A Tale of Two Differentials
By Daniel O’Donnell
So how did this story all begin? I guess it was Ebay, that magical world of random crap. While searching for random Evo stuff I found a place in the UK that was selling an Evo X differential. In the posting it mentioned that the differential could be easily installed on any Evo VII-IX with AYC. I hadn’t heard of this possibility before and I instantly wanted to upgrade to this part. Mitsubishi had dramatically improved the design between the VII and X and I felt our rear differential was a weak point in our car’s performance. The only problem was that a used Evo X differential is north of $1,000 and that isn’t in our budget at all.
So with that in the back of my mind, life went on as usual until the fateful day of September 19th. This was the day of the Corvette Autocross at Grissom Air Force Base. As Professional Awesome has close ties to a Purdue Automotive club, which would be attending the event, it was decided that we should take the car. Well I should clarify this a bit, going to this autocross was up to Grant and me. Mike said specifically we should not bring the Evo as something would break, but the two-to-one majority ruled so we drove the Evo about an hour from our home base to Peru, IN. The one stipulation about running the car at the event was not to drive the car too aggressively off the line or in other words, launch it.
My definition of not launching is to slip the clutch from the line, rather than dumping the clutch quickly. Mike and Grant’s definition is to daintily move the car off the line and then to drive at or below the posted speed limits. Everything was going quite well until the second-to-last run of the day when after a MILDLY aggressive accelerative moment, the rear ring and pinion decided to redesign themselves with slightly fewer teeth. While this did make the car a little bit lighter in weight, it just didn’t seem to work well… or at all.
After my fine uncles, Joe and Pat, helped trailer the car back to the PA garage Grant tore down the differential to diagnose the situation. After the negative prognosis, I started scouring the Internet to find a replacement differential. As some of you may know, as our car is an Evo VII and was never officially imported to this fine country, it’s not exactly easy to find a replacement differential. So it was quite fortunate that I read that Ebay listing about an Evo X differential fitting without issue. The one problem with the Evo X is that even though it was officially imported here, there aren’t many on the roads yet. Luckily they are mostly driven hooligans, so a few crashed cars existed and our new differential was sourced in Nashville. Rather than wait a few days for shipping, the PA crew headed straight down and a lovely Evo X differential was in our possession. We proceeded to make a beeline straight back to the garage and rejoice in our luck (and substantially lighter wallets).
Soon Grant had the differential in place and I returned with the celebratory pizza and sequins only to discover that the driver’s side axle did not fit properly. That night there was no joy and the pizza was thrown away. Next, a plan was in place to take an Evo X axle and fashion a combination of both the X and VII axle and everything would be peachy… in theory.
As we should have learned earlier, nothing goes as planned. The two axles couldn’t easily be combined, no custom machining could be easily done or afforded and things actually looked pretty bleak. I may have lost a few nights’ sleep thinking about what Mike would do to me if a solution wasn’t found. I even went as far as going to that original Ebay posting, finding the name of the shop in the UK, then calling them only to find out they never actually installed an Evo X differential into an older Evo. Apparently they ran into the same problem we did and rather than find the solution, they just installed an older differential because they are lucky enough to be able to get them from Mitsubishi easily. In my search for other options, a random phone call to a bearing company yielded a potential idea: dowel pins.
One thought Grant had earlier was that we might be able to get the two axles to play nicely using oversized needle bearings in our inner joint of our Evo VII axle, but needle bearings are incredibly hard to find individually. Hardened dowel pins, on the other hand, are very common, relatively cheap and sure enough, a common size was extremely close to what we needed. One call to Fastenal, a trip to Indianapolis and a few hours later, Grant had the two axles combined. Shortly there after, everything was in place and finally, after a little help from one Mr. Donald Puetz (he knows why:D), we had the Evo on the road and everything is working quite well.
Time will tell if everything holds up on the track, but we are cautiously optimistic. And unless it can be proven otherwise, I am proud to say that when it comes to swapping an Evo X differential into an Evo VII, Professional Awesome is the first in the world.