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Discussion Starter · #1 ·
Just had a full tune-up on my bike with 105 group set. Over the past 8 years, the bike has seen heavy use over five of those seasons. I have to admit that I haven't treated the bike like a baby. I have had it adjusted a few times and I do clean and lube it a couple times a season. But it is generally parked in whatever gear I ended my ride in.

So after my tune-up, the bike guy told me that my rear derailleur was getting "tired". He said the spring is weakening and that is why there is occasionally some hesitation when shifting in the lowest cogs, and that unfortunately he can't just replace the spring. It isn't bad and I can live with it (and it is SOOOOO much better after the tune up). But I was wondering just how long a derailleur is supposed to last?
 

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In theory a good derailleur (like the 105) should last years and years and give tens of thousands of miles of service. That said, rear derailleur are stressed and the pivots can develop play. They are also abused by laying the bike down on the drive side or taking impacts. Is the weak spring in the parallelogram or is it the pivot spring?
 

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Discussion Starter · #3 ·
Is the weak spring in the parallelogram or is it the pivot spring?
You know, I don't know enough about derailleurs to know to ask that question. He did do something where he put the chain up at the biggest cog and then wiggled the derailleur and said, "Shimano specs said when I do this, there should be no play, but you do have a little." At no point did he suggest I have him replace it. He was just showing me why there was some hesitation. He did say that since I said I was thinking about a new carbon bike that I save my money for that.

And like I said, the shifting is way better after the tune-up and the hesitation on the little cog doesn't really bother me that much.

He also checked the cable for wear along the entire length and checked out the shifter was well. I watched.
 

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Over the past 8 years, the bike has seen heavy use over five of those seasons.
It's hard to judge component life by time. How many miles have you done in those 8 years.
Some people ride 1,000mi/yr. Some ride 10,000mi/yr.


He did say that since I said I was thinking about a new carbon bike that I save my money for that.
I dunno. You could pick up a new derailleur for $50. $20 for a used one on ebay.
 

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It's hard to judge component life by time. How many miles have you done in those 8 years.
Some people ride 1,000mi/yr. Some ride 10,000mi/yr.

I dunno. You could pick up a new derailleur for $50. $20 for a used one on ebay.
This. Miles not time wear out components. This being said, I've never had a derailleur "wear out". This year, I had two right shifters break - a 6800 Ultegra shifter at 10K miles and a 5800 105 shifter at 5K miles. Nothing was wrong with the derailleur on either bike.

But if your problem is indeed a lazy derailleur, consider yourself lucky it's that and not a shifter which costs about 5x what a derailleur costs.

Speaking of this "tune up" you were given, did your mechanic replace the shifter cables and housings? That's the first place I would go when shifting suffers as that is usually the problem.
 

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I've had at least one Shimano 105 rear derailleur wear out; it had so many miles on it that it developed play in the pivots. I suppose I could've disassembled the thing, reamed out the pivot shaft holes, and fabricated new shafts, before re-assembling, but I'd still have a ratty-looking, old rear derailleur. This was on a beautiful late-70's Trek 531 frame, and I replaced it with a NOS Shimano 400 rear I found on EBay for $30.
 

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Just had a full tune-up on my bike with 105 group set. Over the past 8 years, the bike has seen heavy use over five of those seasons. I have to admit that I haven't treated the bike like a baby. I have had it adjusted a few times and I do clean and lube it a couple times a season. But it is generally parked in whatever gear I ended my ride in.

So after my tune-up, the bike guy told me that my rear derailleur was getting "tired". He said the spring is weakening and that is why there is occasionally some hesitation when shifting in the lowest cogs, and that unfortunately he can't just replace the spring. It isn't bad and I can live with it (and it is SOOOOO much better after the tune up). But I was wondering just how long a derailleur is supposed to last?
To sum up the other comments, it's miles (and the number of shifts, and maintenance, and riding conditions) not years. Most likely it will be worn pivots and the mechanic showed you how it was wiggling. I don't know how they made the leap to that being a worn spring. Springs don't really wear out unless they have been extended past their range or corroded. The longest I know of a derailleur of mine lasting is about 100,000 miles, but that derailleur (Campy Record from around 2005) is still in use on my roller bike so I don't know how much longer it will last. On the rollers in never gets shifted, so the only wear is on the pulleys.
 

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I don't know how they made the leap to that being a worn spring. Springs don't really wear out unless they have been extended past their range or corroded.
^^^ This.
Springs don't 'get tired'.

As long as a spring operates within it's design range (which a rear derailleur has to because the range is fixed) it will last virtually forever.
When a load is applied to a spring, the metal deflects. If it deflects within its range of elasticity, it will return to its normal position. If the load exceeds the springs maximum deflection, the material will exceed its stress and suffer fatigue.

The design life of springs are typically in the magnitude of 10 million cycles.
If you cycled the spring 2,000 times every single day for 10 years, you still wouldn't reach 10 million.
 

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Discussion Starter · #11 ·
It is also possible the derailleur was damaged in an accident, but I can only think of one instance in which something might have come in contact with it. I've gone to the ground three times (run off the road by cars) with this bike (and had the bike gone over by the LBS after each one - had to have the wheels trued after one). I do anywhere from 1000 to 3000 miles a riding season, maybe more, depending on when I start in the spring/summer.

The mechanic did not replace the cables, but he gave them a good inspection and lubed them. He also gave the shifters a good going over as well. I watched him do it. And he told me what he was doing and why, and that usually, it is the cable that is to blame, but that my cable was fine. I wanna say the cables were replaced two years ago.

Yeah, I checked out the cost of a new 105 derailleur and I would be fine getting a new one. How do I tell what size my current one is?

The spring should last forever, but nothing is 100%. It is why not everything makes it to it's MTBF. It could of been a slight manufacturing defect that has taken time to rear it's head.

And yes, I realized a little bit after I started the thread that I should have posted in the Wrenching sub, but ogre had already responded.
 

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I do anywhere from 1000 to 3000 miles a riding season, maybe more, depending on when I start in the spring/summer.
So you're well under 24,000 mi. That thing is just getting warmed up!
No way the spring is 'tired'. Nor should the pivots be wearing with play.

The mechanic did not replace the cables, but he gave them a good inspection and lubed them.
Lubing cables is a band-aid that causes more problems than it's worth. Lube attracts dirt and gunk with causes cable drag and shitty performance.

Speaking of this "tune up" you were given, did your mechanic replace the shifter cables and housings? That's the first place I would go when shifting suffers as that is usually the problem.
^^^ This.
Cables/housing is the issue 99% of the time. (unless of course you have Di2 😀 )



And he told me what he was doing and why, and that usually, it is the cable that is to blame, but that my cable was fine. I wanna say the cables were replaced two years ago.
Just the cables? Or housing too?
Two years is a bit of time. This is one area that's affected by time and use. Just from sitting around the cables and housings can oxidize and corrode inside.

First think I'd do is replace the cables and housing.

The spring should last forever, but nothing is 100%. It is why not everything makes it to it's MTBF. It could of been a slight manufacturing defect that has taken time to rear it's head.
Yes but you're talking about an extremely small percentage of failures. I bet Shimano has under 0.5% spring failure in all the millions of springs they manufacture.
A failure would more likely be a break at one of the end loops, not a weakening of the spring rate. Manufacturing defects don't cause a spring rate reductions years later.
 

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^^^ This.
Cables/housing is the issue 99% of the time. (unless of course you have Di2 😀 )
You just couldn't resist that dig, could you? ;)
 

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The wear in the housing will mess up shifting wayyyy more than any non-existent wear on the cable. If you have shifting problems and it's not a cable fraying in the shifter the housing should always be replaced with the cable.
 

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The wear in the housing will mess up shifting wayyyy more than any non-existent wear on the cable. If you have shifting problems and it's not a cable fraying in the shifter the housing should always be replaced with the cable.
That is unless the cables are the cheap galvanized ones. Then they will oxidize, become rough and cause poor shift performance long before housings wear.
 

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I rarely if ever see galvanized cables. Even cheap ass bikes have stainless cables.
Maybe now they do. I have changed cables with so much oxidation, it wasn't even funny.
 

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It happens to stainless cables too.
So then "stainless" cables aren't really stainless? I have changed rough cables on friends' mountain and hybrid bikes without replacing housings and there was a dramatic improvement in shift quality. Would the shift quality have been even better if I has replaced housings? Possibly?

As far as my road and gravel bikes, I have never had a cable where the death of it wasn't caused by being chewed to death by an STI shifter. I do know that I got 10K miles out of the same housings on my road bike and other than the STI cable chewing problem, shifting was always flawless.......until the right shifter finally broke. I decided to replace the housings when I switched to SRAM Force 22.
 

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So then "stainless" cables aren't really stainless?
There are many grades of stainless. Most grades of stainless will rust/corrode. Especially if exposed to salt.

Like steel, stainless steel contains iron and carbon. But stainless also contains chromium which inhibits rust.
Some grades of stainless have a much lower iron and carbon content and are extremely rust resistant. Think kitchen utensils or kitchen sinks.
But these aren't very strong. The iron and carbon is what makes stainless strong. This is why some stainless is magnetic and some isn't. Magnetic stainless is more prone to rusting. Try sticking a strong magnet to your stainless cables.

Wire cables need to be stronger than kitchen utensils so they'll be made of a stainless grade that has more iron and carbon. And more prone to rust.

This is stainless rusting.



18-8 Stainless is basically same as 304 SS. It's pretty rust resistant but it will rust.
316 SS is extremely rust resistant. But not as strong.
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