Help with Shimano Compact chainset problems

sl

Hello again

I have just changed the Truvativ double c/set (39,48) on my Cannondale crosser to one of the fancy Shimano Ultegra/D/Ace compact (50,34) hollowtech c/set's to give myself some lower gears - the cassette is 13/26 9 speed SRAM - the rear mech is Ultegra road

I have some queries

1) In the 34 chainring I cannot engage the bottom two sprockets because the chain starts to "pick" up on the top chainrings lifting teeth because of the adverse chain line - I'm using a 9 speed SRAM 941 chain - I notice the c/set is billed as 10 speed - would I be better of using a 10 spd chain and would that work with the 9 spd cassette?

2) Gear changing is not great - adjust for the upper c/ring and it stops working for the small c/ring - the chain is adjusting so it allows big sprocket/big c/ring to work without small/small being too slack - just enough capacity from the mech to work - question should I change to a larger capacity mech?

3) Will this c/set ever work properly with a 9 speed setup or is are the problems just to do with the wide c/ring difference

Many thanks

Simon

alfablue

You may need some spacers on the drive side to make the chainline correct - did you fit it or the shop?

Smokin Joe

I'd be surprised if you could get the bottom two sprockets from the small ring without some rub on the 50. You should not use all the sprockets from each chainring, the systems are not designed to work like that. Rather than thinking in terms of having eighteen speeds, you have two sets of gears, high from the 50 and low from the 34 with seven useable sprockets from each. Big ring/big sprocket is definately one to avoid as you are putting a lot of strain on the mech.

As for front gearchange problems, this will almost certainly be down to poor setup. Take a trip to the Sheldon Brown or Park Tools website where proper setup will be explained better than i could do.

maddog 2

1) don't use those gears. Small-small leaves the chain with very little tension. Better to shift onto the big ring. As said, did you use the spacers to get the correct chainline? Otherwise the frame could be out of alignment.

2) It's a setup problem. There's no reason why your setup shouldn't work, although the problems in Q1 may be involved.

3) Yes

I've run that chainset on 12-25, 12-27 with a SRAM chain, no problems

sl

Thanks for all replies - I agree with all points about small/small combinations being bad but would still say that chaining picking up on c/ring teeth shouldn't happen regardless - mention of spacers has me worried since I didn't look for them when I fitted c/set - a spacer between c/set and bearing on drive side would eliminate the problem - can you order these separately please?

Maddog - good to hear that you have this combo and it works - I will stick at it!

alfablue

The Shimano tech docs only show a spacer on the non-drive side, however when I had my triple fitted the shop had to fit additional spacers to ensure the chainline was correct, sorry I can't help more

aracer

It's perfectly normal to have problems with the chain catching on the outer chainring when using the little ring ant the two smallest sprockets with a compact chainset. If you do a search you should find other people complaining about exactly the same thing. Because there is more difference between chainrings on compact the big ring gets in the way more, since it sticks out further from the little ring. As others have said you shouldn't be using these gears anyway, and as you've acknowledged that I don't know what the problem is! I certainly wouldn't try adjusting the chainline just to fix this - the chances are what you have now is right, as I'd suggest it's not actually a fault for this to happen.

Is it front or rear shifting that you have a problem with?

sl

Its the rear shifting that's not great - front shifting is perfect -

point taken about extreme chainlines and compact c/set - was just hoping to completely
avoid it for those occasions when I did accidentally get into a small/small combination - the crash banging it creates isn't very nice - I guess this is just the compromise you have with a compact c/set

maddog 2

sl wrote:

I guess this is just the compromise you have with a compact c/set

normal doubles can come with either 13 or 14 tooth gap (53-39=14, 52-39=13)

compacts can come in three main flavours

50-34 (16t gap)
48-34 (14t gap)
50-36 (14t gap)

so it's not "compacts" that are the problem - it's simply the choice of rings
(and your case, possibly some issues with the setup too).

leonlikestrees

just for information, I have used a few compact combinations and all have been fine:

Chainset,rings,cassette, front mech, rear mech, chain
R700,50/34(both R700),Ultegra 12-23 9spd,DA 8spd, DA 9spd shortcage, DA 9spd
R700,50(R700)/36(middleburn MTB chainring!),Ultegra 12-23 9spd,DA 8spd, DA 9spd shortcage, DA 9spd
R700, 48(FSA)/36(middleburn), Ultegra 12-27 9spd, DA 9spd, 105 longcage
SRAM Rival, 50/36 (SRAM), Sram 12-26 10spd, Rival, rival

I have used no spacers on the BB in any of thos combinations. I have the chain pickup 'problem' with the 50t outer combinations, but it's not really an issue for the reasons stated above.

Chain length sounds right, but did you try what is listed in the manual (put it in the 50/12, and a line drawn through the jockey wheel pivots should be perpendicular to the ground), and have you got the B tension set right?

Are the cables ok?

sl

After a little more fettling I rode in today and things are much improved - I adjusted the front changer and the B-tension - the chain length looks OK (any shorter and big/big will strain mech and any looser the chain will droop).

In the 13/34 combo the chain still picks up on c/ring pickup pins - OK I can avoid that combo

The rear change is working well except that its slipping in the middle two most heavily used sprockets - whilst I had added a new c/set and new chain I thought I would get away with the old cassette which is obviously more worn than I realised - I will order a new cassette which I expect will cure problem.

Phil Russell

Regarding the rear change issue and assuming it is not a worn chain / worn sp[rockets issue ...are you sure you have the gear change cable correctly fitted to the rear mech? This may sound daft but it can be easy to do on some mechs and pass cable incorrectly around the securing bolt. I once did it on a Tiagra mech and it caused slipping just as you describe. Why I did it I will never know ... had fastened it before many times but this time I just got it wrong. Eventually, after much fiddling, I noticed my error. A couple of minutes later all was well....
Cheers, Phil