Toyota Land Cruiser FJ40/FJ55/FJ70 Chromoly Birfield Axle Guide and Comparison

You finally broke a Birfield in your Land Cruiser! Or maybe you just want to NOT break a Birfield and you've discovered that you've got options that are way stronger than stock. But...the landscape is so murky when shopping around. Here's what to look for and also some vital information for 1979 and earlier Land Cruisers.
Table of Contents

Fortunately, the aftermarket has been working on making Birfields stronger for years. Now, the basic recipe is 4340 chromoly, heat-treating, and maybe some 300M thrown in for good measure.

But there are still a bunch of different options. It's totally confusing to try and sift through all the available options. You're not an aerospace engineer! What is all this chromoly/spline/zerk gobbledygook!?! And why didn't anyone tell you about your Land Cruiser's hubs?


Trail Gear longfields 30 spl axle set
Trail-Gear Longfield 30 Spline Birfield/Axle Kit for FJ40s, FJ55s, and FJ70s
These are straight-up chromo axles with a single heat treatment.

If you have an early Land Cruiser, you'll also have to swap some parts in order to run the chromoly Birfields that are manufactured today. Don't worry, it shouldn't be too painful! 

It's worth pointing out that there are two classes of upgrades available: "generic" axles and axles with upgrades. Frankly, we don't see a lot of difference in the generic chromoly axles, and neither should you. The "generics" area all pretty similar - you should differentiate them by price and warranty. However, the non-generics truly may have some advantages for you such as more strength and easier maintenance.

What Makes a Strong Birfield?

There are three main things to look at for better Birfields: spline count, materials, and heat treatment. Shaft diameter is a concern for 27 spline axles, but we assume that most people are going with 30 spline.

Toyota Land Cruiser 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 Birfields. If you want the quick version, here it is:

There have been 2 stock spline count configurations. Starting from the hub side they are:

  1. 6 spline hub - 27 spline Birfield joint - 30 spline inner axle : Early FJ40 and FJ55 Land Cruisers
  2. 30 spline hub - 27 spline Birfield joint - 30 spline inner axle : Later FJ40s, FJ55s, and FJ70s

Aftermarket Birfields come in 2 spline configurations:

  1. 30 spline hub - 27 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 27 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 27 spline (except for a very early Ball and Claw type).

30 spline axles are stronger than 27 spline axles. This has to do with the mechanical properties of splines and the fact that shaft diameter increases with spline count. While a factory inner axleshaft decreases in diameter as it enters the Birfield, an aftermarket 30 spline inner maintains a consistent outer diameter. If you buy a 30 spline chromoly axle, it'll be stronger than a 27 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 because if you need to replace a Birfield, you should just put in a used stock unit or a chromoly unit. It seems silly to bother buying a new stock -style Birfield when you can upgrade for a similar price.

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 bearing assembly 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 bearing and 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, a 300M inner bearing assembly, and a 300M inner axle. There is currently only one kit with these characteristics made by RCV.

Fitment Issues For Land Cruisers

Strangely enough, very few manufacturers mention that pre-1/'79 Land Cruisers require extra parts to fit an aftermarket Birfield. Like, there are pages that say, "Fits 1964-1984 FJ40", but don't mention the need for hub swappage. In any case, if you have an earlier Cruiser, you have a little extra work to do.

Fitment Issues for ‘58-9/75 Land Cruisers

These Cruisers either have a ball-and-claw (‘58-‘68) or a coarse drum brake axle (‘68-9/75). We’re not sure what a ball-and-claw requires, but you’ll probably need a full axle swap from a later Cruiser. If you have a drum brake axle, you’ll need to do a disc brake upgrade with 1/79+ live axle Cruiser/mini parts. This will get you the proper stub spline count and hub length.

Fitment Issues for 9/75-1/79 Land Cruisers

You’ll need 1/79-‘89 live axle Toyota hubs and hub dials from a Land Cruiser or mini with a live axle. The Birfield on the late 1970s axles was longer than later Birfields, which means that they have a “special” long locking hub.

Toyota FJ40, FJ55, and FJ70 Series Chromoly Birfield Axles

Here are your options for Birfields. We'll take a look at the offerings from each manufacturer, which ranges from a single Birfield up to a complete set of axle shafts with drive flanges and 4340 hub gears. If we found length and heat treat information, we included them. There are some small variances in lengths between different manufacturers. The standard Birfield (outer axle) measurement is 9.6" long.

Trail-Gear FJ40 Longfield 30 Spline Birfield/Axle Kit

Trail-Gear Longfield 30 Spline Birfield/Axle Kit for FJ40s, FJ55s, and FJ70s
These are straight-up chromo axles with a single heat treatment.
Trail-Gear FJ40 Longfield 30 Spline Kit Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 9.60"
Left inner axle length 28.94"
Right inner axle length 17.13"
Greasable No
Gun-drilled Birfield No
Heat treatment Single
Trail-Gear FJ40 Longfield 30 Spline Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal
Hub gears
Drive flanges

These Birfields from Trail-Gear are probably the least expensive chromoly Birfields that you can get. They don't have any fancy features, but they are a solid, full-chromoly Birf that is single heat treated. Trail-Gear says these are 76% stronger than stock so they're sufficient for any casual wheeler out there. If you need a bit more strength and easier maintenance, check out the Super Set below.

Trail-Gear FJ40 Longfield 30 Spline Birfield/Axle Super Set - DUAL HEAT TREAT, CHROMO HUB GEARS, CHROMO DRIVE FLANGES

Trail-Gear Longfield 30 Spline Birfield/Axle Super Set for FJ40s, FJ55s, and FJ70s
This is Trail-Gear's strongest offering, with double heat treatment, drive flanges, and chromoly hub gears included.
Trail-Gear Longfield 30 Spline Super Set Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 9.60"
Left inner axle length 28.94"
Right inner axle length 17.13"
Greasable Yes
Gun-drilled Birfield Yes
Heat treatment Dual
Trail-Gear Longfield 30 Spline Super Set Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal
Hub gears 2
Drive flanges 2

Trail-Gear's Super Set axles are not the same as their regular 30 spline axles. These are the only aftermarket axles that are double heat treated. They're gun-drilled and have an M8 zerk fitting on the end of the outer axle. This means that greasing the Birfield joint is as easy as popping off the hub or drive flange, attaching your grease gun, and pumping it 5-6 times. Trail-Gear says the Super Set is 102% stronger than stock. These axles also come standard with chromoly hub gears and chromoly drive flanges. Hub gears are a pretty typical upgrade, but we're not so sure about the drive flanges. We like to drive our rigs on the road, so we'd sell those on.

RCV Ultimate 30 Spline Axle Set for Toyota Land Cruiser 40, 55, and 70 Series - 300M BEARING ASSEMBLY

RCV Ultimate 30 Spline Axle Set for FJ40s, FJ55s, and FJ70s
The Birfields' inner bearings of this chromoly axle set are made of 300M. The outers are gun-drilled to facilitate easy greasing.
RCV Ultimate 30 Spline Axle Set Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 300M
Inner axle material 4340 chromoly
Birfield length (outer axle) 9.60"
Left inner axle length 28.94"
Right inner axle length 17.13"
Greasable Yes
Gun-drilled Birfield Yes
Heat treatment
RCV Ultimate 30 Spline Axle Set Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal
Hub gears
Drive flanges

RCV's Birfields are the first aftermarket Birfields that have 300M. These 30 spline axles have 300M bearing assemblies with chromoly Birfields and chromoly inner axles. They are gun-drilled so that they are easy to grease. RCV says that these axles are twice as strong as the stock 27 spliners.

Keep a lookout because RCV sometimes offers these with free chromoly hub gears.

RCV Ultimate 30 Spline Axle Set with 300M Inner Axle for Toyota Land Cruiser 40, 55, and 70 Series - STRONGEST - 300M INNER AXLE AND BEARING ASSEMBLY

RCV Ultimate 30 Spline Axle Set with 300M Inner Axle for FJ40s, FJ55s, and FJ70s
These axles have both a 300M inner bearing and a 300M inner axle shaft. They are the only Birfields axle sets with this much 300M.
RCV Ultimate 30 Spline Axle Set with 300M Inner Axle Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 300M
Inner axle material 300M
Birfield length (outer axle) 9.60"
Left inner axle length 28.94"
Right inner axle length 17.13"
Greasable Yes
Gun-drilled Birfield Yes
Heat treatment
RCV 30 Spline Axle Set with 300M Inner Axle Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal
Hub gears
Drive flanges

These axles are just like the above RCV axles except they have a 300M inner axle shaft! These are the strongest axles available for FJ40s, FJ55s, and FJ70s. They have 30 splines, chromoly outer axles, 300M bearings, and 300M inner axles. They don't come with other parts, but RCV often includes free chromoly hub gears.

The one little caveat with these axles is that you may be moving the "fuse" in your drivetrain to your differential, so keep that in mind. Stripping your carrier splines will be harder to repair on the trail than a broken inner axle shaft.

Marlin Crawler 27 Spline Chromoly Marfield

marlin crawler 27 spline birfield for fj40, fj55, and fj70
Marlin Crawler 27 Spline Chromoly Marfield for FJ40s, FJ55s, and FJ70s
Marlin Crawler 27 Spline Chromoly Marfield
Hub splines 30
Inner bearing splines 27
Differential splines
Birfield material (outer axle) 4340 chromoly
Inner bearing material
Inner axle material
Birfield length (outer axle) 9.60"
Left inner axle length
Right inner axle length
Greasable No
Gun-drilled Birfield No
Heat treatment Single

The first option available from Marlin Crawler is a 27 spline, chromoly Birfield. This outer axle comes with a chromoly inner bearing assembly and is made to work with your stock Toyota inner axle. We consider this a kind of "insurance" axle for vehicles that see light off road duty. The original upgraded Toyota axles were only strengthened and reinforced around the Birfield bell. This Birfield achieves the same kind of thing, protecting against exploding-bell syndrome.  EMPI, a Volkswagen part wholesaler, manufactures these for Marlin. A set of these is a fair bit less expensive than going full chromoly.

They are ever so slightly more complicated to install than an inner/outer axle combo since you have to separate your stock inner and outer axles. You'll likely break your inner axle snap rings during the separation, so make sure you pick up a new snap ring for each side.

Marlin Crawler 30 Spline Chromoly Axle Kit

marlin crawler 30 spline chromoly axle kit for fj40, fj55, and fj70
Marlin Crawler 30 Spline Chromoly Axle Kit for FJ40s, FJ55s, and FJ70s
Marlin Crawler 30 Spline Chromoly Axle Kit Specifications
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 9.60"
Left inner axle length
Right inner axle length
Greasable No
Gun-drilled Birfield No
Heat treatment Single
Marlin Chromoly Axle Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal 2
Hub gears
Drive flanges

For the next level of strength, Marlin Crawler offers a 30 spline chromoly axle kit. Like the 27 spline Marfield Birfield this axle set is manufactured by EMPI, a Volkswagen parts wholesaler. The axle parts are made of 4340 chromoly throughout and have a 30 spline inner bearing assembly.

It's always a good idea to replace your inner axle seals while you're in there and this kit makes it easier with the inclusion of two of Marlin Crawler's EcoSeal.

Nitro Gear Toyota 9.5” 30 Spline Chromoly Birfield Front Axle Upgrade Kit

Nitro Gear 30 Spline Chromoly Birfield Front Axle Upgrade Kit for FJ40s, FJ55s, and FJ70s
This is another set of straightforward chromoly axles.
Nitro 30 Spline Kit Specs
Hub splines 30
Inner bearing splines 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 9.60"
Left inner axle length
Right inner axle length
Greasable No
Gun-drilled Birfield No
Heat treatment Single
Nitro 30 Spline Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal
Hub gears
Drive flanges

The Nitro Axle and Gear are a set of full chromoly 4340 axleshafts. They have a single heat treatment and come in 30 spline.

G2 Toyota FJ40 and FJ55 Land Cruiser Birfield CV Style 27/30 Spline Chromoly Axle Kit

G2 30 Spline Chromoly Axle Kit for FJ40s, FJ55s, and FJ70s
G2 27/30 Spline Chromoly Axle Kit Specs
Hub splines 30
Inner bearing splines 27 or 30
Differential splines 30
Birfield material (outer axle) 4340 chromoly
Inner bearing material 4340 chromoly
Inner axle material 4340 chromoly
Birfield length (outer axle) 9.60"
Left inner axle length 28.94"
Right inner axle length 17.31"
Greasable No
Gun-drilled Birfield No
Heat treatment Single
G2 27/30 Spline Chromoly Axle Kit Contents
Birfield (outer axle) 2
Inner axle 2
Inner axle outer C-clip 2
Inner axle seal
Hub gears
Drive flanges

The G2 kit is a full chromoly axle kit for your 40, 55, or 70 series Land Cruiser. Most kits come only in a 30 spline version, but this kit comes in a both a 27 spline version and a 30 spline version. There is an argument to be made that 27 spline axles leave more material in the star (inner bearing race) inside the Birfield, thus making the star stronger, but we'll always go with a 30 spline. Unless you have funny requirements, you should also go with 30 spline.