A Tale Of Two Differentials

Two Miatas

With the holidays upon us, gather round and pull up a chair by the warm fire and let me tell you a story of how I spent Christmas and the day after a few years ago.

In 2011 I acquired my third Miata. Like the two before it, it was an early NA, with the 1.6 liter motor, in Classic Red. It’s purely coincidence that all of my Miatas have been red 1.6 NAs – it just happened that way. This one had been a dedicated autocross car, but the owner upgraded to an S2000, so I bought this to be my daily driver.

Some assembly required

Some reassembly was required. The go fast goodies were sold off separately, but as this was to be my daily driver it was no big deal. We just had to reinstall the stock parts. Plus the car came with a whole bunch of extra parts, which would be good to help maintain it. By 2011 the early NAs were getting a bit long in the tooth.

That was the main problem I hadn’t foreseen. I still thought of Miatas as bulletproof reliable, like my first 1990 model I got in 2000, and raced and drove hard for the next few years. But that was a 10 year old car. This was 18 years old, and in retrospect perhaps not the best choice of a daily driver. Of course, one could argue that any Miata is not the best choice of a daily driver, but come on – I daily drive a BRZ, for crying out loud.

On Christmas day, 2011, my girlfriend at the time and I took the Miata to her family’s house for dinner. Just a couple of miles out from our destination, I started to hear a clanking in the rear end (the car’s, not my girlfriend’s), once per each revolution of the wheels. A quick look underneath the car revealed nothing, so I slowly, carefully finished our journey, and when it came time to head home it was once again on the back of a flatbed.

Miata on a flatbed

The problem appeared to be in the differential. I had to figure out what to do about it, fast. After all, this was my only car, and though I had the 26th off, I had to go back to work on the 27th. As it stood, I had no way to get there.

Then I remembered that I had a spare differential in my storage unit. Doesn’t everyone? Actually this was left over from my previous Miata. I had removed the open diff it came with and installed a viscous limited slip in its place. I tried to give away the old open diff, never mind sell it, and I still couldn’t get rid of it. But that meant that I had a replacement diff ready to install in this Miata when its original diff died. With no garage, no electricity in the parking lot, and during one of the shortest days of the year, I had to thrash to swap out the diff the following day.

Fortunately, I had some luck on my side as well. There was no snow on the pavement of my parking lot. The weather for December 26 looked good. Temperatures were supposed to be in the 40s with no windchill, and it was going to be sunny, which would help me take maximum advantage of what little daylight I had. Perhaps most importantly, I knew that the differential had been out of this car during the past year. It, too, had been upgraded to a VLSD unit, but the original had been put back in due to issues with the VLSD. This meant that I would not be fighting 18 years of rust to remove it.

I jacked up and supported the car properly (not like this), then got to work pulling the diff. It helped that I already knew how to do it after upgrading my last Miata. Wheels came off. Axle nuts got removed. Rear suspension got partially disconnected to allow enough movement to remove the axles from the hubs. Remove the driveshaft. Unbolt the power plant frame, a sort of girder that connects the differential to the transmission. Past experience had taught me that it’s easier to remove the PPF and diff as a unit, plus my spare diff was still attached to its own PPF – permanently, thanks to rust. Get a jack under the diff. Remove two nuts attaching the diff to the rear subframe. Lower the jack and get the old diff out of there. There goes my morning, but I was pretty much on schedule.

Photo credit: Treasure Coast Miata

Around this time my friend Brian (owner of the Mazdaspeed MX-5 I reviewed) showed up to help. Not only would he give me a hand during reassembly, he also brought beer, which also helped. (Typically I would’ve provided the beer in exchange for his help, but I had no wheels to get to the store.) We set about swapping the carrier from the old diff to the new one – er, the older one, um, no, wait… You know what I mean. In case you don’t, what would be a simple cover on the rear of many differentials was actually a structural part on the Miata’s, containing the supporting arms that bolt to the rear subframe. These arms often break in an accident (by design, to prevent the drivetrain from taking more serious damage), and since my original VLSD swap on my previous Miata came with a broken carrier, I’ve been one short ever since. So I had to swap the one that was already on the car over to the replacement diff. It’s not much more difficult than replacing a standard diff cover.

At this point, contrary to what I experienced reading many Haynes manuals, installation really was the opposite of removal. With the jack holding the diff up, the two of us managed to finagle it back into position and bolt it in. It was fairly simple to remove it myself thanks to gravity, but Brian’s help was invaluable to the reassembly. We could also divide our efforts, each of us installing an axle simultaneously instead of me doing one, then the other. The diff got fresh fluid, and the new seal held. We raced the sun to finish the job and get the car back on the ground before the sun hit the horizon. It was a tie, but that was good enough – I drove a successful test lap around the parking lot just as the sun slipped out of sight. The car got me to work the next day, and that differential install continues to serve its current owner today.


Working on your own car, when doing regular maintenance, on your own schedule, in a garage or driveway, with adequate lighting and no time constraints, can be a very enjoyable activity. An emergency repair, in a parking lot, crammed into a few short hours of daylight on one of the shortest days of the year, is not. But I’ll never forget how Brian and I spent the day after Christmas thrashing to get this done, and completing the job successfully. While the process may not have been fun, we definitely felt a sense of accomplishment afterward – not to mention great relief that I would, in fact, be able to get to work the next day.

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