Four Limited-Slip Differentials For The Viper SRT 10 Positraction For Street, Strip and Track
The ‘Gen III” Dodge Viper SRT 10 was introduced in 2003 with fresher look, more power, and a new version of the Dana’s resilient 44ICA differential, the M44-4. Along with a new housing, the M44-4 was fitted with Dana’s Hydra-Lok limited-slip differential.
Because the 2003 M44-4 housing was designed to accept the Dana Spicer Hydra-Lok, the Viper community was initially left with no positraction alternatives. However, today the SRT 10 owner has four limited-slip differentials to chose from. Two of the units are engineered to meet the most demanding performance applications and a third is found in the 2008 through 2010 “Gen IV” Super 44-4ICA Viper SRT 10.
Dana Spicer Hydra-Lok
Dana’s Hydra-Lok was originally developed by ASHA Corporation in Santa Barbara, California. McLaren Performance acquired ASHA and sold the rights of ASHA’s Gerodisc technology to Dana’s Spicer light duty axle division. Dana completed development of the unit and trademarked the LSD as the Hydra-Lok. Production began in Syracuse Indiana and in 1999, Jeep debuted the Hydra-Lok in the Grand Cherokee.
Gerodisc technology is speed and torque sensitive, operates full-time, and offers proportional torque transfer with progressive action. It uses the differential oil to operate the Gerotor. TwinDiscs provide one coupling per wheel. The fluid is released at calibrated pressures to engage the clutch pack.
The Hydra-Lok transfers wheel torque as conditions demand, ensuring improved traction and handling. Unlike traditional disc-based LSD’s, the Hydra-Lok offers controlled torque transfer. It does not waste power on wheel spin, rather it transfers torque to the wheel with the most traction. The torque is independent of the slipping wheel condition. The Hydra-Lok is speed-sensing meaning that the torque transfer is independent of the slipping wheel’s traction. The amount of torque transferred to the wheel with traction is based on the speed of the spinning wheel. Resulting in nearly immediate transfer of torque from the wheels that slip to those that grip.
According to Dana Corporation, when a Hydra-Lok equipped Viper begins to negotiate a curve, the vehicle reacts as if it had an open differential to reduce the potential of over-steer. As the vehicle continues through the corner, it takes on the characteristics of a limited-slip differential, transferring torque to the wheel with traction. Coming out of the curve, however, the Hydra-Lok allows the Viper to deliver the maximum amount of torque to the ground for improved speed while exiting.
The 2003 version of the Hydra-Lok had an issue with cross pins failures. UNITRAX developed a replacement 300m cross pin to help prevent Hydra-Lok failures. In 2004, Dana upgraded the Hydra-Lok with a heat-treated cross pin. However, side gear and pinion gear failures have continued to plague Gen III SRT 10 owners.
Unfortunately, dependability and durability issues have spoiled the promise of the M44-4 Hydra-Lok. We will now examine the alternatives to the Hydra-Lok.
Quaife ATB Differential
R.T. Quaife Engineering Ltd was the first manufacturer to supply a replacement limited slip differenital for the stock SRT 10 Hydra-Lok. The Quaife ATB (Automatic Torque Biasing) Helical LSD differential was originally developed in the 1980s and is used throughout world. While more widely designed and developed for front-wheel drive vehicles, Quaife Engineereing states the traction benefits offered by the ATB Helical LSD differential can also be utilized in rear-wheel drive vehicles.
The Quaife is an automatic torque biasing helical-gear based differential. Unlike a conventional plate-style limited slip unit, the Quaife ATB relies on sets of floating helical gear pinions that run in pockets and mesh to provide the normal speed differential action. Should one of the driven wheels start to spin however, the helical gears start to generate a torque bias thanks to the axial and radial thrust of the helical gear pinions in their pockets. The result is that there is a progressive transfer of torque away from the spinning wheel of the axle to the driven wheel, which is now capable of transmitting a greater proportion of torque to a constantly varying degree.. The transition of power is smooth and constant without ever completely removing power from the other wheel. The effect is progressive but at no stage does the Quaife ATB lock solid. By getting the power to the ground, the Quaife enables the Viper to accelerate quicker and corner faster.
In cornering, while accelerating out of a turn, the Quaife ATB biases greater power to the outside wheel, reducing inside-wheel spin. This allows you to begin accelerating earlier, exiting the corner at a higher speed. The Quaife ATB provides straight-line acceleration that is close to an an ideal 50/50 power split to both drive wheels when traction conditions are ideal. The Quaife ATB also controls loss of traction when the drive wheels are on slippery surfaces by providing the appropriate biased traction needed to overcome these adverse conditions.
The Quaife ATB powers both drive wheels under nearly all conditions. The differential senses which wheel has the better grip and automatically biases the power to that wheel. However, it must be noted that if one wheel is in the air or on a surface without traction, neither wheel will be driven during that moment in time.
To install a Quaife ATB into the SRT 10 Super 44-3ICA differential, the stock output shafts must be shortened and bore-drilled to accept the anchor bolts.
To maximize the performance of the Viper equipped with Quaife ATB differential, the suspension should be set up like an open differential; stiff springs and a soft sway bar.
The Quaife’s distinctive design offers controllable traction, improves handling and steering, and applies the power where it is needed most. The Quaife ATB is exceptionally strong and generally requires no maintenance.
All authorized Quaife ATB Helical SRT 10 differentials come with a limited lifetime warranty.
The 2008 through 2010 “Gen IV” Viper SRT 10 is equipped with the GKN Visco-Lok. The Visco-Lok has been in production since 1999 and is a standard feature in the BMW M3.
The Visco-Lok is a unique hermetically sealed speed-sensing limited-slip differential. The unit benefits through its high-torque progressive locking characteristics which provides maximum torque transfer in excess of skid torque.
The Visco-Lok operates through a self-contained silicone-fluid filled reservoir and shear pump that actuates a wet friction clutch pack. The pump generates pressure proportional to the speed difference between the wheels. The clutch pack actuates thereby transmitting torque to the appropriate wheel. The locking effect increases with the speed difference across the drive wheels.
This locking characteristic enables the Viper to accelerate well on surfaces with different friction conditions between the drive wheels. Additionally, GKN states that the Visco-Lok allows even better acceleration and less under-steer in cornering than compared to torque-sensing LSDs.
UNITRAX has installed many Visco-Lok LSD’s in Gen III SRT 10 Vipers, giving the SRT owner improved limited-slip performance and in our opinion a substantial upgrade over the Dana Spicer Hydra-Lok. The Visco-Loks have proven to be especially reliable in stock or modestly upgraded Vipers.
OS Giken Super Lock LSD
Starting with a blank slate, the talented engineer, Takuya Tomimatsu of OS Giken Co. Ltd. of Japan has designed the premier Dodge Viper SRT 10 LSD. Using the foundation of 4 years of initial Super Lock development and the world as a proving ground, OS Giken offers their highly respected and race proven OS Super Lock LSD for the SRT 10.
The OS Giken Super Lock LSD is more closely related to the disc-based TracLok LSD found in the Dodge Viper from 1992 through 2002. However, that is where the comparison ends. The revolutionary Super Lock is a true 100% locking LSD that instantly reacts and transitions smoothly from both free and locked positions, combining open differential drivability and limited slip differential performance and stability.
The OS Giken Super Lock features innovative technologies like the adjustable lock timing adjuster. Lock timing can be adjusted by replacing the springs in the pressure ring. Initial torque settings also adjustable through cone springs located at ends of clutch stacks. This allows the Super Lock to be tuned to meet your exact needs for optimum performance. UNITRAX is an authorized tune center and can discuss custom tuning to meet a driver’s specific requirements.
OS Giken is committed to producing an extreme quality LSD. Every Super Lock is manufactured from only the finest materials, regardless of the production cost. The Super Lock housing is manufactured from a proprietary billet steel alloy which is then heat-treated when finished. The side gears and pinion gears are hot forged and hand-finished. This attention to detail improves the precision and performance of the product.
U.S. patented bevel gear-in-pressure ring mechanism has enabled OS Giken engineers to miniaturize each gear, thus providing more space for up to an unprecedented number (28) of all-steel friction plates. The Increased number of friction plates improves the locking force of the LSD enabling it to lock fully and completely. An added benefit to being a fully locking mechanism is that less heat is generated, thus resulting in incredibly higher durability and reliability in even in the toughest racing environments.
OS Giken states that they have tested the Super Lock for over 22,000 performance miles and upon inspection of the unit, there was no wear, no loss of initial torque, and no loss of performance. UNITRAX inspected a Super Lock that was run for three full race seasons. The Super Lock showed no signs of wear and many of the components looked as if they had just come out of production.
The higher locking force provides outstanding straight-line stability at the drag strip. The Super Lock will lock to 100% and transfer torque equally to each wheel.
You will experience less under-steer during cornering. When entering a corner with the throttle closed, the spring inside the pressure control ring will react accordingly and immediately return the Super Lock to its original torque settings. When exiting a corner, the Super Lock’s transition to the 100% locked position is smooth and predictable, resulting in better traction, stability and quicker exit speeds. Additionally, racers and techs have reported that the Super Lock operates significantly cooler then competing LSD units.
One key feature separating the Super Lock from our other clutch type LSD’s is that with the Spec-S (standard) settings, the Super Lock is actually able to function as a open differential at low speed/low torque situations. Thus, when performing a normal slow speed turn (such as a right hand turn on the street) or backing out of a parking space, our differential functions as a normal open differential, allowing smooth turning without premature wheel lock. Of course with performance settings, such as drift which would require a much higher setting of initial torque, some premature locking may occur.
Unlike the Quaife ATB, the Super Lock does not require that the output shafts be drilled and modified. OS Giken engineered the unit to be center-weighted and the Super Lock ships with equal-length 41 spline performance output shafts! Due to the nature of the Super Lock design, featuring 28 all-steel friction plates, the driver may occasionally experience some disc chatter. To temper this characteristic, we recommended the use of O.S. Giken’s OS-250R 80w250 GL-5 synthetic lubricant. The disc chatter in no way affects the performance or durability of the Super Lock. Since the Super Lock runs cool and there are no contaminants from friction material polluting the lubricant, differential oil change intervals can be extended.
The Super Lock is used competitively in the U.S.A., Europe, U.A.E., Japan, Greece, and Australia. It also has a large and growing following in Autocross and Drifting circuits.
To date, there has not been one reported failure of the OS Giken Super Lock in any application. The engineers at OS Giken take extreme pride knowing that the owner of their LSD units compete with the utmost confidence.
The OS Giken Super Lock meets the needs of the most demanding driver who is comfortable with the way his SRT 10 feels with the stock Hydra-Lok or Visco-Lok but wants the tuneability, dependability, and durability that a fully race-engineered and manufactured LSD offers. The Super Lock is quickly becoming the preferred choice in the high-performance community.
If you have any questions regarding limited-slip SRT 10 differentials, please contact UNITRAX at 800.622.4327.
www.UNITRAX.biz • www.GoUNITRAX.com
Copyright © 2011 by UNITRAX Drivetrain, Inc., all rights reserved.