EXNAVI 4 Piston Hydraulic Brake Repair Parts Upgrade kit Ceramic Piston Perfect Substitute for Shimano Brake Caliper 4-Piston M640 M810 M820 M7120 M8020 M8120 M9120

This Disc Brake Piston Kit works well and was very easy to install. But removing the old pistons was quite a challenge. Some came out easily and some were very hard work even with compressed air. But it was great to replace the old pistons and get my brakes to stop leaking mineral oil.

My Shimano Deore XT 4-piston calipers were starting to seize up on my rotor so I removed the pads to press the pistons back into the caliper body (see YouTube videos on this process). While pushing them in I could feel some grinding and realized the back side of the piston, inside the caliper, had broken. Shimano doesn’t sell the ceramic replacements so I bought AND some new calipers just in case. I figured if these replacements didn’t work, I would just replace the whole caliper. So now I have two brand new calipers sitting in boxes because these replacements work great. They come will all new seals. Once you remove the old pistons (see YouTube videos on this process), installing them is a breeze. And because they are not ceramic, I don’t have to worry about them breaking again in the future. If you’re handy, this is a great buy.

Common issue with Shimano brakes. Looks like they just don't care? This issue has been going on for a LONG time. I have a set of M9120 and when I replaced the hose due to it getting caught and it developed a hole. When bleeding, it was leaking between the piston and the caliper housing. Sure enough, it was cracked. Bought these to see if I can salvage the calipers. They were a perfect fit and has been working great. I cleaned my old calipers in a 99% rubbing alcohol bath then blown clean with compressed air. With the oe pistons removed, there was a lot of ceramic dust mixed in with the fluid. After cleaning and wetting the new pistons with shimano mineral oil, they slid in and bled just fine. Lever feels the same and it's been working great. Absolute life saver. Ordering another set for when the front goes out.

Because Shimano doesn't sell OEM rebuild kits for their calipers, I was forced to go aftermarket. Big mistake. These showed up and looked to be of fairly good quality. I installed these into a Shimano BR-M8120 caliper. Bled the caliper and everything appeared to be good to go. I get out on my first ride and the brake is working well. Then, I get some heat in it on some downhill and the brake goes completely away! I mean, lever to the bar with zero braking force! I get it home and think to myself that maybe there was a trapped air bubble in the caliper so I re-bleed the system and get it ready to go for the next ride. The next ride, something similar happened in that the brake is working well until I use it on some longer downhills. This time, though, I lose all braking force because the oil has gone past the seals/pistons and soaked the caliper/pads/rotor and wheel. I've ordered a complete new caliper from Shimano and I'm unable to return this junk because it's not in "new/unused condition". Save your $45 and put towards a replacement caliper instead.

Nice Product - I have high hopes for extended performance!

Caliper had ceramic pistons that kept binding giving me really inconsistent braking, after replacing with these I have great feeling brakes, now I just need finish bedding in the brakes. Fit is way better than the factory ceramic pistons, so far no leakage, price seems pretty reasonable

Once you get the old pistons removed and the caliper cleaned up these installed very easy. I haven't used the caliper yet so can't comment on how good they work. But will update review once I have tried them out

Ordered these in 2022 and they have been great! I ride more than most people and have well over 1,000+ miles on this kit. No leaks and no brake fade on long downhills they just work. I just had another XT piston failure on my eMTB and I am ordering another set now. I have no doubts that they will perform just as good.

Had a cracked piston. Since shimano doesn’t want you to fix your calliper, I had to go third party. I cleaned the calliper to make sure there we no more ceramic chips inside it, installed seals and used mineral oil to lube new pistons while putting them into place. I let original pistons on the other half of the calliper. Since then (1 month)I rode my bike hard and had no issue. Pretty satisfied and have two pistons left.

Same diam as my saints piston. Using stock rubber thing. They also included a bunch of caliper gaskets. Good stuff actually

Worked great on Shimano XTR. Which has the four pistons. In fact the derometer of the rubber and seal design allied me to mix with pairs of oem Shimano without issues.

Bough this to replace cracked pistons in my Shimano MT520 brake caliper. All parts were compatible and the brake works well. Did a day in the bike park recently and had no problems.

Have been using the replacement piston for a couple of weeks on heavy bike park descents. It replaced a cracked shimano piston very easily, no issues so far and no difference in braking power. I only needed one piston from the pack but good to have spares.