Strange issue when pedaling backwards

[l4dva]

Looking to get some advice, I'm installing a new groupset (Deore 10x1 speed) onto an old 90's mountain bike. I haven't wired in the cable yet but I have set the high & low level limit screws just by pushing the derailleur across the cassette with my hand. it is a little noisey at the moment due to the chainring being non standard (you might notice this on the video clip). However that isn't the issue, when pedaling forwards the chain moves freely in the smallest cog. although it is a little tight up against the second smallest cog. when pedaling backwards the chain catches the second smallest cog and lifts a little then drops - the backwards pedaling feel is more resistant than normal.

The chainring itself is in perfect straight line when in the 3rd or 4th smallest cog and then from there to the biggest cog the chain goes really out of alignment, but I don't think I can centralise the chain any more than I have now - already have 2mm spacers on the chainring bolts and no more adjustment in BB. That being said the chain seems to track well enough in the biggest cog, pedaling forwards and backwards. So i dont think the chainring positioning should be a major issue.

Attaching a small video clip link - uploaded to youtube, would be interested to understand where this is going wrong? i presume it isn't normal for this type of group set to do this when pedaling backwards? its a brand new groupset by the way

VIDEO

Thanks

 

[Sharky]

My thoughts ....

When pedalling normally/forward, the chain at the top is being pulled and under tension. Any touching of the chain against the second sprocket has no affect as the tension keeps the chain in place.

But when back pedalling, the chain is being pushed towards the cassette and not under tension. This allows the second sprocket to grab the chain and lift it.

Which sprocket out of the 10 is the one that is in a straight line with the chainring?

 

[Sharky]

Just to add, when you are on the road, there is no need to back pedal, other than maybe to position the pedals when starting or stopping. Mid ride, there is practically no need.

So, I think, don't worry and just ride.

 

[Paulus]

My thought are that the limit screws could possibly need a tweak so that the rear mech moves a fraction more, but, only done that once you have fitted the cable and got the tension and shifting correct.

 

[Yellow Saddle]

That looks like a chainline issue. Was it a 7-speed frame before you bent it to fit a 130/135mm hub in there?

Nice video BTW. It's refreshing to see someone using the focus feature on the camera and, having a bike clean enough to clearly see what's what.

 

[l4dva]

You are correct Yellow Saddle - it was a 7 speed, and has been bent out to 135mm - the rear drop out was actually rewelded back in by a frame builder to get the alignment correct (hence the black paint). The chain line is perfect when the chain is in the 3rd or 4th smallest cog - not ideal but as mentioned above in the largest cog the chain/pedaling seem to be spinning fine.

Thanks for the comment on the video. I have meticulously cleaned this frame, followed by T cut, and wax - seriously overkill.

 

[l4dva]

My thoughts ....

When pedalling normally/forward, the chain at the top is being pulled and under tension. Any touching of the chain against the second sprocket has no affect as the tension keeps the chain in place.

But when back pedalling, the chain is being pushed towards the cassette and not under tension. This allows the second sprocket to grab the chain and lift it.

Which sprocket out of the 10 is the one that is in a straight line with the chainring?

the 3rd or 4th smallest sprocket puts the chain in straight line to the chainring

 

[raleighnut]

Is it a 'clutched' rear mech ?

 

[l4dva]

Is it a 'clutched' rear mech ?

correct

 

[raleighnut]

correct

There is your problem, they don't like being back pedalled

 

[l4dva]

interesting - i did not know this.

I've had Sram x1 groupsetss and never noticed this. i presume they are all clutched but i dont think they have an on/off switch like this deore mech though

 

[l4dva]

I think I will continue building up the bike and see how it goes once the cable is in and i can index it properly. As mentioned above i will only back pedal when stopped at traffic lights etc to get the crank to the correct position ready to ride off again. So long as the gears run smoothly when pedaling forward I should be happy!

Thanks all for the comments / tips!

 

[raleighnut]

interesting - i did not know this.

I've had Sram x1 groupsetss and never noticed this. i presume they are all clutched but i dont think they have an on/off switch like this deore mech though

Google backpedalling with a clutched rear mech.

 

[Yellow Saddle]

I dont think the issue is the jockey clutch. If you look at the video, it is clear that the derailing starts at the top where the chain now enters the sprocket in reverse. Trying a no-clutch RD may or may not confirm.

 

[Sharky]

A solution might be using an 11 speed chain. Internal width is the same, but external width a tad smaller. May just be enough to fix the problem. I would however just live with the issue. You'll only be using the small sprocket on fast descents.