The Rear End Last Update: May 4, 2009 11:01 PM

Racing Concepts made a Version 2 of the kit that I installed after I already had the car running on Version 1. I will include pictures of both as I documented the install of Version 1 much better than Version 2.

The Differential:

For the rear, Racing Concept's kit uses the Ford 8.8 differential. The later model ones like my 2002 Ford Explorer one are aluminum and thus are lighter than the cast iron ones. I had Racing Concepts get my differential for me. Mine has the 3.55 final gear ratio but 3.73 and 3.27 are quite common too. The kit includes the diff mounts as well as custom axles and driveshaft. Below are the details on the install, it was the easiest part of the kit to install and took about 3 hours to install.

The visible bar inside the diff means that it is a limited-slip.

The kit uses the factory mounting points in addition to an extra brace that installs on the rear of the rear subframe. Below is a picture that includes the front "T-bar" diff mount, and the rear diff mount (far right).

Racing Concepts improved the kit with Version 2 of it and part of the improvement was to strengthen the rear diff brace as they found that a heavily modded ls1launched at 5k rpm on slicks would cause this to twist. The new one is said to be good to something like 700whp. The wall is extremely thick as you can see.

Below is the custom driveshaft. It uses the factory ford bolts to attach to the diff. It takes all of 10 minutes to install.

The "T-bar" mounts to studs on the rear subframe that the stock Miata diff "wings" attach to as you can see in the pictures below. The stock Miata hardware and bushings are reused. Nothing to it, takes 5 minutes.

Next you have to enlarge the two outer holes in the rear subframe. Below is the un-altered rear subframe. You can see the two factory holes on each side just about the lower control arms.

Below you can see that I enlarged the two outer holes and touched them up with paint to prevent rusting. I then bolted the front of the diff up to the T-Bar front mount in prep to mount the rear brace. Below is the approximent final position of the diff.

The new rear diff mount uses a bolt that goes completely through the rear subframe with included hardware including a spacer to prevent the rear subframe from collapsing from the bolt/nut compression. The next pictures show it fully installed.

miata ls1 ford 8.8 diff install

Below you can see how the T-bar has vertical tube that is about one-half inch from contacting the rear subframe. This is to prevent the diff from torquing up during aggressive launches. The tube will bottom out on the rear subframe and prevent any more upward movement of the diff.


The axles come in the kit and are custom. They have the Ford inner CV and the Miata outer CV connected with a custom shaft. They install the same way the Miata 1-piece axles do.

Just unbolt the upper knuckle and lower strut bolt and loosen the lower A-arm bolts to allow the rear suspension to swing down and allow a straight shot for the axle to slide in. Snap the inner splines in with a firm push then proceed to line up the outer spline with the hub. Be sure to clean and grease the splines before installing the axles. The cleaner the splines the easier it is on you.

I was able to leave the brake line attached on the passenger side but the driver side one is too short and much be disconnected in order to tilt the knuckle down. Below is the passenger side.


Here is the rear end all installed. Do note that my car is currently sitting lower than stock and that I will probably raise it. In the below pictures, the wheel center to fender distance is about 13.25 inches.