Toyota Pickup and 4Runner Chromoly Birfield Axle Guide and Comparison

Also see:

• Toyota Birfield Upgrades: All About Chromoly, 30 Splines, and Fit For Minis, Pickups, 4Runners, and Land Cruisers
• Can I Drive On a Broken Birfield?

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Toyota pickups and 4Runners are the most popular Toyotas out on the trail. There is a crazy number of solid axle Toyota frontends out there. Besides the pickups and 4Runners that came stock with a solid front axle, tons of newer Toys run it in solid axle swaps (and don't forget all the non-Toys that are running them). The ubiquity of the axle is great for fourwheelers since it's made lots of upgrade options appear and driven prices down.


Of course, anyone doing a solid axle swap or just reading this article is probably interested in a few things particular to fourwheeling: bigger tires, more torque, and more traction. Unfortunately, all of these break Birfields. If you run tough trails, sooner or later you'll see a busted Birfield.

In the early years, there was a lot of experimentation to try and strengthen just the Birfield. Once that was achieved with a thicker bell and chromoly, other parts started to break. And that's how we've ended up with full axleshaft sets that are made of chromoly. Of course, the strength upgrades don't end there. Axles now come with or without some combination of 4340 chromoly, 300M, more splines, and heat treatment. We'll talk about all that below.


Toyota Pickup and 4Runner Axle Basics

We're going to talk about only the solid front axles found in ‘79-‘85 Toyota pickups and ‘84-‘85 4Runners. Fortunately for us, there are no differences between the axle shafts through the different years.


The outer axle, which we'll call the Birfield, is 9.6" long. The length and diameter of the outer axle is the same on the FJ60 and on aftermarket kits for all FJ40s and FJ60s. FJ80s have a larger, stronger Birfield and a wider WMS to WMS. On a side note, 80 Series axles make a good, wide SAS axle, but they expensive to build.


Stock Toyota pick and 4Runner axles are "27 spline". They have 30 splines at the hub, 27 at the Birfield joint, and 30 at the differential.

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 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 Toyota pickups and 4Runners. Starting from the hub side it is:

30 spline hub - 27 spline Birfield joint - 30 spline inner axle


This is known as a 27 spline axle.


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.

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

Toyota Pickup and 4Runner Chromoly Birfield Axles

Below are the currently available Birfield sets for Toy pickups and 4Runners. There is a wiiiiiide range of prices, materials, and characteristics. Some sets even include hub gears and more to eliminate some weak spots from your drivetrain.


You'll probably notice that some of these axle sets are just plain ol' chromoly without any sparkles and glitter. Until it can be proven otherwise, we think all these kits are pretty equivalent. If that's all you need, then take a look at the price and the warranty and see what works for you. If you need more strength and security, get something with more heat treat or 300M. A lubed Birfield will be happier, so also consider gun-drilled axles that can be easily serviced.


Trail-Gear Toyota Pickup and 4Runner Longfield 27 Spline Birfield/Axle Kit - 27 SPLINE BUDGET LONGFIELDS



Toyota Pickup and 4Runner Longfield 27 Spline Kit Specs

Hub splines	30
Inner bearing splines	27
Differential splines	30
Birfield material (outer axle)	4340 chromoly
Inner race material	4340 chromoly
Inner axle material	4340 chromoly
Birfield length (outer axle)	9.60"
Left inner axle length	31.44"
Right inner axle length	15.44"
Greasable	No
Gun-drilled Birfield	No
Heat treatment	Dual

Toyota Pickup and 4Runner Longfield 27 Spline Kit Contents

Birfield (outer axle)	2
Inner axle	2
Inner axle outer C-clip	2
Inner axle seal
Hub gears
Drive flanges

These are probably the cheapest chromoly axles you can buy. They are a little like the early Birfield improvements in that they have a 27 spline outer and are made of chromoly. While we would have lumped them in with the 30 spline budget Longfields, we didn't. Why? It's because these are also dual heat treated. They're still not as strong as the single heat treat 30 splines, but they're definitely stronger than stock. Trail-Gear says they are 41% stronger than stock.


Check price on Amazon

Trail-Gear Toyota Pickup and 4Runner Longfield 30 Spline Birfield/Axle Kit - BUDGET 30 SPLINE LONGFIELDS



Toyota Pickup and 4Runner 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)	9.60"
Left inner axle length	31.44"
Right inner axle length	15.44"
Greasable	No
Gun-drilled Birfield	No
Heat treatment	Single

Toyota Pickup and 4Runner 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 are like the budget partners of the 27 spline Longfields above. However, they have a single heat treat instead. Trail-Gear says they are 76% stronger than stock. These are a perfect axle for budget builds. If you think you need something stronger or easier to grease, keep reading.


Trail-Gear Toyota Pickup and 4Runner Longfield 30 Spline Birfield/Axle Super Set - CHROMOLY AND DUAL HEAT TREAT WITH HUB GEARS AND DRIVE FLANGES



Toyota Pickup and 4Runner Longfield Super Set 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)	9.60"
Left inner axle length	31.44"
Right inner axle length	15.44"
Greasable	Yes
Gun-drilled Birfield	Yes
Heat treatment	Dual

Toyota Pickup and 4Runner Longfield 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

The Longfield Super Set is Trail-Gear's strongest offering. They say these axles are 102% stronger than stock with full chromoly and 30 splines. They're dual heat treated for more strength. Each Birfield is gun-drilled and comes with an M8 zerk fitting so you can easily grease the Birfield joint. You just need to pop off your drive flanges or hubs and shoot in 5-6 pumps. Easier and cleaner than pulling your front end apart!


The Super Set also comes with chromoly hub gears and drive flanges, eliminating more breakable stock components. Of course, drive flanges are for off road only, so you'll probably want to sell them if you put these Longs on a daily driver.


Check price on Amazon

RCV Ultimate 30 Spline Axle Set for Toyota Pickup and 4Runner - CHROMOLY WITH 300M STAR



RCV Toyota Pickup and 4Runner Axle Set Specs

Hub splines	30
Inner bearing splines	30
Differential splines	30
Birfield material (outer axle)	4340 chromoly
Inner race material	300M
Inner axle material	4340 chromoly
Birfield length (outer axle)	9.60"
Left inner axle length	31.31"
Right inner axle length	17.13"
Greasable	Yes
Gun-drilled Birfield	Yes
Heat treatment

RCV Toyota Pickup and 4Runner Axle Set Contents

Birfield (outer axle)	2
Inner axle	2
Inner axle outer C-clip	2
Inner axle seal
Hub gears
Drive flanges

With a 300M inner race and full chromoly axles, these 30 spline axles are some of the some of the strongest you can buy. For some wheelers, the inner race of the Birfield has become the weak part of their frontend, so RCV started machining the star out of 300M. These axles are gun-drilled and can be easily greased like the Longfield axles above.

Sometimes these are offered with free chromoly hub gears, so keep your eyes peeled.


Check price on Amazon

RCV Ultimate 30 Spline Axle Set with 300M Inner Axle for Toyota Pickup and 4Runner - STRONGEST - 300M INNER AXLE AND STAR



RCV Toyota Pickup and 4Runner Axle Set with 300M Inner Specs

Hub splines	30
Inner bearing splines	30
Differential splines	30
Birfield material (outer axle)	4340 chromoly
Inner race material	300M
Inner axle material	300M
Birfield length (outer axle)	9.60"
Left inner axle length	31.31"
Right inner axle length	17.13"
Greasable	Yes
Gun-drilled Birfield	Yes
Heat treatment

RCV Toyota Pickup and 4Runner Axle Set with 300M Inner Contents

Birfield (outer axle)	2
Inner axle	2
Inner axle outer C-clip	2
Inner axle seal
Hub gears
Drive flanges

These are the strongest Birfield axleshafts you can get for your Toyota pickup or 4Runner. After the Birfield is upgraded to 4340 chromoly and the inner race is machined from 300M, the next failure point is the inner axle shaft. So, now you can get 300M inners! These axles have 4340 chromo Birfields, 300M stars, and 300M inner axles. The Birfs are gun-drilled for easy greasing and save a ton of time and mess over axle disassembly.


You may be able to buy these with chromoly hub gears thrown in, so keep a lookout.


One thing to keep in mind is that once all your axle parts are beefed up, what breaks next? It could be your carrier splines, which will be unenjoyable to change on the trail.


Check price on RCV Performance Products

Nitro Gear Toyota 8" Solid Axle 27/30 Spline Chromoly Birfield Front Axle Upgrade Kit - 27 OR 30 SPLINE CHROMOLY AXLES



Nitro Gear Toyota 8" Birfield Kit Specs

Hub splines	30
Inner bearing splines	27/30
Differential splines	30
Birfield material (outer axle)	4340 chromoly
Inner race 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 Gear Toyota 8" Birfield Kit Contents

Birfield (outer axle)	2
Inner axle	2
Inner axle outer C-clip	2
Inner axle seal
Hub gears
Drive flanges

Nitro Gear's Toyota mini axles come in full 4340 chromoly and can be bought with 27 splines or 30 splines.


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G2 Toyota Pickup and 4Runner Birfield CV Style 27/30 Spline Chromoly Axle Kit - 27 OR 30 SPLINE CHROMOLY AXLES



G2 Toyota Pickup and 4Runner Birfield Axle Kit Specs

Hub splines	30
Inner bearing splines	27 or 30
Differential splines	30
Birfield material (outer axle)	4340 chromoly
Inner race material	4340 chromoly
Inner axle material	4340 chromoly
Birfield length (outer axle)	9.60"
Left inner axle length	31.50"
Right inner axle length	15.25"
Greasable	No
Gun-drilled Birfield	No
Heat treatment	Single

G2 Toyota Pickup and 4Runner Birfield Axle Kit Contents

Birfield (outer axle)	2
Inner axle	2
Inner axle outer C-clip	2
Inner axle seal
Hub gears
Drive flanges

G2's Toyota mini axles come in full 4340 chromoly and can be bought with 27 splines or 30 splines.

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Marlin Crawler 30 Spline Chromoly Axle Kit for Toyota Pickups and 4Runners



Marlin Crawler Toyota Pickup and 4Runner Axle 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)	9.60"
Left inner axle length
Right inner axle length
Greasable	No
Gun-drilled Birfield	No
Heat treatment	Single

Marlin Crawler Toyota Pickup and 4Runner Axle Kit Contents

Birfield (outer axle)	2
Inner axle	2
Inner axle outer C-clip	2
Inner axle seal	2
Hub gears
Drive flanges

Marlin Crawler's Toyota mini axles come in full 4340 chromoly and can be bought with 30 splines. They're manufactured by EMPI, a Volkswagen parts wholesaler.


Check price on Marlin Crawler