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Shimano 105 Rear Shifter - Shifts on its own(18 posts)

Shimano 105 Rear Shifter - Shifts on its ownRon AKA
Jul 5, 2002 7:21 PM
Have a 1 year old bike with Shimano 105 components. Last weekend the rear derailleur started to shift gears all on its own. It usually shifts to one or two smaller sprockets, and sometimes between sprockets. I called my dealer and they said no adjustment is possible and it can only be replaced. Said Shimano has very poor warranty policy and they have to remove the shifter and send it into Shimano before they will ship a replacement. Will put my bike out of commission for 2 weeks. Any suggestions or comments? Could it be anything simple? They also say this shifter is the most expensive component on the bike ($180 Cdn). I'm not too impressed! Also what is the standard warranty on Shimano components? My notes when I bought the bike says 2 years, but my dealer is now saying 1 year (but they will probably cover this one).

Thanks for any help,

re: Find a new dealer and visit him.Juanmoretime
Jul 6, 2002 3:01 AM
105 usually will last more than a year and I have never seen a rear derailluer go bad in my 35 years of cycling. I've crashed a few mountain biking but that wasn't the derailluers fault it was mine.It sounds like all you need is a shifter cable adjustment because of cable stretch. Have you removed the cable to the rear derailluer and routed it on the wrong side of the cable clamp? If not, standing behind the bike start turning the barrel adjuster on the derailluer conter clock wise a quarter turn at a time and ride it. It should eliminate the problem. Let me know if this helps. LoL.
same problem,possible solutionyammi
Jul 6, 2002 3:04 PM
i had the same problem on my lemond alp duez with 105 bike is only 3 months old. yesterday i shredded my chain so i splurged and bought a dura-ace chain as the 105 obviously didn't hold up well. today i rode 50 miles without one slip as before atleast a dozen or more slips.shifting all around was smoother then ever,coincidence, i doubtit.may be worth a try.
re: Shimano 105 Rear Shifter - Shifts on its ownSim
Jul 6, 2002 3:20 AM
stay cool, maybe rear deraileur need adjustment. look for a good bike store. it could be a problem with cable tension. some guys just sell parts but don't give assistance. sometimes I prefer to pay a bit more but being sure I am at a good and reliable store. at some places they don't even know how to install an headset system.
re: Shimano 105 Rear Shifter - Shifts on its ownjromack
Jul 6, 2002 3:59 AM
Before you remove the shifters, eliminate other possible culprits.

I would suggest another shop, the one you mentioned arrived at a conclusion without going through a series of logical evaluation steps.

First check the chain for stretch. If that measures okay, then adjust the rear derailleur/front derailleur.

PS If the chain is stretched too far out of spec, then replace it and the rear cassette.

How many miles on your bike?
re: Shimano 105 Rear Shifter - Shifts on its ownRon AKA
Jul 6, 2002 9:42 PM
The bike has about 1200 miles on it. I don't suspect the chain is worn or the cassette.

re: Shimano 105 Rear Shifter - Shifts on its ownjromack
Jul 7, 2002 8:24 AM
Measure it and make sure! Just takes a few minutes.
warrenty = 2 years (3 years for XTR / Dura-Ace)off roadie
Jul 6, 2002 8:58 AM
If you have a receipt that proves purchase within that time, you don't need the LBS to send it in, you can do it yourself. Just go to

IMO, its a pretty generous warrenty, given that I can wear out an entire drivetrain (deore, blech) in 6-8 months. Such wear isn't covered, but they replaced a cassette I busted a tooth off.
Their warrenty on CLOTHING is one year- not bad! Sheesh, I have a 9 month old pair of shoes I cracked the sole on last fall. I better get moving!
Derailleur or shifterKerry
Jul 6, 2002 5:28 PM
Let's assume that you have the cable properly adjusted (shifts the same in both directions when on the work stand, upper pulley centered on the cog after you shift). It's hard to understand how the derailleur could be causing this. Assuming it is the shifter (most likely cause) then try flushing the shifter with something like WD-40, and then chase that with TriFlow. It may just be gunked up, preventing the pawls from engaging and allowing things to slip. If you do this and it still won't work, then it sounds like a warranty problem.
re: Sounds like a cable tension issue. Not der or shiftercyclejim
Jul 6, 2002 7:39 PM
I seriously doubt that your rear der or shifter is causing this problem. I've never seen either component cause that problem. Check your cable tension, more than likely you need to simply adjust it and you will be fine as a couple of others have mentioned. The easiest way would be the adjuster on the down tube if you have one, or the adjuster right on the rear der itself. Zinns book is a good one to guide you thru these kinds of repairs.
re: Shimano 105 Rear Shifter - Shifts on its ownRon AKA
Jul 6, 2002 9:30 PM
Thanks for all the suggestions. I suspect that this is a cable tension issue and have done an adjustment. I found with the chain on the largest front sprocket and smallest rear, the cable was not fully tight. Tried increasing it in 1/4 turn steps to a total of 3/4 turns and it seems to be better now (in just riding around the block. I will do a long ride tomorrow and see if things are better. I also found this site which kind of suggests the same things as you guys have suggested.

One other thing: check the derailleur hanger.Leisure
Jul 7, 2002 4:40 AM
Unlikely unless you can recall a specific incident of hitting it, but just in case everything else fails.
Your dealer is an idiot,Alexx
Jul 7, 2002 4:05 PM
who has the brains of a tree sloth. any moron knows that there is a simple barrel-adjuster right there on the cable. Obviously, this brain-dead jackass has you pegged as a patsy, and he's trying to separate yoyu from your money!
On top of that, I'm betting that the real problem is that your chain is worn, anyway. Still, I wouldn't give that idiot another penny of your business-he's a theif!!!
Your dealer is an idiot, and you are not.davet
Jul 7, 2002 9:26 PM
Ron: Using the info of the Park Tools site is excellent. However, make sure you follow the directions IN THE ORDER given. Each adjustment affects the others and if you adjust out of the sequence, you will never get it right. Adjusting the rear der sounds complicated, but once you get a handle on how to do it, it's quite simple. Good luck.
re: Shimano 105 Rear Shifter - Shifts on its ownRon AKA
Jul 8, 2002 6:43 PM
Thanks all for the help. Tried the adjustment and I've tightened it by about 1 3/4 turns and it may need another 1/4. While potentially not perfect it is very much improved and I'm sure the cable being loose was the problem not the shifter. To be fair to the dealer I only talked to him over the phone. They were quite willing to take a look at it and adjust if possible. On the other side it seems in retrospect that they should have suggested this adjustment to me over the phone, and it was just in the shop for a free tune up 2 weeks ago. Thought they should have caught it then.

Thanks again,

also check this Sheldon Brown article..dotkaye
Jul 9, 2002 9:07 AM

for the other possibility, that the bottom-bracket cable guide might be clogged up..
If it keeps getting worse, look for a frayed cable housing…..TFerguson
Jul 9, 2002 9:08 AM
Last week I was doing a tune-up for a friend's new C-dale and I could not get it to stay in tune. I would adjust the rear cable tension and about 8 miles later it would act like the cable was too long again. I discovered that where the housing goes into the braze-on under the down tube, the rubber was stripping back allowing the rest of the housing (the parallel wires) to slide through. Each time it shifted it would strip back a little more making the housing shorter and the cable effectively longer.
Jul 9, 2002 1:05 PM
Keep it Simple Silly!

There's actually quite a bit of technology and precision involved in the shifting system with the proper care and feeding it can last for a very long time, but it does require some attention. That's not to say that you may not have something seriously wrong with you shifter, but it's not that likely. What is more likely is that something is not adjusted correctly, is out of alignment or just plain gummed up with crud.

What you need is a decent shop with a wiley road bike mechanic or a buddy with the similar skills.

A partial list of potential problems might include:

worn and gummy cables and housing
bent rear der hanger
bent rear der
loose rear der
loose bottom bracket/crank/chain rings
worn out chain
gummed up cassette

The shifter doesn't really make the list even though it is by far the most complicated mechanism. However, if the shifter has failed in some way it is a real bear to fix and infact Shimano claims that it is not repairable out in the field. It can be done if you're very patient and lucky, but I'd advise the warranty option - not that I think that it will come to that.