How often should I check rear derailleur adjustments?

Question

If I remove the (rattling)plastic disc -

1. How often should I check the limit screws on rear derailleur?
2. If the shifter cable tension is less than optimal, would this be a possible cause to drive the chain in between the spokes and the rear cog-set?
3. Excluding the case of debris getting stuck in drive-train; are there any other adjustments besides above two and true-ness of rear wheel that may cause the problem of getting chain between cogs and spokes?

Derailleur in question is a Shimano Deore.

Update: Details- For mileage, I commute about 110 miles/week.

Answer 1

It's really up to you how often to check your adjustments, but I'd say it's not an "every ride" kind of check, unless you're giving your drivetrain a workout! If there's any damage to the derailleur, hanger, or rear wheel, you may want to start there as well.

To specifically address your questions:

1. You should check your limits any time you have a drivetrain issue. That could be poor shifting, dropped chain, or inability to shift.
2. Shifter cable tension should only affect how easily/quickly the derailleur moves. However, there could be a case where too much tension could cause the derailleur to move through the last shift enough to stress past the limit screw, but I think this is unlikely.
3. The rear wheel could be out of dish (centered from side-to-side) which might have moved the cassette further in. Readjusting the limit screws should take care of that, but you might still have shifting issues. (I had the same problem this spring)

Answer 2

1. I don't believe these would move without external force but worth checking at every service.

2. No, the upper limit screw should prevent this from happening. Cable tension can be adjusted (most shifters and some RD have barrel adjusters) to optimize shifting between gears. Outer limits are fixed.

3. 3 I can think of:

   • derailleur alignment, is the hanger bent
   • is the wheel in the dropout properly
   • is the derailleur cage bent

Answer 3

I wouldn't bother checking until you see a problem, like difficulty shifting onto the biggest or smallest ring/sprocket, or the opposite: shifting off it. When this happens, it is not a "show stopper" problem. You can probably complete your ride, or even just pull over and make the adjustment right there.

There is usually a warning that the derailleur is going out of calibration. Before it becomes very difficult to shift to a gear, it first becomes slightly difficult and it progresses from there.

Regarding point 3, perhaps you're missing the plastic guard ring which goes between the casette/freehub and the spokes. Which is not to say that this is what prevents slippage, but it does prevent contact between chain and spoke.

By the way, one potential problem affecting the front derailleur, or at least some types, is that the entire assembly can rotate around the frame post to which it is clamped.

The front and rear derailleurs interact. Notice how it is easier to shift onto the leftmost sprocket when you're on the leftmost ring. So it cannot be ruled out that some rear difficulty is actually connected to a front problem.

One last piece of advice, and that is to install a rear derailleur protector, if you don't already have one. This part which installs on your wheel axle, held in place by the wheel lug nut. It extends a curved steel bar over the derailleur which guards it from being knocked around.

Answer 4

I'd say every week twice. Monday and Thursday are good.