Navara D40 YD25 Gear Reduction

[kylepacemt]

Hi Guys,

I want to dive into improving my drivetrain and I'm wondering if anyone has lowered diff gears on their d40's ?

I did some quick research and stock rations are 3.4/3.5 roughly and I was thinking of going somewhere in the 3.9/4.0

Reason: My truck is Spanish yd25 with a 6 speed manual running 285/70/r17 Toyo Tires and loaded most of the time and it struggles to keep in gear, for example at a hump/speedbump I have to downshift to first as If I try to go in 2nd it'll stall.
I'm from Malta and I wouldn't worry about reducing my overall top speed cos max I can go here is 80km/h though overland I cruise at a 100 usually.

My question is will this effect anything related to gbox/tcase or any issues and i'm assuming the ideal way would be to do both front and rear axles with the same ratios?

I really enjoy my truck but I've been contemplating getting an auto lately but I've spent too much $$ and effort into my truck and I know I got a solid one so it's not worth getting rid of, I just need to improve the ride.

Regards,
Kyle

 

[Old.Tony]

At worst case you're actually reducing the load on the engine and gearbox.

Yes, you have to change both front and rear diffs unless you decide to never use 4WD (and for safety's sake, pull the front drive shaft out).

 

[kylepacemt]

I did some research and I could only find 4.1 gear sets for Frontier (US Navara), but im not sure if specs, gear teeth etc are the same and I need to look into it more as they aren't cheap.

 

[landmannnn]

I did some research and I could only find 4.1 gear sets for Frontier (US Navara), but im not sure if specs, gear teeth etc are the same and I need to look into it more as they aren't cheap.

The Frontier and the Spanish Navara are fitted with the same Dana differentials.

Yes, you can buy different ratio ring and pinions from such as Yukon in the US. Not cheap to buy or install.

In terms of your problem, the slightly lower ratio will not make any noticeable difference, and I suggest your problem is a failing dual mass flywheel.
Failing dual mass flywheels make stalling quite easy, if you have a good one or a decent substitute such as Exedy, it is very difficult to stall.

 

[kylepacemt]

The Frontier and the Spanish Navara are fitted with the same Dana differentials.

Yes, you can buy different ratio ring and pinions from such as Yukon in the US. Not cheap to buy or install.

In terms of your problem, the slightly lower ratio will not make any noticeable difference, and I suggest your problem is a failing dual mass flywheel.
Failing dual mass flywheels make stalling quite easy, if you have a good one or a decent substitute such as Exedy, it is very difficult to stall.

Thanks for the advise man. Ye I was contemplating replacing the whole thing to a single mass flywheel with a juicy clutch. I'll look into it