Nomad2

Hi all,

I have a steel road/touring bike which I had customized and fitted with a Shimano grx 800 2x11 speed groupset. Since I have had it I have had constant issues with the gearing. Like a new or just serviced bike where the gearing works initially and then starts to go out of adjustment as the cable stretches, this is happening to me all the time. This is happening even if the cable hasn’t been changed.

I’ve given up taking the bike back to the shop where the bike was built up as it’s some distance away ( I went there as they were a frame builder), but it is happening even after it’s been to my local bike shop. It starts with the chain struggling to climb onto a larger cog usually midway through the cassette and gradually extends to everything such that the bike is virtually unrideable after a few rides. Barrel adjustments don’t work.

I initially blamed this one using Miche cassettes which I was forced to use as Shimano couldn’t be bothered supplying Australia with 11 speed 11-34 cassettes but since I changed back to Shimano the problem remains.

I had one incident where the cable pulled right out of the rear derailleur clamp the day after it came back from the bike shop, but that has happened only once. Could it be an issue with the clamp (I’m sure there’s a more technical term) being defective? My wife has a bike with the exactly the same running gear (including derailleur length) and hers is set and forget.

Any suggestions would be appreciated. As you can imagine this is pretty frustrating!

FBinNY 

Usually a cable pulling out of or slipping in the pinch bolt is user error, namely not having been tightened enough. OTOH a stripped or partly stripped thread would make proper tightening impossible, so with repeated issues, that's something to check. If in doubt, reset the cable and make a hard bend where it exits the pinch bolt. This both helps prevent slipping, but more important becomes a telltale if the cable does slip. As the bend gets drawn in, the cable will seem to be less bent, proving it moved.

Other issues that may cause your problem include the RD hanger not being properly secured to the frame, The RD not bolted on properly, or numerous possibilities affecting the cable upstream or shifter.

Other than the trick of bending the cable to check for pinch bolt slippage, diagnosing inconsistent shifting is a long process of progressive elimination working from the RD itself upstream to the lever. Experience is a big help to that process.

Crankycrank

I would highly recommend watching some videos from Park Tool & RJ the Bike Guy Also the Shimano manual DM-GARD010-00-ENG.pdf (shimano.com) may be the best place to look. Best to learn how to work on them yourself. It will come in very handy and save you multiple headaches and trips to the bike shop. Not busting your backside, just giving good advice. Since you say the cable slipped in the clamp once already you should check to make sure the clamp bolt is tight and if you have the coated cable that Shimano sometimes uses, scrape off the coating where the clamp is. A slipping cable will have the exact symptoms you describe but not the only possible issue. If whoever setup your bike didn't make sure all the shifter housing pieces were solidly inserted into the various stops at the shifters, downtube stops, and each end of the derailleur loop it could still be creeping until it butts up against the stops. Check these and let us know if you still have problems.

KCT1986

You may want to check that the cable housing has been preped properly. With clean straight cuts and the end caps are correctly sized and of proper quality.

If you are using coated slick cable with a outer coating (teflon...), it is sometimes recommended that the coating be scraped off before clamping.

Mtracer

If the cable is slipping in the derailleur clap, then solve that. As for checking, there's a bunch of ways. You could bend the cable as mention earlier, or mark the cable any way you want to see if it moves. There's certainly nothing inherently wrong with GRX800 shifting. If the cable isn't slipping at the derailleur, then something else is likely affecting the cable. Is the cable run through housing all the way to the derailleur, or are there parts of it where the frame takes up the tension of the cable? If the frame is part of the equation, may there is an issue with a cable stop somewhere.

I had a bike once where the cables were not in housing inside the down tube. The front and rear derailleur cables were crossed inside the down tube. So, shifting the front derailleur and the corresponding change in cable tension, also changed the tension a small amount in the rear derailleur cable. While the issue wasn't so bad I couldn't shift, it made for seemingly random adjustment issues.

Another thing I did once was I put an inline barrel adjuster on a cable between the handlebars and where it entered the frame (bad idea). It took a while to figure out that every time I turned the bars enough in one direction, it would cause the barrel adjust to move a notch. It would gradually keep moving and go out of adjustment.

Anyway, since your problem gets worse and worse by quite a lot, I'm betting on the cable slipping in the derailleur clamp, especially because you said it has done this. Bad clamp, or someone isn't running the cable correctly through the clamp and/or tightening properly.

biker128pedal

Check the cable routing around the pinch bolt. I had a similar issue with my XT 12 sp derailleur. There was an odd routing before the bolt o missed the first time and the cable kept slipping. My cable had broken so I had no idea about the routing.

zacster

It does sound like a slipping cable. As you pull on it to go to a larger cog there is enough resistance that you pull the cable through the pinch bolt instead. As others have said, make sure the routing is correct. Go to the proper manual for you specific derailleur. When I installed a derailleur recently the routing was really strange, although I think it was a front not a rear.

As I've commented on another thread on another topic, you gotta read the fine print on these things these days. Shimano keeps changing everything, but at least they keep track of what works with what even if the chart is pretty cryptic.

Kontact 

I wonder if the housing is seated against the lever under the tape.

Is the cable in good shape inside the shifter?

choddo

I’ve got a GRX800 rear mech. Very straightforward routing (the front mech is, like the other Shimano 11speed stuff, beautifully bizarre with that approach angle adjustment)

Like the “hard bend the cable to see if it’s slipping” trick, that’s clever.

Nomad2 does having the clutch off make any difference?

Iride01 

Your cable doesn't stretch. If you are having adjustment issues that keep you constantly adjusting the barrel or inline adjusters, then you probably don't have the pinch bolt tight enough and the cable is slipping in it a very tiny bit when you shift. Improperly seated and improper cable housing ferrules can also make similar issues. I know this from experience. I was vexed for a year before I realized I wasn't tightening the pinch bolt nearly enough on my bike I'd just put a new group set on.

Depending on what your frame was built for, if you put a GRX crank on that bike, you may have the incorrect chain line to the rear. Most GRX cranks want a wider chain line than a road crank will.

zacster

One thing you may want to do is to get a fresh part of the cable under the pinch bolt. You'll need to shorten the housing somewhere to compensate and hopefully you have enough to do that. Or just get a new cable and route it through the current housing.

I'll have to say though in all my years of doing bike stuff I've never had a cable that slipped and I just tighten by feel. With brakes I'll apply more torque because you certainly don't want those to slip. I've often wondered why brakes don't have a secure routing that's more fail-safe, not that I've ever had an issue.

Nomad2

Thanks everyone for the feedback. I have marked the cable and will monitor it. Now that I look at it I can see a small kink in the excess cable beyond the clamp which might indicate where it was clamped just before I took it to my LBS. Does seem to point to the cable slipping. Can't see why it would be them not dealing with the coating on the cable. My wife's bike came out from the same workshop with no issues and my bike has now been to two bike shops with the same result.

Nomad2

Not sure if having the clutch off makes a difference or not. It may do. I like keeping the clutch on as it avoids pretty horrible chain slap caused by some tree root affected paths. I don't have a chain stay protector. I could get one but I like the look without it....

choddo

Yeah I leave mine on too, just curious. It adds chain tension so I expect increases shifting load and cable tension slightly.