freehub on a Triban easily serviced or is it a disposable job?

drlodge

I very much doubt its the freehub skipping.

I'd first check that the rear derailleur is properly dialled in.

Maglia_Rosa

A friend of mine new to cycling was experiencing a similar issue where he told me it was shifting smoothly on his bike stand but when on a ride and under weight his chain was skipping through the read cassette on a few gears. We went out for a ride together but before put him on my turbo and adjusted his rear derailleur whilst under weight and it solved the issue and he was very happy! I don’t claim to be any kind of bike mechanic but in that case it worked and didn’t cost him anything so might be worth a try.

pblakeney

Maglia_Rosa wrote:

A friend of mine new to cycling was experiencing a similar issue where he told me it was shifting smoothly on his bike stand but when on a ride and under weight his chain was skipping through the read cassette on a few gears. We went out for a ride together but before put him on my turbo and adjusted his rear derailleur whilst under weight and it solved the issue and he was very happy! I don’t claim to be any kind of bike mechanic but in that case it worked and didn’t cost him anything so might be worth a try.

This is one benefit of external cables. Give a pull and if it gets better, tighten the tension.
If it gets worse loosen the tension. Sorted. hopefully.

wolfsbane2k

Cheers all.

Going to close the thread, as the bike has gone in for a new frame ( Cracked at the seatpost/top tube junction - viewtopic.php?f=40012&t=12573143&p=20440566#p20440539)

However, noted that i'll check the following upon rebuild -
Hanger ( Again, I always forget to check the hanger alignment)
Freehub

and the chain for stiff links.

keef66

At work so can't see the pic. Any chance the frame was moving to the extent it affected cable tension and hence indexing?

wolfsbane2k

keef66 wrote:

At work so can't see the pic. Any chance the frame was moving to the extent it affected cable tension and hence indexing?

Nah - cables are on the downtube.

cycleclinic

you have all the things to check but it sounds like you need to go on a course as you are not approaching this in a methodical way.

Vino'sGhost

thecycleclinic wrote:

you have all the things to check but it sounds like you need to go on a course as you are not approaching this in a methodical way.

sounds good. I wish id gone on a course when i started out, it would have saved me a fortune not to mention the stress.

wolfsbane2k

thecycleclinic wrote:

you have all the things to check but it sounds like you need to go on a course as you are not approaching this in a methodical way.

I agree, and going on one has been on my Xmas list for 3 years in a row, but I can't find one locally.

Most are the absolutely basics; fixing punctures , basic rd tuning, and that's about it.

photonic69

Plenty of on-line video tutorials. Park Tools excellent series is all you need. But yes getting hands on experience is very worthwhile too if you can find a course near you

wolfsbane2k

PhotoNic69 wrote:

Plenty of on-line video tutorials. Park Tools excellent series is all you need. But yes getting hands on experience is very worthwhile too if you can find a course near you

Yeah - videos can always be useful, but they can't show the "right" amount of preload for cups and cones hubs, or the feeling of what a new set of cables should feel like..

I've asked about paying mechanics a few more coins to watch and ask them questions as they service my bike before, but they didn't want to do that...