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.

Not sure about an oil that meets both GL4 & GL5 specification - it's either one or the other. Both have different properties and for a good reason!

At the end of the day, a Diff is a simple beast. GL5 oil is the industry standard for 99% of diffs. But you'll do no harm what so ever playing it safe and going with a GL4 if you're unsure.. I'm just frustrated with Suzuki because they've been deliberately 'non-committal'. I bet they wouldn't tell you what grade fluids they use at a Suzuki service station... Probably just standard grades out of a commercial drum like most garages....

The diff in the gen4 is the same as the gen3, which in turn was carried over from the SJ. They are tried and tested, very reliable and there's absolutely nothing fancy about it. Any gear oil will be fine. I use EP90 in mine, which is the gear oil used in almost all plant and agricultural machinery as well as industrial gearboxes. Basically, if it says gear oil on the bottle it will be fine.

Thanks, it's the curse of working in IT where you frequently need to get precisely the right 'thing' or something else doesn't work. It's a struggle for me to go for a good enough option! :silly:

DAGZOOK wrote: Not sure about an oil that meets both GL4 & GL5 specification - it's either one or the other. Both have different properties and for a good reason! ....

I believe it is possible, did some googling some time ago to find how such a thing is possible.
If I recall correctly corrosion inhibitors are added to GL5 to prevent possible yellow metal damage, so it's ok in GL4 applications.
So it's a battle of additives. I guess it's not a problem, but like antifreeze anti corrosion additives they don't last for ever, so sticking to a maintenance schedule is probably more important with combined spec gear oil.

So yes they do sell GL4 and GL5 spec gear oil.
Mike

I've come across GL4/GL5 combinations in marine applications so they can exist but I haven't used any. Chris

Three comments

1) Busta your comment was econonic in detail, therefore incorrect, to use an oil in a diff the oil has to adhere to the GL5 spec for the high shear stress that the hypoid gears put the oil the oil. Not any gear oil but one with a GL5 rating. A GL4 only spec oil will not be suitable in this case.

2) The GL5 oils has added sulphides to cover for the extra shear stress on the oil. In around 1954 the sulphides used to get the GL5 spec tended to shed sulphar out of solution and may well have dammaged gearbox yellow metals.

Since around 1957 oil blenders have used more stable sulphides in GL5 oils and I ask any person here that disagrees to provide a link to actual tests that show a modern GL5 oil ( made in the last 10 years) will damage gearbox internal.

Not a link to a similar comment that they damage yellow metal but show details of an actual lab test with a count of the yellow metals in the used oil analysis that is higher than a test in a similar gearbox that was run with a GL4 oil.

Hint, you wil not find such a test that produces these results.

In the past few years some companies have started using other additives other that these extra sulphides to obtain the additional properties required to obtain GL5 status while also having a GL4 qualification. Total of France being one. They will not advise the additives they use to make the oil a true GL4/GL5 specifications.

I have used my contacts in Total to try and tease the facts out but no info was given. Therefore yes there are now GL4/GL5 oils that do not have an additional sulphide load.

3) The Suzuki 75W oil mentioned in Jimny 4 handbook is a Suzuki specified 75W/80 GL4/GL5 oil. I assume using these new non additional sulphide additives.