Gen4 replacing diff oil

My dealer were a bit rubbish and didn't perform the required diff oil change at the first service. It's going to be easier for me to do it myself, but wanted to check a couple of things from you knowledgeable types.

Fluid listed in manual is 75w85 synthetic GL-4. Seems to be fairly limited options at that exact spec, with many being listed as GL-5 and those that are GL-4 being super expensive.

Loads more options at either 75w80 or 75w90, would it be better to go marginally thicker or thinner?

Is the replacement simply a case of undo filler and drain plugs, let it all drop out, replace drain plug, refull to level of fill plug, replace fill plug?

Any gotchas I should be aware of - any replacement seals/o-rings on the plugs? Best to do when cold or with the oil warm?

Thanks

For ease of work, make sure the diff is warm (go for a drive or leave your inspection lamp underneath it to warm it up). Place the new oil in the airing cupboard to warm it through.

The parts diagram shows copper gaskets on the filler and drain, so I would replace those.

The main worry about GL-5 used to be its re-action with "yellow metals" - which usually means Phosphor-Bronze. Not sure how much Phoshor-Bronze there is in the diff?

Hi Gadget,

Sorry to hear about your first Suzuki service experience - I must admit I'm apprehensive about taking mine in over the next couple of months. They're likely to be running a skeleton crew - I'd almost certainly do a more thorough job myself. Feel obliged for the stamp in the book

As martin has said, go for a drive to warm the Axle housings up (Might be difficult with the front diff because this won't be engaged). Remove the fill plug first so that there isn't a vacuum holding the oil into the axle housing, this also prevents draining the oil and then realising your fill plug is seized meaning you can't fill back up :silly: Then finally drain into a suitable catch can. Very simple really!

As a general rule of thumb, GL4 vs GL5:

- GL5 gear oil in comparison to the same viscosity GL4 contains roughly 50% more phosphorus and sulphur EP additives.

- In very broad layman's terms, this means the gear oil 'clings' to the gear substrates more effectively and provides a higher level of 'shock loading' protection.

- However due to the increase in these additives, GL5 can cause damage over time to sensitive yellow metals.

In my experience, most manual transmissions tend to utilise a GL4 oil due to the sensitive synchromesh materials. Differentials tend to utilise GL5 oil due to the increased levels Torque/Shock load protection along with the absence of any sensitive substrates.

I've got the Gen. 4 service manual in front of me and it's as clear as mud. Have you found a statement that specifically states GL4 or GL5? I can only see this wooly statement: (My 20 year old BMW has the Oil type stamped onto the bottom of the gearbox & diff's that's the germans for you.....)

Just found this:



Ambiguous Japs. I would personally choose a GL4 for the gearbox & transfer box as and when they need a fluid change and GL5 for the front and rear Differentials.

Differential Oil:

(I wouldn't be concerned at all about the difference between 75w 85/90 This is a really standard grade high quality Diff Oil used across the industry - Suzuki seem to specify very unusual viscosities - much like their 0w 16 engine oil which hasn't caught on in the UK yet... purely in place due to EU emissions regulations. Note that all countries outside the EU utilise NORMAL grade engine oil for the same engine :whistle: )

www.opieoils.co.uk/p-737-castrol-syntrax...formerly-saf-xo.aspx

Manual Trans oil & Transfer box:

www.opieoils.co.uk/p-69412-castrol-syntr...car-gearbox-oil.aspx

Thanks both. Not sure where I got the GL4 from, but can't find any reference to it now, so will probably go with GL5. This stuff seems to fit the bill and won't bankrupt me for the 3litres needed!

www.opieoils.co.uk/p-982-fuchs-titan-sin...thetic-gear-oil.aspx

No eBay APP ID and/or Cert ID defined in Kunena configurationThis lubricant is the correct specification, meets GL-4 and GL-5 specs and is a good price.