Chain Breaking and Skipping I need help!

[KenP]

I have a 1999 EVO that has been a great bike for that last few years.  But in the last year I have run into a problem and I am at my stumped so I need help.

For a while I was getting really bad chain skipping under peddling in 2nd and 4th gears to the point where I broke a chain.  So I will start with the simplist thing and work from there, so I fixed the chain and replaced the cable, no joy still skipping.

So I replaced the front chain rings, rear cog and chain, skipping is less but sometimes is still there.  

I like to ride in 2nd cog in the back middle chain ring on the front, if you back peddle sometimes the chain jumps down the rear cog without the derailer moving.  Other times under load you will feel and hear the chain skip cogs in the rear.

Tonight I was riding a wheelie and snap the chain breaks again.  2nd cog mid chain ring.

Setup is as follows.

9 speed Sram 7.0 that is 5 years old
New Sram cog
New Sram chain
New Raceface rings
New cable.

What do you guys think could be the issue?  Is the derailer shot or should I look at the derailure hanger?  The bike shifts fine when I am riding flat but put a bunch of pressure on the drive train and sometimes you get a skip or a chain snap.

[Old Proflexer]

one, did you replace or remove and completely clean the cables? (possible kink some where)

two, did you replace the rear cable housing from the dropout to the derailler and give it plent of bend?

three, did you check to make sure that the cable housing is not being stretched somewhere near the swingarm and is attached properly? (remove shock, shift gears with the swingarm in a variety of postions)

four, did you check the derailler cogs and make sure all is clean and smooth in the derailler?

cinco, is the derailler hanger bent? (take it off, heat it and pound it flat gently on concrete)

six, are you riding a cheap chain and/or is it an 8 or nine speed chain on a nine or 8 speed setup?


there's a few more, but i'd try those first

OP

[KenP]

The only ones you list that I have not tried is checking the deraileur hanger and the derailuer cogs.

The cables are new.
The cable housing is new
I have them routed freely, I fixed the streaching issue 2 years back.
Chain is a 9 speed chain
Chain is good quality Sram chain

What really sucks is on the bike stand everything is great the problem only shows up under tension.

I will check the hanger and the cogs and see what is up.

[shovelon]

Don't forget to check for wobble in your derailleur. If it is an early ESP it is gone.

Terry

[Old Proflexer]

check every single link on the chain for a tight link -
bend both ways and sideways as well -
a single tight link can cause that

OP

[Matno]

The cable housing is new
I have them routed freely, I fixed the streaching issue 2 years back.

I'd double check the housing length. The cable housing section between the frame and swingarm (it's only a few inches long) is the #1 culprit for ghost shifting on these frames, especially when it's fine on the stand. It only has to be 1/4" too short to cause horrible ghost shifting and may not be noticeable when you look at it.

[kiwi]

eliminate matnos observation by running ful length housing through the swingarm.
It sounds like a wobbly rear d to me

[Matno]

I missed this part the first time...

if you back peddle sometimes the chain jumps down the rear cog without the derailer moving.

That sounds like a chainline issue. Are you sure you have the right size bottom bracket? Should be 73 x 113mm. You did replace the entire cassette in the rear right, not just one cog? I'd make sure it's tight (they can develop a lot of side-to-side play if not tightened enough the first time).

When you say 2nd cog, is that second largest or the second smallest? How sure are you that your chain is a 9 speed? Just curious...

Only other thing I can think of is that if you have a carbon swingarm, maybe one of your dropouts has come unbonded from the swingarm and flexes under pressure. Not likely, but possible. If so, it could certainly cause the problems you're experiencing.

[KenP]

You guys have given me every idea that I have tried.  So at least I know I was on the right track.

1)Years ago I changed to full length housing because of ghost shifting.  

2) The bottom bracket has been on the bike for 4+ years with no problems.  I also thought the chain line could be the issue but it looks ok.

3) The second chain I have broken was brand new, so no stiff links there.

4) Yes the chain was a nine speed chain, I would expect more issues then I am getting if the chain was a 8 speed chain.

5) The swing arm is aluminum so no luck on the drop out coming loose.

The derailure is old, at least 4 years old, maybe I will get a new one and try that.  If that doesn't solve the problem then either my bottom bracket is trashed or swing arm is totally bent.

I will let you guys know what happends.

[Simon]

Something I don't think has been mentioned,
have you checked for excessive play/wear in the
freewheel bearings just a thought as you appear to of covered every other option,
when ever I've had chain skipping issues this has just indicated to me that its time for a new chain and cassette,once changed as a pair everythings back as expected,I always use a shimano LX or XT cassette with
Sram/Sach or Shimano chain,
Simon.  

[Sprucey]

I'm in the business.
My first immediate thought has been covered - you have bent the deraiileur hanger.

Re checjk the cable housing lengths - ghots sfiting may be the cause but that would only happend when the suspension is being compressed/extended.

latly, jockey wheels are the last issue. If the rear mech is old it's cheaper to replace the rear mech rather than just the jockey wheels. The springs get soft and th linkage rivets develope play.

Sprucey

[KenP]

I looked at the rear derailuer tonight and boy is there slop in that thing, I compared the slop to other bikes I have and the other derailuers move a little the one on this bike moves a who gear or more.

So I bought a new rear derailuer tonight and hopefully that will fix the issue, if not then only two things left the hanger or the freewheel.

[KenP]

Ok here is an update on the chain skipping.

Replaced the derailuer and chain, still got skipping.  
So started to try some other things, and shortened the chain by two lengths.  Skipping was less so went for a ride in the woods.

Still got skipping, but the deraileur always skipped down to a high cog since I don't have a rapid rise system that means I had slack in the cable.  So while riding started to adjust the cable tension skipping eventually stopped.

So although I can not pin down the exact solution a new derailuer and cable adjustment seemed to do the trick.  If anything with a whole new drive train I am ready for the next two years or more.

[Carbon_Angus]

Thanks for keeping us posted with your efforts, and keep us updated, too!

[smiley=beer.gif]

[Frankd3000]

Well, you get the award for persistence, that's for sure. I'm sorry to hear about this, but admire your attention to detail.

Now you mention, Ken, that you replaced the RD. Okay, that's helped, BUT as suggested by OP - have you looked at the actual RD hanger? NOT the dropout - the hanger.

You mention that you have an aluminum s/arm - does this mean you still have the replaceable RD hanger? If so i'd strongly recommend you do two things;

1) remove the hanger. Take it right off and check for dirt/grit between the s/arm and hanger.

2) check if it's bent when it's off the bike. just put it on a flat surface, like a table or countertop. It should be completely flat. While this WON'T give you the issues you're having (if it's bent and the RD is re-adjusted to compensate then you're good to go - period) it's wise to check it while it's off anyways. Only takes two minutes to do.

Check these. I'm banking on dirt between the two parts.

IF it's not replaceable then ignore this entire post. If it's bent or even if the chainline is out by 2 mm you can always adjust this stuff "out of the equation". The problem you're having is one where excessive play is the culprit. You already mentioned it's all good on the stand.

The freehub/rear wheel bearings, main pivot and other bearing/bushing parts should all be suspected, inspected, checked and "serviced" (at least cleaned and checked for function after cleaning).

Also, check for cracks in the frame and s/arm. If there's a problem only when the bike is "loaded" then you can rule out all "static-induced" problems.