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Winding it up

September 22nd, 2013

NOTE: For our Facebook readers, there are instructional photos included in this blog that Facebook will not show, please click on the above link to see the blog complete with photos.

One of the questions we are very often asked is about lifting the suspension. On Japanese trucks suspension lifts tend to be limited due to the independent suspension on the front end. When you take the front wheels off these trucks you’ll find no coiled spring, or leaf spring for that matter, the spring is slightly different, it is a bar, known as a torsion bar, the spring is derived from the twisting of the bar. The torsion bar runs from the lower wishbone back to a cross member somewhere near the rear output shaft of the gearbox (depending on make and model of course).

Now the torsion bar can be adjusted to wind up the suspension, there are pros and cons to doing this and we’ll cover these at the end.

This photo instructional was originally posted by the author in 2007 on Team Mudlark, it has been plagiarised and credited to other authors on certain forums since then but we have permission to reprint it here!

First job was to jack up the truck and put the axle stands under – had to put them behind the gearbox cross-member otherwise they’d get in the way of the job  Wink

Wire brush all the muck off the ends of the torsion bar bolts – then undo them completely

Measure them at the point where they are no longer under torsion:

Undoing and Measuring the Adjusters
Which worked out to be 60mm (this should be standard on all models)

Once the torsion bar is loose you then have to undo all 4 bolts on the gearbox cross-member – CAUTION only work on one side at a time and put the bolts back once you have finished that side!

Undoing the Bolts on the Gearbox Cross Member

Pull back the rubber gaiter on the front of the torsion bar

Pulling Back the Gaiter

The torsion bar will now pull out of it’s socket

Removing the Torsion Bar from it's Socket

Now index the torsion bar around – clockwise on the left hand side (looking to the front) and anti-clockwise on the right hand side (looking to the front)

The amount to index is calculated as follows:

Distance from pivot point to bolt/measuring point on torsion bar = 120mm

Distance from torsion bar to lower ball joint on wishbone = 400mm approx

Ratio = 3:1 approx which means every 1mm movement on the bolt moves the suspension by 3mm

So I indexed the torsion bar by 20mm allowing me a 60mm lift

Measuring  to get the Extra Lift
So the total amount is 80mm – note the jack used to lift the torsion bar into place and ease the pressure on the bolt while I was tightening it

Finally adjust the bolt so that the final measurement on the torsion bar is 20mm

Tightening up to Final Measurement

Last job is to refix the gearbox cross-member bolts and fit the front gaiter into place.

Repeat for the other side

Pros and Cons:

Pros:

It’s easy to do

Biggest pro is that it’s free – it costs nothing to do

 

Cons:

Once you have done it your steering geometry is going to be totally out – we need to look at the wishbones to understand this. With the front wheels off you will see the hub which is attached top and bottom to two arms which resemble wishbones and that is what we call them.

From the hub attachment to the point on which the wishbone swivels on the chassis you will see that the distance is shorter on the upper wishbone compared to the lower one, the reason for this is to try to keep as much of the middle of the tyre on the road when the suspension is forced up or drops down – example:  the wheel drops one one side (i.e. the chassis is lower on the dropped wheel side) the action of the wishbones pull the top of the wheel in towards the chassis causing the tyre to stay flat on the road even though the chassis is at an angle to the road. The wheel on the other side of the car does the opposite – the layout of the wishbones causes a reversed action.

So when you wind up the torsion you cause the wheel to droop angling the tyre to run on it’s inner edge, although this can (in most cases) be corrected somewhat, there is rarely enough adjustment to pull the camber (the angle that is affected) back to the original position

An additional effect will mean the tracking is out but this can be corrected to normal.

Although the cost of the modification is nothing, the result of the camber being out (if you can’t fully correct it) will mean that the tyre will wear excessively on the inner edge causing an early tyre replacement.

In addition with the hub now running much lower in relationship to the chassis you will find the constant velocity joints are now loaded close to, if not on, their maximum angle for normal driving. When the wheel demands more droop (when it’s articulating) the CVJ is going to be on breaking point – and yes they do break!

Finally many trucks have a bearing (usually a fine needle bearing) between the drive shaft and the hub, especially if there are auto or manual free wheeling hubs, this bearing allows the hub to spin independently of the drive shaft, the strain of a torsion bar lift will wreck  this bearing!

Conclusion: A cheap to do lift that will have long, and big, running expenses. Having said all that there is still a place for this lift for tweaking between 12 and 38mm after you have done a body lift – just to get that extra bit of lift to avoid rubbing on full articulation.

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