Jim’s Tech Talk
By Jim Langley
When you work as a quality control engineer for a company that specializes in making cranksets, as I do – you get a lot of front derailleur adjustment practice. It comes from testing new product and also from maintaining bikes built elsewhere and already on the road.
I’ve been seeing two issues with modern Shimano “braze-on” front derailleurs. This type of front derailleur has no clamp wrapping around the seat tube of the frame. Instead it bolts onto a metal piece designed for it that’s bolted, riveted or brazed onto the frame.
To me, the issues fall under the category of assembly or adjustment mistakes. Because, Shimano’s instructions tell how to mount and adjust the derailleur. However, in the assembler’s defense, it’s possible they never received the directions and/or couldn’t find them searching Shimano online.
I should point out that front derailleurs are one of the more difficult bicycle components to adjust correctly. It can’t be done well unless the mechanic understands how front derailleurs, shift levers and changing gears work. And, front derailleurs are getting more difficult to adjust, so mechanics have to keep up with the changes as new designs hit the road.
So, before attempting to fix yours, be honest with yourself and if there’s any doubt that you know enough, hand the job off to a mechanic who does.
To help you experienced mechanics, here’s an illustration from Shimano’s online instructions, slightly revised to focus on the first common mistake. And, some tips for fixing the mistakes follow.
Mistake 1: Shimano Support Bolt not tight against the frame
The symptoms of this mistake can include anything from the chain rubbing on the front derailleur cage, to sloppy shifting, to throwing the chain. And no amount of adjusting the derailleur – whether it’s an electric or cable shifter will fix the problem.
What’s happening is that what Shimano calls the Support Bolt is not tight against the frame. It has to be that way in order for the adjustments made to the limit screws and for the throw of the derailleur to work correctly.
The Support Bolt is hidden inside the body of the front derailleur. You might need a flashlight to find it. It is turned with a 2mm hex wrench to bottom it out against metal. Do NOT tighten it against a carbon frame. For this, Shimano provides a small peel-and-stick Backup Plate that is stuck to the carbon frame to give the Support Screw a solid and safe surface to rest against.
Notice in the illustration that the Backup Plate needs to be mounted so that the Support Bolt does not rest against the adhesive side of the plate.
I’ve seen the pin resting on the adhesive side; carbon bicycles with missing Backup Plates; the flat Backup Plate incorrectly on curved frame tubes; the pin not tightened against anything; and the pin missing the Backup Plate entirely. These mistakes let the front derailleur cage move out of alignment with the seat tube of the frame during shifting and that’s what causes the rubbing and shifting glitches.
Once you spot the problem, the fix is easy. But, if the Backup Plate is missing, you will need to find one and install it. Bike shops that stock Shimano should have them. They recently appeared on Amazon, too: https://amzn.to/2E8zzE5
If you buy the set you will get two plates (one curved, one flat – use whichever fits your frame best) and a Support Pin.
Positioning the Backup Plate
To locate where to put the Backup Plate, temporarily put a piece of tape on your frame where you expect the Support Bolt to touch. Then install the front derailleur, snug the 5mm fixing bolt and turn in the Support Bolt with the 2mm hex until it makes a mark in the tape. When you remove the front derailleur you will have a mark where to place the Backup Plate (remove the tape first).
Once the Backup Plate is attached, you can install the front derailleur. Be sure the the bottom edge of the outside cage plate clears the large chainring all around – about 2mm clearance. And, as you tighten the fixing nut, press in gently on the cage to hold the Support Bolt against the Backup Plate or the braze on if on your bike a Backup Plate wasn’t needed.
What you’re looking for is a derailleur cage outer plate that’s parallel with the large chainring when the fixing and Support Bolts are tight. Note that if the cage is canted slightly towards the chain after tightening the bolts, you can usually simply tighten the Support Bolt very slightly (turn it clockwise) to get the cage to come parallel.
Check that the front derailleur fixing bolt is tight and now when you make the final derailleur adjustments, they should hold and chain rub, drops and bad shifting will be things of the past.
Mistake 2: Cable Isn’t Tight Enough
Since this issue has to do with the cable, it’s obvious it happens on conventional Shimano front derailleurs, not electric models. And, it happens with the type of cable setups with and without inline barrel adjusters.
An inline barrel adjuster is a small plastic piece found on some Shimano front shift housings (also called “casing”) where they run beneath the handlebars. By turning the barrel adjuster it’s possible to make the shift cable tighter or looser, which changes how far the derailleur moves when shifted.
I did not have a bicycle handy with an inline barrel adjuster to photograph so I found this photo of an adjuster on Shimano’s site. It will probably look different than what’s on your bike, but it gives you an idea what to look for.
Note that it’s possible to purchase and install inline barrel adjusters if you would like to add them to cables. But, it is a bit of work since it means carefully cutting the housing section. And, with older cables, you will probably want to start with a new housing and cable.
Chain Rub And Noise
The symptom of a front derailleur cable that isn’t tight enough is chain rub when it’s on the largest chainring and smaller rear cogs. Because these gears are usually used when riders are traveling at a high rate of speed and pedaling with great effort, it can make a lot of noise and become annoying fast.
The reason the chain rubs is because the cable is too loose. And when it’s too loose, shifting onto the large chainring results in only a partial shift. With sufficient tension on the derailleur cable, the derailleur cage will move to its full outside limit and there will be clearance for the chain – and no rubbing. Yay.
Using The Inline Adjuster
If there’s an inline barrel adjuster, you can shift onto the large chainring and then operate the adjuster watching to see if the cage moves outward and clears the chain. If so, you just solved the problem by tightening the cable sufficiently.
However, be careful. The barrel adjuster only has so many turns. If you go too far you can unscrew the barrel from its holder. At that point you’ve used up all available adjustment and you might even damage the cable or adjuster if you attempt to shift – since the two parts are no longer connected correctly.
Tightening The Cable
If the adjuster doesn’t have enough travel to move the derailleur cage far enough, you’ll need to tighten the cable another way. This is also true for setups without inline adjusters.
Start by shifting the chain onto the smallest front chainring. The shift lever and front derailleur need to be fully returned to their starting positions in order to take all tension off the shift cable so you can remove any slack.
To tighten the cable, if you have an adjuster, start by screwing the inline adjuster all the way “in” so that you will have its full travel should you need it in the future.
Then, to tighten the cable, loosen the cable anchor bolt on the front derailleur. Just loosen it, don’t remove it. And, don’t let the cable slip out. Keep it trapped where it was beneath the bolt and washer. Now, hold the end of the cable above the anchor bolt (sometimes called “pinch bolt”), with pliers. The cable probably has a little cap on the end. Grab the bare cable not the cap because the cap will come right off.
Holding the cable tightly so it can’t slip, pull up with the pliers to remove all slack in the cable and hold it like this as you tighten the anchor bolt to secure the cable in place. It should now be tight enough so that when shifted onto the large chainring, there’s no rubbing. If it still rubs, you should have ample adjustment in your inline barrel to tighten the cable a little more and get the cage clearance you need. If you don’t have an adjuster, you will need to get the cable even tighter.
Front derailleurs can be tricky to get right. I hope these tips help. For more of our adjustment tips, simply search RoadBikeRider for “front derailleur.”
Ride total: 9,108
Mark Barrilleaux says
Hi Jim, Front derailleur adjustment has always been a pretty tedious exercise, due to the lack of any integrated adjustment mechanism. Your article put me in mind of several thoughts:
– Most frames with good old-fashioned external cable routing have an adjuster at the cable stop up near the head tube. Unfortunately this pretty much went away with the advent of internal cable routing.
– Shimano’s latest 9100 and 8000 derailleurs include an integrated adjustment system atop the derailleur. It’s tiny but it works.
– Barrel adjusters have an annoying tendency to lose adjustment (loosen) by themselves. I think this is due cable twist when the handlebars are rotated back and forth. After adjustment put a paint mark across the two halves of the adjuster and see if it is happening.
– I make it a point to cut cables long (about three inches from the clamp bolt). Among other benefits, this makes it easier to grab the cable and pull out slack. I like to use a third hand tool for this.
– Easy front derailleur adjustment is a great feature of electric shift systems.
Mark “Killa” Barrilleaux
Jim Langley says
Thanks for sharing your tips, Mark. Marking the barrel adjusters so you can tell if the adjustment has changed is genius!
I found a video showing the 9100 and 8000 integrated adjuster for cable tension you pointed out:
You’re right about electric shifting systems. In my opinion, the nicest thing about electric front derailleurs is being able to raise and lower them when you want to go to larger or smaller chainrings. That’s a hassle with cable operated derailleurs because the cable might be too short or it might fray when you loosen and tighten it, both meaning having to replace the cable. With an e-derailleur, you just move it up or down – as you well know.
Thanks again Mark. Great tips!
Tom in MN says
The integrated adjuster is also on the FD-5801 upgrade FD for 5800 105. This 11 speed FD also works as an upgrade for 4700 Tiagra, that also used the hard to adjust long arm FD design, which is very sensitive to cable tension.
I also have found FDs hard to select, primarily for small large chainrings, as determining if the bottom of the cage will hit the chain stay is basically impossible without trying it. I did find that Shimano makes the FD-CX70 for 10 speed 105, Ultegra, etc, with a short cage for cyclecross that solves this problem.
Tom in MN says
I should have also said that you definitely need to read the instructions for these integrated adjuster FDs. They have scribe lines you align to set the cable tension.
jim langley says
Thanks for sharing these tips, Tom.
David Schorow says
@Mark Barrilleaux mentioned: “Barrel adjusters have an annoying tendency to lose adjustment (loosen) by themselves. I think this is due cable twist when the handlebars are rotated back and forth. After adjustment put a paint mark across the two halves of the adjuster and see if it is happening.”
That is exactly what is happening with my wife’s bike (with Shimano ultegro). She’ll tell me she can’t shift into her big chain ring. I adjust (unscrew) the barrel adjustment. Next ride she says it is working great. One or two rides later it is back to not shifting into the big chain ring. I can tell by inspection that it has screwed back in.
So, if that is the problem, what is the fix?
Patrick Tomlinson says
a little drop of loctite on the adjuster will help – just make sure you have got the adjustment right before applying – or replace the cable adjuster with a new one.
Gary Turney says
Great article, would have been great to know this 5 months ago. About 50 miles into the Seattle-to-Portland 200 mile ride, my chain started slightly rubbing exactly as you describe under “Chain Rub and Noise”. And yes, it is maddening. Fortunately the ride is well-supported so after 20 miles of this I stopped at one of the bike repair stations. The tech immediately recognized the problem, explained to me the tension was off and that he turned one of my barrel adjusters exactly one click (about 1/8 turn) to solve the problem. However, he never explained to me which way he turned the barrel – tightening or loosening – and I’ve wondered since then. Tightening the cable seems counterintuitive to me (that it would shorten the travel), so my guess would have been completely wrong. Now I know – thanks much!
Jim Langley says
You’re welcome, Gary. I’m glad you got help from that mechanic on STP. That’s awesome ride support right there. Thanks for sharing your story!
Gary Turney says
STP has fabulous tech support. Local shops volunteer, so there’s tech support every 30 miles or so.
Michael Leven says
I gave up on front derailers.
I just use a wide/low compact and stay in the big ring.
I don’t do events anymore though.
In my terrain I can ride the big ring 42T up front and 11-32T 8-speed cassette in back everywhere I go in suburban Howard County, MD for my 23 mile round trip commutes.
Gets a little tough at 8% grades but still doable. I am a weak rider, though.
But very freeing to not have a FD and just use the one ring up front.
Stephen Turk says
Note that not all bikes need a Backup Plate. When I upgraded my 2014 Cannondale CAAD10 to R8000, I was delighted to find that the braze-on mount incorporates a plate for the Support Bolt. My understanding is that the Support Bolt was introduced with Di2, and almost any Di2-compatible frame probably already incorporates a plate for the support bolt as would most newer frames designed for R9100/R8000.
Jim Langley says
Thanks for adding this information, Stephen!
Sergio Alvim says
Hi! Thanks a lot, your article is amazing. I have a Ultegra R8000 in my Cannondale SuperSix and and an old 105 in a CAAD8. My problem was with the supporting bolt and I didn’t realize that was an important issue..
When the supporting bolt was not in the frame, shit was erratic e difficult and now perfect. I believe most of the mechanics don’t now this and for the first time I believe that my from derrallieur had just 3 positions and not 4.
The lesson for me was very hard, one R8000 lost and I have bought a new one, the first I bought I lost trying to tighten the cable and the screw don’t work any more and bought a new screw, very cheap, but I decide for now to remain with my old 105 in my CAAD8, beautiful and reliable.
Thanks a lot!
In cases where the braze on plate is large enough where the support bolt contacts it naturally, I assume use of the backup plate is not necessary. This appears to be the case with my Colnago C50. Can you confirm? Thanks!
Luke Cico says
I’m having a problem with this plate. I’m installing a new r8000 FD on a Trek Emonda. The problem is the screw ends up just behind the FD mounting plate on the bike. The Shimano plate has to Butt up against it. The screw wants to kick the plate because it’s on the end of the plate. Not the center. I overlapped the Shimano plate on the Trek FD mounting plate. Not ideal as it pushed the FD out. I’ll see how well this actually works.
Anyone have this problem?
jeff dalsis says
Jim Langley : Thank you Xs 10 for the info on front deraileur issues. I had been having a bothersom time shifting from small rail to large for some time. tried EVERY THING i could think and read about . domane with 15K . was about to just order a new 6800 LH brifter figuring at 15k even with old man useage in ONLY good weather and maintenance it was just worn out. Then came upon your Front derailuer article and IT WAS the loose hidden bolt that takes 2mm allen wrench. Mistake #1 . “snugged” it down from loose and now shifting “LIKE BRAND NEW ” ! I am a happy pedaler again !
Michael Wong says
I have a steel frame, with a 28.6mm seat tube. The stabilization bolt doesn’t not reach the seat tube (it’s too small diameter). Is this a problem?
Useful article – no mention though of the thin friction-free tube the inner cable runs through on internally-cabled carbon bikes. Replace a cable – how to feed it through this tubing. On my bike this tubing gets squashed and flattened around the bottom bracket, causing tubing to cling to the inner cable and move with it.
Eventually this jams things (especially in cold weather).
How about the use of chaser tubing to simplify moving the new cable through the carbon frame? How does this interact with the friction tubing?
Hi ya, great article. Clears up a few things.
Question, I got a new 2021 Trek Emonda SL 8 with 8050 Di2 front Der.
Issue: there is not enough clearance to install the protective plate.
Contacted dealer and Feedback from Trek was that integrated braze-on bracket was stiff enough for no movement, negating support bolt need.
Strange isn’t it?
Any workarounds noted? Trying to find a thinner plate than provided but nothing there and not sure if OK as could still damage frame if too thin.
Michael McAteer says
Hi, I had the problem, of the chain rubbing on the front derailleur, when I was in the big chainring on Shimano 105 when chainging down to the bottom 2 small cogs.I found that by using 3 clicks the chain stopped rubbing. Click once to change gear, then 2 more clicks will move the derailleur enough to clear the chain. Hope this helps. Michael.
Wonderful article–especially on installing the support bolt plate! I’d heard about the issue of missing plates on new bikes and have now found out how incompetent shop service departments are–the shop I bought the bike from didn’t even install it correctly after I took it back in to have them fix it. I’m now going to do it myself.