Ball Differential

06/08/2015 at 12:41 pm

After talking to a local drifter, Jimmy, I decided to rebuild my ball differential in the GRK RWD.


The GRK uses a Yokomo ball differential for the main components. It looks like the GRK Global comes with pre assembled ball differentials so I may switch over to those later. SD-501DS, grease and optional 850 bearings x2 is all you should need. For the GRK you need their ring gear R31W050 and some 1/8th diff balls. (Street Jam, R31W079, etc.)

GRK Ball Diff

Although the Yokomo ball differential comes assembled, there’s a few thing you’ll want to do to get it to work smoothly. I began by disassembling and cleaning all of the components.

Sand the differential plate side that faces the balls with 1000 grit sand paper. The back side was coated with something to prevent slip so I didn’t sand the back. You’re trying to make the differential plate as flat as possible. I sanded by hand in a circular motion but using a sanding block to ensure flat contact would help as well.

Thanks Jimmy for the sample!

Thanks Jimmy for the sample!

I then replaced the spacers that come with the differential with 850 bearings, and began re assembly. Apply a generous amount of grease on the differential plates and balls during assembly. The ring gear and balls were replaced for something GRK specific in my case as well.

Thrust Spring

Once you’re done greasing, stick the two out drives together and move on to the thrust bearing. Since I used a new differential, I first grabbed the thrust spring and compressed it a few times lightly to break it in.

Thrust Bearing

Then slip the spring on to the bolt, put the first thrust washer in and apply a ring of black grease. Stick all of the thrust balls onto the black grease, apply some more grease on top of the balls and finally place the last thrust washer on. I then ran my finger around the outside to pack in any excess grease that squeezed out.

Assembled Ball Differential

After applying a small amount of thread lock the bolt can now be used to tighten the differential. I slowly tighten the differential, checking to make sure it spins smoothly. Once I feel some tension while tightening the bolt, I lock the two cups and check to see if there is any slip of the differential ring. I currently have my differential set at a point where it barely starts to slip when a moderate amount of force is applied.

Compared to the Yokomo ball differential I had previously that wasn’t as smooth, I am able to hold a larger angle before exceeding the point where my car spins. I’m able to get onto the throttle more while cornering, and the car picks up speed quicker going into the straight as well. Since I don’t use tires to compensate for lack of grip, and currently use tires that are similar in grip level to what the CS drivers are using, picking up speed is very important for me. Definitely something you’ll want to try out if you’ve only used a solid axle yet.