maartendc

Hello all,

I've got a problem with my rear derailleur (Sram Force 10 speed). It shifts perfectly fine, so derailleur is adjusted properly. But every so often, the chain will become dislodged from the bottom pulley wheel of my rear derailleur. This usually happens when shifting into the big ring, or riding rough terrain. This causes the chain to get stuck between the pulley wheel and derailleur cage, and the whole drivetrain locks up.

Last week, this caused my derailleur hanger to snap off, as when the chain locks up, I basically "break" the whole thing off by pedaling.

Now, what is causing the chain to become dislodged from the pulley wheel?

I've just installed a brand new derailleur hanger, and the alignment of the whole bottom half of the derailleur is at an outward "angle". Perhaps this is causing the chain to become dislodged?

- Is this caused by my derailleur cage being bent? (I've had a few small crashes recently so it is possible the derailleur got knocked and bent).
- Or is this caused by wrong alignment of the NEW derailleur hanger? (i.e. should I bend the derailleur hanger to get the derailleur "straight"?)
- Is my derailleur cage warped? I have already taken some pliers and tried to close the "gap" between cage and pulley wheel, as it seemed larger than normal.

Thank you!

JohnDThompson 

Whenever you replace a hanger or rear derailleur, you should check the hanger alignment before mounting the derailleur:

frankenmike 

Geez it sure looks like the pulley is off to one side. Is it possible that a spacer got moved, or something is installed wrong? I would try to get that pulley centered somehow.

bldegle2

Appears the B stop screw is binding sideways, have to be careful it clears the mounting shelf when the derailleur gets attached. Also, you need to Dag 2.2 the hanger to correct position. Tool is worth the investment. I have had no problems since adding it to my collection of biking related tools...

TakingMyTime

That bottom pulley is really off center. Are you sure that isn't supposed to be the top pulley with a little left to right float? Just guessing.

Leisesturm

Nothing can be said about anything at this point IMO. Too many variables changed. New derailleur hanger, new derailleur, past crashes ... ... take the bike to a co-op and let someone with the experience to figure it out have a go. Is the chain long enough, or is it maybe too long? It shouldn't be if it is the OEM chain but I no longer take anything for granted when answering posts.

tFUnK

To add to what's already been said: you might try to adjust the b screw so that the top pulley is closer to the cogset, reducing the length of chain that is getting pulled outward.

Spanner whacker

Have you removed the pulley wheels? Ive seen chains ride off the from being worn and also from them being the wrong way round, some are directional.
It looks like a sram apex or force rear mech and the b screw is where its meant to be.
I would check the hanger first

maartendc

Thanks for the reply. I have taken out and cleaned the pulley this weekend. It looks to be installed correctly. No spacers, apart from a metal ring on either side designed to keep dust out of the bearings. If I reverse the pulley, the pulley wheel brushes up against the derailleur cage, so it is definitely meant to be installed the way it is.

The limit screws seem to be fine and not touching anything they aren't supposed to, if that is what you mean?

I will look into getting that derailleur hanger tool, but it is quite expensive.. But is it possible you need to "bend" the derailleur hanger to such a degree as to straighten out my derailleur?? Seems I would have to bend it, like A LOT, to straighten this situation out, doesn't seem right to me..

I am thinking the derailleur is just broken.

Thanks for the suggestion. I've looked at the pulleys over the weekend, and everything seems to be installed the way it should.

Thanks for the feedback. Pulleys seem to be installed correctly, removed and checked it this weekend. Definitely the right way round. It is indeed a Sram Force derailleur, and the limit screws seem fine.

I will check the hanger, but like I said above, it seems like A LOT of sideways movement. Not experienced with hanger alignment, but it seems I would have to bend it an unreasonable amount to straighten this situation out.

There is also an awful lot of space between the bottom pulley and the derailleur cage, space that the chain gets stuck into when it comes off the pulley. Which makes me think the derailleur (cage) is somehow broken or warped. I might just try and replace the derailleur (can find them on Ebay for about 50 bucks used or 110 new)

100bikes

From my perspective, the alignment is off.
The pulleys are definitely out of alignment in the vertical plane, and may be out in the horizontal plane as well.
A photo from the bottom of the assembly would be helpful, as would a drive side shot of the area.

Was dropout replaced?
Did the bicycle fall over on the drive side?
Was the derailleur removed ?
Potential exists to cross thread it into the dropout( alloy is pretty soft material, relative to the derailleur bolt)
Is the derailleur hanger original? I ask because , from the photo the mounting appears to be a bit wonky.

The derailleur does not seem to be square to the hanger(note the slight gap of the derailleur at the bottom of hanger
and the angle of the derailleur stop on the hanger itself which is off center),

While there is really no replacement for the correct tool(Dropout alignment tool), a simple and gentle
"cold set/ BEND" toward the wheel of the bottom of the pulley assembly would be a bandaid fix.

Good luck.
rusty

woodcraft

I have a Force RD that I held up the pic of yours.

Based on that, the body looks aligned, & the cage does not,

so I think there's little to lose in attempting to muscle the cage back into alignment.

I would take the cage apart and try to bend (straighten) the attached side while not damaging the hanger.

maartendc

Thanks for the feedback. Yes the bike has been involved in some falls, but the derailleur hanger is brand new. The derailleur itself might have been damaged.

I am pretty sure the derailleur hanger is installed correctly and snugly against the frame. It is the correct derailleur hanger for my frame.

I have just ordered a derailleur alignment tool, to see if that brings a solution to the problem. If not, I will try to fix the derailleur itself, or replace it.

Here are some more shots from different angles of the area:







Thanks a lot for that photo, that is really helpful!

I think you might be right, it seems to me that the derailleur cage is warped "outwards" both horizontally and vertically. The bottom pulley is way too far out from the cassette versus the body.

I will first try the derailleur alignment, see if that fixes it. If not, I will attempt to straighten out the derailleur cage. If that doesn't work, I guess I'll need to replace the derailleur.

Thanks!

100bikes

From the photos, your derailleur is definitely off in both planes- horizontal and vertical. The tools will allow you to correct both.

Using an alignment tool should solve your problem.

Take your time, make multiple checks and slight adjustments at various points on the wheel and things should come out near perfect.

The alignment tool should thread into the dropout easily, without any binding. If not, you may have an issue with the dropout itself.

BTW, the replacement dropout looks correct.

rusty

drlogik 

It appears that the derailleur cage is slightly bent and the bottom jockey wheel is off to one side also. Check that the jockey wheel bearing and spacers are installed properly. You may have both spacers on one side instead of one on each side.

You may need to remove the whole derailleur and lay it on a piece of glass to see where and how badly it is bent.

Also use a string, 12" ruler and a measuring tape to check the back frame triangle to see if it is off-center. Do that with the wheel off and no tension on the frame or drop-outs. Set the ruler so that the 6" mark is centered between the drop-outs and use a string from the center of the seat down tube back to the 6" ruler mark. Eyeball to see if both triangles are aligned properly and centered. You'll need a buddy to do this.


-

LV2TNDM

It wouldn't be a bad idea to also check dropout alignment when checking the derailleur hanger. Start with your foundation and work your way up. That said, the photo from below shows the chain and/or lower pulley wheel is not centered between the cage plates. But if you confirmed the pulley wheels are correctly installed, they shouldn't be off-center.

And all bikes suffer dings and falls. These minor incidents don't "bend derailleurs." They certainly don't bend the metal or material between the parallelogram and the binder bolt. It's the hanger that suffers the damage. And you have to know the hanger is straight.

Once you establish proper dropout and hanger alignment, if the derailleur doesn't hang straight (vertical, or perpendicular to the axle plane), then you know it is indeed the rear derailleur. I'd rebuild if if I could. Make sure the spring-tensioner pivot mechanism is in order and not missing any bushings or parts. Same with the binder bolt pivot. If that isn't it, then perhaps the cage was bent. Whenever a derailleur goes into the spokes, it's the cage that usually makes contact and receives most of the force. That may explain why the chain isn't centered on the bottom pulley between the cages.

Checking frame alignment isn't a bad idea either, but unlikely to be the issue. If you do, the string method is a great way and requires no special tools. Just a string and a ruler. Run the string from the inside of the right dropout, past the seat tube to the OPPOSITE side of the head tube, around and back to the other dropout under tension. The distances between the string and seat tube on each side should be equal. I'm sure you can find a YouTube tutorial. And chain length should have nothing to do with this problem.

Good luck.

hrdknox1

I don't think the cage is bent. It looks like your derailleur is threaded crooked into the hanger. There appears to be a larger gap at the bottom where it screws into the hanger than at the top. It could be that the B-tension screw caused it to thread crooked. I would remove the derailleur and, before putting it back, make sure that the B-tension screw clears the hanger.

jadocs

The cage sure looks bent to me. If that is the case, adjusting the hanger is not going to solve that. Check the hanger alignment and make sure it's straight, but if your cage is bent you will have to address that separately.

tFUnK

I second the checking of the b screw. Confirm it's not preventing the rd from threading on flush, and also maybe back off a few turns so that there's less distance between the top pulley and the cogs.

maartendc

Thanks everyone for the responses!

I am getting my derailleur alignment tool delivered today, so I will check:

- the threading of the derailleur into the hanger. (although I am pretty sure it is threaded in there correctly)
- the hanger alignment with the alignment tool.
- If that doesnt solve it: the derailleur cage.

The frame / dropouts are all full carbon, so there is no way to "adjust" or "align" these. I cannot bend or cold set these parts like you could with a steel frame. That being said, I also don't think they can be misaligned (even in a crash) like with a metal frame. Carbon doesn't "bend".

trailangel

Isn't your DR hanger replaceable alloy?

bldegle2

That big shiny screw in da bottom/last pic, that is your 'b' stop screw. There is a little ledge on the end of the hanger the end of the screw must make contact with. If you do not make sure the protruding screw is on the little shelf when installing, then it is possible that the end of the screw is wedged between the derailleur hanger and the derailleur, causing exactly the misalignment you are seeing. Recheck the 'b' stop screw before trying to straighten the hanger. BTW, eyeballing the hanger alignment is very hit and miss...Also, I have done the 'b' stop screw mishap a time or two wile reassembling...as far as alignment goes, even with a new hanger, sometimes adjustments have to be made to make it right....

Crankycrank

Here is a fiche of the Force R Derailleur. As other have pointed out it sure looks like, among other problems, that the lower jockey wheel isn't installed properly. Scroll down to page 10 & 11 here and it shows how it's assembled. https://www.servicearchive.sram.com/...spc_-_revh.pdf Also previously mentioned if the jockey cage is bent you can try to flatten it out. Get these two issues fixed along with getting the hanger aligned and go from there.

mitchmellow62

+1 for the derailleur to hanger interface. It may be optical illusion but the entire derailleur looks as though it is tilted away from vertical.

woodcraft

The OP did say that the RD was yanked back enough to break the hanger so the issues can be beyond normal set up.

I've had that problem of the chain catching, but not enough to do any damage. A slight back pedal frees it.

Mysterious, and disturbing.

maartendc

Thanks for the suggestion, but no, the B stop screw is not wedged and makes correct contact with the derailleur hanger as shown in the Sram official manual

I have checked the manual, and the jockey wheel seems to be installed correctly. I have disasembled and reassembled it... I do agree it looks misaligned. I think it might be damaged, or suffering from the misalignment of the derailleur cage.

So an update:

- I have double checked the installation of the derailleur into the hanger, everything is correctly installed
- I have aligned the derailleur hanger with the hanger alignment tool. There was some alignment required, but unfortunately, to no avail. The derailleur is still "bent outwards".
- I have looked at bending the derailleur cage straight, but the problem is that half of the derailleur cage is made of carbon, so it cannot be bent. It seems like perhaps the attachment of the derailleur cage to the derailleur body (metal) is bent / misaligned, but I cannot by hand get it straightened out.

I have ordered a new derailleur... seems to be the only fix at this point.

Thanks!