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What Oil In The Gearbox

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What Oil In The Gearbox

Postby WelshBoy » Thu Oct 24, 2019 5:24 pm

Hi All
Just about to refill my (manual gearbox) with oil the transfer case and gearbox side manual says to use the same oil thats in the engine 15/40 engine oil any advice??
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Re: What Oil In The Gearbox

Postby isuzurob » Thu Oct 24, 2019 6:39 pm

Can run 75w/90 but can be hard to select gears when cold, 5w/30, 15w/40, anything really I've tried alsorts even 80w/90 works if that's all you have
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Re: What Oil In The Gearbox

Postby WelshBoy » Fri Oct 25, 2019 5:26 am

isuzurob wrote:Can run 75w/90 but can be hard to select gears when cold, 5w/30, 15w/40, anything really I've tried alsorts even 80w/90 works if that's all you have


Thanks will give the engine oil a try will be cheaper to use the same oil in the trans and motor.
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Re: What Oil In The Gearbox

Postby geeves » Fri Oct 25, 2019 2:22 pm

Not quite unfortunately. Modern engine oils have friction modifiers which are great in the engine but dont play nice with syncro rings. It wont damage them if its already in there but when cold hard gear shifts are likely. If its in there and working well dont worry. The 3 options for the gearbox are
A: The cheapest oil of the same viscosity as the engine that you can find. Today that is still better oil than was available when the gearbox was designed.
B: 5 speed gear oil. There are a few brands on the market. Dont worry about the viscosity as gear oil is measured differently
C: Dexron 3 ATF However it likes to find ways out of the box
All the above work. One thing to avoid at all costs is diff oil. Diff oil additives eat brass synchro rings and break down at high temperatures into nasty things
Sanding your knuckles before starting work can help. That way you cant skin them
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Re: What Oil In The Gearbox

Postby WelshBoy » Sat Nov 02, 2019 4:22 pm

geeves wrote:Not quite unfortunately. Modern engine oils have friction modifiers which are great in the engine but dont play nice with syncro rings. It wont damage them if its already in there but when cold hard gear shifts are likely. If its in there and working well dont worry. The 3 options for the gearbox are
A: The cheapest oil of the same viscosity as the engine that you can find. Today that is still better oil than was available when the gearbox was designed.
B: 5 speed gear oil. There are a few brands on the market. Dont worry about the viscosity as gear oil is measured differently
C: Dexron 3 ATF However it likes to find ways out of the box
All the above work. One thing to avoid at all costs is diff oil. Diff oil additives eat brass synchro rings and break down at high temperatures into nasty things


Thanks have tried the engine oil nylon 15/40 will see how I get on
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