Shimano GRX inline (secondary) brake lever (BL-RX812)

Following on from a discussion in the Game Changer thread as this should probably have its own thread.

Shimano brought out an inline hydraulic brake lever some time ago designed for gravel bikes.

I don’t think anyone’s tried it yet, but it looks ideal for some dual position brake action (right and left hand positions without the naff centre mounting, or aero and standard positions). I’d like one for freewheel so I can have ideal braking positions for both hands but as a non-essential thing it’s been pushed to the bottom of the list right now.

It will need some modification/serious shimming to mount properly on a 22.2mm bar instead of the 31.8mm that it’s designed for, but it has reach adjustment and the lever shape looks nice enough.

Also be aware that due to where the hoses mount, you will need to make sure you get the right one for your planned setup or risk ending up with hoses poking out all over the place.
Probably the BL-RX812-R if mounting for your left hand and BL-RX812-L if mounting for your right hand.

1 Like

That’s really neat! Where, and how, do they join each other?

I think there are adaptors to put 31.8mm brake levers on a standard 22mm bar.

1 Like

You’re right. I know two of these adapters are sold with an aerobar I bought last year. But I don’t know where to find others without buying a whole aerobar.
I was thinking about making a custom t-bar ; it could be a great idea to make it a 31.8mm bar. I’ll thought about it.

So, they just fit inline between your existing brake and caliper.

They’re obviously designed to be used in association with the GRX drop bar brake levers but so long as you can get the right inserts/olive setup then I see no reason why they shouldn’t work just fine with the majority of Shimano’s hydraulic line-up.

Regarding the adapters, you will need to make sure that the 22.2mm hole is off-centre, right on the edge of the 31.8mm hole as the housing of the brake needs to rest on the surface of the bar.

I suspect that the metal strap will likely be easy enough to straighten out, drill further along, and then re-bend around the bolt section which was my planned modification. Or even a 3D printed mount/adaptor could be a good option.


I’ve been testing a Shimano GRX setup for a few months now. It is mounted on a Mad4one handle saddle + extension and works quite well.

The GRX lever is weaker than the normal Shimano levers and a bit awkward to hold since it is so close to the handle. Therefore, I wanted the normal Shimano lever to be closer to the saddle (more control for muni) and the GRX far out. The GRX works fine in this position, which I only use for smooth (dirt) roads.

I either use my ring finger and pinky on the GRX lever with the index and middle finger on the handle or the index and middle finger on the GRX lever with the ring finger and pinky on the GRX body.

Usually, the GRX is between the normal lever and caliper. The hose between the levers that comes with the GRX is quite short (maybe 20 cm). For my setup, I had to buy a longer hose (1 m). As already mentioned, you need an adapter for the clamp. Marco made one for me out of a seat post tube and some plastic filling.

The initial setup is a bit of work, in particular preparing and connecting all the hoses. Filling the system with brake fluid and bleeding was pretty easy. I didn’t have to mess with it since then.

I personally use this setup for long-distance gravel riding - mix of easy single trails, dirt roads, and paved roads. The flexibility with the two levers is quite useful for this purpose.


Have you tried mounting it the other way around? This shall be possible since the hose does not stick out of the end like with normal brake levers. So you could grab it like it was designed to be.

1 Like

Ahh, that’s great - thanks for the insight!

The pictures are really useful to see the comparison between the two.

The reduced power comment is interesting as it looks like a similar lever setup (to the cheaper Deore brakes at least) - does your standard brake has Servo Wave? Could that explain the power difference? Or might the lever position be causing some of it?

I also wonder whether it might work nicely the other way around (more like a bike) although with the relatively shallow angle of your bar perhaps not?
The other way around would put the hoses on the outside though so you’d want the RH lever instead for a permanent setup like that.
Do you think that with the closeness, a 3D printed part that shimmed the whole setup further away from the handle would work to get it where you’d want it? Being made long the whole brake could rest on it, and it could be adjusted by rotating.
Here’s one I knocked up just now:

It could probably be split in two places to allow use on continuous bars as well.

Indeed, the GRX is better to operate when turned around. I once tried it turned around and mounted on the left tube of the handle saddle for left-handed braking. If I remember correctly, it worked pretty fine. I ended up with the current setup because the hand position is closer to the end of the handle, which was my goal - being able to brake with my hands at the end of the handle.

The GRX lever definitely feels weaker since it doesn’t have Servo Wave (the Deore does) and it is also shorter, meaning less leverage. On roads, even steep ones, it’s not a problem at all though.

Sounds interesting! For my setup, the length of the lever would still be an issue though - it’s quite a bit shorter than the normal Shimano Servo wave levers - which are already quite short! If you turn the lever around, the closeness to the handle bar is not so much of an issue.

Would you be able to provide measurements? They don’t look particularly different in the pictures.

From pivot to tip: about 75 mm for the Deore lever, 50 mm for the GRX.

Maybe I’m missing something, but if it’s for a hydraulic system, why not just add a T or Y and add whatever second lever you want?

Almost all hydraulic brakes these days have auto-adjusting pads which doesn’t work with having two cylinders. This is handled at the lever end rather than the piston end.

1 Like

That is short!

I guess as an additional brake lever on a gravel bike they don’t see the need to make it as good an experience as the primary levers.

1 Like

Even without auto-adjusting pads on a normal single lever system fluid is free to flow back into the reservour when the lever is released. If pressure was added with a second lever the pressure would be relieved at the first lever.
Here is a diagram.

1 Like

Ahh yes of course it does. I knew there was some more general reason

I cannot understand why no one consider modding the lever. The work in this topic isn’t faster or easier than a single new brake lever. I hope that you will try with an old spare part so you could understand what I mean. Maybe you will find out that I’m wrong, but maybe you’ll avoid lots of other mods

So I thought about modding the lever, but the setup is quite different to Shimano’s current offerings, more similar to the setup on older Magura MT2 brakes so there aren’t any direct drop in replacements as far as I know.

Making a lever is no small undertaking and not something I could just 3D print.

Yes you could maybe chop off the curved end of the existing lever and bolt on a longer one, but that has its own usability disadvantages (bolts through part of the lever that you may want to hold), and I don’t have a spare brake lever (nor one of these GRX levers for that matter). Welding something is beyond the tools and skills of most people.
It’s very much a non-reversible mod if you hack the existing lever too. All of these other things can be changed without damaging the GRX lever so there are no disadvantages to just trying them all first.

Let us know how you get on if you do decide to get one and modify the lever, but I know you’re already a fan of big lever extensions!

From the look of it, the lever of a BL-M401 may fit. (Unfortunately, knowing Shimano, they won’t be for sale seperately…)
I’ve toyed with the idea of diy levers before, and ended up deciding that it may be possible to come up with a design that you could lasercut and bolt/JB weld together…I’d try to find some existing lever that fits first though.