Thread: Hilux inverted leaf springs

Originally Posted by Tommy

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!
--https://vehicleinspection.nzta.govt.nz/virms/in-service-wof-and-cof/general/steering-and-suspension/steering-and-suspension-systems
the springs or shock absorbers are direct replacements, and
replacement springs are contained within unmodified OE seats throughout full suspension travel (Note 8), and
replacement springs are self-retaining in their seats at full extension, without the use of non-standard devices such as wire-ties, straps, or external spring locators, and
replacement springs have not been heated or cut, and
springs and spring seats are not height adjustable by any means (unless OE) (Note 9), and
replacement shock absorbers, including air-adjustable units, fit unmodified OE mountings (Note 8), and
suspension maintains sufficient travel for safe operation (Note 10), and
suspension components maintain sufficient clearance from unmodified bump stops when fully laden (Note 11), and
Suspension retains at least 40mm of rebound (droop) wheel travel (Note 12), and
a minimum of 100mm ground clearance (unladen and without driver) exists below any part of the vehicle structure, or any steering, braking or suspension component (Note 13) and
the normal relationship between front and rear suspension height is not unduly affected, and
clearance is maintained between all components, when tested from lock to lock at full droop

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.
Yup, you'd chuck some decent shocks at it too
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.
Yep

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. Again, that's going to require cert - "Note 8- Strut or spring spacers always require certification."

Ahhh - that's how those particular ones I got are able to do it then. The lower spring cup is a separate part to the shock body on the foam cell struts I got which is where the spacer goes - between the lower cup and the strut body and cup stop ring. The spring remains fully contained within the designed elements of the strut and factory upper mounting. It's a designed system and non-adjustable once the spring is in place and serves to only control the preload on the coil spring. Probably a better term is a preload adjustment element rather than spacer? It's not a spring spacer or a strut spacer according to that definition. Good to know... Thanks.

On the other hand - how in the hell do ute makers claim that their products meet WOF specs at full load when with half of them the vehicle is sitting ON the bump stops at 500Kg below max rear axle weight? I've often asked this and get the 'mumble mumble mumble' reply.