Technical Info

"What the heck was that popping sound?" exclaimed the driver of the newly lifted and locked Samurai with 31's. Balanced on a series of large boulders, the driver began backing up to try and get a better angle for tackling the obstacle. A knobby Thornbird on the front of the vehicle clawed at the rocks as it rose into the wheel well. Grabbing hold of the inside of the fender as the truck inched backwards, the soft rubber of the tire sucked itself into the contour of the wheel well. A series of loud metallic snaps were heard. A few bystanders knew what happened but only one brave soul stepped forward to tell the driver the bad news.

"Hey Buddy, I think you just finished off a Birfield!"

What is that darn Birfield anyway?

If SJ series Suzuki's are a new venture to you, you might have heard warnings about the Birfields and how they are a weak link in the drive train. These weak links are the two steering joints located on the front axles. On your typical Jeep, be it an old Flat Fender or a modern Wrangler, a small u-joint is used. Suzukis, along with Land Rovers, Land Cruisers, Subarus and other foreign four-wheel-drive vehicles use a different kind of joint that is protected from the elements and provides a tighter tuning radius. While this joint is an excellent, strong design for stock SJ series Suzukis and is easy to maintain and replace, it has proven to be the weak link in the driveline when bigger tires and lockers are added to a trail rig.

I've never broken a Birfield

It is possible to have a good wheeling career without breaking a Birfield joint. The stock axels and gears are very strong. One of my Zuki buddies has 33's on his Samurai and could not understand what all the fuss was about people breaking drive train parts. One day he went to Moab in his Samurai and broke just about every moving part in his axles at some time in his trip.

Why was this? A samurai with 33 inch tires is running on a tire that is around 25% larger than that of a stock samurai. Add crawling gears and that is a lot of stress on the driveline. Our Zuki buddy's rig had spent years playing in mud and on loose surfaces. The driver and truck had never experienced the added grip while rock-crawling, which is completely different to the mud slinging fun some off-roaders are used to. The gentleman in question had a well-built rig with all the flex that he needed for flinging mud. He had built his truck for mud and his driving experience was mud, not rocks. The added traction on the Moab slickrock proved to be too much for the way he had his rig set up.

Why and how do Birfields break?

It is possible to have a very capable Samurai where the occasional broken Birfield is not considered a big deal. In fact, breaking the Birfield is far less traumatic than breaking the ring and pinion. The Birfield could be considered the "fuse" that protects the ring and pinion. But if the rig of your dreams is constantly breaking Birfields, it might be time to look at changing your set up.

People usually break a Birfield when backing up over a tough obstacle. I've done it myself. Usually the wheel is cranked hard and somewhat jammed aainst a rock or a surface that has a lot of grip. Keep in mind that depending on what gearing you have in your axles, the Birfield joints and axles have 3.73 (or greater) times the torque than the u-joints of the front and rear drive shafts. When driving in reverse, the front tires have more grip as the vehicle's weight is transferred to the front. On top of this, when the front wheels are turned the strength of the Birfield joint is reduced.

Having a locker up in the front differential is also a big culprit. A locked differential means that if one front wheel is turning, the other one must also turn. If one wheel is stuck hard on an obstacle, something in the driveline must give, and that give is usually at the Birfield joint.

Body rub is also a cause in blowing Birfields. It is hard to imagine that some simple body rub would put so much stress on the driveline, but it's true. Throw in a front locker mixed with a good dose of body rub and I guarantee the Birfield will go soon. Why is this? With the exception of up and down movement from the springs, the axles and wheels never deviate from their position in relation to the body. When the wheel contacts the body, it is in actuality trying to drive up and over the body, which is physically impossible. I have found that when one part is trying to overcome the impossible, something usually fails. The failure here has to be somewhere in the driveline, and that point is thankfully, most often, at the Birfield instead of the ring and pinion.

Another time a Birfield can break is in jumping the truck. If the front axle is off the ground and the engine is spinning the front tires, when those tires hit the ground, the stress can blow the Birfields. The way to avoid this is to disengage the clutch before the front wheels hit the ground, helping to relieve the tension in the driveline.

How do you live with Birfields?

A variety of things can be done to minimize Birfield breakage, much of which relies on how and to what extent your rig is to be modified. The biggest key to not breaking Birfields would be to not have them. Some people don't mind the extra weight and expense of having custom made Dana axles under their rigs, eliminating the Birfield joints. For those who want to stay with light weight, relatively inexpensive Suzuki parts, there are upgrades to stronger components to compensate for larger tires and lower gears.

First off, let's figure out what type of four-wheeling is going to be done. While it is nice to have big meats underneath a trail rig, it is not always necessary for a Samurai. If back-country roads and the occasional winter trip to the snow is all your Suzuki will ever see, 31x10.50 tires will never do you wrong. If there is mud in your future, wide Mud Terrains and a locker or limited slip differential in the rear are a must. For rock crawling, big soft tires and low gearing are the favorite.

Since the big tires and low gearing of the rock crawling rigs is where the most Birfield stress occurs, this is where we will concentrate. To help save your Birfields and reduce driveline stress, the first decision to be made is: Does it make sense for you to have a Locker in the front differential?

It has been years since I decided that a rear locker was not for me. My Samurai is my daily driver and I did not want the harshness that came with driving around on a rear locker. So, to get the added traction I desired, the locker went in the front of my Samurai. Because of this, my front end spends a lot more time and energy keeping the rear end in line. This added stress means it is necessary to carry extra front axles with me as replacements.

While it was nice to have the open rear end for on-road driving, I was missing the total traction of a rear locker. The ultimate set up would be an air-locker in the rear (like the ones made by ARB), and a limited slip differential in front. This would be a very trail-worthy and street friendly set up, but the ARB is expensive and no one makes a front LSD.

So dreaming aside, the next best thing would be to have an ARB or KAM type differential at each end. That way, if a tire was stuck hard, it would be possible to unlock the differential to try and save the axles. Unfortunately, this is too expensive for most people.

Another idea is to do the opposite of what I did, and keep the front differential open and put a locker in the rear. That way the rear does a majority of the work, and keeps the Birfields stress free. This is a very cheap option, costing just the price of a locker and installation.

For those who must have a locker in front, like myself, there are a couple of new items available. There are three companies that are now making a reinforcing ring for Suzuki Birfield joints. The original Spidertrax Birfield Ring is machined to very tight tolerances then pressed on over the exterior of the Birfield making for a greatly strengthened axle. (see the Feb. issue for an ORC review of the Spidertrax Birfield Rings)

A business in Medford, Oregon has developed a swap that uses larger Subaru Birfield joints, larger axle shafts and larger side gears. This is where dreams come true, because Trail Tough designs this set up to use the rear side gears, and now the rear limited slip differential can be used in the front axle. This is great because the LSD allows for some slippage, which puts a lot less stress on the drive-train.

Even though these strengthening products and upgrades are great, they can still break, or redirect the breakage to the ring and pinion or axle shafts. Because of this it is still important to reduce the stress on the front end. This can be achieved in a number of ways: 

First, minimize that tire and body rub problem. Taller springs, shackles or a body lift might be necessary to fit the tires you want. Second, keep that front end from working so hard and get some sort of locker in the rear. Last, keep the traction shifted more to the rear tires by airing the rear down more than the front when on the trail. If this starts causing you rear axle breakage, it might then be time to upgrade the rear axle on your extreme machine. (Check out next month's issue for a great rear axle upgrade!)

Happy wheeling!

--Adam Leach