Bildon Motorsport - Volkswagen Racing Parts

The Torque Biasing Differentials (TBD), also know as a Torsen Type or Gear Type are made by companies such as Peloquin and Quaife. These differentials are an excellent choice for dual purpose cars that see both street and competition use or where the customer wants to install it and forget it. They are "zero" maintenance differentials.

The Torque-Biasing differential behaves as an open differential until a loss of traction occurs at one wheel. When the loss of traction is sensed, the differential automatically biases up to 80% of the engine torque to the wheel with better traction (The description "torsen" is derived from Torque-Sensing.) The operation is automatic. No adjustment is required (or possible) on the differential. All adjustments are made simply with springs, sway bars, and shocks. Torsen type differentials do not bias traction once a wheel leaves the ground or spins without resistence. In this case it again acts as an open differential. Therefore it is not optimal in conditions where the car's driven wheel leaves the ground such as rally bumps or apexing over track curbing.

The Clutch Type Differential (LSD), also know as a Mechanical Differential or Salisbury Differential is a true racing differential. These units deliver uncompromising performance under all racing conditions. However they do require a short breaking in process and occasional inspection and maintenence to assure many years of service.

The Clutch Type Diff has an adavantage in that it is adjustable. The cam profile, clutch plate quantity and size, initial torque of the preload springs and the lubricants can all be changed to offer a large number of adjustments. These units can be set up with varying amounts of preload to suit individual driver preference and particiular conditions. In Rallying they offer the additional advantage that, in the event of failure of other transmission elements, e.g. a broken drive shaft (even at low levels of preload) they may still provide sufficient traction to drive out of a stage and back to service.

How does it work?
The clutch plate rings are attached to the side gears which are attached to your driveshafts. The pinion and the pinion gears are housed inside the pressure rings and behind the pressure rings are a number of clutch plates. When torque is applied to the differential, the differential case will rotate and force the pinion shafts into the pressure ring cams (or ramp angles). The pressure ring is then pushed out against the clutch plates thereby squeezing them together. This in turn causes the wheels to gradually lock together, depending on the power applied. This effect limits the wheel spin during hard cornering and applies power to the wheels evenly when more power is applied. On acceleration and deceleration, it provides even grip and on neutral power, it frees up for less drag and easier turning.

The percentage number denotes the percentage of torque applied to the slower turning wheel from the faster turning wheel. In a straight line, both drive wheels turn at the same speed, so no limited slip action is occurring. In a turn, or when one tire is spinning more than the other (such as a race car in a drift or rally car on gravel, snow or ice), with a limited slip differential, 25, 40, or 75% etc, of the torque applied to the faster wheel is applied to the slower wheel, effectively 'limiting slip'. A higher lockup percentage will cause increased tire wear on the inside tire during cornering -- the tire itself will have to slip slightly to counteract the limited slip's desire to have both tires turning at the same speed. It will also increase oversteer (RWD) in wet or slippery conditions, but it will also increase understeer in tight corners under dry conditions. This is simply due to the fact that with a limited slip, the drive wheels tend to want to turn at the same speed, making the car tend to want to go in a straight line. When it is slippery, however, both drive tires will tend to lose traction at the same time, increasing oversteer (RWD) or understeer (FWD). The advantages are less inside wheelspin when accelerating out of a tight corner. This also translates into more horsepower to the pavement and faster times -- provided that the suspension is tuned for the limited slip. The ability to accelerate out of corners without excess wheel spin can be a great advantage.

Recommendations: Which type of Diff for what use?
A) Fast Street / Autocross - We recommend the Torque-biasing type for fast street use. This is manly due to the lack of maintenence required.
B) Street / Track - We would recommend a torque-biasing diff. if the car experiences light-duty track use, with a relatively stock suspension. A 40% limited-slip diff. can be used if car has stiff suspension and/or power upgrades.
C) Rally and Track only - A full limited-slip differential or spool.

Some comparisons:

LSDs provide lock-up on both acceleration and deceleration. Lock-up on deceleration allows aggressive entry into a turn and late braking, reasons why all Professional race teams (that we are aware of) utilize LSDs, rather than TBDs.
Torque-biasing differentials provide lock-up on acceleration only. The amount of lock-up (5-80%) increases as the amount of torque increases. On deceleration, lock-up is negligible, making the TBD the ideal diff for the slower speed turns of autocross. (In the same slower-speed turns, an 80% LSD would most certainly cause understeer.)
A torque-biasing differential performs like an open diff whenever one of the two drive wheels lifts off the ground. Lock-up and traction are lost until both drive wheels are again planted firmly on the ground.
There seem to be two very distinct groups, one favoring the use of LSD, and the other favoring the use of TBDs. We at Bildon Motorsport try to avoid making the decision for the customer. We would rather our customer confer with the race shop or transmission builder performing the installation, in order to make an informed choice.

Break in / Servicing of clutch type differentials:

All Bildon mechanical differentials require a break in period.
Upon differential installation, and trans fluid top off, proceed to drive vehicle to an open area where several 'figure eights' can be performed. Drive vehicle (at idle speed) in 20 figure eights, full lock to full lock. Then drive (at idle speed) in 20 full lock circles left, and again 20 full lock circles right. Try to accelerate only while driving in a stright line. Do not "test" your new differential by accelerating hard at this point. Generating excessive heat at this stage could permenantly damage your LSD.

For vehicles used for circuit racing one day of track use is recommended break in. Follow normal 'figure eight' LSD break in initially before tracking the vehicle. During break in period, drive vehicle moderately without extreme load differences such as shocking (hard shifting with swift clutch use). Maximum track speed should not be achieved during break in process. After one day of track use, change oil in differential using recommended fluids.

Non compliance of provided instructions most definitely will cause driveability issues. Service intervals are also listed with provided instructions.

About Transaxles Fluids with LSDs.

The FWD racing transaxle is a unique device. And also one in which selecting the proper gear oil is not an easy choice. For smooth shifting of your gearbox you want an oil that is sometimes at odds with the oil you want lubricating a hypoind ring & pinion and again it may not be appropriate for the friction required between limited slip clkutches in your differential. Unlike most RWD cars, or non LSD FWD cars, you need an oil that does all 3 things well. Please see the fluids we have recommended here.