Question about faulty service & repair

Cletus van_damme · 22-10-2015 9:16am #1

Hi,

I'm hoping someone with better knowledge of bikes than me might be able to help with a problem, here is a bit of detail about the problem.

I recently had an accident, a car hit me from behind and caused minor damage, after this I left my bike in for a repair and a service as it was due one.

The problem is that after collecting the bike, the front derailleur stopped working correctly within 10 meters of the bike shop, it wont change down unless the bike is on level ground. I returned to the shop and they tried several times to fix it but always had the same fault, even with fitting a new derailleur.

The mechanic tried the bike himself and had the same problem before telling me there was nothing more they could do, obviously I said no to this and I left the bike there for a few days for them to work on.

When I rang to check the shop told me it was "100% guaranteed working", when I got to the shop I was told four people had checked it and all agreed it was fixed. The same problem was back in under two minutes. I was also told that the problem could be because I was not slowing down enough before trying to change gears!

I was asked to take the bike and use it for a week or so to let the new parts wear in so that they will start working, i did 8k on it and it has gotten worse.

So my questions, that I hope someone can answer are, does anyone know what might be causing the derailleur to fail on an incline? and will using it for a week make it start working?

Thanks

Beasty · 22-10-2015 10:36am

Presumably you have observed what's happening while off the bike? So when you look at what's happening as you try to change down - is the FD correctly moving between the large and small rings? It may be something very simple like the limiter needs adjusting slightly (although I would have expected that to be one of the first things the shop looked at)

Cletus van_damme · 22-10-2015 10:52am

Beasty wrote: »

Presumably you have observed what's happening while off the bike? So when you look at what's happening as you try to change down - is the FD correctly moving between the large and small rings? It may be something very simple like the limiter needs adjusting slightly (although I would have expected that to be one of the first things the shop looked at)

The derailleur works fine when the bike is on a stand or level ground, no problem moving up or down the rings, once I try an incline it will not go down, you can see the derailleur begin to move the chain but it does not respond until its on level ground again.

As you guessed adjusting the derailleur was one of the first things they tried, even switching it out for a new one did not fix the problem.

2 Wheels Good · 22-10-2015 11:12am

Cletus van_damme wrote: »

The derailleur works fine when the bike is on a stand or level ground, no problem moving up or down the rings, once I try an incline it will not go down, you can see the derailleur begin to move the chain but it does not respond until its on level ground again.

As you guessed adjusting the derailleur was one of the first things they tried, even switching it out for a new one did not fix the problem.

Is it possible something else is broken and when the drivetrain is under pressure on the incline it's flexing and causing the issue?
Could you get someone to cycle/walk behind you and see if they spot anything, might be easier to troubleshoot

Cletus van_damme · 22-10-2015 11:32am

2 Wheels Good wrote: »

Is it possible something else is broken and when the drivetrain is under pressure on the incline it's flexing and causing the issue?
Could you get someone to cycle/walk behind you and see if they spot anything, might be easier to troubleshoot

I cycled it up and down an incline on a couple of occasions while two different people from the shop watched, after that they switched out the derailleur for another new one, that did not fix it so I would have thought the problem was somewhere else too but they cant find it.

Do you think using it for a few weeks will get it to work correctly?

nordicb · 22-10-2015 11:35am

I had similar experience with one of bikes that was brought to do a quick adjustment. The combination of either poor components but most likely wear made it nearly impossible to adjust the front derailleur - it either would not go up/down or rub the chain. More over the person didn't want to spend a quid... Just saying there are situations when it's hard to get this thing working as it should. The chain, chain ring or the derailleur can be worn making the adjustment window very small or non existent...

2 Wheels Good · 22-10-2015 11:46am

I hate to say it but the fact that you were hit by a car may mean your frame may be the issue and the minor damage isn't so minor. The derailleur may not be the issue, it could be the frame is either bent or there's a hairline crack somewhere.

smacl · 22-10-2015 11:49am

I've found adjusting front derailleurs can be finicky, in that they can perform differently under a heavy load than a light load. What has worked well for me in the past is to do the adjustment with the bike set up on a turbo with high resistance to simulate the load you get pedalling uphill. In addition to the limit screws, you have the FD height and orientation to get right, along with ensuring the chain is the right length. I go with height that allows about 3mm clearance between the mech and teeth on the big ring, with the mech centred and parallel to the chain when it is in a middle gear. Personally, I find this easiest by starting from scratch with the mech not connected rather than fiddling with it with cables in place. YMMV.

Cletus van_damme · 22-10-2015 11:52am

nordicb wrote: »

I had similar experience with one of bikes that was brought to do a quick adjustment. The combination of either poor components but most likely wear made it nearly impossible to adjust the front derailleur - it either would not go up/down or rub the chain. More over the person didn't want to spend a quid... Just saying there are situations when it's hard to get this thing working as it should. The chain, chain ring or the derailleur can be worn making the adjustment window very small or non existent...

They are all new parts that they have just put on and they were not cheap.

Cletus van_damme · 22-10-2015 11:57am

2 Wheels Good wrote: »

I hate to say it but the fact that you were hit by a car may mean your frame may be the issue and the minor damage isn't so minor. The derailleur may not be the issue, it could be the frame is either bent or there's a hairline crack somewhere.

I asked for a full check due to the accident and they check it over and said the only damage that could be due the the crash was a rear buckle and a bent peddle, they know it was involved in an accident but maybe its something they could look closer at.

Cee-Jay-Cee · 22-10-2015 12:31pm

Did they replace the cable with a new one when they changed the FD?

com1 · 22-10-2015 12:34pm

2 Wheels Good wrote: »

I hate to say it but the fact that you were hit by a car may mean your frame may be the issue and the minor damage isn't so minor. The derailleur may not be the issue, it could be the frame is either bent or there's a hairline crack somewhere.

The front derailleur will not change when the bike is under different stresses and it works fine when the stress is removed. Sounds like the frame is flexing more than normal - bent or cracked as 2 Wheels Good said.

Cletus van_damme · 22-10-2015 12:40pm

Cee-Jay-Cee wrote: »

Did they replace the cable with a new one when they changed the FD?

Looked like it but I cant say for certain, I had new cable on about 3 weeks ago so worst case the cable is still fairly new.

Cletus van_damme · 22-10-2015 12:46pm

com1 wrote: »

The front derailleur will not change when the bike is under different stresses and it works fine when the stress is removed. Sounds like the frame is flexing more than normal - bent or cracked as 2 Wheels Good said.

OK, that sounds like an explanation, I would have thought that knowing the bike had been hit by a car that they would have checked for something like that.

If the frame is cracked is it a good idea to still be cycling it?

2 Wheels Good · 22-10-2015 1:03pm

Cletus van_damme wrote: »

OK, that sounds like an explanation, I would have thought that knowing the bike had been hit by a car that they would have checked for something like that.

If the frame is cracked is it a good idea to still be cycling it?

No, speaking from experience. Got hit from the side when in college. Thought all was ok after replacing a buckled wheel/pedal. Year later the frame snapped in two while cycling home one evening, I was going slow enough so no damage done, could have been worse though.

cruizer101 · 22-10-2015 1:10pm

To be fair to shop it could be a very slight bend in frame that isn't noticeable but is causing slightly different distribution of forces causing the problem.

Cletus van_damme · 22-10-2015 1:11pm

2 Wheels Good wrote: »

No, speaking from experience. Got hit from the side when in college. Thought all was ok after replacing a buckled wheel/pedal. Year later the frame snapped in two while cycling home one evening, I was going slow enough so no damage done, could have been worse though.

The bike shop have said that using it as I normally do will fix it, my doubts about that are increasing. I will have a look for obvious signs of damage to the frame and when I get back to the shop I will ask them to check for cracks.

Thanks

Cletus van_damme · 22-10-2015 1:16pm

cruizer101 wrote: »

To be fair to shop it could be a very slight bend in frame that isn't noticeable but is causing slightly different distribution of forces causing the problem.

I can understand if its very slight there could be no way to catch it by looking at it but every time I have tried the bike it has failed within 10 meters of the shop. Having this happen after being told that 4 people had cycled it and had no problem is a different problem altogether.

Question about faulty service & repair

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