Toyota Land Cruiser FJ80 and FZJ80 Chromoly Birfield Axle Guide and Comparison

How do you prep the fattest, heaviest Land Cruiser for the trails? After you've built your 80, filled it with gas and supplies, and people, it's going to be approaching 7000 lbs! If you're hitting hard enough trails, you're going to start worrying about how the stock drivetrain will hold up, especially the Birfields. Here are the specs on all the available chromoly axle kits and the vital info on installing them in an 80.
Table of Contents

There are two things 80 Series Land Cruisers are good for: luxurious backcountry travel and scavenging axles and diffs for solid axle swaps. There are tons of used 80s out there and a huge aftermarket of parts. If you have an 80, you may have noticed it gaining weight. This is inevitable - the 80 platform is well-suited for expeditions but needs to be kitted out if you're going to live out of it and explore far away places. And so we come to the Birfields. The more your 80 weighs, the bigger your tires, and the tougher the trails you're on, the more likely you are to break a Birfield.

The solution is easy: chromoly Birfields. Well, actually, it's not that simple! Things are a little more complicated for the 80 since it has full-time 4WD and chromoly is softer than stock. But we're getting ahead of ourselves. So, first we'll talk a little about the stock axles, axle upgrades, then how to deal with the full-time 4WD issue.

Toyota Land Cruiser FJ80 Axle Basics

The FJ80 front axle is the largest easily available solid front axle that Toyota produced. It came stock in 1991-1997 FJ80 and FZJ80 Land Cruisers. They have coil spring suspension and are the widest Toyota solid axle you can get. Some of them came with a reverse-cut, high pinion, electric locking differential. These axles also have the largest Birfields of the Land Cruiser line. They have two drawbacks that you can fix with aftermarket parts:

  1. Full-time 4WD: We'll concede that for some people, this is extremely desirable. However, the full-time system wears out front end parts more quickly and gives you fewer options while fourwheeling without a 2WD option. More on this below.
  2. Low-steer: Every other Toyota axle has had several high steer options available for years, but due to the knuckle design, high steer was impossible. That is, until HellFire Fabworks designed a new, stronger high steer knuckle and steering arm.

SAS Swaps with FJ80 Axles

The FJ80 axle is probably the ideal axle to do a SAS on Tacomas, 4Runners, and early Toy pickups. Here's why:

  1. It's wide. It's around 63.5" wide WMS to WMS without any hub trickery, spacers, or aftermarket kits.
  2. It's strong. The Birfields are the largest of the Toyota line.
  3. Has a high clearance, high pinion 8" differential that takes a standard 8" carrier.
  4. Some have an electric locker.
  5. Plenty of aftermarket parts.

But it's not all pretty. Even with lots of fab skills, these can be expensive to build. Toyota mini trucks are all over the place, but 80s just aren't as plentiful or as frequently built, so parts are more expensive. If you throw this under a Tacoma and run leaf springs, you have a lot of coil spring brackets to cut off!

And yes, we know that calling is a SAS Swap is redundant, because it's like saying solid axle swap swap. But whatever.

What Makes a Strong Birfield?

There are three characteristics that'll make your front axleshafts stronger. They are materials, spline count, and heat treatment. We don't look at diameter separately because an increase in spline count automatically gives you a larger diameter.

Toyota Land Cruiser FJ80 Axle Spline Counts

If you want to know about stock Toyota Birfields, spline counts, how the parts go together, and more, check out our article on Toyota Birfield axles. If you want the quick version, here it is:

There has been 1 stock spline count configuration for FJ80s. Starting from the hub side it is:

30 spline hub - 24 spline Birfield joint - 30 spline inner axle

This is known as a 24 spline axle.

Aftermarket Birfields come in 2 spline configurations:

  1. 30 spline hub - 24 spline Birfield joint - 30 spline inner axle
  2. 30 spline hub - 30 spline Birfield joint - 30 spline inner axle

The first option is known as a 24 spline axle and the second is known as a 30 spline axle. We differentiate between the two only on the number of splines inside the Birfield joint. There are no factory Toyota 30 spline axles. They are all 24 spline.

30 spline axles are stronger than 24 spline axles. Generally this has to do with the mechanical properties of splines and the fact that shaft diameter increases with spline count.  For the most part certain diameter shafts have certain spline counts. However, 80 axles have an unconventional "large" 24 spline inner joint. These splines are probably cut to achieve their pattern on the axleshaft. Chromoly 30 spline axles will all have rolled splines that are stronger because of the manufacturing process. If you buy a 30 spline chromoly axle, it'll be stronger than a 24 spline chromoly axle.

Toyota Birfield Materials - Stock, 4340 Chromoly, and 300M

Aftermarket Birfields come in two materials, stock-like and 4340 chromoly. We're not going to discuss the stock-like replacement Birfields. You can get a stock replacement for your 80 which has more hardening than chromoly, but which also makes it more prone to breakage.

If you're buying a Birfield and you want chromoly, make sure it actually says "chromoly" somewhere in the description. We've heard of a few people that bought new Birfs who thought they were getting chromoly just because it was an aftermarket Birfield. This is not the case. An aftermarket Birfield that is not made with chromoly is not any stronger than stock.

All upgraded Toyota Birfield axles are all made with 4340 chromoly at a minimum. This means that the Birfield, inner axle, and inner bearing assembly are all made of chromoly. For most of us, this is strong enough.

One really important idea to keep in mind is that by strengthening one part, we are moving the failure point to a new location. Yes, the old failure point is stronger, but eventually we may move the failure point to a location that's more difficult to repair on the trail. Think about that idea during the next couple of paragraphs.

The next level in strength is to use 300M. 300M is stronger than chromoly. Now you might think that there would be 300M Birfields, but there aren't. Chromo Birfields seem to hold up pretty well, but the inner race and the inner axle become the next failure points. Both of these can be made of 300M.

Beyond these materials, you're looking at swapping in 1 tons! Once you've swapped in a chromo Birfield with a 300M inner axle, you'll start destroying the splines at the carrier. This is way more difficult to swap on the trail than a Birfield or an inner. Perhaps this is why we see the occasional Dana 60 center with Toy outers?

So, to recap, 300M is stronger than 4340 chromoly which is stronger than stock axle material.

Axle Heat Treatment

There isn't much to say about this except that more heat treatment is better than less heat treatment. Some aftermarket axles have a single heat treatment and some have a double heat treatment.

The Strongest Birfield Axle

The strongest and best Birfield you could buy would be a 30 spline axle with a 4340 chromoly Birfield and a 300M inner axle. There is currently only one kit with these characteristics made by RCV.

Chromoly Birfield Issues for FJ80s

There are a couple of annoying issues with swapping in chromos in your 80. Here they are:

The Birfield Length Changed

FJ80 Longfield with Double Snap Ring Grooves
All the available aftermarket FJ80 axles come with double grooves in the outer axle for different drive flange and locking hubs. Outer axles are always the later FJ80 "long" version.

In April of 1994, FJ80 Birfields changed in length from 246mm to 251mm. Since 80s have full time 4WD, they use drive flanges on the end of the axle shaft. Because there are two different length Birfields, there are also two different sizes of drive flange.

The early drive flanges are known to be a weak point and wear out more quickly than the later flanges. The later flanges plus longer Birfields have more spline engagement and are thus stronger than the early short Birfields and drive flanges. If you want to run chromoly Birfields on a pre-April 1994 FJ80 with drive flanges, you need the later, longer drive flanges. These are Toyota PN 43421-60040. If you have a post-April 1994 80 Series chromos will drop right in.

All aftermarket chromoly Birfields come in the long version and have dual snap ring grooves machined in the end. With these grooves you can use drive flanges or locking hubs.

Chromoly FJ80 Axles with ABS

If you want to keep your ABS working, you need ABS tone rings on your Birfields. The tone rings provide the signals that your ABS system needs to function and must be attached to a Birfield and spinning in order to work. ABS will not work if you install a part time 4WD kit because the Birfields will not spin and provide a signal.

Trail-Gear includes ABS tone rings with their Longfields kits. With other manufacturers you'll have to remove the ABS tone rings from your stock Birfields and press them on to your new axles in order to have functional ABS. If you don’t do this, your ABS will not work, and your ABS light will come on.

How to Remove the Tone Ring

You can remove the ring from the old Birfield by first putting the axle in a vice, bell side up, to hold it securely. Wrap it in a rag to keep from marring it. Next, you can use a large brass drift (this is essentially just a short brass rod) and a big hammer to slowly and evenly knock the ring off. If you’ve never done something like this before, try hitting one side one or two times, then go to the opposite side and do the same. Continue working each side like this and the ring will move a small amount each time. Brass drifts are very useful for this type of work since they are softer than steel and will not mar it.

To get the ring back on, you can try the brass drift again. However, it will be easier to use a piece of pipe that is the approximate diameter of the ring and a little longer than the axle stub. Square up the ring on the Birfield, position the pipe on the ring and tap the end of the pipe until the ring seats.

FJ80s Are Full-Time 4WD and Chromoly Is Soft

Chromoly axles might not be for you. Because chromoly is softer than the stock axle material and 80s have full time 4WD, you’ll wear out your 4340 axles faster in an 80 than a typical mini, 4Runner, FJ40, etc. This can be solved easily with some cash, or you can leave it if it doesn't concern you. Here's what you can do:

  1. Install a part-time 4WD kit: This keeps your Birfields from spinning unless you need 4 wheel drive. You can get this at Slee Off Road, Advance Adapters, or just the transfer case spool at Trail-Gear. You basically need to install a spool in the transfer case and put part time hubs on the front. Check the end of this article for some more links about this conversion.
  2. Don’t worry about the wear: In many thousands of miles, once your axles start to click, you can buy a kit to replace the joint internals.
  3. Skip the chromos:  If you have a non-hardcore daily driver with less than 35” tires, you don't need chromoly axles. A daily driver might wear out chromoly Birfields in a couple of years, rather than the relatively long life of the stockers.

Just to reiterate an important point: You will lose ABS in 2WD with a part-time kit. Without the axles spinning, the tone rings can't send signals to the ABS system.

So, with excessive wear, if you do get the click with stock or aftermarket Birfs, you can try pumping your knuckle full of grease to quiet it. This is a temporary fix, but you won’t be driven insane by front axle Birfield clicking.

We’ve heard that there were some Birfields put out by Bobby Long that were heat-treated to cut down on wear on the joint, but we don’t know what generation these were or the specifics of the heat-treat process. Some of the below axles are also dual heat treated, so we'd like to know whether they're holding up any better than earlier versions.

Can I Use Mini Truck Locking Hubs on My FJ80?

Well, this article isn't about that, but you can. On the early short Birfields, the hubs will swap right on. The longer later shafts are too long and will hit the inside of the locking hub. However, since aftermarket chromoly axles have two grooves machined for snap rings, you can use the inside groove for the snap ring and trim the end of the shaft to fit inside the locking hub. This will void your warranty, so if you're worried about that you should just buy a full part-time kit with the correct hubs.

You should also be able to use a spacer to push the hub out and use the outer snap ring groove. We're not sure where to buy this in the US, but Mark's 4WD in Australia has spacers.

Toyota FJ80 Chromoly Birfield Axles

Below are the currently available Birfield sets for 80 Series Land Cruisers. There is a range of prices, materials, and characteristics. Although the images may not indicate it, all manufacturers say that their Birfields have dual grooves machined in the outer axle.

Trail-Gear FJ80 Longfield 24 Spline Birfield/Axle Kit - BUDGET CHROMOLY

Trail-Gear FJ80 Longfield 24 Spline Birfield/Axle Kit
These 24 spline Longfields give you a lot of bang for the buck and will probably be the least expensive chromos you can find for your 80.
Trail-Gear FJ80 Longfield 24 Spline Kit Specs
Hub splines 30
Inner bearing splines 24
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner race material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 251mm
Left inner axle length
Right inner axle length
Greasable Yes
Gun-drilled Birfield Yes
Heat treatment Dual
Dual snap ring grooves Yes
Trail-Gear FJ80 Longfield 24 Spline Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
ABS tone rings 2
Dust caps 2

This is a great kit if you're doing a budget build on your 80. The axles are full chromoly with a 24 spline Birfield joint. Because the kit includes high-hat dust caps, you can use short drive flanges. However, we think you should still upgrade to the taller flanges to get more spline engagement. This kit also saves you from having to take off your old ABS tone rings by including new ones. Longfields are also the only chromos for 80s that are gun-drilled for zerk fittings. This make maintenance super easy - just pop off your hubs or dust caps and pump 5-6 shots of grease in with a grease gun.

Trail-Gear FJ80 Longfield 30 Spline Birfield/Axle Super Set - BUDGET 30 SPLINE CHROMOLY AXLES

Trail-Gear FJ80 Longfield 30 Spline Birfield/Axle Super Set
These dual heat treat, chromoly axles come with tone rings so you don't have to take your old ones off. 30 splines is definitely an upgrade from the stock 24.
Trail-Gear FJ80 Longfield 30 Spline Kit Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner race material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 251mm
Left inner axle length
Right inner axle length
Greasable Yes
Gun-drilled Birfield Yes
Heat treatment Dual
Dual snap ring grooves Yes
Trail-Gear FJ80 Longfield 30 Spline Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
ABS tone rings 2
Dust caps 2

This kit is only slightly more expensive than the 24 spline Longfields above, but they are 30 spline throughout. These are the strongest Longfields you can get for your 80. Like the 24s, you get high-hat dust caps, dual snap ring grooves, dual heat treatment, and ABS tone rings. They're also greasable through zerks in the end of the stub shaft and will be much stronger than stock!

RCV Ultimate 24 Spline Axle Set for Toyota Land Cruiser 80 Series

RCV Ultimate 24 Spline Axle Set for Toyota Land Cruiser 80 Series
These full chromoly axles are still plenty strong with the stock spline count.
RCV 24 Spline Axle Set for 80 Series Specs
Hub splines 30
Inner bearing splines 24
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner race material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 251mm
Left inner axle length 34.13"
Right inner axle length 17.75"
Greasable No
Gun-drilled Birfield No
Heat treatment
Dual snap ring grooves Yes
RCV 24 Spline Axle Set for 80 Series Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
ABS tone rings
Dust caps

This is RCV's entry-level axle set: it has 24 splines and is full chromoly with dual snap ring grooves.

Ultimate CV Axle Set for Land Cruiser 80 Series with 30 Spline Upgrade

Ultimate CV Axle Set for Land Cruiser 80 Series with 30 Spline Upgrade
Switching to 30 splines from the stock 24 splines makes these Birfs that much stronger in your 80 Series.
RCV 30 Spline Axle Set for 80 Series Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner race material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 251mm
Left inner axle length 34.13"
Right inner axle length 17.75"
Greasable No
Gun-drilled Birfield No
Heat treatment
Dual snap ring grooves Yes
RCV 30 Spline Axle Set for 80 Series Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
ABS tone rings
Dust caps

RCV's 30 spline axle is the next bump up in strength for your 80. It has full chromoly construction.

Ultimate CV Axle Set for Land Cruiser 80 Series with 30 Spline 300M Shaft Upgrade - STRONGEST

Ultimate CV Axle Set for Land Cruiser 80 Series with 30 Spline 300M Shaft Upgrade
These are probably the strongest Land Cruiser axles you can get. They have the largest Birfield dimensions, 30 splines, and full chromoly with 300M.
RCV 30 Spline Axle Set for 80 Series with 300M Inner Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner race material 4340 chromoly
Inner axle material 300M
Birfield length (outer axle) 251mm
Left inner axle length 34.13"
Right inner axle length 17.75"
Greasable No
Gun-drilled Birfield No
Heat treatment
Dual snap ring grooves Yes
RCV 30 Spline Axle Set for 80 Series with 300M Inner Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
ABS tone rings
Dust caps

With a 300M inner axleshaft and 4340 chromoly everywhere else, this is the strongest overall axle set you can buy for your FJ80. In fact, given the 80's large Birfield size, this might be the strongest axle set you can put in any solid axle Toyota. It is 30 spline.

Nitro Gear Toyota Land Cruiser FJ80 24 Spline Chromoly Birfield Front Axle Upgrade Kit

Nitro Gear Toyota Land Cruiser FJ80 24 Spline Chromoly Birfield Front Axle Upgrade Kit
Nitro Gear FJ80 24 Spline Chromoly Kit Specs
Hub splines 30
Inner bearing splines 24
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner race material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 251mm
Left inner axle length
Right inner axle length
Greasable No
Gun-drilled Birfield No
Heat treatment Single
Dual snap ring grooves Yes
Nitro Gear FJ80 24 Spline Chromoly Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
ABS tone rings
Dust caps

Nitro Gear's 24 spline Birfield axle sets are full 4340 chromoly.