What's the big Diff? Differential replacement for gen 3-4 Vipers

[Speedtactics]

What's the big diff?

   A few months ago, I was approached by So Cal Viper Club president, Lance Kouchi. He asked me if I had ever replaced the differential in my 2006 SRT10 Viper. My answer was quick "No, Why?" He told me that Autotech (http://www.wavetrac.net) was looking for a Gen 3 Viper to install their new Wavetrac differential. Well, my next question was why do I need it. I didn't seem to have any problems with my current differential, so why change it? The simple answer was "They have been known to fail". Well I did some investigating and called a few other knowledgeable people, including previous SoCal president Dan Everts. He promptly asked me "How many miles do you have on your car?" I told him 31,500. He was amazed that my differential was still the original Dodge part, called the "hydrolok".  In typical Dan fashion, he laughed and said "The way you drive, you better get it checked out". True, so true.
   In case you didn't know, here is what the differential does. The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed. In automobiles and other wheeled vehicles, a differential allows the driving road wheels to rotate at different speeds. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other. Got that?
   Now some history.  Dodge used variations of this Hydrolok system in all the Gen 3 Vipers. In talking with Devon from Unitrax (http://www.gounitrax.com), he told me that one of the problems with this system was the metal used in creating the differential's internal gears or spider gears. This metal was not the best quality for the high stresses that are subjected to the internal parts and thus the metal begins to break down and fail. Dodge attempted to correct this in later versions, however, parts were still prone to failure. Gen 4 Vipers got a whole new differential called the "Visco lok" which cured the poor metal problem. Since Dana is in the business, he has seen plenty of Viper differentials in his time and shops all over the country send him Viper differentials as well as diffs for other makes and models to be rebuilt.
   Well armed with this new knowledge and knowing that my car is not a garage queen. I decide to call Dana Clark at Autotech. They wanted to have a Gen 3 Viper to test fit and install their new differential. The design was already proven since they had been running it on the SRT8 Jeeps. With some modifications, it was a quick fit to go in the Gen 3 Viper. Dana explained the process and told me they would need my car for the day.
   Showing up bright and early at Unitrax and with my car on the lift the process began. Removing the diff is surprisingly, not that difficult.  Remove the rear wheels, skid plate and E-brake lines. Removing the upper "A" arm bolts on the driver side to give some range of moment and space. Pop off the half shaft and the drive shaft. Loosen the bolts holding in the diff and with an extra pair of hands, the diff drops out. I'm not going to go into all the details of the procedure since this is not a technical bulletin but rather a review and documentation of the entire process.
   From the outside at least, my diff looked great!  Over to the bench it went. The Unitrax technician drained the fluid and cracked open the case. Let's see what's inside this bad boy. Then the bad news. The tech started fishing out pieces of metal. These pieces were not small either varying from 1mm to  5mm or larger.  As I'm sure you know, there should be no metal pieces floating around at all. So where did they come from. Some quick checking found  that the spider gears were starting to fail. Teeth on some gears were chunked and others were gone. Once the metal pieces start to move around inside, they get caught up in the gears and create more damage. My differential was only miles away from eating itself alive. Since I had no indication this was happening, it could have failed anywhere. Once it fails your Viper can come to a screeching halt! Talk about Snake bite, ouch! This can result in very high costs as you can imagine. A differential failure could cost anywhere from $2,500 on up depending on what needs replacing.
   I was somewhat fortunate in that the damage for me was only on my spider gears and not on my ring gear or pinion gear, and everything else looked good. The Wavetrac part was just what I needed. In the process I had Unitrax replace all the seals bearing races etc. Its a cheap thing to do and a must when rebuilding the diff. After a quick steam clean up, the diff is closed back up.
The procedure for putting it back in the car is as simple as the removal. A test drive later and everything is working great.
   Dana explained to me a little bit about why the Wavetrac unit is a better design. As far as function goes, I will attempt to explain it in layman terms. When corning briskly the inside wheels are receiving less weight than the outside, pretty simple right. With the stock Gen 3-4 differential in the car the inside or unweighted wheels will continue to receive power, and can spin faster then the weighted wheels. Thus when the weight starts to even out and that wheel gains traction the car becomes unsettled or "upset" and this could result in problems. Just imagine rounding a high speed turn and having the car unsettled and start to move around in the back. Sound familiar to you, as a Viper owner, this is an all too common problem.
   One of the benefits of the Wavetrac design is that when you have a unweighted wheel, this design does not continue to send power to that wheel. Instead it shifts the power to the weighted wheel. Thus traction continues and the car is not "upset" by the power. Makes perfect sense, why didn't we have this before? I know I will be a lot less upset with this new diff installed and so will my Viper. There is also the added benefit that their differential is bomb proof. The quality of the parts and machining that went into its design and production are top notch. That's why they stand behind them and give them a lifetime warranty.
   I have had this diff in my car for a few months now. In that time I have done some street cruising, auto-cross, and track events. I'm glad to report that there has not been a single problem with this install or differential. My two days at Spring Mountain Raceway recently where great. The Snake was very predictable in the corners. I got to the point where I was getting into some of the turns and getting on the gas much earlier. Getting the car to give me a predictable drift, allowing me to finish off the turns better and get the drive onto the following straights. Great fun and no drama.
   In conclusion I would highly recommend this differential to any Gen 3 owners who need to replace their stock HydroLok system. Also to any Gen 4 owners who are looking for that little more of an edge and performance gain.
   A big thanks to Dana at Wavetrac for offering this opportunity to me. Also thanks to Devon at Unitrax for doing the install and letting me hang out during the process. A couple of great guys that are happy to answer any questions about your car's diff or just talk shop. Its companies like this that help us keep our Vipers going and that's what it's all about, so we have to support them as they support us. Please contact them if you have any other questions about your differential in your Gen 3-4 Vipers.
More information can be found in the Moparmax.com story found here : http://www.moparmax.com/tech/2012/vii_7-wavetrac-1.html

Autotech Driveline
Dana Clark
29 Journey
Aliso Viejo, CA 92656
Tel: +1.949.362.8700
email: [email protected]
http://www.wavetrac.net

Unitrax   
Toll Free: 1.800.622.4327 Local: 1.714.630.4327   
1280 N Sunshine Way Anaheim CA 92806 • Email: [email protected]
http://www.gounitrax.com

[Scottp]

Great write up Scott - good info.

ScottP

[PCH VIPER]

Good info and pretty cool seeing the Wavetrac gear cluster versus the OEM gear cluster.
Wavetrac's diff is definitely a quality piece.

[Banzai Ben]

Nice write up Hirk!
I did notice that when I do donuts the inside wheel is smoking more than the outside. So I guess that means the power is not going to the wheel with more traction. >m

[Speedtactics]

Ben,
That is true, but you can rotate your tires back there and get more mileage out of them.  ^8

[ViperX]

Nice write up Hirk!
I did notice that when I do donuts the inside wheel is smoking more than the outside. So I guess that means the power is not going to the wheel with more traction. >m

The Gen IV diffs work pretty well, much better than the Gen III diffs.  They do require regular fluid changes if you track your car. 

They are a limited slip type diff but "progressively" get close to full lock under load, like doing an extended burn out.  This means that both tires will be spinning at about the same speed, so if the inside tire is spinning about the same speed as the outside but is traveling over a shorter distance, it will "smoke more".

See you at the track,


Dan  <2

[Banzai Ben]

Cool, so mine is working right and does not need an upgrade.  >v

[ViperX]

Cool, so mine is working right and does not need an upgrade.  >v

Correct.

You do want to change the diff fluid every 3 or 4 "summer" track events though.

Dan  <2

[HyperViper]

Nice write up Scott  <1

[Speedtactics]

I just did two days at Laguna Seca and the diff worked great. The car is hooked up and pulls out of the turns without drama. Now I just need bigger..... to go faster  ^8