Drivetrain

Drivetrain Overview

The VR4 drivetrain is, from the gearbox on, almost a clone of the Lancer Evolution drivetrain for the Evolution IV-VI model years.

Similarities and Differences to Lancer Evolution Drivetrain

Component	Details	Differences to Lancer Evolution	Additional Notes
Manual Gearbox	W5M51 gearbox	Different bellhousing Different gear ratios
Transfer Case		No LSD from factory	Evo 4 through Evo 6 are a drop-in replacement transfer case Evo 6.5 is also a drop-in but the internals cannot be swapped with earlier cases or VR4 case Magna transfer case also fits but is same as Evo 6.5 internal dimensions Evo LSD units are a drop-in replacement for the front LSD located in the transfer case. This includes OEM LSD units from Mitsubish, as well as aftermarket LSD options.
Rear Differential	Active Yaw Control, or open differential		The open differential can have the internals from an Evo RS installed to make it an LSD.

Manual Gearbox

Manual gearboxes while same model as used on the Lancer Evolution, have different bellhousing for the 6A13 and slightly different gear ratios.

Common Issues

	Symptom	Cause	Solution
3rd gear welds failing	No 3rd gear	Each gearset has an inner and outer ring. The welds holding the inner and outer rings together for 3rd gear are known to break on high power output applications.	Re-welding of the 3rd gear
Shifter bushes failing	Mushy shifting or very difficult to shift into gear	The shifter bushes that connect the shifter cables to the gearbox are known to degrade and fail.	Replace shifter bushings with new OEM replacements or solid CNC machined aluminium

Automatic Transmission

Early W5A51 transmissions are prone to failure due to the wavesprings.

Planetary gearset pins are usually welded to prevent them moving.

Transfer Case

The transfer case uses a Viscous Coupling Unit (VCU) as the means of limiting the difference in wheel speed between the front and rear wheels. This "Viscous" coupling is the reason for the "VR4" nomenclature - literally "Viscous Realtime 4WD".

Note that the center differential is an open differential located inside the gearbox housing, but the VCU provides the mechanism of applying Limited Slip capabilities.

Reliability of the transfer case is fairly high, however it is possible to strip the ring and pinion gear through severe launches and general abuse.

Front Differential

The stock front differential is an open differential, located within the transfer case.

Rear Differential

The stock rear differential depends on the VR4 sub-model and year.

Sub Model	Rear Differential type
Type-V	Open Differential
Type-S	Active Yaw Control

Issues with AYC

The stock AYC differential in the VR4 is known to fail. This has been determined to be caused by weak castings for the differential housing. Your mileage may vary, but the risk of rear differential failure is high. A stronger rear differential is practically a requirement for high power applications.

Modifications

Front Differential

The front differential located in the transfer case can be replaced by a Limited Slip Differential. This is a highly recommended modification to improve power delivery and handling.

Any Evolution 4 to 6 LSD option will fit, however the OEM LSDs are known to break some of the screws and bolts that hold the LSD assembly together.

Rear Differential

The rear differential for the VR4 can be upgraded via a few options, depending on whether your car came with an AYC rear differential or not.

Rear Diff upgrade option	Details	Notes
Super AYC	The Super AYC differential from the Evolution 8 is a drop-in replacement (no tuning or electronics required) for the stock AYC differential. Only some spacers are required for mounting to the diff carrier, which could be made from a stack of washers (although a CNC machined aluminium spacer is recommended and available from TME).	If your VR4 was supplied from factory without AYC, upgrading to AYC is infeasible as there are multiple additional components required, including the AYC computer, the AYC sensors and potentially a replacement wiring harness. Super AYC increases differential strength and is able to apply more torque bias to each rear wheel.
Magna LSD	The LSD from the AWD Mitsubishi Magna or Diamante is a drop-in replacement, however you will also need the Magna inner CV joints. This LSD is a viscous LSD.	Drivers side spline as as second smaller spline to engage with the Viscous unit within the centre. Passenger side inner joint spline is shorter than the VR-4 spline. Need to put the Magna joints onto the VR-4 driveshafts + outer CV. Need to use the VR-4 diff cover on the magna diff case so mounting bolts will work with VR-4 subframe. Some others have used spacers and longer bolts.
Evo RS centre	This is an internal modification to the stock differential housing for the open diff.