Bicycle Mechanics - Rubbing after changing cassette

I have an old (10 years) Scott bike that I'm slowly refurbishing. The original set up was a 7 speed freewheel and I have put on a new wheel with a 8/9 cassette hub. I have put on exactly the same 11-34 cassette as I had freewheel but with a spacer that I was sold with the new cassette. The problem is I am getting a rubbing/grinding on every cog as if the chain is either not lined up correctly or is too wide for the cogs. This only happens when I'm riding so i can't find exactly where it is rubbing. Do I need to change the rear derailleur or do I need a different chain?

It only happens when you're riding?

Do you mean it doesn't happen when you turn the bike upside down to suss it out?

So, you've put on a 7spd cassette, which has the same spacing as your old 7spd freewheel, right? If it's the same chain, it can't be too wide.

When you say, 'as if it isn't lined up correctly,' I take that to mean you've made sure it is.

If my assumptions are correct, that sounds a bit weird.

If it's a question of chain or sprocket width it'll be visible at any or no speed. Set the bike up and see of a business card can pass between the chain and larger adjacent sprocket in each gear. If so, you're OK as far as width goes.

As far as diagnosing it further, you'll need a trainer and a friend to see if you can pin down the origin of the noise under load.

The problem is more noticeable under load. I can pass a business card between the chain and larger sporcket but having looked very closely it does seem that the derailleur wheel is slightly off centre to the sprocket.
I suppose I assumed that with exactly the same acssette and with the spacer they would line up the same. How do I adjust the derailleur so it lines up better with the sprocket, to see if this solves it?

Ok, when I pull the wire slightly by hand it moves the derailleur wheel further inward and lines it up better and there is a definite improvement in noise. How do I make this adjustment permanent?

Where the housing ends at the RD, or up at the lever there's an adjusting barrel which fine tunes the cable length. Turn it out (lengthen the housing) to bring the trim inboard, or inward to trim outward. Do it by degrees trial and error, until the RD centers properly and shifts equally well in and out.

Hah! Now you know how to get a derailleur to index. I didn't realise you were unfamiliar with the barrel adjuster...

Yes, I'm a bit of a novice when it comes to maintaining my own bike, I usually take it to the shop. Thanks for all the advice, I'll try that in the morning it's getting a bit late here in the UK.

Yes, I'm a bit of a novice when it comes to maintaining my own bike, I usually take it to the shop. Thanks for all the advice, I'll try that in the morning it's getting a bit late here in the UK.



One more step while you're at it

If replacing/respacing the cassette was enough to throw the trim off, odds are that the limit screws also need to be re-adjusted. This is another critical step even more important than adjusting the trim because proper limit adjustment is the difference between the chain or RD going into the spokes or not.

Locate the two small screws on your RD which control the extreme limits of travel, often marked "H" for high gear (outer) limit, and 'L" for low or inner limit. Adjust the outer "H" limit first by setting the lever in high gear, and using your thumb on the lower pivot to shift to the next cog. While holding it there turn the screw in one full turn, then let go and pedal. The RD should be sluggish to return to high. Repeat and back off the limit by degrees until the shift happens crisply and the RD trims on high gear correctly.

Repeat a similar process for the inner "L" limit screw. Shift to the second largest sprocket then make the last shift by direct thumb pressure. Tighten the screw until you cannot shift to the largest sprocket that way then back off by degrees until the shift is smooth, and the trim is correct, making sure that you cannot overshift the chain ir RD into the wheel. Now check the adjustment by shifting using the lever.

It's important to test the limits by direct pressure because the click in the lever might act to hide a mis-adjusted limit otherwise, until one day while climbing you overshift past the last click and......(Oops)