Solid Rearend Upgrade

http://home.4x4wire.com/erik/diffs/

Brief Toyota 4x4 history/definition of terms (for North America):

• "First genereation" 4Runners are '84-89, 2nd gen are '90-95, 3rd gen are '96-03, and 4th gen are '03-up.
  
  
• "Mini-trucks" are Toyota pickups prior to the '95.5 model year change to the "Tacoma."
  
  
• The "mini-trucks" are also known as the "Hilux" in other parts of the world.
  

Toyota Axle Widths:
(all widths are measured wms-wms, wms=wheel mounting surface)

* '79-85 front axle~ 55.5", rear axle~ 55"

The 4cyl 8" diff:

• All pre-'95 4-cylinder 4wd mini-trucks & 4Runners use the Toyota 8" 2-pinion differential front and rear (except turbo models). This is known as the "4cyl diff." This diff is by far the most common diff in older Toyotas.
  
  
• Ten 10mm ring gear bolts, 27 spline pinion shaft.
  

The V6/Turbo 8" diff:

• 4cyl Turbo and V6* 4Runners and mini-trucks use the Toyota 8" 4-pinion differential in the rear. This diff is known as the "V6/Turbo diff." It has larger carrier bearings, is generally stronger than the standard 4cyl version, and is a direct swap into axles that use the 4cyl 8" diff. Separate gear sets are made for the V6 style diff (only from Toyota and Precision Gear), but cheaper, more readily available 4cyl style gears are commonly made to fit- the only difference being a very slightly larger pinion gear on the V6 style gear (the actual strength difference in gear sets is debatable). The strength increase in this diff over the 4cyl diff comes mainly from the beefed up housing, which stiffens the entire assembly, keeping the gears in proper (stronger) alignment.
  
  
  
• Although somewhat rare, there is a version of this diff that came from the factory with 4.88 gears. The carrier (3rd member housing) has a different pinion offset so that the ring gear doesn't need to be as thick. This means that no gears other than the factory 4.88's will fit this particular diff. However, diff cases, commonly called carriers (factory, LSD, lockers, etc.), for the standard V6/Turbo diff should be interchangeable (4cyl and V6/Turbo carriers are NOT interchangeable).
  
  
• A few V6 trucks and 4runners have been found to have come with the 4cyl style diff from the factory. Nobody knows why.
  
  
• Ten 10mm ring gear bolts, 27 spline pinion shaft.
  

Axle Housing Identification

• 4cyl/V6/E-locker has a dome-shaped cover.
  
• T100/Tundra has deeper, blocky cover to accomodate the bearing truss.
  

Diff Housing (3rd member) Identification:




4cyl has 3 ribs on each side. V6/Turbo has 4 ribs on each side and the trapezoid shaped top rib.

Note- Starting in about '96, the V6 diffs started using a casting that looks nearly the same as the T100/Tundra casting from the outside. However, it doesn't have the trussed bearing cap on the inside, and the outside uses the smaller 8mm mounting studs.

Retrofitting a Supra LSD in a V6 8" Axle

http://www.4x4wire.com/toyota/tech/supra_lsd/

By: Frank Falcone. 10/2002

Editor's Note: The following was taken from the 4x4Wire Trailtalk Forums. After running a welded carrier on his daily driven 4Runner, Frank started looking for an inexpensive alternative that would offer increased traction over an open differential without the handling quirks of the welded carrier.

The 1986.5-1992 MKIII Supras were equipped with an 8" differential housed in an independent rear suspension (IRS). Most turbocharged Supra models of this generation should have the limited slip differential (LSD), the naturally aspirated Supras only got the LSD with the Sport Package.

The assembled carrier in the third member:


The Supra rear third member isn't a �drop-in� affair because it is laid out a differently (IRS vs. straight axle). The carriers, however, are transplantable. The Supra carrier uses a four pinion design, just like the rear axle in V6 equipped pickups. The Supra carrier will only retrofit into the V6 third member, not the more common 4 cylinder third member. Although I did not do this, it would be a good idea to replace the carrier bearings at this time too, since you have everything apart.

Installation

The carrier setup is in every way identical to any other with one exception, you install one of the bearings from your old carrier onto the loaded side (opposite the ring gear teeth) of the carrier. On the other side, just leave the original Supra bearing, which is smaller and allows more clearance for the preload adjuster. Use both of the 8" outer races from your existing third member, as the pickup axle races are narrower than the Supra races.

It should be noted that it is difficult to get many threads on the unloaded side. Given the narrower Supra bearing, having someone take off .030" or so from the outter race with a lathe could remedy this, as well as the issue described below. This may or may not need to be done depending on the tolerances of your differential. In my case it necessary to make a little more room in the axle housing opening in order to squeeze the third member back in. Basically, just grind conservatively where the protruding adjuster hits. You don't need to grind much, .010-.020 inch tops.

Untouched, mini-truck race:


Clearanced race to fit the carrier.


As the last step, each axle shaft needs to be shortened by 1/8 inch. If equipped with a bench mounted grinder, as illustrated in the photo, it is possible to take each one down in about 5 minutes a piece. Just put the axle against the wheel and turn one of the lug nuts.


Grinding the axle shafts down:


Compared to the welded rear differential in my 4Runner previously, this thing drives like a dream. It almost seems weird to just turn a corner, no big production, no chirping/bucking, just turning. Now if I get on the throttle, the inner tire will start to make some noise but not in that squeely open diff way. You can tell the limited slip is working.



UPDATE: 1/25/03

I recently disassembled my rear third member and decided to further investigate the inner workings of the Supra limited slip. In the center is this spring. It pushes the outside gears (that attach to the axles) against the inside of the carrier with the clutches inbetween. If there is slippage, an axle spins faster or slower than the carrier and friction transfers torque.

It should be noted that because of the way spider and ring gears are shaped they not only try to turn one another, but they also push themselves away from one another because of the tooth tapper. That means that as torque increases, the spider gears start to spread and push harder against the clutches. So it seems that these clutch type LSD's are also "torque sensing" in that they do apply more friction and therefore torque transfer as loads increase. Operating under this theory, brake biasing should work with the Supra LSD and provide some torque even if a wheel is off the ground. This is not true for other limited slip differentials such as the Truetrac.

I also shimmed the differential for more preload. This proved to be very easy. Just pull it apart and identify where the spring is and where the washer goes. I drilled out a washer to shim my shpring to 0.25", but there is enough room to shim further. Perhaps as far as 0.4".