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Parts Needed to Add Hydraulic Disc Brakes to a Trailer


Trailer disc brake assemblyidler hub

Whether you are adding hydraulic disc brakes to a trailer that has no existing brakes or changing to disc brakes from electric or hydraulic drum brakes, you need some basic information before you start building a system that will stop your trailer safely and dependably. The following article and tables explain your options and will help you find parts that work together. If you just want to find parts quickly, see the table below, "Parts for Adding Hydraulic Disc Trailer Brakes."





Why Choose Hydraulic Disc Brakes?


Hydraulic disc brakes can provide a safe, secure braking system with strong stopping power for your trailer. And because a hydraulic braking system lacks electrical parts, a trailer with hydraulic brakes can be safely backed into water. This makes hydraulic brakes perfect for boat trailers. In addition, when compared to hydraulic drum brakes, disc brakes stop harder and require less maintenance. That's because they have fewer moving parts.





Parts Reference Table



Parts for Adding
Hydraulic Disc Trailer Brakes
Part Brake Mounting Flange Spindle Disc Brake Assembly Hydraulic Disc Brake Actuator Brake Line Kit
Brake Mounting Flange Spindle diagram Disc Brake Assembly Hydraulic Disc Brake Actuator Brake Line Kit
Consider Axle diameterBearing and seal dimensions
Seal contact surface (B) -
Inner bearing (C) -
Outer bearing (D) -
Axle capacity -
Bearing spindle seal

Wheel bolt pattern
Select

Hydraulic surge brake actuator
Type of axle

Number of axles




Trailer Brake Mounting Flanges


Brake Mounting Flange

To operate the brakes, a brake mounting flange must be attached to your trailer's axle behind the existing hub assembly on each side. Most axles have these flanges, and if your trailer already has brakes (electric or hydraulic) it will. But if your trailer has no brake mounting flanges, you have two options.


1. You can replace the existing axle with a properly rated axle on which brake flanges have already been welded in place. Ordering a new axle that comes complete with hydraulic disc brakes may actually cost less than buying separate parts. However, before you can order a complete axle you will need to know the axle capacity, wheel diameter, wheel bolt pattern, spindle type (that is, drop or straight) and type of brake assembly - in this case, hydraulic. You will also need to know the distance between your trailer's leaf springs (center to center) and between the hub faces.


2. You can purchase brake flanges and have them welded to the axle by a qualified welder. When a brake mounting flange is attached to an axle, it must be welded square and concentric. This usually requires a jig to hold both parts in position. A trailer shop should have the equipment and personnel to weld brake mounting flanges to your axle.


Pictured (above, right) is the most popular brake mounting flange. It's a square, four-bolt pattern that is used on most axles up to and including 3,500 pounds. The next-most-popular flange is the five-bolt design, which is commonly used on 5,200, 6,000 and 7,000 pound axles. The pattern of the holes in the flange is standard, so all you need to note is the axle diameter and the number of holes in the mounting flange.





Disc Brake Hub and Rotor


If you have a brake mounting flange on your axle or plan to have one installed, you have two options.


Over the Hub Disc Brake KitOver the Hub Disc Brake Rotor

1. If you have idler hubs, you can either replace them with an integral hub and rotor or install a disc brake kit that uses an over-the-hub rotor. An over-the-hub rotor kit makes it easy to upgrade an idler axle to a disc brake axle. Before you can select an over-the-hub disc brake kit, you have to know the wheel bolt pattern.


With over-the-hub disc brake kits, your trailer wheels must be 14 inches or larger. You will also need to consider fender clearance and wheel stud length because the wheel-and-tire combination is spaced 1/2 inch farther out - a result of adding the disc brake rotor.


Integral Disc Brake KitSpindleSpindle diagram

2. The more popular choice is a disc brake kit with integral hub and rotor. If your trailer already has drum brakes and you're upgrading, this is definitely the way to go. To make sure that the hub-and-rotor assembly you're looking at will work with your trailer spindle, you will have to either measure your spindle or get the part numbers from the existing bearings and seal. Along with the axle capacity, wheel diameter and wheel bolt pattern, knowing either this spindle measurement or the part numbers will help you select the correct hydraulic disc brake kit for your trailer.


If you cannot find part numbers for the bearings and seal, you can measure the spindle (see spindle diagram) at the inner bearing surface (C), the outer bearing surface (D) and the seal contact surface (B). Once you have these measurements, you can look up the part numbers of the bearings and seal that you need in order to select the right disc brake kit.


Disc brake parts are manufactured with one of several different finishes - raw metal, e-coat, silver cadmium, or Dacromet or they are made entirely of stainless steel. Parts vary in price and in the degree of resistance to corrosion, depending on the finish. For example, the ability of brake parts to resist corrosion would be important if you typically use your trailer around water, especially salt water. Of the different finishes, "raw" offers the least resistance to corrosion. Better than a raw finish is e-coating, which fights rust and corrosion with a paint-like coating. But a downside to e-coating is that the paint can wear off or get chipped, allowing rust to start. Both silver cadmium and Dacromet plating offer better alternatives for corrosion resistance than either a raw finish or e-coat, and they hold up very well. But parts made of stainless steel stand up best to corrosion because they are reliably rustproof. The only downside here is that stainless parts are much more expensive than parts having any of the other finishes.





Brake Line Kits for Trailers


Next, you will need a brake line kit to plumb the trailer from the disc brake calipers to the hydraulic surge actuator. Brake line kits are selected according to the number of axles on the trailer. Because of the way disc brakes work, they require flexible lines at the brake caliper, so the part of the brake line that connects to the caliper is usually made of rubber. This same flexibility is needed for brake lines installed on torsion axles because the hubs on those axles move so much during operation.


Disc Brake Caliper Brake Line Kit Brake line installed along axle



Hydraulic Disc Brake Actuator


Hydraulic brake actuator

Another item that your trailer will need is a brake actuator, a device that applies pressure to the brake lines to activate the brakes. The actuator is bolted or welded to the trailer at the tongue and connects to the ball on the hitch of the tow vehicle. The actuator works by compression. When the tow vehicle slows, the trailer pushes against the actuator, causing it to apply the brakes.


The brake actuator that you select must meet or exceed your trailer's GTWR. The actuator also has to match the size of the hitch ball on the tow vehicle. You can select manual or electric reverse lockout options if you would like to have these features in your actuator. Reverse lockouts ensure that you can back your trailer. Because actuators work by compression, they will apply your trailer's brakes when you back up. The lockouts let you override the actuator, preventing it from applying the brakes.


Finally, you should select a brake actuator that is designed specifically for disc brakes. Hydraulic disc brakes operate at a higher pressure (1,500 psi) than drum brakes (1,000 psi), so you have to make sure that the actuator you want to use is compatible with disc brakes.





Common Combinations of Trailer Brake Components


Typical Components of Integrated Hub and Rotor Hydraulic Disc Brakes
Direct Mount to Spindle
Axle SizeEZ Lube OptionBrake FlangeBearingsSealDisc Brake KitFinishRotor Bolt PatternSurge ActuatorBrake Line Kit
2,000-lb Axle

1-3/4" Diameter
Standard 4-34 Inner - L44649
Outer - L44649
10-9 Single axle - K2HR2E
E-Coat5 on 4-1/2" T4715400
T4715420
Single axle - T4829900
EZ Lube4-34 Inner - L44649
Outer - L44649
RG06-020 Single axle - K2HR2E
E-Coat 5 on 4-1/2" T4715400
T4715420
Single axle - T4829900
3,500-lb Axle

2-3/8" Diameter
Standard 4-35 Inner - L68149
Outer - L44649
58846 Single axle - T4843100
Double axle - T4843700
Silver Cad5 on 4-1/2" T4839100 Single axle - T4829900
Double axle - T4830000
EZ Lube 4-35 Inner - L68149
Outer - L44649
10-19 Single axle - K2HR35D
Double axle - T4843700
Silver Cad5 on 4-1/2" T4839100 Single axle - T4829900
Double axle - T4830000
5,200-lb and
6,000-lb Axle

3" Diameter
Standard 4-44-1 Inner - 25580
Outer -
15123 or
LM67048
GS-2125-DL
or
GS-2250-DL
Single axle - K2HR526D Dacromet6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
Inner - 25580
Outer -
02475 or
14125A
GS-2125-DL
or
GS-2250-DL
Single axle - K2HR526D Dacromet6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
EZ Lube 4-44-1 Inner - 25580
Outer -
15123 or
LM67048
RG06-090
or
RG06-070
Single axle - K2HR526D Dacromet 6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
Inner - 25580
Outer -
02475 or
14125A
RG06-090
or
RG06-070
Single axle - K2HR526D Dacromet6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
7,000-lb Axle

3" Diameter
Standard 4-44-1 Inner - 25580
Outer -
15123 or
14125A
GS-2125-DL
or
GS-2250-DL
Single axle - K2HR712 Raw finish8 on 6-1/2" DM8204311
T4750720
Single axle - T4829900
Double axle - T4830000
EZ Lube 4-44-1 Inner - 25580
Outer -
15123 or
14125A
RG06-070
or
RG06-090
Single axle - K2HR526D Dacromet 8 on 6-1/2" DM8204311
T4750720
Single axle - T4829900
Double axle - T4830000


Typical Components of Rotor Only Hydraulic Disc Brakes
Mount over Idler Hub
Axle SizeEZ Lube OptionBrake FlangeDisc Brake KitFinishIdler Hub Bolt PatternSurge ActuatorBrake Line Kit
3,500-lb Axle

2-3/8" Diameter
Standard 4-35 Single axle - K2R35DSDacromet and
stainless
5 on 4-1/2" T4839100 Single axle - T4829900
Double axle - T4830000
EZ Lube4-35Single axle - K2R35DSDacromet and
stainless
5 on 4-1/2" T4839100 Single axle - T4829900
Double axle - T4830000
5,200-lb and
6,000-lb Axle

3" Diameter
Standard4-44-1 Single axle - K2R526E E-Coat6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
Single axle - K2R526EE-Coat6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
EZ Lube4-44-1Single axle - K2R526EE-Coat6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
Single axle - K2R526EE-Coat6 on 5-1/2" T4750800
T4750600
DM8104311
Single axle - T4829900
Double axle - T4830000
7,000-lb Axle

3" Diameter
Standard 4-44-1 Single axle - K2R712DACDacromet 5 on 4-1/2" DM8204311
T4750720
Single axle - T4829900
Double axle - T4830000
EZ Lube4-44-1Single axle - K2R712DACDacromet5 on 4-1/2" DM8204311
T4750720
Single axle - T4829900
Double axle - T4830000

Updated by: Raymond P.

Last updated: 7/6/18





Popeye

8/17/2020

I have a Bass Tracker boat on a Trailstar trailer. Currently it has no brakes installed but does have the 4 hole brake mounting flange. It has 13” tires on a 5 x 4.5 bolt pattern wheels. I don’t know the axle rating but the data sticker says GVWR 2700lbs, GAWR 2700lbs and MAX LOADCAP 2210lbs. 3000lb, 3500lb rating? I am looking to install surge brakes am not sure what to buy (or even where to start looking). Disk or drum with this light of a trailer? I like the idea of free backing. The trailer has a swing-away tongue and I would like to keep that feature, but if push comes to shove, I will replace the pivot pin with a bolt and make it not fold. I am not installing a brake controller in the car so I am not looking at electric operated brakes. Can you offer a complied list of what I would need?

Etrailer Expert

Jon G.

8/28/2020

The difference between hydraulic drum or disc brakes is that disc brakes tend to have more power. Since you have a smaller trailer I'd just go with drum brakes. If you can let me know what inner and outer bearing is used for your idler hubs I can recommend the correct hub/drum assembly from the linked selection. Aside from that you'll need the following: Hydraulic Brake Kit # AKFBBRK-35-D Brake Line Kit # 18SI-BLKIT Trailer Brake Actuator # 8605001

Popeye

8/28/2020

@JonG The outer bearing is L44649 and the number on the inner bearing is super hard to read but looks like L68149.
Etrailer Expert

Jon G.

9/2/2020

@Popeye Thanks! With that info you can use part # AKHD-545-35-G-K which has the standard grease cap or part # AKHD-545-35-G-EZ-K which has the EZ Lube grease cap.
See All (6) Replies to Popeye ∨

Mario M.

7/30/2020

can you add disc brakes to a goose neck dump trailer ? 2 - 7000# dexter axles

Etrailer Expert

Chris R.

8/10/2020

Of course! I'm assuming you're going to an electric over hydraulic setup. I've linked a great article below that details making this specific conversion.

Bill Y.

6/27/2020

I recently purchased an R-POD 192, by Forest River. It of course has electric drum brakes and they don’t appear to be working. After studying electric drum brakes and how they work, I have big concerns about them. Disc brakes seem much more reliable and safer. My tow vehicle is a Ford F-150 with factory tow package. I’d like to talk to someone about what I would need to convert to hydraulic disc brakes. Thanks.

Etrailer Expert

Chris R.

7/1/2020

I can definitely help pick out the right component to make this conversion, but I'll need a little more info on your R-Pod. Do you know the actual axle capacity. Also, would you be able to pull one of the hubs and check for what inner and outer bearings are used (there will be a number stamped inside the bearings themselves).

Bill Y.

7/6/2020

@ChrisR So right now I’m trying to deal with Forest River. If they don’t satisfy my needs I would consider converting to disc brakes. I’m interested now in determining conceptually what I would need for a conversion and ballpark cost. My trailer is in storage, not at my residence so pulling a hub is a bit inconvenient at this time.
Etrailer Expert

Chris R.

7/10/2020

@BillY I gotcha! We actually have a great article that breaks this down pretty well. I've linked below. In short, you would need new hub/drum and brake assemblies, a brake line kit, and a surge actuator for the trailer.
See All (5) Replies to Bill Y. ∨


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