Toyota Tundras have long had delusions of grandeur, until now that is. Previously they had a V-8 and were bigger than the mini-truck Tacoma, so Toyota called them a fullsize truck. Unfortunately, every-body else's fullsize was, well, much fuller, and though the Tundra was a quality product it was not quite up for the fight in the 1/2-ton market. Lately things have definitely changed with the new '07 Tundra. Toyota has stuffed a man-sized 5.7L V-8 under the hood with 400 lb-ft of torque, a six-speed automatic transmission underneath, and bolted a true fullsize body on top. On top of that, in the rear of this new heavy hauler resides an axle comparable to the rest of the market's 3/4- and 1-ton trucks.
We recently returned from a trip to Australia with ARB, and while there we got to work with some of the engineers who were examining the Tundra rear axle for a future Air Locker. We took the opportunity to tear into this big rear end and see if the guts are as burly as the package, and we were happy to find they are. This axle had us brainstorming about some creative new applications for custom housings and big drop-out-style third members.
The big rear axle under the new Tundra is a stamped-steel housing with a drop-out third member similar in design to every Toyota rear axle ever made, but much, much larger. This axle is produced through Toyota's medium-duty truck division Hino, so there is plenty of load-carrying-capacity engineering invested in it. This axle is the BD26B and is only available with the 5.7L V-8. A smaller 9.5-inch variant known as the BD24B is available with the 4.0L V-6 and the 4.7L V-8. The front independent axle is an 8.7-inch referred to as the SD22AD. | 
The semi-float design supports both the vehicle's weight and load as well as transmits rotational driving force to the wheels. This is pretty common for a 1/2-ton truck, but makes us wonder if a full-floating version is in the wings for a 3/4- and 1-ton truck. Here is one thing we're confused about. Why did Toyota use a new 5-on-150mm (5.9-inch) bolt pattern? Toyota 4x4 trucks have always been six-lug, so why go to fewer lugs for their biggest truck ever? The aftermarket choice of wheels for this Tundra is going to be rough we would assume. However, we do like the big 18-inch wheels on all the Tundra models because it means there are brakes so big underneath that nothing smaller would fit. | 
The Tundra diff is definitely big for a 1/2-ton and more comparable to a 3/4- or 1-ton as is seen here; (clockwise from upper left) Dana 80 1-ton, '07 Toyota Tundra 1/2-ton, pre-'07 Toyota Tundra, and GM Corporate 14-bolt 1-ton. A limited slip differential is standard in the Tundra, though we're excited that ARB is stepping up to develop a rear selectable Air Locker as well as an Old Man Emu 2 1/2-inch suspension and a front Bull Bar. Plus we've heard rumor of a supercharger coming from URD for the 5.7L V-8 so the accessories market is definitely addressing this new 1/2-ton. However, we would love to see lower gearing options and a fabricated housing from the rest of the aftermarket so this big gearset could be used as a custom front axle for a solid-axle swap under the Tundra. That would be really cool. |
The rear brakes for the Tundra use massive 13 9/16-inch rotors and single-piston calipers which support the nearly 14-inch front rotors with four-piston calipers. This is equivalent to the industry standard for 3/4- and 1-ton trucks. | 
We pulled the axleshafts and started counting splines and found 36 of them with an outside diameter of 1.457 inches. This is comparable in diameter to a GM Corporate 14-bolt (1.5-inch) and in spline count to some Dana 60s and 70s (35-spline). | 
The axleshaft, brake backing plate, and outer bearing are held in place with four bolts. Many Toyota axles use a solid-state tone ring for each wheel speed sensor and the Tundra is no different. These rings look like an axle seal, but are actually embedded with magnets that allow the speed sensor to know how fast the wheel is turning and which direction, and are helpful for both antilock braking systems and traction control. Also note how large the axleshaft is at the bearing where it supports the weight of the truck. From there it gradually necks down to the splines. |
The massive 10.5-inch Tundra rear ring gear, comparable to a 14-bolt or Dana 70. The big axles were offered with both 4.10 and 4.30 ring-and-pinions. Since most are found with the tow package, the majority will be 4.30:1. The smaller 9.5-inch diff is available with 4.10 and 3.90 gears, again the lower with the tow package. We like that this low-pinion axle is not extremely low like a 14-bolt or a Ford 9-inch. This results in a higher rear driveshaft, less heat created by the gear engagement, but slightly less pinion-to-ring-gear-teeth engagement due to less hypoid drop. |  | |