oldbarntom

Hi -

Been riding bikes for almost 50 years now, first time posting.

I bought a 3x9 Marin touring bike a few years ago at a local shop. Has Shimano Acera "mega drive train" shifters and a Shimano Alivio rear. I don't put a huge amount of miles on this, so I was surprised when, soon after I bought it, I returned to the shop to have the shifters adjusted because the upshift/downshift action (I almost exclusively use the rear shifting) wasn't at all in step with the shifter clicks.
They adjusted and explained that the cable stretches a bit after new. Fair enough (although, having played guitar, I wonder why not pre-stretch the cable?). Anyway, not more than a couple hundred miles later I'm back for another adjustment. I think I've had it done at least 3 times so far, and I believe they even tried a new cable at one point. Riding the other day, it was missing shifts, then slamming up or down into the next gear (quite a bit of time after shifting) when I would pull away from a stop or while mildly accelerating. UGH! Seems like bush league stuff, to me.
Any clues to solving? Yes, I ease up on the pedaling when I shift.

VegasTriker

The bike shop is right that you may have to adjust the rear derailleur on a new bike after hundred miles or so but the cable does not stretch much after it is first broken in. I use a higher level Shimano Deore RD and I can go many months without needing to mess with the adjustment. Check to see that the cable has been securely attached to the rear derailleur. It should be tight enough to keep the cable from slipping when you put tension on it to change gears but not so tight you damage the cable. If the cable slips, it will upset the adjustment. That's the first place I would look. The second is a binding cable. Have you ever lubricated the cables on this bike? It could be binding on the housing and then releasing after you start out.

If you have been riding bikes for 50 years, it is time to learn the basics for adjusting the RD so you don't have to drag the bike to a bike shop and pay them to do the adjustment. It's the only adjustment you need to do to fix your problem. There are numerous tutorials online. Here are three taken at random from those available with Park Tool often being suggested by readers here:

Rear Derailleur Adjustment Park Tool Company https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment

How to Adjust a Shimano Acera https://www.sportsrec.com/7720916/ho...-mountain-bike

How To: Adjust Shimano Rear Derailleurs

oldbarntom

LOL - dunno, seems like having done anything for 50 years I should be able choose my luxuries. I might change a clutch on a car to save $120/hour but I'm going to give myself the grace to pay a bike shop the near minimum wage hourly rate they charge. I'm sure I could adjust the cable on my own (thanks for the links). I'm more wondering why it seems to go out of adjustment so quickly. I've had a couple other bikes with indexed shifters and I didn't experience this.

Miele Man

The bike shops where I am charge around $40.00 CDN per hour. and round up to the hour.

Check your cable adjusters and make sure the locknuts are engaged. Also check the spring under the barrel adjuster on the rear derailleur to makes sure it's not overly weak.

Cheers

tyrion

It's not that the cables stretches, it's that the housing compresses and seats into the housing stops.

It could be the housing wasn't cut perpendicularly, so there is slop where the housing meets the housing stops. Or the housing wasn't fully seated in the ferrules, or something like that.

At the second time the system needed adjustment the bike shop should have been troubleshooting the housing.

The other potential trouble spot is the derailleur hanger - if it's not aligned you'll have bad shifting. The bike shop should have looked at that too on the second analysis of shifting problems.

rumrunn6

last year I changed my rear derailer cable & adjusted it just fine

but recently, when it came to my front cable's replace/adjust, I took it in to my LBS. only cost $28. but his adjustment was waaaay off! I was going thru the motions of adjusting it myself, but then noticed another issue, I want a pro's opinion on. my guy is good at some stuff but I know another shop that is downright masterful, so I'm bringing it there

if I were you, I'd try that guy again since you've ridden it a bit

Unca_Sam

Seconded. You may be able to sight along the gears and chain from the rear of the bike to see if the bottom of the derailleur cage is in line with the chain as it comes from the chainring. Usually this is accompanied by sloppy shifting overall. Minor alignment issues are harder to pinpoint visually, though there is a for that.

TiHabanero

Friction shifting will fix the problem permanently. Set it up and no adjustments needed for years to come.

Unca_Sam

Even with an out of alignment hanger?

m3tal070

Have you taken it to different shops, with the same result? Maybe a different shop might get it right?

Retro Grouch 

Usually.

Retro Grouch 

This ^^^^

oldbarntom

I could try a different shop. The first couple times were free, since I had purchased the bike there.
I guess I could go back to friction shifters, too. Not sure that is a satisfying solution, though.

joelcool

Something is wrong... you already know that, that's why you posted. A brand new bike should not go out of adjustment regularly.

The smart people on this form will lead you in the right direction, but don't think you should accept this as acceptable.

I messed around with my rear derailleur quite a few times and eventually got it right.

A bent hanger is a bad thing, and not easy to see.

BobbyG

All it takes to bend a derailier hanger is to laythe bike down on its drive side. Or in my case I tend to bump it againt my other bikes in the shed (or the shed door).