Derailleur setup

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ipcookson
Posts: 18
Joined: 19 Apr 2018, 9:28am

Derailleur setup

Postby ipcookson » 11 Feb 2019, 12:33pm

After my new bottom bracket, chain and cassette fiasco I've now found the gearing is all to pot.
As the new BB is a couple of mm wider, the front derailleur won't shift into the largest chainring properly, which I think I can adjust with the H adjustment screw. I'll skip the fact that I can't turn the L screw to adjust the inner range for now!

But the rear derailleur doesn't want to shift the chain on to the largest two sprockets on the rear cassette, which was a shimano compatible, but slightly narrower cassette than I had on, so I added a 1mm spacer.

My question is ... what's the best way to go about setting it all up properly without giving it to my LBS? Gear cable length first? Rear derailleur first then front?

Yours faithfully.
Confused of Stockport.

thelawnet
Posts: 2077
Joined: 27 Aug 2010, 12:56am

Re: Derailleur setup

Postby thelawnet » 11 Feb 2019, 1:00pm

Have you tried this video/text? https://www.parktool.com/blog/repair-he ... adjustment

The shifting to the large sprocket is achieved by pulling the gear cable - when the gear cable is loose and has no tautness, the derailleur should sit below the small sprocket, and each click of the shifter should move it one sprocket inbound.

Therefore the first thing to do is to loosen the rear gear cable bolt so the cable is not pulling at all, and adjust the H screw so the derailleur is directly below the smallest sprocket (see video above for more guidance on this).

When the H screw is correctly adjusted, you can tighten the cable bolt so the cable is barely taut, check that the derailleur is not shifting when you pedal and the shifter is in the smallest cog (if it is the cable is too tight, it will cause the derailleur to move), and then use the shifter to shift down a gear. If it's not shifting that means the cable is too loose, and you can tighten it progressively using the barrel adjuster until it does shift. If your barrel adjusters are cheap and nasty it's not that easy to tighten, but at any rate try to adjust the barrel adjusters so they have both directions of movement BEFORE tightening the cable bolt

Once the shift from small sprocket to second-smallest is achieved by ONE click of the shifter, you can continue shifting up the range using the shifter. If it shifts 10-9-8-7-6-5-4 etc but is not able to shift to the largest sprockets that means the L screw is too tight, and you should loosen it until it can make those shifts.

As a note, you can make the L screw VERY loose and this will eliminate any possibility the L screw is stopping your shifting. The L screw is a safety mechanism against shifting the derailleur into the wheel - it will shift fine without it. Obviously when your shifting is working well otherwise you should set it, but it's not required during the initial 'it doesn't shift properly' stage. From your post it's not clear if it's shifting correctly from the smallest cog (in which case it should be an L screw issue), or if it's requiring several clicks to move off the smallest cog (a cable tension issue)

You can & probably should look at the B screw as well, but I wouldn't start wildly twiddling until you've dealt with H, and cable tension.

As far as the FD goes, yes you can do that afterwards - the main thing with the FD is to check cable tension & limits so that big ring/small cog and small ring/big cog are just a mm away so that they don't rub on the derailleur cage, but do shift smartly.

I would have a nice screwdriver for derailleur screws, don't attempt to adjust them with multitools if you can help it. A nice screwdriver with a rubber handle and a well-machined head.

thelawnet
Posts: 2077
Joined: 27 Aug 2010, 12:56am

Re: Derailleur setup

Postby thelawnet » 11 Feb 2019, 1:25pm

also it probably would be easier if you posted this to your previous thread, for context

viewtopic.php?f=5&t=127878

cookie_monster72
Posts: 10
Joined: 4 Jun 2016, 2:56pm

Re: Derailleur setup

Postby cookie_monster72 » 12 Feb 2019, 7:42am

thelawnet wrote:also it probably would be easier if you posted this to your previous thread, for context

viewtopic.php?f=5&t=127878
Thanks for the detailed reply. Very helpful! I did think about adding it to the previous thread but thought for clarity it was better on its own.

Cheers!

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