rear derailier end stops?

dirkdiggler69

i have just bought my first road bike for a couple of years and i'm well pleased with it.
however out on a decent climb today and when i had the bike on front small ring rear biggest gear it would go on the biggest rear gear but jumped back down a gear after around 20 yards.
is this due to the end stop on the derailier and if so which screw is it i should adjust it with and in which direction?
btw its a 10 speed centaur derailier

lucan

Do a search on YouTube. There are lots of videos showing you how to set it up properly.

dmch2

It could be the endstop (or less like the adjustment from the sounds of it).

If you put the bike in bottom gear and give the cable a tug I'd expect it to feel absolutely solid if you're against the end stop.

The derailleur will have an end stop for the low and high end. Give one endstop an anticlockwise turn and you should see the derailleur move. If it doesn't then you've got the High one (On the Shimano ones I've seen they have a barely visible L and H - not sure about other makes) so screw it back a turn and try the other one.

You obviously want to adjust so the RD moves lower so it stays in first. Try it with one turn and see how you go. Spin the cranks to make sure nothing catches. Then if you take a screwdriver with you on your next ride (or do a test ride to a hill) then you can always tweak it a bit.

the secret is small changes each time and to remember what you've done.

woodywmb

Not the limit screw. Assuming your derailleur is Shimano 2003, Sora, Tiagra or 105, turn the plastic adjuster (at the end of the cable outer as it enters the mech) anti-clockwise. Keep turning it a quarter of a turn at a time till the chain settles in the biggest cog and stops trying to drop down to the next biggest cog. Do it on a stand. . . or get someone to lift the bike at the saddle with one hand and flick up and down first and second gear using the shifter with the other hand. You turn the cranks with your right hand and fettle the adjuster at the back with your left. Should take all of two minutes. (The adjuster works in reverse for any derailleurs above Shimano 105).

dmch2

If it's only in first then surely it is the limit screw? If the RD doesn't move when you pull the cable then it's hard against the limit. If it does then something else is going on

woodywmb

dirkdiggler69 wrote:

. . . it would go on the biggest rear gear but jumped back down a gear after around 20 yards.:)

1. It's not the limit screw if it does lift onto the biggest sprocket.

2. Didn't see mention of Centaur gearing. Sorry folks. Rules are the same as Shimano but don't know if the adjuster goes clockwise or anti-clockwise.

dmch2

Good point... Hmm... but why don't the other gears jump out? Is it just the chain angle pushing a slightly out adjustment over the edge?

woodywmb

The chain's at its biggest stretch on this part of the cassette and more prone to moving because there are many more teeth engaged and the derailluer spring is at its tautest. I have checked Zinn and he confirms that Centaur is sprung from high to low, which means the biggest cog will have most pressure on it.
A few simple tweaks as outlined above will have it lined up and purring perfectly.

dmch2

That's me learned something for the day then! Only 40 minutes into the day as well