Parts Needed to Convert 2021-ish Trail Runner 21JM to Electric Over Hydraulic Disc Brakes

Updated 07/21/2026 | Published 07/17/2026

Question:

Have a 2021-ish Trail Runner 21JM, yer basic Thor, 7k tandem photo of axle tag attached Ive previously replaced the 3500 springs with 4500 and the 14 tires and wheels with 15s for clearance. Wheels are 5inch on 4-½ Prepping for a trip to the west coast were near Joplin inspected the brakes and shoes and drums are surprisingly good but the magnet and drum surface is very ridged and worn. My brakes are weak, wont lock at 10, partly because of the added tire diameter and probably partly because of the magnet/drum faces not mating well. So, either replace the drum /magnet and the shoes because Im there, Or scrap the drums and go with a hydraulic over electric kit. Im thinking this disc kit part HYD22FR. Im not sure on the spindle size but will attach some photos of tag numbers. Need to know if bearings etc will fit and what additional items Ill need. Basic budget level for a basic trailer is what Im looking for

asked by: Mike B

Axle Tag
(click to enlarge)

Expert Reply:

Hey Mike, this is a really great question but it looks like you actually already ordered the Hydrastar Disc Brake Kit w/ Actuator for Tandem Axle Trailers # HYD22FR already just the other day. The great news is this is the correct kit you would need so you are already set with getting the right parts needed to convert your trailer to disc brakes and you will be really happy with this upgrade. The braking performance and power will be so much better than what you have now and it will be a lot more reliable as well.

expert reply by: Jameson C