Numpty Questions on SRAM Rear Derailleur Install

phil-t

Hi, I've got some basic questions on 'issues' I have while setting up a new SRAM SX4 rear mech (On a new bike)..

the cable was half fitted, but not clamped to the mech, but looking at the installation instructions that's fine, you do the basic end adjustments without it attached..

The problem is, when aligned with the smallest cog using the 'high' screw (The natural sprung position of the mech) when you move the chainring to the smallest ring, the mech folds up on itself, and the chain then rides accross the top 'idler' gear (or whatever it's called), since this has a metal L shaped guard on it, the chain is riding accross that...

I saw in the instructions that the 'B' screw is used to lower/raise the rest position of the mech, and so I wound that in to try and unfold the mech a little to stop the chain contact, however the 'b' screw is all the way in and the chain is still just about touching.. I can't adjust the 'b' screw any further (it's only got 1mm of travel left) before the mech hits the hanger stopping any further adjustment.

This has me stumped, I have a little engineering experience, and it just doesn't look right.. I've looked at a mates bike in work this morning, and his mech folds up and the chain almost touches when it's on the two smallest cogs.. surely this isn't normal?

Looking at the mech operation, I can see that when you move it by hand, the mech will pivot around a little bit before starting to move accross, making we think perhaps you can use the cable tension to start unfolding the mech a bit to give the chain some clearance?

The bike was a new bike in box (From Halfords, they have a 10 day lead time on bookings), so I know the mech should fit/work..

Can anyone help a numpty out and give a more detailed explanation of installation of the mech (Its the same for the SX7/9 according to the instructions), and what to look out for, especially with how much slack to pull through when clamping the cable?

Thanks,

Phil

nicklouse

sounds like you are in a poor gear combo.

the 2 small cogs should not be used together,

put the chain on the middle cog for setting the rear mech.

phil-t

Hi, thanks for the speedy reply,

Following the manual, they (correctly) get you to put the chain on the largest front/smallest rear and vice-versa for the two end adjustments, and that seems to be easy to do..

It's more of an observation when I then noticed that after doing that, when on the two smallest cogs, the mech was folding up so much and causing the 'rubbing' of the chain..

This just stumped me, assuming this can't be the case, as if you use that gear combo on the road, you'd quickly wear the chain/rear mech out, which seems a daft design!..

Just wondering how 'normal' it is, and I noticed that the mech will pivot (unfold) a bit before the mech moves accross, so can you use the cable tension to pivot(unfold) the mech a bit and use the adjuster screws to compensate for this?

Ciaran500

Is your chain just too long? Had a similar problem when I bought a new chain and didn't shorten it enough

phil-t

It does look/sound like the chain is too long!..

The correct way according to the instructions to get the right length is to put it around the largest cogs bypassing the mech, and then add 2 links... which again sounds reasonable!..

I've gone and looked at all the bikes I can see in work, and surprsingly they also seem as bad.. I can also see on the largest 2 cogs the mech is quite stretched to the other extent.. so I assume it's designed like this!..

I'll double check it when I get home, I phoned Halfrauds and they said the chain lengths are pre-cut for the bikes, and it's extremely rare to be wrong.

stu8975

If your chain is rubbing in the two smallest cogs then your chain will be too long. Have a look here to find a solution.

http://www.parktool.com/repair/readhowto.asp?id=26

phil-t

Cheers for the replies..

I have checked the chain length and it's spot on using the calculation method from the above link..

I've re-set it up using the SRAM instructions, and although very close the chain is not actually hitting it under normal load..


I then re-adjusted the front mech, and went for a ride with a screw driver and allen key with me!!..

Following the instructions to the letter, it's a simple front mech setup, but boy oh boy either there is an art to this, or the SRAM SX4 is as the price indicates, a bit rough, on extreme angles (large to small cogs) it rides slightly on the front cage, adjusting either way means it won't upshift or downshift, depending on the wind!..

I think I'll admit defeat and get my LBS to set it up, I'd rather pay them to do a proper job then risk Halfords, they are just under too much pressure and time constraints to be as conciencious as they should be..

I've got old Shjimano XT gear (worn out) on my trust old rigid MTB, and that was a dream to use in comparison, it never baulked changing up or down, and I never remember it catching on bad gear combinations.. ho hum..

I may even check the 'bay out and see if I can bag some cheap SRAM SX9 gear or is it best to stick to Shimano?