Transmission Clunking when Power Increases

desdeadly

Hiya

I have a look 585 with SRAM Force.
When it is on the big chainring on the front (it doesnt matter on the back) and i apply force to the pedals it clunks, kind of sounds like something is slipping.
At low torque its ok

Thinking it was the freehub i swapped to my other set of wheels (which i know are ok) and the problem persists.

I have had a look and i cant see anything obvious.
Any ideas?
currently the groupset has done around 600 miles i would guess.

Cheers

Lig

Hi,

Sounds like bottom bracket cups. I have had this often. you just have to strip down regrease and rebuild.....

Try it if no one else comes up with an easier solution to try first..

Lig.

Ben6899

What does it feel like when the clunk happens?

desdeadly

Cheers Lig

Ben - it feels like the chain (or something) is slipping. Perhaps not quite coming off as there seems to be a bit of resistance. It makes an awful sound also. Again like metal slipping/missing/skipping on metal. its quite loud.

Clem

I have the same problem. I suspect it's not having your indexing setup absolutely perfectly.

When my Airborne was a Campag 9 speed, seven years ago, I took it for a once-over at a bike shop and they said I'd done a pretty good job on setting up the transmission. Sadly when I swapped to 10-speed I clearly didn't get it right... I get the feeling 10 is a lot more fussy than 9. I get one end of the range to work fine at the back and the other isn't happy and vice versa. Get the middle wrong and it clonks away on climbs and the levers need 'nursing' to shift the gears up or down.

One day I'll strip the whole thing down and start again!

balthazar

Consider loose chainring bolts also. Often forgotten.

Clem

Very tight on mint condition chainset... I'm going to change my levers and cables next. Can't do any harm and I have spare levers.

Ben6899

Check the chainring bolts for tightness for sure, as someone mentioned upthread.

If the indexing isn't quite right, then could that cause the chain to ride on top of the sprocket teeth on the cassette?

Clem

Well Ben, it must be something like that. If not riding on top then going to the 'wrong' place on the sprocket.

What baffles me is why some cogs should work fine and others not... perhaps there are chain issues but I've used Campagnolo and two other makes with pretty much same results.

desdeadly

Checked chainring bolts, striped down the BB last night, cleaned and regreased. put back together and still the same.
Then I noticed the chainrings themselves, i think i overlooked the obvious, DOH
http://www.facebook.com/photo.php?pid=3 ... =516143907

Clem

My problem's at the other end and all my cogs are in good nick but I hope that solves your problem.

markos1963

I see nobody has mentioned pedals yet. Could be the bearings on them if all the other areas have been tried.

Clem

It certainly isn't the pedals in my case. Changed them with no improvement (I didn't do this to see if there would be an improvement if the chain does run cleanly at the rear sprockets wouldn't seem to be down to pedals)...

keef66

Nice pic! I'd say your chainring's reached the end of it's useful life and is almost certainly responsible for the phenomenon you describe.

You certain you've done that to it in 600 miles? I'd have a good look at the cassette and check the chain for wear while you're at it.