Replacing a Discovery 3 front differential
How to replace the front differential on a TDV6 Discovery 3 and Range Rover Sport
This 2007 Discovery 3 TDV6 had recorded around 135,000 miles when the owner started to hear noises from around the front axle and the front differential. An inspection in the workshop found the front diff was indeed making a loud grating noise, even when the front wheels were rotated slowly by hand. The oil in the diff was discoloured and had a burnt smell about it. The inspection also revealed that the front diff’s breather pipe, which runs from the diff up through the engine bay and comes out between the side of the engine and the power steering fluid reservoir, was blocked. This has been a known problem on both Discovery 3 and Range Rover Sport, and may have resulted in the front diff overheating and eventually leading to bearing failure.
The Discovery 3 front differential is a self-contained unit fixed to the vehicle underframe, rather than sitting inside an axle assembly, as in older beam axle Land Rover models. They have generally proved to be reliable, however the breather pipe was modified to prevent it becoming blocked, which could result in moisture building up inside the diff casing which, thus contaminating the oil and possibly causing overheating, leaks or bearing failure. That might have been the cause of the problem in this case.
No electronic equipment or special tools (other than a vehicle lift) are required. Needing to have the vehicle raised with both front wheels removed and with enough space to work underneath is not considered practical or safe with this vehicle type with normal DIY equipment. And, like many jobs on newer Land Rover models, although replacing the affected part is relatively easy, the difficulty is in removing other parts to reach the defective component.
For these reasons, this feature, rather than explaining how to do the job, concentrates on showing what will need to be done by the garage so that, if your vehicle needs this work, you will have a good idea what they will be doing, and the costs involved. Here, we show how Madison 4x4, near Thirsk, tackled the job. Both axle halfshafts need to be removed. The pictures show the driver’s side halfshaft being removed first, before moving over to repeat the job on the left side.
Fitting the new differential
Once the new diff is in place against the chassis, some manipulation is needed to align the mounting holes before fitting the bolts and tightening to the specified torque settings. We made sure the plastic breather pipe was securely connected to the short breather tube on the top of the diff, and that the pipe was free and running clear up through the engine bay. Otherwise, re-assembly is a straightforward reversal, using a new O-seal on the driveshaft support tube and sealant on its flange face, and with a few extra pointers in the pictures below.
Vehicle lift, general workshop tools including 13 mm, 22 mm, 23 mm, 24 mm spanners and sockets, long extension bar, large pry bar, E10 Torx bit.
Parts and costs
The final drive front differential is part number TAG500140. Prices range from around £690 upwards to over £1750. Many replacement differentials are sold as an exchange unit, with a surcharge if the old unit is not returned. The front diff requires 0.61-litre of alonglife fully synthetic 75w-90 oil, part number TYK500010 and costs around £20 per litre. This oil contains unique additives which Land Rover say “enhances the differential’s operation”, whilst the service specification says that no other oil should be used in the front diff.
Time: 4-5 hours Costs: £700
The work was carried out by Maddison 4x4, Water House Farm, Station Road, Topcliffe near Thirsk, YO7 3SG.
Health and safety
• When planning to work underneath a vehicle, ensure lifting and support equipment is correctly rated and in serviceable condition. • Ensure the vehicle is securely supported and cannot be dislodged. • Work should always be carried out to Land Rover specifications and procedures. This job is not suitable for DIY unless you have the required competence, knowledge and facilities.
Click on the gallery below for our handy step-by-step guide…