Gears skipping at random

[Super Sywurm]

Try replacing your cassette before you try anything else, you say you replaced the chain but not the cassette? I'm willing to bet it's that.

Bent hanger!!

I've been in this industry around 15years and worked for some world class riders/ teams as mechanic so I'm qualified to shoot through closed toilet doors If it is a closed cable system on the bike then it could be quite a few other things- loose freebody/cassette, bent derailleur hanger( but I don't think so as this will be permanent problem), shifter internals damaged, derailleur wheels, very F**d casset, frayed cable, ferules not positioned correctly in frame and shifter. The derailleur could be set to far away from the cassette and so the list grows. But I'd rather shoot through the toilet door as this is a common problem on dual suspensions.

Check that the wheel is properly tightened

Often the problem is the cable loop into the derailleur is too tight, try increasing the loop size to give an easier flow on the cable to stop it catching and hanging up.

 

I think I found the problem, it's not the chain, the wheel, bent hanger, rear derailleur or the cassette, but the frame. I have a dual susp that can lock the rear shock and I can lock my frame.

 

When I lock my frame, the problem seems to sort itself out. I now told my lbs I want it repaired under warranty (bike is less than 5 months old) or I want a new bike, lets see what the outcome will be.

[quickdraw]

I think I found the problem, it's not the chain, the wheel, bent hanger, rear derailleur or the cassette, but the frame. I have a dual susp that can lock the rear shock and I can lock my frame.

 

When I lock my frame, the problem seems to sort itself out. I now told my lbs I want it repaired under warranty (bike is less than 5 months old) or I want a new bike, lets see what the outcome will be.

 

The problem is the gear cable housing lengths are probably a bit too long/short and is kinking when the bike goes through it's suspension travel. Check the lengths of housing especially where it connects the front triangle to the rear. Good way is to remove air from the rear shock and then check that the cable does not pull when your suspension goes through it's travel - also ensure the inner cable still move freely.

[V12man]

Bent hanger!!

 

It doesn't take a lot of bend for this to happen - take it off the bike and check it on a flat surface - granite kitchen counter should be good enough.

[quickdraw]

Because the gears are skipping at random and only when suspension is in motion it is the gear housing setup.

 

Bent hangers, chainlinks, etc will result in a constant skipping irrespective of whether you riding on the road or mountain.

[droo]

+1 for cables. Take the shock off and make sure the swingarm can move through its full range of motion without kinking or pulling the cables.

[Super Sywurm]

Thanks for the advice, my lbs has to fix this, because there is another gear related problem they have to fix.

 

This problem started the first time I got on the bike and they can't fix it. When I shift gears from small to big at the back, it tends to jump back 1 gear (where it was originally). So, I have to shift 2 gears and then it jumps back 1.

[Old school]

I think I found the problem, it's not the chain, the wheel, bent hanger, rear derailleur or the cassette, but the frame. I have a dual susp that can lock the rear shock and I can lock my frame.

 

When I lock my frame, the problem seems to sort itself out. I now told my lbs I want it repaired under warranty (bike is less than 5 months old) or I want a new bike, lets see what the outcome will be.

 

That means I was correct and that you need a uninterrupted housing for your gear cable which will solve the problem as it will inhibit any suspension movement to go over to your gear cable tensioning which causes shifting on bumps, again see my first post. This is the problem with many new dual mtb's.. Good luck, this would also be my last post on the subject. Just for interest which frame do you have (brand name)? To test this shift your rear so the chain is around the middle on the cassette lean over the bike compress the shock downwards and see how the derailleur moves across the cassette. You will have a huge fight with the distributor over this as it will cost them A-LOT to get all the bikes fixed they sold. In the end you will most probably be back doing the full cable housing from shifter to derailleur. I'm waiting for my six pack...

[janneman72]

When I ride off road over rocks or corrugation, my mtb keeps skipping and shifting gears at random (when I go over bumps in the road). I have a brand new chain on and had the bike at my lbs and they did some adjustments on my rear derailleur, but they did not fix the problem.

 

What to do???

The chain might also be too long as it is a new chain. Most lbs miss that part when installing it.

[Super Sywurm]

That means I was correct and that you need a uninterrupted housing for your gear cable which will solve the problem as it will inhibit any suspension movement to go over to your gear cable tensioning which causes shifting on bumps, again see my first post. This is the problem with many new dual mtb's.. Good luck, this would also be my last post on the subject. Just for interest which frame do you have (brand name)? To test this shift your rear so the chain is around the middle on the cassette lean over the bike compress the shock downwards and see how the derailleur moves across the cassette. You will have a huge fight with the distributor over this as it will cost them A-LOT to get all the bikes fixed they sold. In the end you will most probably be back doing the full cable housing from shifter to derailleur. I'm waiting for my six pack...

 

It's a 2012 Mongoose.