[Mr. 5]

Let's face it...
if you have a production date of March of 2007 to Present, you have a welded ring gear and you can't install an LSD. You have to spend about $3,700 AND have to send back your own diff. Right?
Wrong!
Autotech (Wavetrac) has come up with a solution to separate ring gears from the OEM carrier and tap the ring gear so it can be used with the Wavetrac LSD for about 700 bucks. So, for just under 2k, you can have a limited slip differential installed on your previously welded ring gear!

I gave a complete 3rd member to Autotech a while back hoping they could separate my ring gear from the carrier. Not only were they able to work with my ring gear, but they were able to come up with a solution and a process for all of those who have welded ring gears.
I have a manual transmission which has the 3.08 rear end. Up until now, those with welded ring gears who have done the LSD upgrade have had to change their rear end to the auto ratio (3.46). Some have chosen the 3.46 because it winds up quicker, but for those who wanted to keep the 3.08, they were out of luck because it is almost impossible to find a bolted 3.08. Now, it doesn’t matter.

Now I know that it’s all about personal preference with what ratio is used, but I really wanted to stick with the 3.08. IMO, since our cars have so much torque that gets hit at lower RPMs, then I think that it’s better to have taller gears in the back to take advantage of the torque band.

The Separation

The first picture is the OEM carrier with the ring gear attached.



Here is a close up of how BMW welds the ring gears to the carrier.



I’m not exactly sure what method was used to cut the ring gear off the carrier, but here is a picture of the ring gear that was just separated.



The surface was then smoothed out and tapped for the attachment to the Wavetrac unit.



Here is what the end result looks like.











The Traction
I knew the entire time that an LSD is the best modification that one can do to a RWD car, but it really hurts when someone makes a quote of around $3700, especially when you can get other mods for much less. But, it’s common knowledge that although you have more and more power, if you can’t put the power to the ground, it’s wasted.

The moment I got into my car after the Wavetrac was installed, my car felt much tighter and planted. Even when driving in a straight line, the car just felt much more controlled.
The times that you really notice the difference though is when rounding corners. Some of you guys have seen my video of when I rounded turn 4 at Laguna Seca and completely lost it doing a 540 into the gravel. I know that it most likely had to do with driver error, but I’ll guarantee that if I had this Wavetrac installed, I would have most likely saved it before my spin.
This is a slomo of my wipeout at Laguna Seca:

Differentials

Open Differentials

An open differential does a great job of transferring the power from the drivetrain to the wheels. The problem with an open differential is that the torque always takes the path of least resistance so if one wheel starts to slip, the torque will continue to drive the slipping wheel.

Clutch LSDs

These LSDs respond to driveshaft torque, so the more torque that is input by the driveshaft, the more the clutches grab giving more of the wheels equal amount of power.
The problem with this type of LSD is that it locks the rear end when enough torque is applied, which creates a recipe for disaster for those who aren’t used to drifting.

Torque Biasing LSDs

Torque biasing LSDs takes the torque and divides it between the 2 wheels and increases the “bias ratio”. The bias ratio is the amount of torque that one wheel gets over the other. For example, some torque biasing diffs have a 2.5:1 bias ratio compared to the 1:1 in the open diff. With this example, if one wheels starts to slip, the gears in the LSD will multiply the torque that is going to the slipping wheel by 2.5 and transfer it to the wheel that has grip. The problem with this type of LSD is that if there is little to no load on one of the wheels, then this means that there is little to no torque that will be multiplied and transferred over to the other wheel. So, no matter how high the bias ratio is, if there is no load on one of the wheels, the Torque biasing ratio behaves like an open diff.

Wavetrac

The Wavetrac differential is a torque biasing differential but has a device inside the diff to react when there is little to no load on one of the wheels. This device creates a load inside the unit to be multiplied against even when there is no load on one of the wheels.

Here is a quick video to show how well it transfers the torque to the wheel that needs it.

Installation

Thankfully, I had a shop near me do the install. Unitrax is a company that strictly deals with drivelines and they’ve been doing it for 25 years. They worked with installing the ring gear, setting up the backlash, and replacing the seals. I’ve never seen so many differentials in one place in all my life. http://www.gounitrax.com/

Here are a couple pictures that I took while I was at Unitrax.
You can see the stand of differentials here:



Here’s a rack of some Viper Differentials that they just completed:





What else can I say, the Wavetrac is incredible!
I'm really excited that somebody finally came up with an affordable way of working with our welded ring gears.

Videos will come shortly!

[ericsmc83]

This is definitely great news for us with welded ring gears (including me)!

Looking forward to more info and videos.

[aut0sh0cker]

WOW this is awesome

[XPO186]

Early Xmas for me!

[roozie2001]

looking forward to seeing video and b4 and after traction for 0-60

[Sparky66]

Congrats on your diff...........Best performing solution at a competitive price

Originally Posted by Mr. 5

Let's face it...
if you have a production date of March of 2007 to Present, you have a welded ring gear and you can't install an LSD. You have to spend about $3,700 AND have to send back your own diff. Right?
Wrong!

My cars a MAY 2007 ...............my ring gear was not welded but it's a step.

Originally Posted by Mr. 5

Autotech (Wavetrac) has come up with a solution to separate ring gears from the OEM carrier and tap the ring gear so it can be used with the Wavetrac LSD for about 700 bucks. So, for just under 2k, you can have a limited slip differential installed on your previously welded ring gear!

I gave a complete 3rd member to Autotech a while back hoping they could separate my ring gear from the carrier. Not only were they able to work with my ring gear, but they were able to come up with a solution and a process for all of those who have welded ring gears.

Seems like most reputable diff shops geared up for this, can perform this machining. My local diff installer has been machining and cutting of welded ring gears for the last 2 years on many 335/135's to install Quaife units.

Originally Posted by Mr. 5

Torque biasing LSDs takes the torque and divides it between the 2 wheels and increases the “bias ratio”. The bias ratio is the amount of torque that one wheel gets over the other. For example, some torque biasing diffs have a 2.5:1 bias ratio compared to the 1:1 in the open diff. With this example, if one wheels starts to slip, the gears in the LSD will multiply the torque that is going to the slipping wheel by 2.5 and transfer it to the wheel that has grip. The problem with this type of LSD is that if there is little to no load on one of the wheels, then this means that there is little to no torque that will be multiplied and transferred over to the other wheel. So, no matter how high the bias ratio is, if there is no load on one of the wheels, the Torque biasing ratio behaves like an open diff.

This explanation you explain above is typical of a generic style of Torsen differential. The presence of "No Load" is deceptive when considering a better Torsen Style of Diff like the Quaife. This unit is very sensitive to load conditions and one would have to totally have their rear wheel off the ground to get in a condition you describe above and make it behave like an "open diff". In the case of a Quaife ATB Helical LSD Differential, it does not have a fixed bias ratio; this is not the principal by which it operates since the Torque bias is constantly variable. The Quaife differential constantly adjusts the torque across the axle to achieve a balanced drive to both wheels. Torque is constantly and automatically biased over a ratio of between 0-80% away from the spinning wheel. The resultant friction forces the differential to transmit a greater proportion of the torque to the non spinning wheel. The effect is progressive and at no stage does the differential lock solid.
I have tested for these features to prove a point by providing different loads to each rear wheel to test for myself to see exactly what improvements I had gained via it's installation. To help amplify the situation, it was performed going up a hill with one wheel on wet very slippery grass surface and the other on a dry road surface. The car provided enough effective torque to the non-spinning wheel (in this case being the one on the road surface) and the car launched away no problem.
In regards to the WaveTrac, you are provided extra grip if you off load wheels, as one would in a rally or racetrack situation. Since you track your car this is very appropriate for situations like yours but for most people driving their cars on the road, they would never notice the difference between a WaveTrac or Quaife fitted car.

I guess many here have seen this video of how an LSD performs on wet road surface.

Guys, enjoy your LSD's ........

[Mr. 5]

Originally Posted by Sparky66

In regards to the WaveTrac, you are provided extra grip if you off load wheels, as one would in a rally or racetrack situation. Since you track your car this is very appropriate for situations like yours but for most people driving their cars on the road, they would never notice the difference between a WaveTrac or Quaife fitted car.

Many people track their cars here and drive spirited so if they drove them back to back, there's a really good possibility that they would notice the difference.

[GreenPlease]

Great writeup! For ~$2k it seems like a hell of a deal

[ar design]

Very nice! Great job guys!

[kenneth]

Mr. 5 Thank you for taking the time to share. Can you clarify what Autotech (Wavetrac) did and what the Diff shop (Unishop) did.

Did Autotech build you the whole pumpkin and all Unishop did was to install? Thanks!

[Mr. 5]

Originally Posted by kenneth

Mr. 5 Thank you for taking the time to share. Can you clarify what Autotech (Wavetrac) did and what the Diff shop (Unishop) did.

Did Autotech build you the whole pumpkin and all Unishop did was to install? Thanks!

Sure.
I gave Autotech the 3rd member (the pumpkin) and they developed a process to cut the ring gear off and machine it.
Unitrax is a company that installed the ring gear to the LSD and set up the backlash. They also do the actual diff swaps. Unitrax has 3 lifts to work with.

[Digital.James]

wow this is great news... definitely number 1 on my priority list!

[jonm42]

What was the turnaround time, i.e., how long was your car inoperable?

[scottp999]

So what is the easiest process of ordering one to replace a welded diff? Is it Harold at HP Autowerks that I should go through?

[Mr. 5]

Originally Posted by scottp999

So what is the easiest process of ordering one to replace a welded diff? Is it Harold at HP Autowerks that I should go through?

Harold is a great option because I believe he already has a couple diffs already. Once you get the diff then I believe all you have to do is send your unit back.

[Mr. 5]

Originally Posted by jonm42

What was the turnaround time, i.e., how long was your car inoperable?

I actually purchased another diff from another member hoping that Autotech could do it. They assured me that they could.
It took a couple months but this was only because they were working on a standard process for everyone else.
i believe that the standard process is only about 3-4 days turn around time but you could contact Autotech for a more acurate time frame.

[OpenFlash]

Craig-- what would have probably saved you from losing control of the car is keeping your head pointed to where you want to go. The second you take your eyes off your desired trajectory (as you did when you began the slide), the hands will naturally take you towards the unintended direction. Common mistake of course. Not necessarily fixed by adding an LSD. Laguna's a great track btw. Despite me crashing there 10 years ago at turn 9. Similar driving error.

Shiv

[Slidewayz]

Does that mean we lucky bolted diff dudes can get this bit of kit, parts and labor, for $1.3k ?

[Mr. 5]

Originally Posted by shiv@vishnu

Craig-- what would have probably saved you from losing control of the car is keeping your head pointed to where you want to go. The second you take your eyes off your desired trajectory (as you did when you began the slide), the hands will naturally take you towards the unintended direction. Common mistake of course. Not necessarily fixed by adding an LSD. Laguna's a great track btw. Despite me crashing there 10 years ago at turn 9. Similar driving error.

Shiv

Agree that Driver error had a lot to do with the spin but what I've been noticing so much about this Wavetrac is that the rear of the car just loves to go with wherever the front wheels are pointed.
I tried to turn the steering wheel in the correct point while still holding the pedal, but my rear end wasn't responding at all.

Originally Posted by Slidewayz

Does that mean we lucky bolted diff dudes can get this bit of kit, parts and labor, for $1.3k ?

Contact Autotech. I believe that there is a little labor to install the diff onto the ring gear. I believe that part of that labor is included in the 700 price.

[zsapphire7]

glad to see my diff back in action!! I really would like to feel out the difference between wavertac and quaife. The only times however, i would definately notice are steep ditches where i can get one rear wheel to life. Currently, the car cant move anywhere and spins only one wheel until the DSC kicks in. I dont think ive ever had those situations except after i installed the m3 rear sway bar. Anything stock wise would never reach a situation where one wheel is in the air...

[HP Autosport]

Just to clarify a few things. A complete 3.46 Quaife or Wavetrac final drive unit does not require the purchaser to send back their own final drive at all. There is no core charge on these units.

The only time a core is required is the 3.08 Quaife or Wavetrac built from a low mileage final drive. In the case of the 3.08 Wavetrac, the purchaser will need to return the core for a core refund. Alternatively, they are welcome to keep their existing unit with no core refund issued.

Sending your unit in for modification will mean some down time with your car awaiting the return of modified unit. A quicker solution will be to purchase a Wavetrac Final Drive unit and return your existing unit for a core refund.

Harold

[HP Autosport]

Originally Posted by Slidewayz

Does that mean we lucky bolted diff dudes can get this bit of kit, parts and labor, for $1.3k ?

Parts:

Wavetrac $1295
Axle seals $35
Gear Lube $20
Misc chemicals $?

Labor:

Autotech to modify your welded ring gear $700

Your tech to install the unit 3-4 labor hours


Buy one complete... $1995 + $800(Refundable core charge) + Freight