DIY Shimano 12-speed mechanical road bike shifters

I’m migrating this thread from the VeloClub Slack to save space there, so it doesn’t get automatically deleted, and because this forum format is probably better for a long writeup like this.

To summarize: I had taken apart my 5800 series 105 shifter and noticed that it might be possible to convert it from 11 to 12-speed with the replacement of two parts and some judicious filing of another. So I’m designing those two parts.

Here’s the progression of prototyping I did. Though I did a number of iterations of both kinds of 3D printed pieces, I’m only showing one set.


The upper row is the secondary ratchet used for downshifting. The bottom row is the primary ratchet for holding the cable takeup spool in the correct position depending on the gear.

The white pieces on the left are FFF/FDM 3D printed PLA parts. They were to get the rough dimensions and see that they worked in the shifter, albeit without actually being connected to a derailleur- they would not survive the impact forces of a spring-pulled cable.

The gray pieces are MSLA 3D printed resin parts. They were good for fine tuning the the shape of the modified parts, especially as there were clearance issues with the gear ratchet teeth being slightly closer together. But they were more fragile than the PLA parts- a tooth sheared off when a pawl just slid over/through it.

The silver pieces are laser cut stainless parts for full functional use. These are what I currently have installed in the shifter.

And the black pieces on the right are the original parts.

After reassembling the shifter with the new steel parts, shifting wasn’t quite optimal- it wasn’t shifting into the largest cog without adjusting the cable tension and causing problems in other cogs. It looks like I may have miscalculated when respacing the teeth, so I have sent out redesigned parts to be laser cut.

And that’s where I left things on the VeloClub Slack.

I’ve since filed down the takeup spool endstop a bit more (circled in green) to allow it to move more cable.


In front of that (to the left in the photo) is the primary ratchet, though only the last tooth is visible. And in front of that is the secondary ratchet.

On the workstand the bike shifts across the whole cassette now. The chain gets into the largest cog easily enough, but there’s some slight hesitation shifting both up and down especially in the smaller cogs- the wheel sometimes needs to do a half revolution or more before the chain completes the shift.

I think this is more of a cable or lubrication issue. The cable is a generic replacement that I put on when the shifter was 11-speed, though it doesn’t have that much use on it. A polished cable should cut down on some stiction I’m seeing, and the cable housing might be over five years old. I should also replace the lube inside the shifter, especially since that I wiped off most of the grease that was originally there after taking it apart a few times.

I need to squeeze in a quick ride to see how it actually shifts on the road.

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Chapeau!

That’s brilliant engineering.

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Amazing, if you get it to work properly, you should make it available to buy. Do the same thing like the guys from Ratio technology.

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What to say… You are GREAT!
As lube you should use the factory recommended Shimano Chain Dry Lube (that is Teflon based), the bottle we all know… also cheap.
Just one question. You are setting it up for a new original shimano 12s cassette? Or a sram xdr one? Or a Campagnolo 12s?

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Posting to express interest. I want moar cogs.

Well… does anyone know if shimano 12 speed chains works well with their 11 speed cranks? Would I be able to get away with just the ratchet, cassette and chain? I assume the answer is yes.

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With no specific experience using a 12 speed chain on an 11 spd crank, I can say that there is usually at least a “one generation” overlap between cranks and drivetrains. IOW, I have used a 10 spd crank successfully with 11 spd drivetrains, and even gone multiple generations in some areas (currently using an 8 spd Mavic crank on my trainer with a 10 spd drivetrain).

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I have uploaded a video of disassembly of my shifter. Maybe it’s been done before- I’ve certainly seen someone else take apart other shifters but I didn’t follow them closely enough to see if they did that to shifters that run the shift cables under the bar tape.

Having taken apart to fix 7-speed Ultegra and 10-speed Dura Ace shifters, this 11-speed 105 is much easier and doesn’t require any particular manual dexterity: remove the shifter from the bars, remove the cables and brake hood, unscrew the screw at bottom of hood and remove the two cover pieces, remove circlip and brake lever shaft to remove brake lever, push out the spring pin at back of hood, unscrew the pin spanner bolt at back of hood, unscrew the screw visible through front of hood, loosen the 1.5mm setscrew on top inside of hood, and pull out the shifter unit.

From there it’s possible to clean out any possible strands of shifter cable that are gumming up the works or dip the unit in solvent to loosen any dried out grease. Regreasing would be a bit more difficult since there are a couple of bushings hidden in there, but maybe a light oil could be used instead.

Further disassembly is done in the video getting to this:


Reassembly is a bit more complicated.

The shift cable takeup spool is the most complexly shaped part after the plastic hood, but the gear ratchets are simple stamped steel pieces, though one is also notched on the flat area. That led to my idea of this 12-speed conversion.

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Reassembly of the Shimano shifter is much more complicated than with the SRAM. I doubt many people would want to take it on, severely limiting the market for such a conversion unless I ran a conversion service where people send in their shifters for conversion, much like the crankarm power meter conversions.

Also, this is only one, previous generation shifter. Since I don’t have them on hand to take apart, I don’t know if the same parts would work with any generation Ultegra or Dura Ace, or even R7000 105.

This is using a third party (SROAD) cassette. Cog pitch seems to be the same as SRAM at about 3.63mm vs. 3.55 for Shimano mountain, at least according to the dimensions I found on Weight Weenies. I have not been able to get my hands on any Shimano 12-speed road cassettes or their dimensions, but I assume they’ll be the same as their mountain spacing.

The difference between Shimano and SRAM spacing is about 2-3/4 percent, which people haven’t found to be a major problem on mountain bike setups, but since my current parts are already a bit off in the wrong direction, for a Shimano cassette, I may need the slightly different parts that I have already sent out to be laser cut.

I’ve heard of people running 12-speed chains on otherwise 11-speed drivetrains because it was quieter. Personally, I only have a couple hundred miles of running my 12-speed chain on my 11-speed crankset, but I haven’t noticed any problems.

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one more cog would worth all this?

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I’m not going to try to justify the amount of work I’ve put into this. I freely admit that I have way too much time on my hands.

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This is awesome, I must have missed it on the Slack, I’d certainly be keen on some tinkering once 12 speed cassettes are more commonly available.

A quick Google shows one of the 12 speed Ultegra cassettes has the following ratios, which looks pretty handy. I’d like to see what sets they do and whether there is an equivalent to the Junior 14-28 cassette (I really like this one for most of the riding I do).
11-12-13-14-15-16-17-19-21-24-27-30 teeth.

I’ve currently got Ultegra 6800 shifters (cable brakes) but I guess it would make sense to use whatever levers makes the job easier, be it 105, SRAM etc.

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Pretty sure back in the day, my race cassette was the same 12-21 combo in the middle of that cassette. :joy::joy::joy:

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Beyond brilliant! Thank you for sharing this modification. Cheers.

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So I took my setup for a short 20 mile ride yesterday and it shifted well. Sometimes the chain sort of clunked into gear, but I think that’s more a function of the third party cassette than the shifter. It probably shifted over in someplace other than the where the shift ramps were. I did fine tune it a bit more by loosening the barrel adjuster half a turn and found it still had no problem going to the largest cog.

After the ride I replaced the cable and housing with new SP-41 housing that I’ve had around and a supposedly bulk Shimano Optislick cable that I picked up from a bike shop on my ride. It feels pretty rough, not as nice smooth as other die drawn cables, but with some blueish coating. That change fixed my stiction issues, but optimal shifting is still in a narrow range that can be thrown off by just a quarter turn of the barrel adjuster.

I figure if the Shimano 12-speed road cassette is a 3.55mm pitch rather than the 3.63mm that this current cassette is, then shifting would be pretty much perfect. I’ll switch the shifter over to the new primary gear ratchet when it shows up later next week and see how well it works with this cassette.

Compared to the SRAM setups that I also converted to 12-speed, I like the low force of the 105’s front shifter, but I still dislike how if I fat finger an upshift of the rear by slightly hitting the big lever too, the shift just doesn’t work. This is really a problem with the Shimano vs. SRAM shifting systems in general, not my conversion. Also, since the 105 has a bit less mechanical advantage, I dislike how the brakes require so much more force- and this is with the 105 calipers.

Once I get this 5800 setup working perfectly, I might just go back to the SRAM Force and see about making its front shifting a bit lighter- probably reduce the diameter of the cable takeup spool as much as I can without changing the gear ratchet. The only other drawbacks to my SRAM setups are that the shift force gets a lot higher going to the bigger cogs and the shifters are a lot louder.

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Incredible. Well done!

amazing stuff @Mark_H. that is superb engineering.

I’ve taught myself to dis/assesmble shifters. It’s surprising how much easier the new generation ones are. They have really improved the design - simpler. You could probably start a business with this if you can get it working reliably.

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Just posting to say that I’m loving your posts @Mark_H. Can never get enough of bike engineering nerdery despite myself not being very capable!

Thanks everyone for the encouragement and good words.

Honestly, it’s not as good of engineering as I’d like- measuring parts with just calipers and estimating angles by overlaying a picture of the part in my CAD software. I mean all I’m doing is reproducing a couple of parts (only 2-1/2D at that!), changing the spacing between the teeth, and adding an extra tooth. And still getting the spacing wrong.

Good, so it’s not just my imagination.

How many of the newer shifters have you disassembled? Hydraulic and cable brake? Rather, do they look like they might use the same shifter mechanism? Or do Ultegra and Dura Ace have different internals that make them better?

My concern with making this a product would be needing to make parts for each tier and each generation of shifter. If it’s a matter of better materials, fit, and finish, then I’m not sure if I’d want to go overboard and get Dura Ace quality parts hardened and wire EDM cut. Maybe water jet.

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I haven’t touched any of the new stuff. a lot of 6800 stuff. they tend to break at the casing so I’ve been donated a few. no one is donating their serviceable new stuff :slight_smile:

I’ve found the design follows generations - i.e. 5700/6700/7900 (?) is basically the same design and parts. That makes me smile when you consider how much extra you’re paying for Dura Ace!

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In the CT slack channel I recently mentioned my interest in modifying a road shifter to work with my Shimano Alfine 8-speed internal hub. My initial thought was to design a ratchet for a SRAM DoubleTap shifter since Ratio have successfully demonstrated that this is straightforward to do. One responder pointed out that the cable pull between clicks for my hub would be roughly 50% larger than required for a SRAM road derailleur, which would have strange effects on the DoubleTap functionality. It looks like perhaps this would not be an issue with a Shimano retrofit because there are 2 complimentary parts that both need to be replaced as a pair, so if designed correctly any arbitrary spacing could be supported. Does that sound right to you?