Install a Torsen in a '90-93

Peter Allendorfer

Recently I changed out my open diff from my '91 Miata to a TorSen diff from a 94r that I found in a wrecking yard. When purchasing your 94+ diff, you will need the half-shafts and drive shaft out of the newer car. The 90-93 Diff is a 6" ring-gear and the 94+ diff is a 7" ring-gear. This makes the Halfshafts about 1/2" shorter (For the wider larger diff carrier.) and the new driveshaft is about 1" shorter (For the larger around ring-gear and the larger pinion to go with it). Here are the steps (To the best of my recollection).

I found a TorSen diff from a '94. This was a Type I Torsen. Meaning that it has the same type of Stub Shafts as the 90-93. This also meant that I did not have to pull one side of the suspension to get the new half-shafts in.

When removing the old differential, unbolt the driveshaft, but do not remove it from the back of the transmission. Unbolt the halfshafts from the diff and then unbolt the axle nuts. You will most likely need a 3/4" drive socket and Breaker bar. I broke a 1/2" drive breaker bar. Luckily it was an old craftsman tool, and dad still had the Lifetime Warranty statement on the reciept. Unbolt the diff from the PPF, but do not unbolt the PPF from the back of the trans. This will help you lower down the old diff without having to bench-press it, and raise the new diff un, and help you line it up with the Subframe. I then unbolted it from the subframe. And lowered it down.

With the new diff out of the car, fluch it out and refill it with new GL5. I used Redline. NOTE: There is no need for the LSD Additive that so many people tell you to use with an LSD. The TorSen LSD is functionally different from the Clutch type LSD. The KAAZ and Mazdaspeed units do require you to use LSD Additive, but not the TorSen or the VLSD.

Bolt the new diff to the PPF and slowly raise it back up into place, and bolt it to the subframe, being sure to have the rubber mounts lined up correclty. Bolt the new halfshafts into the hubs with the big Axle Nuts and torque them down to spec. Line up the flanges on the stub-shafts and bolt those together. Now, remove the old driveshaft and quickly replace it wiih the new driveshaft. The new one is 1" shorter than the old one. Waiting 'till now reduces the amount of gear-oil that comes out of the trans. Bolt up the driveshaft to the front of the diff. You are now done.

You will loose some of your "zip" as you have just installed a "taller" gear ratio. You can keep the same ratio, however, if you find a 99+ 5-speed TorSen diff. the 90-93 diff is 4.303:1. The 94-97 diff is a 4.1:1. And the 99+ 5-speed is a 4.303:1 diff again. You can also replace the speedo-gear from the tailpiece in the trans at this point, to get your speedo/odometer back in line, but I found that the stock speedo on my car was very optomistic. Leaving the old speedo gear in place actually made my speedo more accurate.


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17 September, 2002