Cassette Spacer Conundrum 10 speed

[Andy JB]

A have swapped over a 10 speed 11-28 cassette for a 12-27 ratio (Shimano 7900) onto my older summer Mavic rims, however, since fitting i cannot get the changer to shift onto the 10th sprocket (highest/smallest) despite the mech adjustment at its extreme.

I removed the 1mm spacer which then meant the cassette wouldn't tighten properly so i played about with the spacers adding and removing them to no avail. Odd thing is its the same 7900 10 speed cassette, simply with different ratio's, i put the original one back on and all okay. Cassette spacers between sprockets all correct so now i'm completely baffled......

[Herman Toothrot]

B tension adjustment due to different sized cogs?

[Andy JB]

Thanks i'll try that, however, we're only talking 1 tooth difference at either end so didn't think it would change but worth a punt

[Matt_N]

You always need to run the provided spacer with Mavic wheels if you're 10 speed, I don't know how but they the foresight to increase freehub length in order to take an 11 speed cassette quite some time ago.

Have you tried adjusting the barrel adjuster on the cable into the rear mech?

Quite often you need to give it a tweak when swapping a cassette over, get behind the cassette and pulleys and tweak the barrel adjuster until the chain line is perfectly aligned.

Then go from there.