Back in the saddle

[Tel]

Hi chaps, I`ve just started riding again after a 3 month lay off due to a prolapsed disc in my back, I love my XPX but it took some begging to lure Mrs. Tel to let me have it back. I`ve now got a noise coming from my rear mech and it looks to me as if the mech is rubbing the new cassette Mrs .Tel had fitted, when I`m in middle ring and gears 1 and 2, would a new longer chain cure this or is the something else needed. the rear mech is a few months old and does`nt seem to have the same screw to wind into the mech hanger the old XT one did to ajust the angle to and fro. any advice
 Cheers, Tel.

[Colin]

Hmmm, until you said............"and doesn't seem to have the same screw to wind into the mech hanger...... "

That was what I was going to suggest to check!

What model RD is it?

It isn't bent is it? or the Hanger?

Very odd that it doesn't have one! Is it maybe missing? I though all RD's had a "B-Tension" adjuster? If it's missing that would mean the RD could get too close to the sprockets.

Is it a "Long cage" RD? Generally you need one for big gear ranges.

Are gears 1 and 2 the biggest rear cogs?

What teeth range have you got on the front and rear?

I think you need to check that the RD has got the "capacity" to cope with the difference in teeth between front and rear.

Both front and rear derailleurs have a listed Chain Wrap Capacity. For the front derailleur this is the difference between the number of teeth on the largest chainring and the smallest chainring.

Rear derailleurs usually have both a largest cog quoted and a capacity listed. 
Capacity =(biggest chainring - smallest chainring) + (biggest sprocket - smallest sprocket)

e.g. my 4000se runs a RD-M750SGS (Long Cage) which has a stated capacity of: Largest Cog: 34 teeth and Chain Wrap Capacity: 43 teeth.
I run 22/34/44 chainrings and a 11-34 cassette.
so: (44-22)+(34-11)=45   
Uh Oh!!  Looks like I'm a naughty boy, but you can get away with exceeding the capacity by a couple or three if you are a Good Boy and don't use Naughty "crossing gears"!

It's also definitely worth checking that the chain length is correct, various guidance on this, but if you have a Shimano set up then it's best to follow their guidance.

Col.

[Tel]

Hi Colin, yes it is a long cage RD. Shimano xtr carbon shadow, and it looks as if I can buy a new chain to over come the problem, but I will dig out the destrution sheet that came with the rear mech and check I`m not excceding cog cappacity as the new cassette seems to have a bigger cog (nearest the spokes) than my old one did and may be causing the problem.
 Many thanks mate and I`ll keep you posted, Tel.

[craiga]

Hi Tel,
You've increased the size of the cassette quite a lot, the old one from my XP-X was a 14 - 28 (just checked it). I replaced it with an 11-30.

The rear mech must have some way of adjusting surely.

[Thunderchild]

I run short cage Shimano DX rear derailleurs with 32 rear 8-speeds cassettes.  They indicate 28 being the max, ha ha.  As mentioned, you have to pay attention to what gear your in.  I basically use the big chainring with the outer four gears.  The middle chain ring with all gears and the inside chainring with the inner four gears. 

Yeah, they haven't made those in years.  I worked in a bike shop years ago and stocked up.  I am always watching for them as well.  Last summer, I picked up an old Cadex  Mountain bike at a garage sale for $5.  Of course all I wanted was the DX short cage rear derailleur.  I have one on my Oz, my 5000, my KHS hardtail, and my Nishiki Alien.

Thunderchild