bing tracking image

Parts Needed to Add Hydraulic Drum Brakes to a Trailer


Trailer drum brake assemblyidler hub

Are you thinking about adding hydraulic drum brakes to your trailer that has no brakes? Or perhaps you want to change from electric drum to hydraulic drum brakes. In either case, you will need some basic information to build a system that will stop your trailer safely and dependably. The following article and tables provide information about your options and will help you find parts that will work together. If you just want to find parts quickly, see our Parts Reference Table, below.





Why Go with Hydraulic Drum Brakes


Hydraulic drum brakes can provide a safe and 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 safely be backed into water. This makes hydraulic brakes perfect for boat trailers.





Parts Reference Table



Parts for Adding
Hydraulic Drum Trailer Brakes
Trailer
Part Brake Mounting Flange Spindle Drum Brake Assembly Hub and Drum Hydraulic Drum Brake Actuator Brake Line Kit
Brake Mounting Flange Spindle diagram Drum Brake Assembly Drum for trailer brakes Hydraulic Drum Brake Actuator Brake Line Kit
ConsiderAxle diameterBearing and seal dimensions
B -
C -
D -
Axle capacity -
Bearing spindle seal

Wheel bolt pattern
Hub diameter

Hub bolt pattern
Select

Hydraulic Surge Brake Actuator
Type of axle

Number of axles




Trailer Brake Mounting Flanges


Brake Mounting Flange

To operate the brakes, your trailer's axle must have a brake mounting flange attached behind the existing hub assembly on each side. Most axles have these, 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 axle with a properly rated one that already has brake flanges welded in place. Ordering a new axle complete with hydraulic disc brakes may actually cost less than buying separate parts. However, to order a complete axle you will need to know the axle capacity, wheel diameter, wheel bolt pattern, spindle type (whether it 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 a qualified welder weld them to the axle. When a brake mounting flange is welded 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.





Trailer Hub-and-Drum Assemblies


Spindle diagram

If your trailer axle has brake flanges and you plan to add the other brake components separately, you must select hub-and-drum assemblies that are compatible with the trailer spindles. The numbers stamped into your trailer's existing bearings and seals will help you determine the proper hub-and-drum assemblies. You will also need to know the wheel bolt pattern of your existing hubs so that the new hubs will match up with your existing wheels. For help with determining wheel bolt pattern, see our article, Determining the Bolt Pattern of Your Wheel. If you cannot find part numbers for the bearings and seals, you can measure the spindles (see spindle diagram) at the inner (C in diagram) and outer (D in diagram) bearing surfaces, as well as the seal contact surface (B in diagram).



Trailer hub-and-drumspindle

This is our most popular setup for a 3,500-lb axle. Notice the tapered spindle. It uses L68149 inner bearings (dimension C) and L44649 outer bearings (dimension D). The 10" hub-and-drum with a 5 on 4-1/2" wheel bolt pattern is also pictured.


If you're switching from electric drum brakes, you should be able to use your existing hub-and-drum - just note its inner diameter.





Hydraulic Trailer Brake Assemblies


Hydraulic brake assemblyHub and drum dimensions

Once you've selected a hub-and-drum, you can choose a compatible hydraulic brake assembly. You need to know that the brake assembly is compatible with the brake mounting flange and with the drum's diameter and depth. The labeled drum shows the measurements that you need to know to select a brake assembly.





Brake Line Kits for Trailers


Brake Line attached to brake assembly Brake Line Kit

Next, you will need a brake line kit to plumb the trailer from the hydraulic surge actuator to the drum brake assemblies. Brake line kits are selected according to the number of axles on the trailer. If your trailer has a torsion axle, you will need to get a brake line kit that includes flexible lines to the brake assemblies. This will allow the line to flex with the movement of the axle.





Hydraulic Drum Brake Actuator


Hydraulic brake actuator

Another item 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, thereby causing it to apply the brakes.


When selecting a brake actuator you must select one that meets or exceeds the GTWR of the trailer. The actuator must also match the size of the hitch ball on the tow vehicle. You can also select manual or electric reverse lockout options if you would like to prevent your actuator from applying your trailer brakes when you back your trailer.


You should also select a brake actuator that is designed for drum brakes. Hydraulic drum brakes operate at a lower pressure (1,000 psi) than disc brakes (1,500 psi), so make sure you select a compatible actuator.





Common Combinations of Trailer Brake Components



Typical Components by Axle Capacity for Adding Hydraulic Drum Brakes
Axle SizeEZ Lube OptionBrake FlangeBearingsSealBrake AssemblyHub/Drum and
Bolt Pattern
Surge ActuatorBrake Line Kit
2,000-lb Axle

1-3/4" Diameter
Standard 4-34 Inner - L44649
Outer - L44649
10-9LH - 7" x 1-3/4"
RH - 7" x 1-3/4"
4 on 4" - 8-276-5
5 on 4-1/2" - T1554500042
T4332900
Single axle - T4829900
EZ Lube 4-34 Inner - L44649
Outer - L44649
10-60LH - 7" x 1-3/4"
RH - 7" x 1-3/4"
5 on 4-1/2" - 8-271-7UC3-EZT4332900
Single axle - T4829900
3,500-lb Axle

2-3/8" Diameter
Standard4-35Inner - L68149
Outer - L44649
58846LH - 10" x 2-1/4"
RH - 10" x 2-1/4"
5 on 4-1/2" - 84546UC3T43329007K
T43397007K
Single axle - T4829900
Double axle - T4830000
EZ Lube4-35Inner - L68149
Outer - L44649
10-19LH - 10" x 2-1/4"
RH - 10" x 2-1/4"
5 on 4-1/2" - 84546UC3-EZT43329007K
T43397007K
Single axle - T4829900
Double axle - T4830000
5,200-lb and
6,000-lb Axle

3" Diameter
Standard4-44-1Inner - 25580
Outer -
15123 or
LM67048
10-1
or
42385
LH - 12" x 2"
RH - 12" x 2"
6 on 5-1/2" - 42656T2477600
T2478100
Single axle - T4829900
Double axle - T4830000
Inner - 25580
Outer -
02475 or
14125A
10-1
or
42385
LH - 12" x 2"
RH - 12" x 2"
8 on 6-1/2" - 42866UC3T2477600
T2478100
Single axle - T4829900
Double axle - T4830000
EZ Lube4-44-1Inner - 25580
Outer -
15123 or
LM67048
10-10
or
10-36
LH - 12" x 2"
RH - 12" x 2"
6 on 5-1/2" - 8-201-5UC3-EZT2477600
T2478100
Single axle - T4829900
Double axle - T4830000
Inner - 25580
Outer -
02475 or
14125A
10-10
or
10-36
LH - 12" x 2"
RH - 12" x 2"
8 on 6-1/2" - 42866UC3-EZT2477600
T2478100
Single axle - T4829900
Double axle - T4830000

Updated by: Raymond P.

Last updated: 7/6/18





Questions and Comments about this Article

Dave A.

I have 7k dexter axles my trailer mechanic put 6k dexter axle seals because he said they fit better have you heard of this before? He put axle grease in them

Etrailer Expert
Reply from Jon G.

With grease seals it's more about the size of the seal than anything. There are common seal sizes for axle weight ratings but I've never heard of a grease seal having a specific weight rating. As long as your mechanic installed seals with the correct inner and outer dimensions I wouldn't be as concerned with what size axle they normally fit.



Departments

Towing

Sports and Recreation

Trailer Parts

Vehicle

What our customers are saying:

"The phone operator was very helpful and made my purchase easy. I will keep this website handy."

Harold
Gillsville, GA

Popular Vehicles