Vented brake rotors and upgraded...
Vented brake rotors and upgraded calipers are available from Marlin Crawler and provide a significant increase in braking power and fade resistance.
Brake Upgrades
The factory brake calipers and solid rotors only do a marginal job of stopping small stock tires, so when you add more weight and leverage they are really overwhelmed. Vented rotors from an '81-or-later FJ40 can be used in conjunction with calipers from an IFS pickup for improved braking force and less fade. The later V6 calipers had larger pistons that provide more braking force than the earlier IFS calipers.
All-Pro D60 Hybrid
Many of the aforementioned upgrades have been bundled into one beefy axle from All-Pro Off-Road.
All-Pro replaces everything from the knuckles out with 1-ton components. The company's hybrid axle features F-450 U-joints, bearings, and hubs with Wilwood calipers and rotors that provide increased stopping for large tires. The brakes fit under 15-inch wheels and even retain the stock 6x5.5 bolt pattern.
High-Pinion Third Members
FJ80 Land Cruisers used a front third member that is interchangeable with the solid axles found in pickups and 4Runners. The Land Cruisers used a high-pinion third member with a reverse-cut ring-and-pinion that is stronger than the low-pinion third member used in stock front axles and which offers 4 inches more ground clearance for your driveshaft and pinion flange.
The factory third member in...
The factory third member in the front of mini-trucks and 4Runners uses the same low-pinion third member as the rear axle. The low-pinion can cause the driveshaft U-joints to bind with large lifts or extremely flexible suspensions.
Axle Truss
Large tires increase leverage, which can result in bent axlehousings, particularly if the vehicle is jumped. All-Pro Off-Road sells a truss that can be welded to the top of your axlehousing for improved rigidity with no loss of ground clearance.
Stock Rear Axle
Toyota used a solid rear axle with an 8-inch ring gear and 1-5/16-inch 30-spline axleshafts exclusively through '95, and even later in some Tacomas, T100s, and 4Runners. Early axles were 55 inches wide to match the front solid axle and increased by 3 inches when the switch to IFS was made in 1986. With the added width in '86, the axletubes grew larger and the brake drums were also enlarged from 10 inches to 11.6 inches. All pickups and '89-and-earlier 4Runners used leaf springs, while later 4Runners used a four-link and coil-spring suspension, making these axles more difficult to retrofit into other vehicles.
Rear Axle Upgrades
V6 Third Members
The third member from a V6 or 22RTE turbo-powered truck bolts directly in place of the standard four-cylinder third members yet is stronger due to the four spider gears, larger ring-and-pinion, larger bearings, and stiffer third-member housing.
Upgraded Axleshafts
Poly Performance offers upgraded axleshafts made from 4340 chrome-moly. The shafts accept stock bearings and brakes and use rolled splines and a tapered design for maximum strength.
 Toyota rear axles are incredibly...  Toyota rear axles are incredibly strong for their size. We have witnessed many owners successfully running 39-inch-tall tires on these axles. |  Poly Performance's chrome-moly...  Poly Performance's chrome-moly rear axleshafts feature rolled splines and are tapered to allow increased torsional loads. | |