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The r3pro Piston Release Tool is a genius bit of kit for servicing stuck or sticky four-piston Hope callipers. It makes an otherwise devilish job a piece of cake.
If you run a four-piston calliper like Hope's excellent V4, at some stage it's highly likely one of those pistons will get sticky and not want to advance at the same rate as the others. This leads to uneven pad wear and rubbing.
On a two-piston calliper it's easy to rectify this – you hold one piston in with a dedicated tool or just a ring spanner, while squeezing the lever carefully to advance the recalcitrant piston out. Once it's at its maximum (but not so far as to eject completely), you can clean it up using a cloth, bottle brush or, my go-to, some alcohol-moistened string wrapped around the piston and sawed back and forth to wear off any caked-on muck.
But a four-piston calliper is a completely different sack of rodents. You're now trying to hold back not one but three pistons as you squeeze the lever. Even if you have a spare person and the right shaped tools to all fit into a tiny calliper entrance, there's likely to be colourful language and the real risk of going too far and popping the piston out, facilitating a huge faff reinstalling it and a full bleed.
Enter Phil Lee from r3pro (pronounced 're-pro'). Phil founded r3pro to make 3D-printed bits for mountain biking, and the tool on test here solves the above issue of freeing up or advancing a single piston at a time on a four-piston caliper. This particular one is designed for the Hope E4, V4 and RX4 callipers. If you have the Shimano version of the RX4 calliper (as I do), the pistons differ from the SRAM version, so you order the E4 version of the tool.
The concept is fiendishly difficult, the solution elegant in its simplicity. The tool is simply a block of plastic, with a cut out area that lets one piston advance while holding back the other three. The tolerances are sub-millimetre, so the piston advances exactly as far as it needs to without risking leaking fluid. Whether the piston was genuinely stuck, a bit sticky, or you just wanted to be proactive in cleaning it up during a pad change, the tool does the job perfectly.
As well as this tool designed for Hope E, V and RX4 callipers, there are also versions for SRAM Code, SRAM Guide, Magura MT5 and Shimano's common four-piston callipers such as XT, XTR, Saint and Zee.
What it's not, obviously, is a bleed block. r3pro sells those too. It also sells calliper alignment tools for various brands, to help get the calliper perfectly central over the rotor.
If you buy multiple tools at once, you get a £2 discount. Notably, it doesn't sell a pad or piston push-back tool, but as these are metal tools with handles it's not r3pro's 3D-printed vibe.
For £11.50 delivered, in one of nine colours, it's a bargain, and given the pretty much inevitable problem it solves both easily and quickly, a must-have for anyone running four-piston brakes.
Genius tool that solves a very real problem at an affordable price
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road.cc test report
Make and model: r3pro Piston Release Tool
Size tested: Hope E, V and RX4 callipers
Tell us what the product is for and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
It's for people with 4-piston brakes who want to keep them running sweet.
HELP FREE THOSE SEIZED PISTONS IN YOUR HOPE E4/V4 CALIPERS WITH THIS TOOL
Tell us some more about the technical aspects of the product?
Hope RX4 (Shimano version select E4 tool)
3D-printed from hard plastic, looks great.
Fits and works perfectly.
It's only 10g – if you put it in a travel bag or tool case you wouldn't notice.
It's a unique tool, so I can't say it's better or worse value than rivals as there aren't any... but for £11.50 delivered, given the huge faff and pain it solves, it's well worth it.
Tell us how the product performed overall when used for its designed purpose
Tell us what you particularly liked about the product
The precise fit.
Tell us what you particularly disliked about the product
Did you enjoy using the product? Yes
Would you consider buying the product? Yes
Would you recommend the product to a friend? Yes
Use this box to explain your overall score
As this is a unique tool that works perfectly, and doesn't cost much for the problem it solves, it's one for the 'exceptional' tag.
About the tester
I usually ride: Sonder Camino Gravelaxe My best bike is: Nah bro that's it
I've been riding for: Over 20 years I ride: A few times a week I would class myself as: Expert
I regularly do the following types of riding: cyclo cross, general fitness riding, mtb, G-R-A-V-E-L