Stripping the Discovery Front Axle

I have finally started work on the Discovery front axle in preparation for the axle swap. The axle needed a good clean and inspection, rectifying any defects found.

The first job was to remove and strip each end of the axle.  This was done one end at a time, cleaning and sorting each piece as it was removed (not fun when all the contents of the swivels are covered in a thick coat of one-shot grease).  Everything was cleaned right back, with all brackets and the swivel seal retaining rings treated with rust converter.  The swivel outer housings were cleaned with a drill powered wire brush until all rust was removed and were then sprayed with zinc based primer.

Unfortunately, the right hand swivel had been showing a notch in the middle of its sweep, suggesting something had worn in the straight-ahead position.  It was impossible to diagnose prior to stripping, but testing the swivel after removing the CV joint seemed to show an increase in this notchiness, pointing towards the swivel bearings.  This photo of the top bearing shows radial indentations from the rollers on the inner race.  Close inspection of both CV joints showed wear grooves in the middle of the thrust faces of each ball-slot on the outer cases, so they need renewal too.  This is one rare instance where I may use Britpart components – not only are they remarkably cheap, but Ashcroft Transmissions’ destructive bench testing showed them to be significantly stronger than the original GKN units.  I just hope that it’s not just due to insufficient case hardening leaving them less brittle as that would make them more prone to wear under normal use.  The bearings will be replaced with Timken bearings, just like LR used.

After the shafts had been removed and inspected, it was the turn of the differential.  The good news is that the dented diff pan had not contacted the crown wheel (there had been no unusual noises when turning the diff when buying the axle, so the risk seemed low).  The diff is in truly excellent condition, with factory tolerance backlash and no evident dirt, damage or wear.  Even the pinion seal is in tip top shape, so the whole unit has been bundled into an old pillow case to keep it clean and will not need further work.

Finally, the axle case was bare.  The dent in the pan was surprisingly easy to tap out with a hammer and drift and is back to the correct shape.  Once painted, it should be impossible to spot the former damage.  However, the currently fitted axle will donate its QT diff guard to prevent any possible recurrence and to protect any residual weakness from the working of the metal.   The casing will have its coil spring mounts and radius arm brackets removed.

The bump stops need alteration so that their tops are parallel to the rubber blocks on the chassis – coiler axles have theirs set on a slope (front end low) to allow not only for the different chassis profile around the bump stops but also for the manner in which the axle rotates around the rear end of the radius arms as the springs compress (Series axles maintain their orientation as the leaf springs flex).  The bump stops need to be reset by 14 degrees, and while it would be possible to cut them away from the tube and weld them back after rotating them, I may just build their height up at the front by welding on a wedge.  This will make the bump stops quite tall, but I could remove the 1-ton spec rubber bump stop extenders from the chassis to compensate, still allowing full axle articulation.  The reason for doing it this way is to retain the Panhard Rod brackets, as I am considering fitting a Panhard Rod later to reduce the lateral motion of the front axle in relation to the chassis, tightening up the steering and getting rid of most of the wander and steering correction on cambered roads. Ideally, however, the Panhard Rod bolt axis would be close to parallel with the spring saddles and bump stops (inclined only a few degrees off the spring axis, as the axle moves slightly aft on leaf spring compression), as this would put the least strain on the rod system when the suspension flexes, and to achieve this require removal and resetting of all the brackets.  It all depends on how easy it appears to cut the existing welds without damaging the brackets or casing.

Once the bump stops are done, I will have a good datum from which to set the spring saddles – they are parallel to the bump stops on Series vehicles and are perpendicular to the swivel pin axis, the 3 degree castor angle being set by the vertical displacement of the rear spring eye below the front spring eye on the leaf springs.  I’ll be using my unfitted third leafs for the front springs to work out the depth of saddle required in order for the track rod to clear the top of the spring unladen – I think 12mm (1/2″) clearance over an unladen spring (maximum camber) should be fine to allow for all axle articulation and axle wrap under heavy torque loads from the brakes or transmission in low range.