June 2020 - TLC during lockdown 4

The return of the rear mech. 

I mentioned in a previous post that I was a bit gutted that the bike shop had fitted my rear mech as I was really hoping to give it a go myself. 

Well as it happens, they happened to have fitted the wrong one. They had used a mech designed for 8 gears rather than the 9 that mine has. This doesn’t sound too important, unless you a. Have an idea what that part does and b. Know that the reason you started changing bits was because the gears just kept jumping. 

So which bit is it and what does it do? 

The rear mech is basically a couple of cogs held on a moving hanger that he held in place by a big spring and a wire attached to the gear shift changers. As you loosen the wire, the spring moves the gogs away from the wheel. The wire is released by a specific amount each time you click the gears. So with everything lined up perfectly, the cogs allow the chain that’s running over them move onto the different sized cogs of the cassette attached to the back wheel. 

Lining them up to allow the chain to move perfectly between the cogs is called indexing. 

The mech I was given was working better than the one that had been removed, but I didn’t want to hit any issues that might be caused by a possible incompatable system (and possibly more of a driver - I wanted everything to match) I decided to change the mech. 

This was actually fairly easy (and again explained much better than I ever could in a Park tool video.) While I was at it, I replaced the hanger too. 

This is a small piece of softer metal that attaches between the frame and the rear mech. It is designed to be the weak link in the system - if the mech gets hit, the cheap hanger will bend and can be replaced rather than a costly repair or replace of the frame. 

Once I had everything back together I had to index the gears - this involved tightening or loosening the cable to get the cogs in just the right place to change gear. It was a lot like tuning a guitar. Not tight enough, it wouldn’t make the next cog, too tight and it would jump two. But after a while of fiddling, we hit a Goldilocks position. 

Finally it was out for a test ride. 

To my relief, it worked. But that’s a bit of an understatement really. It not only worked. It honestly feels like a new bike. I will leave you with a quote from the comments on one of the Parktool videos, which I wish I had written myself as I can echo with its sentiment ‘I would perform open heart surgery if Calvin had done a video and talked me through it.’ 

So apart from the bike feeling so much better to ride - what have I gained from this experience. A few more tools in my toolbox - both the physical one and the skills bag we all possess. But most importantly I have so much more confidence that I can sort a mechanical issue with my bike. I know there will be times I will need to hand it over to the experts, but the basic stuff is much easier than I thought. Now I just need to keep practicing!