30 June 2023
How to fix a diff pinion leak and stop it from happening again
Need to know
Time: 1 hour
Difficulty: 2 out of 5
Models: Series III, Defender to 2002.
Tools needed: Socket and spanner sets, propshaft nut tool, drain pan, torque wrench, bearing driver set, hammers, dot punch, wheel bearing outer, Allen key or drill bit, brake cleaner.
Parts and costs: Salisbury diff pinion oil seal, leather, to 1998 (AEU2515G), £4.49; pinion seal, rubber, 1998-on (STC4401), £4.69; updated flange kit, (STC4457), £59.99; JGS4x4.co.uk.
• Raise and support the vehicle securely on rated equipment.
• Wear the correct PPE at all times.
• Dispose of old oil responsibly at your local recycling centre.
It’s a running joke that all Land Rovers leak oil. Perhaps it’s true that they dribble and weep slightly more than the average car, but leaks are still problems that need to be addressed rather than ignored or accepted.
A common weep spot is the differential pinion oil seal, and it’s hardly surprising given the demanding job this particular seal has to perform. Drive runs from the transfer ’box via the propshafts, where it needs to be turned 90 degrees along the axles to the wheels. The input to each differential is called the pinion – a gear on the end of a shaft that spins thousands of times every time the Land Rover is driven. The pinion seal does exactly what it says on the tin, sealing the axle oil in and keeping all the muck, water and other contaminants out. However, as with any other seal, it can wear and become torn or damaged over time, letting oil past.
Changing the seal is simple on a Rover-type axle, as the pinion shaft’s bearings are adjusted and set using shims, so the nut that holds the drive flange to the shaft has no effect when changing the seal. But things are trickier on a Salisbury axle, as used on some Series III 109in models as well as Defender 110 up until 2002. The preload on the pinion bearings is set by a crush tube which is squashed down by the flange nut, so you have to be a bit more careful when disassembling and reassembling after replacing the seal. Don’t worry, though, it’s all still well within the skill set of a DIY mechanic.
A drippy diff: The differential pinion runs through the centre of the seal seated in the nose of the diff, and spins at high speed when driving. Once the pinion seal starts to leak, the axle oil level can drop surprisingly quickly, risking premature wear to the diff bearings and gears.
Unbolt the prop: First up, the propshaft must be unbolted from the differential flange. The nuts and bolts are 9/16th UNF, and the proper tool (DA1065 or DA1119) makes life a lot easier. You can either remove the prop completely, or just release the differential end and tie it up out of the way.
Make your marks: Because the pinion nut on the Salisbury axle is used to set the preload on the pinion bearings, it’s vital that you mark the relation of the pinion shaft, nut and flange for refitment. Use a hammer and dot punch to mark the three parts in line.
Undo pinion nut: Use a 32mm socket on a breaker bar to loosen the pinion nut. Ask an assistant to hold the brake pedal down to stop the pinion from turning as you apply torque. Once free, count the number of turns it takes for the nut to come all the way off. Remove the washer.
Slide flange away: The diff flange should slide off relatively easily if it has been leaking, but if it’s stuck, give it a gentle tap with a copper or hide hammer. Position your drain pan to catch any oil that escapes when the flange is removed. There’s no need to drain the axle completely.
Prevent dirt ingress: Caked-on muck and grime will be loosened when the old seal is prised out, so carefully remove as much as possible from the area with a scraper and cloth. Take care not to let it fall into the nose of the diff, as it will contaminate the oil.
Lever seal out: With the nose of the diff cleaned up, use an oil seal remover or long flat-blade screwdriver to prise the old seal out of its housing. You may need to work your way around it to get it started. This diff had a rubber-type seal fitted, but we’ll be refitting the correct leather one.
Check sealing surface: Blast the diff flange with brake cleaner and clean it up with a cloth. Inspect the machined surface that the seal runs on. Light wear like this is okay, but if the surface is deeply scored then a new seal won’t help, and a new flange and seal kit (STC4457) is needed.
Prepare new seal: The leather-type seal, which is correct for this Series III, needs to be soaked in gear oil to soften it before fitting. Rubber seals don’t need to be soaked, but do benefit from a smear of grease around the inside to help lubricate the surfaces on reassembly.
Easy does it… Remove any corrosion or burrs from the seal housing, then offer up the new pinion seal. Push it in with your fingers to get it started, taking care to keep it even all the way around, then use an aluminium bearing driver to knock it in gradually and evenly without denting it.
Drive it home: Once you’ve got the seal flush with the nose of the diff, you need to switch to another driver. The flat side of an old wheel bearing race is ideal, and helps spread the load as you tap it in. Direct the pressure at the very outer edge of the seal, whichever type you are fitting.
The correct depth: Helpfully, the Salisbury diff has a shoulder built into the nose that sets the depth of the seal. Keep tapping the seal in evenly until it meets the shoulder, then stop. If you don’t set the seal all the way in, the mud shield on the back of the flange will bind against it.
Refit the flange: Smear grease lightly on the sealing surface, then push the differential flange back into place on the splines. Take care not to nick the seal, as the pinion shaft will be able to move around. Refit the washer, then apply a drop of threadlock to the nut and start it by hand.
On your marks: Wind the pinion nut back on the same number of turns it took to remove, then carefully tighten it until the dot punch mark aligns with the one in the pinion shaft. The official torque figure is 40lb-ft; check for end float and binding, then refit the propshaft with new nuts.
Take a breather: Look up on top of the axle tube and locate the breather. It will either consist of a banjo bolt with fitting and plastic tube (9/16in spanner), or on Series III, a one-way valve like this one (5/8in spanner). Remove the breather, taking care not to let dirt fall in through the hole.
What does a breather do?
As driveline parts warm up and cool down, so does the fluid and air inside the casings, expanding as it warms and contracting as it cools.
It’s vital that air can track in and out of the casing; if it was completely sealed, the casing would pressurise when warm, pushing oil past the seals, and suck air and moisture in through them as it cools back down. Breathers allow the casing to ‘breathe’ as the temperature changes – but only if they aren’t clogged with muck.
Clear it out: For a tube-type breather, blow the tube out with compressed air and ensure the banjo bolt isn’t clogged. On a valve type, degrease the breather with brake cleaner, then gently tap an Allen key or drill bit into the opening to unstick the ball bearing, then flush again. Refit.
Top up the level: With the new seal in place and the axle breather cleaned out, the last thing to do is to top up the axle oil level with fresh EP90 gear oil. Undo the ½in square drive bung from the backplate, pour oil in until it dribbles from the filler hole, then refit. Job done!
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