Suzuki Jimmny Gearbox, Trasfer Box & Diffs

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Unsure if America got the Suzuki Jimmny but it's essentially a little capable off roader with a even littler 1.3 litre 4 pot lump with variable vale timing.

It belongs to my Mother who bought it brand new in 2013 and does a great job of not looking after it.

Engine oil requirements are very basic. Any viscosity from a 0w20 to a 20w50 (little bar chart showing the appropriate temperatures for each grade of oil) that meets API SM which we all know some grades of cooking oil could meet. OCI's are every 4k or 6 months for severe duty or otherwise 9k or 12 months. My Mother is a typical 'servere duty' driver doing lots of slow speed town stop/start driving where the engine never really gets up to temperature. To add insult to injury my Mother doesn't perform any maintenance unless the car stops running. It's lucky to get an oil change every 18 months, usually about 15k which is why I run Castrol Edge 0w30 A5/B5 and not some cheap dino oil.

However, I'm unsure about the lubricants for the gearbox/transfer and diffs. When the car was about a year oil I changed out all the fluids as per the manufacturers recommendation. I used mineral oils from my local Motor Factors that met the appropriate specification. The book suggests the following...
Gearbox & Transfer Box - 75w90 GL-4
Differentials - 80w90 GL-5

These oils are now coming up to 4 years old and done around 40k. I imagine they are way past their best.

As the car is so poorly maintained I'm looking to use Synthetics throughout hoping that they hold up better for whatever duration they are in.

I cannot find a fully synthetic 80w90 in the UK that meets GL-5 for the differentials.

Castrol in the UK at least produce a fully synthetic 75w90 gear oil that meets GL-4 and GL-5. It's an oil I would gladly pick for the gearbox, but am I likely to run into any issues if I was to run it in the diffs too?

Any other advice welcomed. My Mother is going to be driving my Son around in it when he's born in May so I may have to start being more strict about the maintenance on it.
 
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Oh, I wish we got the Jimny here. We got the Samurai up until 1995, and I bought two of them. After that, we got the Sidekick/Tracker. Now we don't get anything but jacked up cars that they call CUVs.
/rant

As far as the oil, the GL-# shouldn't matter much for the differentials. For the transmission, use whatever GL-# is recommended. I have seen some great improvements in shift quality when switchting to synthetic gear oil in old manual gearboxes, but any new oil is going to be better than the old gunk.
 
Originally Posted By: CT8
Syn oil will not help it last longer.

I thought that was a major advantage of Synthetics? Otherwise what is the advantage of using them in the transmission?

Originally Posted By: eyeofthetiger
Oh, I wish we got the Jimny here. We got the Samurai up until 1995, and I bought two of them. After that, we got the Sidekick/Tracker. Now we don't get anything but jacked up cars that they call CUVs.
/rant

As far as the oil, the GL-# shouldn't matter much for the differentials. For the transmission, use whatever GL-# is recommended. I have seen some great improvements in shift quality when switchting to synthetic gear oil in old manual gearboxes, but any new oil is going to be better than the old gunk.


All it asks for is GL-5 for the diffs which after a bit of googling seems to be for hypoid gears which makes sense.

I'm going to assume gear oil is much like engine oil where the 'W' rating just needs to be low enough for your lowest ambient temperatures and it's the '90' which I should be more worried about?
 
In the transmission use GL4 not GL5. Most of the Japanese made transmissions have brass synchros in them and GL5 will harm them because it contains sulfer. If you can't find a GL4 gear oil you can run 10w30 or strait 30 motor oil or any of the synchromesh type manual transmission fluids. Shell makes a spirax fluid for use in tractors that is also approved for manual transmissions. I currently have that in my jeep wrangler and it shifts fine which is saying something because the AX15 (with brass synchros) is in general a notchey shifting transmission to begins with. Rotella strait 30wt or T5 10w30 has been in it too. It shifted like junk with royal purple gear oil.
 
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Originally Posted By: Sealbilly
In the transmission use GL4 not GL5. Most of the Japanese made transmissions have brass synchros in them and GL5 will harm them because it contains sulfer. If you can't find a GL4 gear oil you can run 10w30 or strait 30 motor oil or any of the synchromesh type manual transmission fluids. Shell makes a spirax fluid for use in tractors that is also approved for manual transmissions. I currently have that in my jeep wrangler and it shifts fine which is saying something because the AX15 (with brass synchros) is in general a notchey shifting transmission to begins with. Rotella strait 30wt or T5 10w30 has been in it too. It shifted like junk with royal purple gear oil.



Suzuki asks for an oil that meets GL-4 in 75w90.

The oil I want to use meets GL-4 & GL-5. Therefore it shouldn't pose any issues to the transmission?
 
Originally Posted By: Bailes1992
Originally Posted By: Sealbilly
In the transmission use GL4 not GL5. Most of the Japanese made transmissions have brass synchros in them and GL5 will harm them because it contains sulfer. If you can't find a GL4 gear oil you can run 10w30 or strait 30 motor oil or any of the synchromesh type manual transmission fluids. Shell makes a spirax fluid for use in tractors that is also approved for manual transmissions. I currently have that in my jeep wrangler and it shifts fine which is saying something because the AX15 (with brass synchros) is in general a notchey shifting transmission to begins with. Rotella strait 30wt or T5 10w30 has been in it too. It shifted like junk with royal purple gear oil.



Suzuki asks for an oil that meets GL-4 in 75w90.

The oil I want to use meets GL-4 & GL-5. Therefore it shouldn't pose any issues to the transmission?

No issues other than 'unpredictable' hard/soft shiftability with any GL4/transmisson combo under cold temperature.
Current GL5 harms brass synchros is a myth.
 
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