10 to 24 Spline Conversion
To improve strength, reliability and offroad traction performance during remote area touring of Australia, I’m rebuilding my Land Rover Defender front axle with upgraded components.
The build includes replacing:
- the weak 10/32 spline half shafts with Maxi-Drive 24/23 spline uprated shafts
- the Land Rover 2-pin differential with a Detroit Truetrac ATB limited slip diff
- the later style CV joints RTC6862 with the earlier and much stronger AEU2522 CV’s
- and changing the drive flanges to Maxi-Drive uprated drive flanges
My 200TDi Defender was produced with a front axle 10/32 spline combination. 10 splines at the diff end, and 32 on the CV. This is the weakest spline combination produced, and prone to failure around the spline region.
10 splines have a history of the splines twisting or the ends shearing off in the diff.
32 splines have a history of the splines shearing off due to their fineness, or the end snaps off in the CV.
The replacement shafts I’m using are Maxi-Drive uprated 24 spline diff end to 23 spline CV end shafts. They are manufactured from aircraft material known as HY-TUF nickel chrome moly steel and heat-treated to 1550 MPA, producing axles about 50% stronger than the original, plus with the benefit of being a stronger 24/23 spline combination.
The below table of shaft diameters measured at the spline area shows how the newer 24/23 shafts are greater in diameter compared to the original.
The original Land Rover 2-pin differentials are a known weak point. Although named 2-pin, they only have a single pin which holds two spider gears. The pin is known to crack, the spider gears crush or the pinhole wears oval in the diff housing, eventually causing failure.
I’m upgrading to an Eaton Detroit Truetrac Automatic Torque Biasing Limited slip differential. I chose this unit as it is a simple design using gears not clutch packs. It has no electrics or airlines and doesn’t need special diff oils. The Truetrac requires no maintenance. It will transfer up to 3.5 times more torque to the wheel with greater traction when the opposite wheel is spinning, thus driving the vehicle with the one wheel.
If traction is very poor, the helical worm gears are forced out into the carrier producing friction. This friction reduces the spinning of the spinning wheel and helps divert more torque to the wheel which still has traction. The downside of this design is if one wheel lifts entirely off the ground, it acts like an open diff. However, with some left foot breaking, the Truetrac can be fooled, and the additional resistance on the airborne wheel can help force it to transfer torque to the opposite wheel.
I chose an ATB over a full locking differential as it is used 100% of the time to improve traction, compared to the 2% of times I may need a full locker. My style of touring doesn’t take me into extreme rough tracks.
Constant Velocity Joints
The early 1-ton army style county CV’s are said to be the strongest Land Rover ever produced. These may also be upgraded later to aftermarket Ashcroft or KAM CV’s which are made from stronger materials.
Maxi-Drive drive flanges, made from stronger materials, have a little more spline contact area and provide better sealing, keeping the oil in and water out. The day’s of rubber caps knocking off is finished.
DOWNSIDE OF AXLE UPGRADE
The downside of this upgrade, is I have strengthened the whole axle, which would now transfer stress to the weakest link. This is likely to be either the gearbox, transfer case, or the ring and pinion. Though I think it unlikely I will have any issues as my gearbox and transfer case have already been rebuilt, along with the rear axle.
During the first week, the steering was much firmer in its return to the centre, requiring me to hold the wheel a little tighter till I got used to the feel. After a few weeks of driving, I no longer notice any difference and have become accustomed to it.
Before the upgrade, I tested for driveline slop by jacking up a front wheel and rotated it till the front prop shaft began to move. I could take it from the 12 o’clock to 1 o’clock position. After the axle upgrade, I could only rotate the wheel 1cm before the prop shaft moved, so it removed much play in the front.
Offroad to date it is handling well. In loose sand or slippery mud tracks I can feel the traction swapping back and forth to the wheel which has the most grip.
The only noticeable downside is the centre differential lock has been difficult to disengage, possibly due to the lack of driveline play. At times it may take 2-300m of driving on dirt/gravel tracks before it releases. Otherwise, I must stop the vehicle and reverse 20m till it pops out. Sand driving at this point appears to disengage normally.
The axle upgrade came in around $4000AU for the full rebuild, which included the half shafts, CV’s, Truetrac, drive flanges, bearings, seals, oil and labour.