All-Trac

All-Trac was a proprietary all wheel drive system used on a variety of Toyota badged models from late 1986 to 2000. It was considered a revolutionary advance for all-wheel drive automobiles into the mainstream consumer market and its electronically controlled locking center differential was a first for Toyota in a passenger car.

Technical information

The All-Trac system was comprised of five main parts: the front differential, rear differential, central locking differential, the transmission, and the driveshafts. The transmission and front differential hang off of the lower back region of the transversly mounted engine and act as a single unit. The transmission bellhousing and frontal differential plating bolt onto each other and the whole unit can be removed as one part. The transmission feeds power into the frontal differential which distributes the power to the front wheels. A driveshaft exits the transmission and connects with the center differential which transfers the power to the rear differential. This rear differential then drives the two back wheels. Two small halfshafts exit directly from the frontal differential to power the front wheels, and two longer ones exit from the rear differential and power the back wheels. In most of the models, the majority of the power is routed to the front wheels as would be in a traditional Toyota FWD automobile. In normal operation, the center differential allows for slippage, which allows the wheels to turn at different speeds. This is important because without this, small differences in wheel speeds can result in torque being applied across the transmission causing "wind-up" and damaging the transmission.

There is a small button inside the vehicle labelled "Center Diff. Lock" and when activated, the center differential locks, resulting in the exact same number of revolutions of the engine being transferred to the back wheels as the front. This does "not" mean that they all turn at the exact same rate, only that the two sets of wheels turn nearly the same number of times. This is because there are still the front and back differentials allowing for small amounts of wheel slip left to right. The final result of this is that if the vehicle is in a situation where traction is uneven or poor (ie. muddy or snowy), no wheel has the potential to spin on its own like in a traditional 2WD setup. All four wheels will turn roughly together, allowing the vehicle to use the wheels that still have traction to move the car while the others do not waste the car's power spinning.

Model series

*1988-1991 Camry, DX and LE trim, 4cyl 1998 cc 3S-FE
*1986-1989 Tercel, DX, SR4, SR5 trim, 4cyl 1594 cc 3AC
*1988-1992 Corolla, std trim, 4cyl 1587 cc 4A-FE
*1990-2000 Previa, DX, LE, LE supercharged trim, 4cyl 2438 cc 2TZ
*1986-1993 Celica "All-Trac Turbo" or the JDM, EUR, and AUS "GT-Four" 1988-1990 in USA, 4cyl turbo 1998 cc 3S-GTE

Predecessors and successors

Toyota's All-Trac system lasted for only a few years but was just one step in their 4WD history. The All-Trac system originated in the 1983-1986 Tercel, which featured a true 4WD system. There was a low range gear that was only accessible once a lever on the floor was pulled into "4WD" just like on many modern day trucks. The 1984 Corolla and Sprinter improved on that system and set up the groundwork for All-Trac.

The GT-Four in Japan (Celica All-Trac Turbo in North America) sported the All-Trac system in its initial years but in 1990 Toyota made some significant upgrades to the system in order to improve upon that car. Where All-Trac had laid the groundwork, Toyota engineers continued to improve upon the center differential setup and changed the center unit over to utilize viscous coupling rather than mechanical, and the rear unit to a Torsen differential. This, the All-Trac system's successor, went on to become one of Toyota's most popular sports car drive train setups.

ee also

* quattro - the famed Audi branded four wheel drive system
* 4motion - Volkswagen branded four wheel drive system
* 4Matic - a four wheel drive system from Mercedes-Benz
* ATTESA - a four wheel drive system from Nissan
* xDrive - a four wheel drive system from BMW