SRAM Red RD and small cog help

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Posts: 167
Joined: Mon Apr 19, 2010 10:33 pm

by styrrell

Anyone have any issues with getting a Sram red RD to run on the small cog effectively. On my build it wants to click onto the next highest cog. Eeverything else is perfect. It doesn't skip but but does catch a tiny bit. The limit screw isn't the issue and the B screw is fine. It pretty much feels like the spring doesn't have enough tension to move it over that far.

When I first put the bike together it was a big issue so I put a thin spacer between the RD and frame. That helped but I am wondering if their is a better solution.

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by sungod

if you completely remove cable tension does the rd sit in the correct position?

if it's never worked ok i'd be checking from scratch

for instance, is there a spacer on the cassette? is it superfluous or the wrong size?

by Weenie

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by styrrell

with no cable tension and the limit screw out all the way still no luck. the cassette is a shimano 10s on a shimano 10 speed only hub. No extraa spacers.

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by Lig

Hi Styrrell,

It might be worth getting your rear hanger checked for alignment...


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by 743power

Very rarely I find I need to add a very small shim between the rd and hanger to alleviate this problem. I think this is a known issue on certain specialized bikes and it pops up every now and then on others. The shim basically alters the rd position to allow the return spring to have a higher tension in the highest cog. Its a bandaid fix that i dont particularly like, but certain wheel/frame/hanger/rd combos dont leave enough space between the 11t and the outside of the hanger to let anything else work. Before this, I would check hanger alignment. Also, make sure there isn't a large amount of paint between the frame and the hanger. I would carefully scrape it off with a razor if there is. The last thing to check, is to make sure the rear piece of housing is long enough with the sram rd. without a b-spring, the housing length, if too short can pull the rd back and away from the 11t which can amplify skipping.
"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction."

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by styrrell

Thanks all,
Yep checked the RD hanger and its a ti frame so no paint. I'll likely just add a shim, but was hoping their was a way of getting more tension out of the RD spring.

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by eric

If you grab the der and pull it out (with cables removed and high limit screw backed off) does it track on the cog ok? Then it's the spring. If not, the der doesn't have enough outwards travel. If that's the problem you'd need a shim.

The spring is Ti so I'd be leery of bending it to get more preload.

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by styrrell

Yeah, when I push on it just a touch the noise goes away. It probably needs about 0.1 mm lthough it sounds worse in the stand that on the road.

by Weenie

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by indigo

I think I recall seeing this problem with SRAM Red whereby when the head of the limit screw is fully loosened, the silver screw on the knuckle is not completely flush and touches the parallelogram. Just reducing the profile of that screw may be what you need. If you do not know what I mean let me know and I will post a pic tonight.

Also, this was a Zinn column (SRAM specific issue at the bottom) :

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