JXB Retrofitted WaveTrac Rear Limited Slip Differential for Audi B8 S4/S5 and C7 S6/S7

The JXB-retrofitted WaveTrac rear LSD is the only true rear limited slip differential available for the B8 S4/S5 and C7 S6/S7. It retrofits into the regular differential housing, replacing the stock open diff. It has many advantages over the factory differential options.

We have confirmed we can do this retrofit into the following 0BC rear differential casings. Codes:

• JKP

• JKQ

• JKS

• MFS

• MFT

• MNB

If you have a Sport Diff with any of the following codes, you can convert by switching as follows:

• MKY —> MFT

• MKX —> JKS

• MKU —> MNB

Please note if you are switching from Sport Diff you will need to source different rear axles. See AXLE PART NUMBERS FOR CONVERSIONS FROM SPORT DIFF section below. You will also need to code out the Sport Diff. On the B8 this is possible using VCDS. On the C7 we have not figured out how to do it cleanly, so you will have a Sport Diff error on the dash. It does not affect anything.

The “regular diff” is just a standard open differential. That means as soon as one wheel loses traction, all torque is delivered to it. It makes for crappy handling characteristics in low traction situations (ice and snow), off the line, and in corners. With the LSD:

• Acceleration - you’ll get off the line faster with less wheel spin.

• Cornering - you’ll be able to put much more power down in the corners, since torque is split to match available traction. No more spinning the inside rear.

• Drivability - the LSD does not create any additional NVH. It is purely gear-based. It creates no noise or strange handling characteristics. It’s a 100% OEM+ kind of mod. It just does everything better.

• Strength - The LSD’s helical construction is much stronger than the 2-pinion spider gear open diff. You won’t break it.

The Sport Diff is a great differential for road course racing, autocrossing, or when you’re pushing to the limits in a corner. It has a lot of weaknesses though. The first is that at it’s heart it’s actually an open differential, just like the regular diff. The Sport Diff is a “torque override differential” which means it has a special clutch-pack-driven override gear that can apply more torque to the outer axle in a turn. Because of this, the differential itself must be open by design, as an LSD would fight the torque override gear. That means anytime you’re in a low traction scenario or lift a wheel in a turn, the differential becomes open. In our autocross car, we always wear out the insides of the rear tires first, and on a particularly violent course, we actually find the inside of the rear tires smoking!! That’s the typical sign of an open diff.

It’s other great weakness is in strength and durability. There are several weak points in the design. The casing is weak at the attachment points and has been known to break free from the car on launches and 1-2 shifts, damaging other components. The spider gears in the heart of the differential are weak and can break. Clutch packs can wear out over time, limiting the effectiveness of the torque override gear. Not to mention all the other components (pump, sensors, control module) that can break or develop faults.

All-in-all, the Sport Diff just isn’t very robust. It’s great for a couple specific things, but that’s about it. Plus it’s really heavy.

So, compared to the Sport Diff:

• Strength - This is where the LSD truly shines compared to the Sport Diff. The casing and gears of the Sport Diff are weak and prone to failure. The LSD is much more robust.

• Acceleration - the LSD is able to keep the wheels locked together, even under wheel spin conditions. You’ll have more traction off the line.

• Weight - the LSD is over 35 lbs lighter than the Sport Diff. In the 1/4 mile, 100 lbs is conservatively worth 0.1s, so this weight savings alone is worth in the neighborhood of 4-5 hundreths based on weight alone.

• Drivability - the LSD does not create any additional NVH. It is purely gear-based. It creates no noise or strange handling characteristics. It’s a 100% OEM+ kind of mod.

The WaveTrac LSD is a helical gear style differential. There are tons of YouTube videos showing their operation. The result is very simple to understand.

• Under equal traction conditions, both wheels spin the same speed. While turning, the wheels are allowed to spin whatever speed they need to without binding.

• As one wheel loses traction, the gears inside the LSD engage progressively, sending more and more torque to the wheel with more traction. This limits torque sent to a low traction wheel while increasing that sent to the high-traction wheel, resulting in drastically less wheel spin.

• If a wheel gets near to a zero-traction situation (wheel spin is about to occur), the LSD becomes fully locked, stopping the low traction wheel from spinning faster than the high traction wheel.

The following PNs are for non-Sport diff axles. If you are converting from a Sport diff to the JXB/WaveTrac rear LSD, you’ll need to purchase a pair of these or equivalent. Used OEM axles go for $30-90 each on eBay, new aftermarket ones about $100, and new OEM ones…we won’t go there.

8R0-501-203-C

• For use with MNB

8K0-501-203-N

• For use with JKS or MFT

Your car’s trans and diff codes are found on the build label. It’s located in the trunk and in your maintenance guide on the warranty voucher page in the warranty and maintenance manual.

If you’re under the car, you can also find the code of your regular diff engraved on the bottom.

If you can get to the top of the diff, it’s also printed as the 4th-6th characters on the bar code sticker (if it’s still attached).

On the Sport Diff, the code is engraved on the bottom side near the front.

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