Extra leaf springs on a Nissan Navara to carry extra kilos!

Action 4x4 n° 73 - May 2010

Article by Bastien Poursin.

Note: Euro4x4parts publishes this information for the benefit of clients but cannot be held responsible for any use or misuse of this advice.

Pick-ups and other working vehicles fitted with modern leaf spring suspension often show themselves up when it comes to handling close to maximum permitted loads. Their dynamic abilities are significantly reduced and long distant travel becomes tiresome and sometimes even dangerous! If you have experienced this then suspension reinforcement is highly recommended.

Technical article

Vehicle: Nissan Navara D40

Installation - degree of difficulty: 2 / 5

Tools required:

Time required: 4 to 6 hours at the quickest!

There are numerous extra leaf spring kits available for all types of usage, with or without lift, offering varying degrees of rigidity and stiffness, according to your requirements, etc...

For this workshop test we've decided to try the "Add-a-leaf" model by Trail Master which is available in 2 versions: one for a constant load of 400 kilos and another reinforced for a rated 800 kilo load.

We installed the latter version. The leaf springs supplied in the kit are nice and thick and reinforce the suspension so much that unladen use is not practical.

This mega kit is aimed in particular at owners adding a camper cell to their pick-up. For standard use the first model is more suitable.

Leaf springs - the oldest system

Quick reminder: suspension is comprised of elements that link non-suspended masses (wheels, brakes, etc...) to suspended masses (chassis, engine, etc...). The suspension serves to reduce the impact of the effect of variable levels of road surface and also ensures contact between the wheels and the ground despite these variations. This is the prerequisite for road handling.

The suspension system also carries the weigh to the vehicle and the load.

Suspension systems are normally comprised of a spring (leaf, coil or pneumatic...) and shock absorbers. Leaf spring suspension is an old concept and was first used on carts and other solid axle horse-drawn vehicles. The main advantage of this type of set-up is a simplified installation whereby the axles is held and directly guided by the spring.

The leaf spring is a series of superimposed plates of ever decreasing length, presented in the form of an upside down pyramid. The ends of the longest plate are the vehicle attachment points and the wheels are attached in the middle.

The longest plate, known as the "master leaf", must have cross-section large enough to bear the "brute load", as well as acting as the link between exterior elements. The ends are always shaped according to use. To avoid "sagging" in other words when the plates come apart, the plates are increasingly curved as of the longest (master) leaf to the shortest. The cross-section of each leaf has to be progressively reduced so as not to overstep the limit of flex.

That's about it for this month's theory lesson, now let's get to work!

Last reminder: the method for adding additional leaf springs is generic and can be applied to all types of models.

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To validate our test we start off with our standard navara loaded with a palette of pink quartz weighing almost 700 kilos. As a result, the rear suspension, already pretty tired is seriously suffering!

The leaf springs are actually curved in the wrong direction!

The vehicle loses 8cm under this load.

You need big axle stands to chock a pick-up as big as a navara.

Block the vehicle so that the rear axle is suspended ready for you to work on.

On this particular model, having been used for lots of towing work, the leaf springs have lost their curvature.

The additional leaf springs are quite...

...impressive!

Before starting, undo this small hose to avoid damaging it.

Start off by undoing the suspension U bolts.

Remove.

Unscrew the front bolt.

Then move on to the rear shackles.

Remove the front bolt.

Here is the collection of parts removed.

Remove the bump stop.

Now remove the shock absorber lower mounting bolt.

All that remains is to slide out the leaf spring set.

The leaf springs are now removed.

Now remove the leaf spring shackles.

The extra plate sits behind the last curved plate.

To tighten the set of plates with the extra leaf we recommend pre-assembly using a large vice.

Show the leaf spring ready to be reinstalled.

The extra plates are so thick that...

...longer U-bolts need to used when reinstalling.

Before heading off onto the road, don't forget to put the hoses back into position.

The Navara now supports the laden weight of the palette with ease.

Thanks to Euro4x4parts and to Combs Automobiles Garage (77380 Combs-la-Ville, France) for their help preparing this article.