The other day I went to run my Losi Lst 3XL-E it noticed it started making a loud grinding noise when I would hit the throttle. After checking it over, I found it to be the Rear Differential. So, I wanted to write this article on the Rear Differential Repair to help anyone that may need a little guidance with the repair.
Before Making The Repair
Repairing the rear differential on the LST 3XL-E is a fairly quick and easy process. I will walk you through the steps to preform this differential repair to help get you back up and running. The first thing to do is, make sure you have your tools ready.
The tools you will need to repair the rear diff: 1.5mm, 2.5mm Allen, a small flat blade screwdriver, silicone diff fluid, some spray cleaner and paper towels. I like to use blue shop towels instead of regular paper towels, they are thicker and stronger (but That’s me). Paper towels will work fine.
Of course, you want to have your parts, so you can get back to bashing quickly. You can buy everything individually, a rebuild kit, or a complete assembled differential.
Prep Your Work Area
Lay down an old bath towel or shop towel on the bench or table that you will be working on. Set the truck on top of the towel and put the tools you will be using on the work area next to your truck. The towel helps keep your work area clean and makes faster clean up after the repair.
Removing The Rear Differential
The first thing we need to do is to remove the rear bumper. To do this remove the two very rear 1.5mm screws from the underside of the chassis and the one 2.5mm screw from the bumper bracket in the center. Pull the bumper rearward and off the truck. Set it aside.
Now, remove the (4) 1.5mm screws from the rear cover plate and pull the plate out. Once the plate is off, there is a holding block on each side of the diff, they just pull out. If they are stuck, use the small flat blade driver to slide them out.
At this point, you can now grab the differential and pull backwards to slide it out of the truck.
Repairing The Rear Differential
Pay close attention when pulling the differential apart, Any shims that are inside the differential need to be put back in. Make sure they get put back exactly where they were.
There are three (3) 2.5mm screws that hold the diff case together, remove the 3 screws and carefully pull the cases apart.
The differential will now just lift up out of the case. Take the differential out and look over the ring gear real good, use cleaner to clean off the old grease from the ring and pinion gears. Check both the ring and pinion real good for any damaged, worn, missing, or broken teeth.
Remove the ring gear from the differential assembly. Take out the (4) 1.5mm screws holding the ring gear on and pull the gear off. There is a beveled gear on the inside of the ring gear. Clean the beveled gear off and check it over real good.
Use cleaner to clean out the rest of the differential and gears. Make sure to check everything over really good for any worn, missing, broken, or cracked teeth.
Replace any parts that are worn or damaged with new parts.
If you need to replace the axle hubs or the beveled gears, Use the small flat screwdriver and lightly pry up on the gear to slide it off. To remove the axle hub, slide the holding pin out and slide the hub out of the case.
Reassembling The Differential
Slide the axle hub into the diff case, make sure the seal is in place and slide the pin through the hub shaft. Take one of the bigger beveled gears and slide it on the shaft, making sure the grooves align so the gear sits down fully.
Take the side gears and slide them onto the holding shaft, along with the shims and the retainers. The grooves in the center of the shafts need to align and fit together. The round ends of the retainers need to go down into the diff, flat end up.
Put the other axle hub through the ring gear, making sure the seal is in place and install the pin through the shaft. Install the last beveled gear onto the ring gear. If the pinion was removed, make sure to set it back in along with the bearing.
Fill the differential with the silicone diff fluid. Most folks use 200k fluid. I use 500k in my differential and it works great. It gives it more torque (I know it does not need more torque) I just like the way it runs with this in it. I fill it right up, and put the ring gear on and fasten it down. Clean up any fluid that came out, then smear some grease on the ring and pinion just to ensure they have some good lube.
Put the differential back int the case, making sure the bearings and diff are fully seated. Install the case halves together and tighten it up.
Install The Rear Differential
Pay attention when putting the differential back into the truck. You need to line up the center driveshaft and both of the axle shafts so they will slide into the hubs. Slide the differential all the way in.
Install the holding blocks, and put the cover in place and tighten it down.
Set the bumper back in place, make sure the bumper fits between the chassis and bulk head. Install the 3 holding screws.
Clean up your tools and paper towels and your truck is ready for a test run.
When taking apart the differentials, it is not necessary to replace everything. Unless you really want to do a rebuild, you can replace just what is bad or broken.
After you have done it once, you will be able to pull the diff out and repair it and install it in no time. I just did mine the other day and it really only took me 35 minutes to complete.
For more information on the LST check out my Losi LST 3XL-E page.
Check out the video of the first bash after repairing the rear differential.