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Discussion Starter · #1 ·
After reading a ton of differential threads here, decided to replace the front differential fluid as preventative maintenance (had a couple bottles of mobil 1 75w90 in the garage, so figured why not). Love that I can just put the car into offroad ride height and crawl underneath. Underbody panel was pretty easy to remove - no seized bolts. Thanks to the great DIYs here, finding the fill and drain bolts was easy - as always, removed the fill bolt first before I took the drain bolt off. Having a set of allen key sockets for your wrench is very useful for the fill bolt and the drain bolt is easily removed just using the square piece of a 3/8" wrench. Quick tip for those doing this the first time - the drain bolt is on the passenger side of the differential and the fill bolt is on the drive side.

First thing I noticed when I removed the fill bolt is that the diff seemed overfilled - gear oil started to trickle out as soon as I removed the fill plug. The gear oil was actually in decent condition - was definitely dirty and dark grey in color so glad I replaced it, but I've seen worse condition fluid from lower mileage BMWs I've owned. Drain bolt had some metal shavings, but not any more than I've seen in other cars with comparable mileage. I'm going to assume that either it's had the fluid replaced before as a preventative maintenance, or it's just a virtue of being driven conservatively. It's at 81k miles now and I'm going to assume that at least half of them are freeway due to the area it lived in (not much opportunity for much urban driving).

I measured out about .61-.62 liters of 75w90 gear oil and using a handy pump that mounts onto the bottle, refilling was easy. Wiped it down and then before I put the underbody panel on, I took it for a few block drive and crawled underneath again to check for any leaks and give the bolts another quick tightening just in case. Thankfully an uneventful maintenance with no surprises - so far pretty happy with how easy the RRS is to maintain (a week into ownership :)).
 

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Discussion Starter · #2 ·
Update - followed it up with rear differential fluid change and was shocked at how dark, gritty and metallic the gear oil was. Definitely worse than the front differential, which is surprising considering the stories here about how the front diff is more trouble prone. Granted, the rear diff is physically larger and holds more fluid, but there was definitely more metal shavings on the magnetic drain plug. So either I have a really strong front diff, or its fluid was replaced at some point. Puzzled over the driver side of the differential for a bit, wondering if it had the actuator that would denote it's electronic locking. As the FAQ states though, it's pretty obvious once you get your head in there, and I confirmed it has an open rear diff - not surprising. Filled her up with mobil 1 synthetic 75w90 gear oil. Now onto the transfer case and transmission oil...
 

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2006-2009 Range Rover Sport
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Supark, congrats.

Let me state that I'm a Mobil 1 synthetic gear lube fan, and I use it in my other vehicles w never any issues. But I almost wonder since these RRS diffs (IMO) are prone to seal issues and in general seem to be a bit less robust than they should be, if just using the OE fill fluid is just a bit safer.

I have no experience with M1 in these diffs to support this feeling, just saying.
 

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Discussion Starter · #4 ·
Isn't the oem fluid sunthetic as well? Only car that I put special diff fluid in is something like my M3 that needs special friction modifiers to make the limited slip not make a total racket. My diffs were actually very dry and free of any telltale leaks. Almost all of my bimmers have had a little leaking around this mileage, so I'm impressed with how tight the RRS is. I wonder if the perception that these diffs are prone to leaking is a little exxagerated? Rubber seals shrink with age, metal surfaces bed in with each through heat cycling and wear - so honestly isn't some leakage inevitable? People start to suffer leakage as they age, why should cars be any different? ;)
 
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