Thread: Hilux inverted leaf springs

Originally Posted by Tommy

Just keep in mind that adding cut down springs to spring packs, and airbags, all require cert.

A replacement spring pack perhaps? They're not expensive

https://motortech4x4.co.nz/product/o...hilux-2015-on/

Huh, didn't know that airbags require a cert. Also didn't know that a cut down leaf required a cert as well... I'm amazed if they are getting that strict that you can replace the leaf pack with an aftermarket and not need a cert!

But yeah, those leaf packs look about right from where my experience of these things go - they aren't that dear as indicated. But add to that price doing the rear shocks as the factory gas struts just won't handle those springs at all, the biggest single change you can make is replacing the shocks and even just doing the shocks will make a hell of a difference to how the factory springs behave.

I think that the main issue with the factory shocks is that they are designed and calibrated for the vehicle unloaded and they do that well, expect that we in NZ suddenly hang towbars on the back and expect the vehicle to suddenly do the work it's designed to do empty but at full axle loads. Something has to give, and in this case the gas-oil factory shocks suddenly find their operating cycles go up a huge amount and the result is heat. Heat is the enemy of shock oil, the viscosity lowers as the oil heats up and it passes through the shocks valving much more quickly and reduces the damping effect. This in turn means that the springs start getting smacked in to next week with no damping, and this is how the springs end up going past their elastic limit.

The next problem is the suspension at both ends must work together to keep everything pointing the same way - if you upgrade the back end the front will feel like absolute garbage. As a minimum get the matching set of front struts to the back, and retain the factory springs. You may require a spacer on the spring to increase the preload slightly - my understanding of the rules is that provided you don't increase the lift past 50mm and don't have anything adjustable without disassembly you are able to do this without cert. For reference, most of the ute double wishbone front ends run a 2-1 design ratio which roughly means a 10mm spacer increasing the preload on the factory spring gives about a 20mm lift at the wheel. You won't notice the effect of the spacer on travel or articulation in normal conditions.