Fitting The Roll Cage

You Have To Get This Right!

Last time, we “modified” the Pajero with some metal artwork, courtesy of an angle grinder!

It doesn’t matter what type of car racing you’re into, a quality roll cage is critical. Without being melodramatic, a roll cage can be the difference between surviving an accident or not.

All painted and ready to fit out!
It took a lot of work to get to this point. The cage is complete.

Firstly, A Few Words About The Paj. No doubt lots of you will be thinking, “They’re crazy. How can you cut the guts out of a monocoque and expect it to still be strong?”

Well, you could be right. Time will tell.

Test-fitting the roll cage in the Pajero ute
Test-fitting the roll cage. This cage was removed from Dave’s previous rally Paj.
Test-fitting the roll cage in the Pajero ute
Needs lots of work, but the cage will definitely fit.

However, those Japanese Engineers are pretty clever. Yes, the Paj is a monocoque. But have a closer look. It actually has chassis rails. No, they obviously don’t form a separate ladder frame chassis with a body on top. There are chassis rails though, integrated into the body pressings.

My Generator Black Friday sale now on.
Black Friday Sales specials at My Generator.

Dig a bit deeper and you’ll see these chassis rails are multiple layers of high tensile sheet steel, spot welded, bent and folded in a million places for strength.

So there’s hope yet…

The Roll Cage Becomes The Structure

So clearly, the roll cage needed to be strong. Not just for safety, but also to give the body extra strength.

Let’s step back for a minute and state a few obvious and not so obvious things.

  • Any roll cage has to be super-strong, to form a protective cocoon around the occupants. That’s a given.
  • A standard cage consists of a main u-shaped hoop behind the seats and then lots of triangulation.
  • In a body-on-chassis vehicle, the cage goes through the floor pan and is welded to the chassis rails.
  • The roll cage has to be built to Australian Standards, using chrome-moly tubing.

Where to attach the cage in a monocoque? Well it turns out the Paj has a super-strong area at the front of each footwell with a fully formed chassis rail underneath. Makes sense – this is a weak point in most vehicles.

Details of the front bottom corner of the roll cage
Front left corner of the cage.
Details of the front bottom corner of the roll cage
Closer view. Fully welded to a footplate, then the footplate was fully welded to the floor. This sits directly over the chassis rail.

And behind the seats – in what was the rear seat floor pan – is another really strong body/chassis point. This is also stiffened across the vehicle, from one side to the other. Perfect!

Detail of how the cage mounts to the floor behind the drivers seat
In behind the driver’s seat. The footplate steps down and again is fully welded directly over the chassis rail. The high part of the foot is mounted directly over a stiffener that runs across the vehicle.
Behind the passengers seat. Details of how the roll cage attaches to the floor pan.
In behind the navigator’s seat.

What About The Rear End?

This is an interesting one. Obviously, the rear suspension cradle gives this area strength. Also, a folded and spot welded chassis runs all the way to the back. Lots of complicated bends and folds in the floor also stiffen up this whole area.

But we’ve just removed the top half of the body. What to do?

Well, we decided to run braces from the top of the cage down onto the wheel arches, then triangulate this back to the bottom of the main hoop, then triangulate down to the floor. Another cross brace – again triangulated to the floor locks it all together in the side-to-side direction. Confused? See photos below.

Details of the roll cage over the rear wheel arches.
Bracing down from the main hoop onto the top of the wheel arch, then triangulated back to the bottom of the main hoop. The additional brace to the floor is there just in case the body decides to twist. It is directly over the rear suspension cradle.
Details of the roll cage over the rear wheel arches.
Another view showing how the rear end was strengthened from side to side. The bar running to the back corner is another “just in case” bar.
Rear view of the roll cage.
Lots of triangulation!

How Do You Prevent The Roof From Caving In?

With lots of triangulation! One place often forgotten when building a cage is the centre of the roof at the front. We’ve triangulated the roof, then continued it down to the transmission tunnel.

Details of the roll cage under the roof
Details of the roll cage under the roof (windscreen at right of photo). Note how the front centre has been strengthened.
Bars from the roof to the floor help to prevent the cage from collapsing
These vertical bars help to stop the cage from collapsing downwards. They continue down to the transmission tunnel.
A neat solution for mounting the steering column
A neat solution for mounting the steering column.

Will The Paj Hold Together?

We’re confident it will. Having said this, off-road racing is brutal on cars. So if there’s a weak point, we’ll know about it pretty quickly!

If you look closely in the photos, you’ll see lots of welded tags – flat bar folded and fully welded both ends. They make a world of difference – the body is effectively locked into the cage. In the photo below for example, you can just make out two sets of tags on each of the cage bars. These particular ones lock the B-pillar into the cage. And the bottom bar has three tags which lock the floor to the cage.

Side intrusion bars protect the navigator
Side intrusion bars protect the occupants. Note the bar along the bottom. This ties the whole thing together to form a cocoon. It you look closely, you’ll see all the tags locking the body to the roll cage.

Next time: Doing the bodywork… so time-consuming.

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4 thoughts on “Part 7. Let’s Build A Race Car – A Pajero Ute. Fitting The Roll Cage.”

  1. Has anyone ever put An LS1 into a registered 96 NJ Pajero and used it as a daily Driver? If the answer to that question is a yes could I be advised as to what type of running gear I’m going to be needing it and adaptor plate eccetera


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