It seems every few months I have to bring my bike back into the shop to fix the rear derailleur. It always starts to jump around in the back after a while. It's a triple so that might have something to do with it. I have to bring it in again, feels like I was just there....

You may want to ask the LBS what exactly they're doing, and what's causing it instead of asking us to guess a billion different answers which may or may not be correct. And which there is no way of verifying if it's correct.

I saw that link you posted in the other thread, maybe I'll have to learn how to do it myself.

https://www.parktool.com/repair/byregion.asp?catid=53

There is nothing inherently "high maintenence" about your Cannondale so either there is a mechanical defect somewhere in your drivetrain or your LBS sees you as a continuing source of income.

First step is to learn how to adjust the cable tension of the rear der. 99% of shifting problems are the result of cable tension. Adjustment only requires that you turn one adjuster on the der and takes just seconds, so learn how to adjust and you will avoid many problems.

That helped me a lot with my bike problems, less trips to the LBS, less time wasted, less money spent, more riding.

Check this out, I found this extremely helpful:

https://bicycletutor.com/

Adam

Your triple front has nothing to do with your rear derailleur falling out of adjustment. I think it really sucks how BF has instituted this whole "triples are bad, mkay" mentality. I haven't experienced any more maintenance issues with triples compared to doubles compared to compact doubles.

As stated above, you really need to learn to turn the little adjusting barrels yourself.

If you haven't yet, get a good book on bicycling and bike maintenance. It wil give you the basics on how to keep things runnning smothly on your bike. Most maintenance items on bikes can be handled with the minimum of tools and time and learning how to service/adjust your bike yourself will definitely lessen the frustration of always having to depend on your LBS to keep it on the road and safe.

Chombi

Get the Park Blue Book.

Could be: r shifter, r cables/housing, r derailleur, chain, cassette, frame.

Derailleur, chain, and/or cassette could be worn, cables not sliding smoothly through housing, shifter issues. Check derailleur hanger alignment, frame alignment. If you're only getting it in the largest or smallest cog, could be the der stops need to be reset.

But yeah, ask the shop what's up.

Cable tension only needs adjustment in the first few weeks after a new cable is installed, to compensate for housing bedding in to the stops. Smoothe shifting then depends on keeping the system clean - cables and under the bottom bracket. Bent rear der hanger can cause persistent shifting problems, but this isnt something that happens gradually.

Rear derailleur adjustments should last longer than that.

Ask your shop to check the ends of all of the cable housings. I've encountered a couple of cases in which the cable housing end cap wasn't doing it's job and the cable housing was gradually shortening itself. When that happens, a derailleur adjustment will make the bike shift fine, for awhile, but it deteriorates rapidly. That sounds to me like the situation you described.

Or one tricky cause to your constant out of tune gears could be that your derailer chain wheel has collapsed. if theres a large amount of sideways give in it the centre support may have collapsed... this is not a common problem but can also go unnoticed...

Funny, OP has this problem. When i was breaking-in my DBR Podium 1 yesterday, I noticed the RD was skipping when getting up to the larger sprockets. 1 1/2 clockwise turn of the barrel adjuster later and it's all smooth.

??

Hey Operator i suppose it only really happens on the low end derailleur with the large chain wheels, ye know what i mean, have you ever seen it!..

The OP's bike is a Cannondale CAAD8. It seems safe to conclude it has components above the Wal-mart bike level.

Number one i would make sure they are not changing your cable every time you go in because that is for sure not the issue and cables will stretch over time during use. So if they are changing it out every time that may be the problem and by the time it stretches out you think it is not shifting right although the cable just needs to be tightened up a bit or just the barrel adjuster turned a quarter of a turn or so. number 2, make sure you are not laying the bike down on the drive side if you are. This can cause the shifting to go out if the derailleur is bumped. third. I am guessing your bike shop would check but have them double check the derailleur hanger, it could be very slightly bent. forth option is that some corrosion may have happened inside the cable housing that is causing the shifter cable to not slide correctly through the housing. Lube can fix it, but sometimes it only works temporarily and could cause it to have issues soon after.

No they just adjust it each time, and then it works flawlessly. I just adjusted it myself, it seems to be working good so we'll see.

Cables don't stretch. The inner liner of the housing wears and so do the components of the shifter and cable stops. But 1.1-1.2mm stainless steel cables are more than up to the task of pulling a derailler without stretching.

They do, just not significantly enough to be of any importance. High quality derailleur cables are pre-stretched at the factory. Seating of ferrules, and cable and housing units into their respective places would totally mask any miniscule effect of actual cable stretch.

As you have pointed out.

Take it to another shop and explain to them the problem. I have seen this before and the cable wasn't clamped in the rear dérailleur properly, causing the cable to slip and subsequent poor shifting.

I think it is a loose fastener between the shifter and the seat

No, no, no.

Learn to understand this simple system for yourself. There really isn't much to it.

You shouldn't need to spend a cent when you have such quality gear, unless you've bent something or it's getting old.

Minimise friction in the cables, ensure the housings have no reason to be mushy (kinks or poorly cut ends) and are a good length (no unnecessary bends, but as large a radius as possible), and adjust.

end of thread