Thursday, 21 June 2012

Lakes ride - prep 3

One of the items on the checklist for this weekend is "working bike". Put there by Sam, presumably as a piss take, but obviously essential.

For a couple of months now I've had some noise coming from the rear mech, which is SRAM X7. It hasn't really been shifting badly, except it would rarely drop into the highest gear unless my speed was up or a knock on the back wheel jolted the mech further along its travel.

I know its my fault, I should maintain it more regularly etc but it is 18 months old and has seen some miles.
The jockey wheels have small, pointy teeth, rather than the broad, flat-topped examples I looked at on the net last night. In the lowest gear the chain barely stays on the lower jockey wheel, instead slipping over the inside edge. The main problem I was having last night was setting the b-tension screw to give the correct chain gap between sprockets and top jockey wheel. The closest I could achieve was around 10-15 mm and adjusting the other way allowed me to drive a bus through through the gap. Looking at the mech installation instructions and comparing against my mech, it looks like there is a piece missing from the rotating collar where it attaches to the hanger. The hanger looks fine incidentally and the chain is the same length as the previous one.

I had the bike serviced at my LBS last October and had the problem of not dropping to the smallest sprocket since not long after that. My guess is the parallelogram spring has been stretched. I'm beginning to wonder if the missing piece was lost in the service as I did get a replacement hanger fitted.

Today I hope to get a half day holiday and take the mech to a shop and be able to compare the b-adjust set up. I think it may have to be a new mech as I doubt I can get spares for b-tension or new jockey wheels at such short notice.

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