Jul 062008

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 44 differential, the M44-4. Along with a new housing, the M44-4 was fitted with Dana’s Hydra-Lok limited-slip differential.

2008 Dodge Viper

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 “Gen IV” Viper SRT 10.

Dana Spicer Hydra-Lok

Dana’s Hydra-Lok was originally developed by ASHA Corporation in Santa Barbara. 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 the cross pins breaking. UNITRAX developed a replacement 300m cross pin to prevent Hydra-Lok failures. In 2004, Dana upgraded the Hydra-Lok with a heat-treated cross pin. Side gear and pinion gear failures have continued to plague the SRT 10 owners.

Unfortunately, dependability and durability issues have spoiled the promise of the M44-4 Hydra-Lok.

Quaife ATB Differential

The first manufacturer to supply a replacement for the stock SRT 10 Hydra-Lok was R.T. Quaife Engineering Ltd. The Quaife ATB differential was developed in the 1980s and is used throughout world.

The characteristics of the Quiafe is that it progressively locks as torque increases; there are no plates or clutches to wear out. By getting the power to the ground, the Quaife enables the Viper to accelerate quicker and corner faster.


The Quaife is an automatic helical-gear based differential. Sets of floating helical gear pinions mesh to provide the normal speed differential action. To pre-load the gear packs there is a selection of centre spring discs available. In the event of wheel-slip, torque bias is generated by the axial and radial thrusts of the pinions in the pockets. The resultant friction force enables the driving road wheel and sun-gear to transmit a greater proportion of the torque. The effect is progressive, but at no stage does the Quaife lock solid.

The Quiafe ATB Differential 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. The transition of power is smooth and constant without ever completely removing power from the other wheel.

In drag racing, the Quaife provides straight-line acceleration that is close to an ideal 50/50 power split to both drive wheels.

In cornering, while accelerating out of a turn, the Quaife 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 Quiafe differential 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 Quiafe’s distinctive design offers maximum traction, improves handling and steering, and applies the power where it is needed most.


To install a Quaife ATB into the SRT 10 differential, the stub axles must be drilled so that bolts can anchor them in.

In order to maximize the performance of the Quaife ATB differential, the suspension should be set up like an open differential; stiff springs and a soft sway bar.

The Quaife is exceptionally strong and requires no maintenance. 

Quaife UK does not offer a warranty on their products sold in the U.S.A. Check with your installer or dealer on the latest Quaife USA warranty details.

OS Super Lock LSD

OS Giken Co. Ltd. of Japan has recently introduced its highly respected and race proven OS Super Lock LSD. The Super Lock was in development for four years before its initial release.

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 tuning for a variety of environments.

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 gears are all hot forged. 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 has inspected a Super Lock that was run in three race seasons. The unit 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 excellent straight-line stability at the drag strip. The Super Lock will lock 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.

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.


The Super Lock does not require that the stub axles be drilled. The OS Giken engineers designed the unit to be center-weighted. The unit comes with a new long stub axle so both stub axles will be the same length. It is recommended to use O.S. Giken’s or Schaeffer’s 80w250, or Synergyn Syngear II.

The Super Lock is used competitively in the U.S.A., Europe, U.A.E., Japan, Greece, and Australia. It also has a large following in the drifting community.

The OS Giken Super Lock meets the needs of the 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 may quickly become the preferred choice in the Viper race community


GKN Visco-Lok

The 2008 “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 several Visco-Lok LSD’s in competition Vipers and to date, the units have proven to be especially reliable and in our opinion, a substantial upgrade over the Hydra-Lok. The Visco-Lok offers the SRT 10 owner improved limited-slip performance at a very reasonable price.

If you have any questions regarding limited-slip SRT 10 differentials, please contact UNITRAX at 800.622.4327.

Copyright © 2008 UNITRAX Drivetrain, Inc.

Jul 062008

The Quaife torque-biasing posi unit is currently on sale at UNITRAX. This premium LSD unit offers excellent traction control, performance and durtability. The Pontiac Solstice Quaife will also fit the Saturn SKY and Cadillac CTS 6 cylinder.

UNITRTAX can also ratio change your Getrag differential when installin Quaife LSD.

Call UNITRAX at 800.622.4327 and mention this blog for an exceptional price on the Solstice / SKY / CTS Quaife.

All Quaifes come with a lifetime warranty.