Installing Electric Brakes on a Vehicle Tow Dolly

Updated 01/12/2021 | Published 01/07/2021

Products Featured in This Question

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etrailer Electric Trailer Brakes - Self-Adjusting - 10" - Left/Right Hand Assemblies - 3.5K

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Easy Grease Trailer Hub and Drum Assembly for 3.5K Axles - 10" - 5 on 4-1/2 - Pre-Greased

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Mounting Hardware for 10" Brake Assemblies

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Deka Heat Shrink Butt Connector - 16-14 Gauge - Nylon Insulation - Blue - Qty 10

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Performance Tool Crimping Pliers - 10 to 22 AWG Wire - 9-1/2" Long

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Question:

I have a WTD35D tow dolly Id like to put electric brakes on. What information do I need to come up with? The spindles do have the 4 bolt flange for backing plates. Ill need backing plates and drums. The tow dolly is rated for 3500lbs

asked by: Jim

Expert Reply:

You have a 3500 pound axle, with a 4-bolt axle flange, spaced 4” apart each. You also have tires and wheels with a 5 on 4.5 bolt pattern. To put brakes on your West Texas Dolly # WTD-35D you will need a left and right trailer brake kit like the etrailer # AKEBRK-35 rated for 3,500 pounds, and 10” x 2-1/4” brake pads. Mounting bolts are included but nuts and lock washers # BRKH10B are not. If it were me I would purchase the etrailer # AKEBRK-35-SA self adjusting brakes so that I would not periodically have to get behind the brake and manually adjust them.

You will additionally need a brake drum/hub. Since we know 99% of the time a 3500 pound axle uses a standard hub, you can go with the etrailer # AKHD-545-35-K hub and drum assembly which is pre-greased. If you want to be 100% certain you can look at your bearings which should be numbered #L68149 for the inner bearing with a 1.378” ID, and #L44649 for the outer bearing with a 1.063” ID. (Note: This is for a standard drum and hub. If you have an “EZ Lube” style spindle then choose the etrailer # AKHD-545-35-EZ-K instead.)

You will need to run wires to your brakes. You can use the Deka # 10-1-1 blue 10 gauge wire. You should probably get 20 foot. (I have attached a document on trailer wiring including brakes.) Each brake has two wires, one blue for power and one while for ground. Crimp a ring connector on the ground like # 44-5310A connector. I would order 4 plus one extra. Use a self-tapping screw like the Fastenal # 101131802 to attach to the trailer frame. For the brake power wires I would use the Deka # DW05744-10 heat shrinking butt connectors. (Note: the brake wires do not have polarity, you can use either wire for power or ground.)

Your dolly likely comes with a standard flat 4 pole trailer lighting wiring harness, which does not accommodate electric brakes. If so you can use the Bargman # WG54006-043 coiled 7-pin cable. I would snip off the 4-pole and connect your old and new brake wiring. I would also recommend the # HS381-9000 junction box kit. You 7-pin cable will fit in one side and all trailer wires from the other side. This makes for neat and tidy work and keeps the weather off of your connections.

If you don't already have a good crimping tool you may want to get the Performance Tools # PTW30764 crimping pliers to make a strong crimp every time.

Finally, if you need a connector on the tow vehicle side and a brake controller for your dash you can just submit a new question (or email me back) with your year, make, and model vehicle for a recommendation on that.