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Hayes Dominion A4 Brakeset Review

Updated: Mar 5, 2020

What it is: Hayes' powerful and adjustable 4 piston Enduro/DH brakeset


I generally find myself agreeing with the other reviews on these brakes. They are powerful, modulate well, and are very well thought out compared to some of the other options on the market.

That said, there are a few aspects of the brake design that these reviews overlook, which I'll try to cover here.


Not something I really spend a ton of time with, but it's worth noting that the brakes come with both pad compounds (metallic and resin), along with a bleed block and shortening fittings:


The caliper is a burly looking contraption, especially compared to the more compact calipers used by SRAM:

The caliper has two bleed ports, which allows you to flush the caliper with brake fluid, if required:

The pads load from the bottom of the caliper, which is a tad annoying compared to other options, but it's a minor complaint.

One of the most interesting features are the grub screws they put on the caliper to ease alignment:

You can use these screws to shift the caliper's position left, allowing for a much more consistent alignment. When you have to remove the caliper, re-installing it with proper alignment is just a matter of pushing the caliper to the side and tightening from the rearmost bolt first. There is no need to eyeball alignment after the initial install.

An added benefit to this feature is that it seems to reduce instances where the caliper moves during riding or due to bolts working themselves loose. I've found with other brakes, the caliper will shift slightly over time and require re-alignment, even with proper torque on the bolts. These appear to resolve that problem.

Similar to most other calipers, you can use a 4mm to adjust the angle of the hose, as well. Hayes also sells rebuild kits and has detailed instructions for rebuilding calipers on their website, making them fully serviceable, unlike some other brands (Shimano, in particular).

Worth noting is that the caliper's size and shape means you will have to use Hayes adapters:

Clearance on the frame shouldn't be an issue, but SRAM or Shimano adapters have a flatter shape and the caliper won't fit on them.

Lever Design:

The lever design is fairly straightforward:

The lever itself pivots on a bearing, rather than a bushing, which prevents lever flop from forming over time (Shimano, R/RS level SRAM). There is a reach adjustment knob, which is stronger than the others I've used and more user friendly, it's not as flimsy feeling as SRAMs. There is also contact point adjustment, however I haven't used it to see what it does.

There is also a bleed port, as expected.

The lever blade is curved to the outside, which prevents your finger from slipping, and is textured. All fairly typical.

The only beef I have with the lever design is the clamp. Unlike SRAM and Shimano, the clamp design uses two bolts to tighten the lever in place. While this is a modular mechanism allowing you to clamp different faces for mounting shifters/dropper levers, it's kindof a pain to install and I inevitably drop bolts. A silly, minor gripe, but the lever is solid and stays in place once it's bolted down.

I haven't used the adapters for the shifter or dropper lever, so I can't really speak to their durability or ease of use.


I don't have a ton to say on the rotors, except that they are thick. If you are going to use these brakes, you need to use the Hayes rotors, as SRAM and Shimano rotors lack the thickness provided by the rotor that the system is designed for.

I've had no issues with scarring, noise, or warping. They're round and metal, they stay in place, seem to resist warping (I tend to warp rotors), and handle heat well. Not sure what else I can say there.

Ride Impressions:

I tested with a 203mm rotor up front and 180mm in the rear, I ran both pad compounds on my Sentinel Carbon. I weigh ~215lbs, so I'm on the heavier side and often have issues with brake fad and/or power, but had no such issues here.

The brakes have a Shimano-esque brake lever feel, where there is a bit of slack in the lever, followed by a fairly strong bite. They do modulate better than Shimano brakes, but they are more powerful than SRAM and have a stronger bite than both. If you let the lever further out, you can get a very powerful feel from the levers, more than any other brake I've used to date.

Unlike the Codes, these brakes require the lever to be a bit further out to achieve the same power, mainly due to the slight slack in the lever. Once the power kicks in, though, they have a very nice feel, without being overly grabby or too soft. The metallics pads providing a very strong, quick bite, with the resins providing a more SRAM like, modulated feel.

Despite absolutely roasting them on a few long downhills, I experienced no fade with either pad compounds and they remained very consistent. I experienced no inconsistencies due to outside air temperatures, either.

I do wish there was less slack in the lever, but aside from that, these are the best brakes I've used and have an excellent feel. The power that you can put down, especially with the lever a bit further out and the metallic pads, is really incredible.


I didn't grab photos of the hose trimming process. It's fairly easy and, if you are careful with the lever position (keep it pointed up) when you cut the hose, you could possibly get away with an install that doesn't require bleeding.

The hose barb Hayes provides is more engaging and easily used than others I've had, simply pushing into place rather than using threaded pins or loose olives like on other brakes.

If the levers get squeaky, which mine have, there are small grease ports that allow you to put some grease on the axle and prevent it. That's a nice, well thought out touch.

Where all of this gets messy is the bleed process.

The levers and caliper are both tapped for the same threads used by the SRAM bleed kits, however the lack of a good seal on the threads makes this really messy and not recommended. I tried it once and ended up with DOT fluid everywhere because the seal from the oring on the syringe wasn't strong enough for the bleed. You may have better luck, but I went directly to the Hayes bleed kit:

The Hayes bleed kit was a bit off putting at first compared to SRAM, the latter of which uses much nicer syringes. I've often found the thin plastic syringes, similar to what Hayes ships with their bleed kit, to be a bit sticky and difficult to use, but that's not the case here at all, these are very smooth and easy to use.

You have to put the hoses and attachments together. That's a bit annoying, but was not a big deal for me. Once together, the syringes look like such:

The kit comes in a nice box, which helps keep it all together.

From here, the bleed process is documented by Hayes. This is, IMO, the biggest drawback to these brakes compared to SRAM. The bleed process is kindof involved and has a few drawbacks:

  • The brakes should be removed before bleeding - This isn't an absolute requirement it seems, I've successfully bled them on the bike, but it's really critical to be careful with the syringes and dripping DOT fluid on your bike. If you can, I'd remove them for the first bleed unless you have internal routing.

  • The syringes do not initially provide a good seal against the brakes - Unlike the SRAM bleed fittings, the Hayes fittings will leak some if you do not tighten them properly: that is, beyond hand tight. I have to use a small set of pliers to SLIGHTLY tighten the fitting, otherwise they leak. They will also spew fluid out as soon as you remove them.

  • More bleed ports = more work - You don't necessarily have to flush the caliper by itself, I've yet to do that and find any air, it seems like it's more for when the caliper is rebuilt, but I end up doing it anyway. It does add a bit more work, though.

SRAM's Bleeding Edge is such a great system for bleeding brakes, I really wish something similar was available here. If you do it right, it's not that bad, but it's absolutely key that you tighten the syringes slightly beyond hand tight with pliers. Don't over do it or you'll strip something.

I'd also be careful to wrap the frame up with a thick rag or old t-shirt to absorb any fluid, which will inevitably dump out when you remove the syringes. Also be sure to clean the pistons out really well, otherwise you will get DOT on the pads, which can contaminate the pads through the backing plate.

Once done, the bleed seems to hold really well and I've not had any air come into the system. After the initial bleed, I found myself making less of a mess and being more effective, but it is a messier process than with other brakes I've used.

On a more positive note, the bleeding block design is really interesting:

You may note that one side of the block has some flanges that poke out and is almost exactly half the size of the other side, that is intentional. The thickest side is used for bleeding, you insert it and it spreads the pistons to a specific point that allows for proper fluid volume. The other side, which is what is interesting and unique, allows you to insert the bleed block into the system, pull the lever, and safely push the pistons to a point they can be lubricated, without popping out.

Over time, brake pistons will develop some funk on them and require working through the seals/fluid to remain smooth and/or require cleaning. The challenge is often how to do this without popping the piston out too far, damaging an irreplaceable seal (Shimano) or requiring a bleed. Using the bleed block above on the Dominions, you can insert that half into the caliper, then work the lever to push the pistons out safely without the risk of dislodging or pushing out a piston. It is a small thing, but one that really helps maintaining the brakes and keeping them smooth.

In all, maintaining these brakes is comparable or easier than SRAM or Shimano offerings, with the exception of the bleed process. I'm willing to deal with the bleed process for the other perks of maintenance and installation, but it's worth noting how messy the process can be. So who would I recommend this to?

Anyone looking for a powerful enduro or DH brake, especially those annoyed with Shimano's temperature related issues and SRAM reliability problems. If you are on the heavier side of 200lbs, these are a great option also, although lighter riders might find them a bit on the grabby side (The 2-piston A2 may be a better option in these cases).

They're probably a bit much for XC or light trail riding, but there is an A2 variant that is lighter and only uses 2 pistons, which is an alternative for those applications. The calipers are interchangeable, allowing switching back and forth.


vs. SRAM Code RSC : The Code lever engages almost the moment you grab it and they provide excellent modulation, but they lack the overall power of the Dominions. The Codes lack some usability features that the Dominions have (ease of alignment, better adjusters, multiple pad compounds shipped with the brakes), but bleed a lot easier. The upside of dealing with Hayes is that you can reach out to them directly as an individual, whereas SRAMs end user customer support is nonexistent. Both can be rebuilt using service tools, both use DOT, both are consistent in cold temperatures, and both have good fade resistance, although I'd give a slight nod to the Dominions over the Codes in the fade area. They're both great brakes, it'll depend on what feel you want to go for and if end user customer support is important to you or not.


  • Powerful, well modulated brake engagement

  • Excellent heat management

  • Caliper alignment system is brilliant and eases installation/removal of the caliper considerably

  • Hayes customer support is great for end users

  • Ships with both pad compounds

  • Very well thought out features, from the bleed block design that allows you to use one side to lubricate pistons to the smooth action syringes provided in the bleed kit

  • Hoses are easy to trim without using several parts or worrying about the barb getting jammed crooked in the lever

  • Thick rotors handle heat well and resist warping

  • Multiple bleed ports on the caliper make flushing air out of the caliper, where it often gets stuck, easier

  • Lever ergonomics feel great, but this is likely more preference than anything. They are a good in-between of SRAM and Shimano designs.

  • Bleed kit is well thought out, syringes are smooth and easy to operate


  • The bleed process is not as smooth or clean as the SRAM Bleeding Edge system allows and requires extreme care or removal of the brakes from the bike

  • A bit more slack in the lever than I'd like, but not excessive

  • Use of SRAM bleed syringes, despite being the same threads, resulted in a huge mess and air ingestion, although this could be due to my syringes/seals (I didn't get a chance to try with another set).

  • Bleed kit syringe fittings/hoses require some minor assembly

  • Requires use of Hayes rotors due to specific thickness rotors that are different from SRAM/Shimano and others

  • Use of Hayes brake adapter may be required due to the size of the caliper

1 Comment

Ashwin Amanna
Ashwin Amanna
Jul 13, 2020

Hi, thanks for all the information in this post. You mentioned a grease port of helping get rid of squeaky lever. Can you describe this more or show a picture. Mine are starting to develop a squeak. I like these brakes, but am struggling with the bleed process. Sometimes I get it, others not. The solid bleed doesn't seem to last as long as I'd thing, which leads to me to believe I am still not doing it right.

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