Sunday, July 1, 2012

Differential Swap

Hey everyone
Unfortunately, since I don't update this as often as I wanted to, a bunch of information and pictures have gathered up but still need to be organized. To start sifting through all the data, I decided to tackle an aspect of the car I want to discuss and illustrate what I did and how I did it.

In this post, I will be concentrating on upgrading my drive train.

The stock S2000 differential is infamous for being weak and fragile. Even with the stock ~200Hp engine, the car has the capability of destroying its differential if you're having a bad day. Upgrading to a turbo system nearly guarantees eminent failure of the differential.

Stock S2000 Differential

Differentials are responsible for equally dividing the power delivered by the motor, to the two rear wheels (for a rear wheel drive car).
Generally, a transmission, a clutch, a torque converter, or all three, are sufficient in protecting a car's differential setup. As it just so happens, once the electric car conversion is complete, I will have none of those.

In addition to lacking substantial buffers prior to the differential, the two electric motor's are capable of producing 700+ horsepower, and 1500ft/lb's of torque under certain conditions. Specifications like these make stock s2000 differentials shudder in their sleep.

Consequently, since I was adding gratuitous amounts of power to the car, the differential needed to go.
A little research on the topic wasn't very hard, and I found out I had 3 options

1. Send my stock differential to be cryogenically treated by Puddy mod himself
2. Purchase an R32 Skyline differential
3. Purchase an 8.8" Ford Differential

I chose the third option.

S2000 Differential Vs 8.8" differential with explorer cap

Option 1 was a little too expensive for my tastes. Puddymod does amazing work, however I couldn't bring myself to pay the $2000+ for the work. Not to mention, even after I had the differential beefed up, I would have to find a way to adapt it to support Dana 1350 drive line components. However, the obvious advantage would be that I would be able to remove the differential, and put it back in with little to no trouble. This would have saved a lot of time, but its ok.

Option 2 was also rather expensive. A used R32 differential goes for ~$400 and are much more difficult to find than Ford 8.8". Another disadvantage would be that the gearing (rack & pinion gears) aren't easy to find. Lastly, the differential would have to be modified to fit the s2000, however (evidently) the axle flanges are compatible with the stock s2000 axles.

Option 3 was the winner. The Ford 8.8" independent differential was the perfect match for the s2000. Numerous reasons contributed to the choice. Gearing is abundant for the differential, the differential itself is practically indestructible, 1350 pinion flanges are easy to come by, and it is cheap! It just so happened that I was able to pick one up off craigslist for $75 about 10 minutes away. I really lucked out on that one.
However, there are some drawbacks to the differential. One major set back is that the axles are completely different, and had to be custom made for my car. Additionally, it requires custom mounting, and once installation began I realized that a major problem existed in the inability to install the axles without tearing down the entire rear end.

The (nearly) final product
In order for the 8.8" differential to fit, I needed to figure out how to adapt it to honda's existing differential mounting points. In order to simplify the process, I chose to reuse as much of the mounting hardware as possible. To do this, I ordered a Ford explorer differential cover, which greatly simplified the process of bolting the stock support arm to the new differential. With the differential back plate installed, I began fabricating.

Differential sans-rear cover
Using Autocad inventor, and Cambam, I created a simple drawing that I exported to G-code, and ran on my router. The router cut into a 1/4" aluminum plate which I had mounted on its table. I decided to get artsy with my work...

Here is the completed plate, once cut

todo completo

I ended up drilling the remaining holes on my drill press, since alignment of the differential was rather difficult. Ideally the differential would have been rectangular, with the pinion flange in the center of one end, and the mounts symmetrically placed on another end. However, the ford 8.8" is the least symmetrical piece of hardware in the entire car. Everything is lobside, uneven, and arbitrarily placed.

Eventually I got the plate drilled, and the stock mounting arm bolted onto it.
I mounted it in the car, and proceeded to make the front mounts out of some 1/8" steel. This was my first time welding anything, so I practiced a little before hand and dove right in.

Front mounts (notice minimal clearance)

Measurements were taken for the axles, and the data collected was sent to the Drive Shaft Shop, who promptly delivered some high quality custom axles to my door, big shout out to them!

Custom DSS axles

When it came time to sell the stock s2000 differential, I was contacted by a man named Ben Herne by email who was interested in my differential. Rather than giving me the full asking price, he offered to trade me an 8.8" limited slip differential, professional installation, and some cash for the differential. After looking up the name, it didn't take long to stumble upon his company, Puddymod racing. His work is revered as some of the best work in the industry. He builds the strongest stock s2000 differentials that have become parts of hundreds of cars.

I took a trip down to Bradenton Florida to have the LSD installed, and it turned out great! Can't wait to see how it works with the car.

After removing the differential, I decided that it was mounted too low in the chassis and was susceptible to touching the ground when going up large curbs etc. So, I chose to move it up about 2". I modified my 1/8" mounts, but ended up having to throw them out because I overlooked something.

A rather provocative view of the pinion flange 

The pinion flange for a 1350 setup is huge, far larger than the stock s2000 flange. The diameter of the flange almost overlaps the s2000's differential mounts. With the previously designed front differential mounts, the pinion flange had about 2 mm of clearance between the mounts. To increase the distance between the flange and mounts, I had to re-do the design. Rather than going out and up, I had to go straight up, and out.

A day or two later, I had completed the new mounts, and painted them.

New Vs old

I reinserted the differential, and made sure it did not rub or anything. Everything checked out well!

New mount

The last step was to install the stock axles. Another obstacle appeared here; the wheel hubs needed to be removed in order to install the axles. 
Some hours pass, the axles are installed, and the wheels are back on.
I took some additional time to take out the torque wrench and ensure all my bolts were correctly torqued. I don't want my axle flying off on the highway!

Buttoned up :--)

Since the rear end is completed, I went ahead and reconnected the brake lines, ESC sensors, and hand brake lines that I removed when I uninstalled the rear sub frame to remove the gas tank.
Dropped the car, pushed it, and the pinion flange rotates! Success!