IIIPRO E4 4-Piston Hydraulic MTB Brakes - Are they to be trusted?

[Tijoe]

What makes you want so much rear brake power?

It's not that I want so much power, it is that I want to have one reliable rear brake at all times. I have had way too many problems with my IIIPro rear brake system.  I have had 3 complete rear brake failures out of 8 bikepacking trips since I started using the IIIPro brakes.   I plan to install one IIIPro rear caliper (and other brands) to test and compare with the Hope Tech E4 caliper,  assuming I can get other brand Chinese calipers to operate on 2.3mm wide rotors, and rebuild them/replace their seals, to EPDM compound, so they are compatible with Dot 5.1 brake fluid, rather than mineral oil. 

I suspect that my caliper tests will prove that the IIIPro hydraulic piston/levers assembly is the root cause of these brake failures.

[gribs]

I'm not sure I see the point if you're having to change the seals. If you can't change the seals in the IIIpro levers to work with DOT fluid does it mater if you can make the callipers work with different seals? In the UK Shimano callipers have by far the worst reputation for micro leaking. Is that a function of using mineral oil?

[Tijoe]

I'm not sure I see the point if you're having to change the seals. If you can't change the seals in the IIIpro levers to work with DOT fluid does it mater if you can make the callipers work with different seals? In the UK Shimano callipers have by far the worst reputation for micro leaking. Is that a function of using mineral oil?

I consider the Hope Tech E4 caliper to be the baseline popular design for numerous variations of Chinese 4-piston, 16mm diameter calipers.  Replacement Hope E4 calipers cost between $100 and $150 per Caliper.   The Chinese versions cost up to $50 per caliper.   If I can test calipers such as IIIPro E4, Frog Wake, ONIRII IV4R. Wheeltop E4, or the Peerage calipers these could be great replacements for the Hope calipers. (About $30 in replacement seals if one decides to run with a Hope Tech 3 or 4 brake lever assembly)

Of course I am not going to try to find EDPM seals to install in any of the Chinese brand hydraulic lever sets I have purchased and try to run Dot5.1.     

I will be running testing out the recent Frog Wake and Wheeltop brakes on different bikes spring of 2026.  Top date, I believe that the IIIPro levers are the problem with my rear brake problems.

[Fat Larry]

I'm not sure I see the point if you're having to change the seals. If you can't change the seals in the IIIpro levers to work with DOT fluid does it mater if you can make the callipers work with different seals? In the UK Shimano callipers have by far the worst reputation for micro leaking. Is that a function of using mineral oil?

At least spare parts are easy to find. I have some leaking TRP slate callipers and TRP told me to buy new brakes rather then sell me replacement seals or even give me the dimensions of the seal so i could source my own replacements.

[Tijoe]

I have a bit of on update on my brake testing project.   A month+ ago I purchased a set of Hope Tech Duo (RH Dual lever assembly and 2 E-4 calipers.)   For testing, I mounted a modified Aliexpress dual rear caliper holder along with a 203mm rotor and both Hope Tech E4 calipers.   I have been able to get in 2 shorter test rides.   Hope Tech uses DOT5.1 fluid, the assembly and calipers bled so much easier and faster than the IIIPro rear calipers.

When I started the project, I ordered EDPM 16mm square O-rings and EDPM round o-rings to be able to rebuild several of the IIIPro calipers to be compatible with the DOT5.1 fluid.   

Today I rebuilt one of my IIIPro calipers with the EDPM seals.   

Back in early December 2025, I ordered several NFOX brake line unions, so I will be able to swap to different calipers faster and easier.   

https://www.aliexpress.us/item/3256810011225058.html

Unfortunately, the original order has had no delivery progress since Dec. 19th, 2025 and appears to be lost after leaving US customs.   (Refund request to be made soon.)   Therefore during the latest January sales, I order some new ones.

When these arrive, I will be able to test a IIIPro caliper on the Hope Tech levers.    My thoughts are that this might make a decent system to save some money if I can test and figure out what variations of the Chinese E4 caliper could work with Hope Tech levers.

OTOH, If I want to spend bigger dollars, I could rebuild the Hope E4 calipers to be compatible with Mineral oil. I have spare seals to do this. Then I could try Hope Tech calipers with some of the Chinese lever/hydraulics that are available.

So many mix and match possibilities.

[Tijoe]

Update.  Since the weather has been unseasonably warm and all of the snow has melted,  I have been able to get out and test ride the brakes.

After test riding the Hope Tech E4 calipers for about 40 miles, I decided to install the IIIPro caliper that I rebuilt to run DOT brake fluid.

During the installation, I noticed that the dual caliper bracket was bending despite my reinforcement, so I had to machine and install an angle section onto the bracket.   
Note:  The dual brake caliper bracket is very weak and I personally believe that it should be removed from being sold to the public as a safety issue.  The names it is being sold under are TTPro and ATEWINA.

I installed the IIIPro caliper, centered it, and then bled the brake.
Note:  The IIIPro calipers really are difficult to get all of the bubbles removed. It takes at least 3X the time to coax all of the air bubbles out versus the Hope E4 caliper.

It went on a test ride and at first the brake appeared to stop the same as the Hope E4 caliper.   Then about 1/2way down a 1+ mile descent, the brake completely failed.  (100% why I am glad I am running a dual ear caliper for testing.)

Back home, I removed the IIIPro caliper.  It appears that one of the seals I installed was leaking.   I removed the caliper and replaced the seal with a new one.
After going through the bleed process, I worked the brake with a test block installed at least 100 times.  No leaks so far.   

The bike is ready for the next test run.

Observations:   I am incrementally becoming more methodical setting up the 2 rear calipers.  After the last installation of the IIIPro, the caliper was really dragging on the rotor.   I ended up using feeler gauges to measure the pad clearance on both sides of the rotor.  The HOPE E4s require 2.3mm wide rotors, the IIIPro normally run 1.8 wide rotors.   With the Hope E4 caliper pistons pushed back, I had 0.3mm of pad clearance.  On the IIIPro calipers, the clearance was .15mm  -  With the pads being so close to the rotor it took a lot of time to gradually tighten down the mounting bolts in order to keep the pads parallel to the rotor.  (PITA, such that it took 5 iterations of aligning, tapping, tightening, loosening to get the pads parallel.)   

Out for the next test ride tomorrow. 

[Skepsist]

short update on the speedone soldier which is basically an E4 with ceramic piston. I had the bike stored for the winter and the brakes lost all the pressure without leaking? dont know how that works but they dont bite anymore and since bleeding them absolutely sucks i swapped them for some cheap shimano 4-pistons which where also stored in the same room for over a year and they still work.
The R2X4 still work very well tough the brake pads you get with them suck.
I would not recommend these brakes and im not gonna use them anymore since they seem to be unrealiable.
Ill keep using the R2X4 until they brake aswell which they will problably do at some point.

[Fat Larry]

Sounding more and more like cheap shimanos are a better bet. Deore 6100 or BR520s, both of which can be found pretty cheap on Ali.

Biggest problem I have with them is hate the ways shimano's levers look. Much prefer TRP evos or even Srams lever aesthetics to shimanos weird angle tube thing.

[Skepsist]

i really like the way those brakes look but i just cannot recommend them to anyone.
Not the E4 and i suspect the R2X4 to somehow break once the bikepark season begins. I'll update you on how that goes.
At least in germany you can get deals on Shimano MT200 sets for 25-40€ and MT500 for 80
sure they look like shit but they work and getting replacement olives and pins will cost you almost nothing. even you lokal bikeshop will have those.

[Tijoe]

Looks like my attempt to use one of my IIIPro E4 calipers mated to a Hope Tech hydraulic lever has come to a close.  The rear caliper, rebuilt with Dot5.1 seals, worked for perhaps 30 miles of downhill stopping.   Then several days ago, I went to ride the bike and the rear lever pulled all the way to the bars, and the calipers didn't move/grip the rotor.   I said "screw it", I am done with piddling around with them!  I installed the Hope Tech E4 caliper, bled the brake, and will run only these on the back of this bike.
- When I discovered the lever had no action, removed the caliper, inspection of the caliper revealed no leaks or fluid in any of the fittings or the seals.  Basically, my final judgement is that the IIIPro E4 brakes SUCK!   

As a side note, I still have the same IIIPro calipers on 2 other lesser ridden bikes.   As they fail, (and I expect them to)  I will migrate to a different brand of brakes.

My trust in IIIPro brakes has dropped well below the most recent polls regarding the effectiveness of POTUS.

[kbernstein]

Has anyone had a bad experience with the XG4 flat mount calipers only? It seems all bad reviews are about the MTB levers or directmount brakes.. I could get them locally for a very good price, I'm tempted

[Tijoe]

Has anyone had a bad experience with the XG4 flat mount calipers only? It seems all bad reviews are about the MTB levers or directmount brakes.. I could get them locally for a very good price, I'm tempted

Looking as the images of the XG4 flat mount calipers, it appears to me that the functional part of the caliper is exactly the same design as the E4s.   Same outside caliper caps, same 16mm pistons and seals, same pads.   I doubt if they will last/pertform any differently than the E4s.   
Believe me, I would love to have someone write that they have had a great experience with this 4-piston design, and prove me wrong regarding their longevity.

For me, when they start out new, all of my E4 calipers had great stopping power.  They do have more drag on the rotors versus my Hope Tech E4 calipers, and it seems to me that after you replace the first set of pads, they start to degrade.  - Perhaps air being drawn across the seals into the caliper?   Who knows.   Since I have 4 out of 8 calipers that I can no longer to get working or bled well enough to get good lever feel, I gave up.