The Racing Factory Blog

At the EFRA Off-Road Euros we were told by TRF drivers Hupo Hönigl and Marc Rheinard about one of the tricks they have used on their TRF415’s lately.

This involves a small modification to the rear diff that will significantly improve the performance and life of the diff on the TRF415. As the power produced by the latest generation of cells and brushless motors has risen dramatically the diffs are now subjected to extreme forces. This has seen the time between rebuilds get shorter so an improvement is more than welcome.

Here’s a quote from John Doucakis coverage of the TC Euros on his JD Racing blog:

Also Marc’s car, maybe the rest of the cars as well, had a rear diff made of parts from the 4WD offroad car 501. The diff is now very reliable and has been the same on his car since the Reedy race which he won.

Marc also told us this at the Off-Road Euros. He had run the same diff at the Reedy Race plus lots of practice at the Euros track without touching the diff at all. Sounds pretty impressive!

Here’s a short explanation how to make the 16 ball diff for the TRF415.

In addition to the normal diff parts you need the following.

- One 51212 TA05 Ball Diff Pulley
- One packet of 51287 TRF501X Diff Plates
- Two packets of 53124 3mm Tungsten-Carbide Diff Balls

You need to use the TA05 ball diff pulley as the modified diff uses the outer ring of holes for the diff balls. The outer ring has 8 holes. To make the diff you drill 8 more holes in between these for a total of 16 diff balls.  The TRF501 diff plates are used as these have a larger outer diameter and therefore reach the outer ring of holes.

The next step is to remove some material from the diff pulley. You need to remove the raised plastic rings around where the diff balls normally go. You should remove this on all holes, both inner and outer ring and both sides.

This might sound difficult but in reality it is quite easy. Just take your time. The finish don’t need to be perfect as the diff rings will run against the diff balls anyway, and won’t touch the pulley. 

You can remove the plastic in a few different ways. I found that a small Dremel grinding tool worked quite well. If you want you can finally sand the surface with some medium-grit sandpaper to smoothen the surface.

Red arrows points towards the raised plastic rings you should remove.

Next up you should mark where to drill the 8 holes in between the current ones.

The easiest way to mark them is to draw a circle the same diameter as the outer ring of holes (center). Then on this circle mark where to drill the holes in between the current holes. Just use your eyes and try to make the mark in the center between the current holes.

After marking with a pen i used a sharp reamer to mark where to drill. This will make the drilling easier.

Again you don’t need to be worried if the holes are not exactly in the center.

Then drill out the holes with a 3mm drill. First you might want to use a smaller drill and follow with the 3mm drill.

After drilling you can clean up the edges by hand with a drill or reamer.

Time to start assembling the diff.

Make sure to clean all the diffparts, including the pulley, plates and balls etc.

Use a liberal amount off diff grease (Muchmore Diff Grease used here).

Put the diff grease on the outer edge of the diff rings as the diff balls will run on the outer edge.

Next up place the 16 diff balls in the outer ring of the diff pulley with diff grease. Then put the other diff plate on the other diff joint and put a similar amount off diff grease and the outer edge of that diff plate.

Next up the thrust assembly, use quite a lot of Muchmore Thrust Grease on the thrust bearing. This time we used the Squat S192 Thrust Bearing 2×6mm which seems to be a very high precision and high quality thrust bearing.

Then assemble the diff with the diff screw as usual. Tighten the diff screw a little at a time, holding the diff vertically. Between tightening the diff always work the diff a little by hand, then tighten more and so on. Continue til you have tightened the diff completely, then back off the screw by 1/8 to 1/4 of a turn.

The diff should now be properly adjusted and very smooth. After running a few minutes or one pack maximum, chech the diff tightness and adjust if needed so that it don’t slip.

With double the amount of diff balls and larger diff plates one could think that the diff would be considerably heavier.

I decided to check this with the very precise Muchmore True Weight.

Here’s the result.

Standard TRF415MSX MRE diff

New 16 ball diff

As you can see the difference is only 1.3 grams. A very small price to pay for a much more reliable  and better working diff!

Try it out, the results will probably amaze you!