Slipping chain on middle ring of triple chainset

dphb

Hi all,
firstly, apologies if some of this sounds a bit confusing, i'm relatively new to cycling so not 100% on all terminology.

I took a 2009 specialized tricross sport into my local bike shop for a full service. None of the components on my bike had previously been changed.
So all the components were as listed here

http://www.specialized.com/gb/en/bc/SBC ... nuItemId=0


They changed the bottom bracket, the chain and the rear casette - the chain was worn down and they said the chain had worn the teeth on the rear casette, hence I was getting slipping gears on the back.

So, I took the bike home, and strainght away I noticed that as soon as I put any force through the pedals (i.e. I stood up), the chain slipped off the middle chain ring and I did up to half a rotation on the pedals "freefalling". - This didn't happen prior to the service.

I took the bike back to the shop & they looked at the middle ring and said the profile looked ok, but the teeth were a bit short, so they decided it needed changing.

So, 1 new chain, 1 new rear casette and 1 new 39t middle ring later..... I did 3 miles this morning and the chain slipped twice on the brand new middle ring!!

I would understand the slipping if it was on the top or bottom ring as it would mean the gears aren't adjusted properly, but the middle ring??

Anybody have any suggestions as to what I should do?

The new middle ring is a 39t shimano ring (previous one was 39t FSA), the new chain and rear casette are SRAM (previous were all shimano). The gear ratio of the casette is the same as the old one.

Any help is much appreciated as it feels like I'm just throwing money at the bike and it's getting worse!!

Many thanks

desweller

Sounds to me like your LBS have not got your chain length correct.

Also sounds to me like they've done you out of a few bob if they've changed the BB for no good reason. BBs normally last for ages, shouldn't be failing on a 1-year old bike.

Wappygixer

I doubt its chain length as it would do it on the big ring and granny ring.
Can you get it on the big ring and that largest sprocket and will it run on the smallest ring and smallest sprocket?
Bottom brackets can fail in a couple of months, its all to do with the conditions you ride in and the quality of the unit in the first place.
I'm wondering if its not your drive chain at all and maybe its your freehub body thats slipping?

dphb

Thanks for your replies.
I can get the chain in the granny ring and use all the gears on the back without any slipping.
The same goes for the large ring.

They said the BB was a standard factory one that's put into a lot of bikes and that they're rubbish (being relatively new to cycling, I could well have been lied to here). They said it was worn out.
I've done around 2000 miles on road.

What's the freehub body and how do I check for slipping?

Thanks!

soveda

If it's only in the middle ring it doesn't sound like the freehub is slipping. It could be mech alignment but it's hard to say without seeing the bike.
Does it shift OK between chainrings?
When in the middle chainring does it slip in any gear or just some of them?
When the chain is on the middle ring and you look down at the mech is it centred around the chainring?