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Discussion Starter · #1 ·
I have a Mach 5 w/ XT crankset and front derailleur. Rear derailleur is SRAM X-9 and I'm running two-rings plus bash in the front. On long rough downhills with no pedalling, the chain often drops off the inside chainring, even when starting on the middle ring and derailleur set to middle.

Does anyone have a suggestion to retain the chain better? With no seat tube in the BB area, it's hard to mount a simple N-Gear Jump Stop or similar.

Thanks...
 

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Not just famous; infamous
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1) With the chain in the smallest ring/biggest cog combo, set your FD limit screw until the cage touches the chain, then back it off slightly. This will help keep the chain from falling off the inside ring.

2) Make your chain shorter. With the chain on the middle ring (since you have a 2 ring setup) and biggest cog, pull the chain until you don't have a lot of movement left in the RD cage. Count up the extra links and remove them. This should help keep the chain on the middle ring. Disclaimer: please use common sense with this and don't make the chain too short. You don't have to get rid of every single extra link. Keep in mind that the suspension travel will create some chain growth. You should never allow your derailleur cage to completely stretch out, even at full travel. You may want to unbolt the rear shock, sag the suspension fully and then count the links, just to be sure.

Hope that helps.
 

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Discussion Starter · #3 ·
Thanks for the suggestions.

Since the chain drops even when I am shifted onto the middle ring, I don't think the lower limit screw will help much. I haven't looked too closely, but is there a way to vertically adjust the front derailleur? Without a big ring, ideally the cage should be moved down.

I was fairly agressive in removing links when I fitted the bash guard. I'll double check that, but I'm probably not too far from the limit.

Thanks again.
 

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You can move the cage slightly down, as I did, because factory installed, the chain was rubbing the bottom of the cage pretty bad in all but the last 2 gears and the small chainring. However, I found I was not able to move it down by much, maybe 2-3mm, because it only appears to want to adjust the whole thing up and down (slotted holes on the derailleur mounting). I was able to get rid of all chain drag by moving it as I did though...
 

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geogecko said:
You can move the cage slightly down, as I did, because factory installed, the chain was rubbing the bottom of the cage pretty bad in all but the last 2 gears and the small chainring. However, I found I was not able to move it down by much, maybe 2-3mm, because it only appears to want to adjust the whole thing up and down (slotted holes on the derailleur mounting). I was able to get rid of all chain drag by moving it as I did though...
it does sound like the chain length. since you are running a double you should be able to shorten the chain quite a bit.

to get the proper chain length break the chain and wrap it around the chainring and largest cog( bypass the derailleurs) and add one link. rerun it through the derailleurs and you should be set
 

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Yep, and by chainring, he meant the largest one, obviously. I sized mine that way, however, there are a few things I should point out.

When I used that method, I first moved the rear suspension and found the longest point of chain length, and used that as my "chain length," then I added a link (two bar sections, or three pivot points). I am a fan of the SRAM PowerLink, so, unfortunately, that added another half link (due to the way the chain has to be configured to use the PowerLink). When I put the chain back together, if I was in small chainring, largest cog, the chain had slack in it that was not taken up by the derailleur. This is on an XTR SGS (long cage) derailleur. This of course, was with the suspension completely sprung (meaning, it was all the way down). Maybe during normal riding, it would have been okay, but I did not like seeing the chain that way.

After asking a few questions, and with some other's recommendations, I removed two links from the chain (so, this actually means that I only have half a link of overlap that is recommended by Shimano, since I had the two link overlap, plus half a link for the PowerLink). This is actually only half a link of overlap at full suspension travel, so it is closer to about 1.5 links of overlap with the suspension fully down.

I feel comfortable with this, and it seems to be okay. You might check your chain slack at small chainring, big cog, with the suspension all the way down, and see what it is like. I bet, if you have slack, this is what is causing your chain to come off when you are hitting some rough downhill, as you would see the case where your rear suspension would overcome the sag in the back, causing it to fully extend, leaving slack that your RD cannot take up, causing the chain to bounce off the chainrings...

Just some of my observations.
 

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Discussion Starter · #7 ·
Ok. Here's what I've found out.

Re lowering the derailer position: It's already at it lowest setting. Ideally, because I have no big ring, it should be lowered about half an inch. It looks like the suspension link doesn't leave much room in this area, so I don't think any improvement is likely. I think that someone with the right metal-fab skills could make an anti-chain-drop guide plate that mounts under the heads of the derailleur-mount screws...

I checked on the chain length by letting all the air out of the shock, compressing the suspension, and rethreading the chain around the largest gears, bypassing the derailleur. Surprisingly, the length meets exactly at the maximum suspension compression, not counting the Powerlink. :eek: There's a bit of slack in the chain, so I have between 1/2 and 1 link extra. No margin at all to make the chain tighter!

CyProg: I'm an Austinite, so if this problem continues to vex me, I'll drop by your shop someday. I've been meaning to anyway to inquire about updating my shock to 2009 model specs.

Thanks again for the suggestions. Is no one else having chain-drop problems?
 

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It hasn't been mentioned, but have you turned the rear derailleur b-tension screw in? Increasing the b-tension adds lower chain tension and would reduce chain drop, but it also makes rear shifting slightly less crisp.
 

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Discussion Starter · #9 ·
derby said:
It hasn't been mentioned, but have you turned the rear derailleur b-tension screw in? Increasing the b-tension adds lower chain tension and would reduce chain drop, but it also makes rear shifting slightly less crisp.
I looked into this a bit today and you might be right. At first, I looked at the distance from the jockey wheel to the sprockets (big+big and small+small) and it didn't look promising. The jockey is quite far from the sprockets. So I played with the adjuster and found that there is no way to get the gap anywhere near the few millimeters that the instruction manuals prescribe.

This puzzled me for a while and then I noticed how much slack was in the chain, even in the big+big combo. Hmm. Oh, right, it needs that much slack with the suspension fully extended (on the stand) in order to have enough left under compression. Putting this idea together with the derailleur adjustment, it occured to me that perhaps I need to adjust the b-screw while holding the suspension in compression.

That's as far as I got today. I haven't taken the time to actually look under compression to see what's up, but it seems like a plausible idea to check out. I'll let you know what I find out.
 

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Just to point something out to you, if you want to adjust things with the shock under compression, I found that it is easiest to remove the top link of the shock (just takes two allen wrenches, one on the red bolt, and one on the silver bolt and unscrew the silver bolt until it is loose). You don't actually have to have all the air out of the shock, because there is just a tiny bit of movement left in the linkage, to allow you to get the top link out, without having to compress the shock at all.

This allows you to place the bike in a stand, close to the ground, and move the suspension to the compression you want, and let the stand hold it there for you. Works really well, at least, if you have a stand that you can lower almost to the ground...

Just a suggestion, it made my adjustments easier, plus, I wanted the rear brake cable routed in between the shock and the frame, not outside of the shock cavity, so I took that opportunity to insert the brake line inside the shock cavity, similar to how the derailleur cables are run. Looks much cleaner, and protects the brake line.
 

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Ninja, You can more easily turn the b-tension screw while rotating and holding the rear derailleur main body rearward. That takes pressure off the b-tension screw.

If it's a Shimano derailleur the screw may be pretty short and only have a few turns in to max. An old trick to gain more tension is to remove the derailleur and remove the b-tension screw and screw it in backwards, so that the screw head faces the der-hanger stop and so adds to the b-tension screw's reach and tension. Sram b-tension screws have more than enough of length.

I haven't owned or checked the spring tension of Shimano rear derailliers in over 2 years, but back then Sram had more derailleur cage spring tension giving tighter chain tension. I'd imagine the new Shimano Saint derailleur has more tension than XT or XTR too.
 

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Discussion Starter · #12 ·
Geogecko: Thanks for the tips. Just letting air out of the shock was not working very well. It still wanted to extend a bit and I had to rig bungee cords to get the set-up stable.

Derby: The derailleur's a SRAM X-9 with a long screw and an allen-head so it's easy to turn. :thumbsup: Thanks to you too.
 

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Is there a solution for mach 5 and no iscg tabs?

Hi Folks
I have a 09 mach 5 with a press fit bb running sram xx 2x10
Great bike but when i bounce around or god forbid jump at all the chain drops (mostly to the outside)

My chain is as short as feasible
Has anyone come up with a solution?
Would a blackspire stinger even work? my guess is not due to the press fit bb (which is plastic?)

I saw some other threads about an outside mounted bashguard (but its dicey given the design of sram xx 2x10, not a 3ring with the outer ring taken off) crank

Any pics of people's work arounds?

I have a transition blindside for freeride with a hammerschmidt, but that def wont work

Thanks
G
 
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