Can I Drive On a Broken Birfield?

Also see:

• All About Stock Toyota Birfields
• Toyota Birfield Upgrades: All About Chromoly, 30 Splines, and Fit For Minis, Pickups, 4Runners, and Land Cruisers

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Birfields are the definite weak point of Toyota solid front axles. If you break one you should stop and change it immediately if possible to prevent other parts from being mangled and to keep your steering from binding up from the broken pieces floating around inside your enclosed knuckle. 


Why Do Birfields Break?

Birfield axles break because of weak Birfield bells in extreme turns and inner axle shafts necking down to 27 splines.


Birfields usually break at the bell. This seems to almost always occur at extreme angles, meaning you've got the steering wheel cranked all the way over to one side. At this extreme angle the bearings inside the joint are distributed like this: Some are positioned inside the bell and some are close to the edge of the bell at its weakest point. Add some larger tires and low gears, and you'll easily shatter the bell at the weak little pressure point you've created. This was the most common failure point for Birfields until people started reinforcing them with rings, then making them out of chromoly.


Once everyone installed new chromo Birfields (AKA the outer stub axle), everyone started breaking inner axle shafts where they neck down to enter the Birfield. A typical Toyota shaft starts at 30 splines at the carrier, reduces in diameter and splines to 27 splines in the Birfield joint, then increases back to 30 splines at the hub. So next came 30 spline chromoly inner axle shafts.

With a full 30 spline axle shaft made of chromoly, Toy wheelers added more horsepower and bigger tires so that they could destroy Birfield joint internals and then inner axles shafts again. So now you can get full 30 spline Toyota chromoly axle sets with 300M inner axles and 300M inner races.


How Can I Keep My Birfields From Breaking?

If you want to keep any Birfield from breaking (stock or aftermarket) make sure that your steering stops are properly adjusted and that your steering stops aren't mashed to ineffectiveness. If your Birfields effectively function as your steering stops you've got two problems in an extreme turn:

1. The bearings near the center of the bell can run out of race and bind.
   
2. The bearings near the edge of the bell are even nearer to the edge than they should be.
   

We'd suggest jacking up the front of your rig and turning your front tires all the way to the left and spinning each side with the hubs engaged. If you detect funny noises, see that the stops aren't contacting the knuckles, or suspect binding, adjust the stops out until everything seems okay. Then turn the wheel all the way to the right and repeat the process. While you're in there, save your knuckle studs and torque them.

Can I Drive on a Broken Birfield?

No. The problem is that the Birfield joint is contained in the enclosed knuckle housing. If you break parts, there is nowhere for them to go except spin around and grind other stuff to pieces. Driving with broken Birfield pieces can also cause your steering to bind up. Suddenly not being able to turn your wheels is, ahem, a large problem. What's worse, you could end up jamming parts together, making it even harder to disassemble when you finally go to repair it. It doesn't take much to wreck parts - a couple hundred feet could easily do it.

What kind of stuff can you wreck ? How about the trunion bearings, the inner axle seal, and sometimes even the spindle, locking hub, and wheel bearings. It'll also gouge the inside of the knuckle housing which may or may not require some deburring depending on where the damage is.

If you were in an emergency situation, you could unlock your locking hub and attempt to drive out in three wheel drive (assuming lockers). However, your inner axle shaft will continue to spin - if the star is intact it'll keep wreaking havoc. You could also put it in two wheel drive which will prevent your inner axle or outer axle from spinning. But in both the 3WD and the 2WD scenarios, you still need to worry about your steering binding up. We suggest moving the minimum distance in 2WD if possible and immediately removing the broken parts.


At the very least, you can remove all your broken Birfield axle parts and still drive out in 3WD.