Bodywork - "There are things to be said about having a chassis..."
This section is really just a list of the weak points we found in the existing Commodore shell.Roll-Cage
When purchased the car already had a roll-cage installed. The amount of metal in the cage was about twice what the CAMS regs. required, including thick-walled tube and extensive additional bracing. One problem we had was the tubes running forward of the main hoop towards the front A-pillars were almost directly above the driver and navigator's heads. Rather than move the tubes, we decided to lower the seats to provide enough clearance between our helmets and the tubes (min. 50mm clearance to the roof). In hindsight, the resulting loss of forward vision was probably a 'bad thing'; it certainly made avoiding some obstacles more difficult.
Bracing didn't pick up the rear suspension/shock mounts, nor was there much bracing in the boot area.
Rear Suspension Mounts
The mounting points for the upper control arms are very suspect. Not only do the arms cop a bashing but the mounts themselves will eventually tear out of the monocoque. We had a couple of billet-ally arms made for us complete with a Heim joint at either end, which seemed to last quite well. As for the body mounting points; we eventually plated the entire mount location (on both sides) and the replacement arm mounting bolt was long enough to pick up a decent Nylok inside the chassis rail.
Rear Shock Mounts
The wheel arch upper shock mount seems to do a reasonable job of holding the unit in place, however when we decided to run dual shocks (less load on each, thus less heat, thus they run longer before fading out due to heat stress) the inner mounting point made a nice mess of the arch. Running a monocoque has the disadvantage of having no respectable metal around any suspension mounting point. So to solve the shock mounting problem we fitted a large RHS above the rear parcel shelf and boxed the chassis up to that. Some additional bracing back to the roll cage completed the strengthening. The boxed section picked up some longer shocks with stock polyurethane bushes at the top and Heim joints at the axle. Problem solved.
Boot and the Fuel Tank
The stock Commodore boot floor is an simple folded piece of sheet metal, supported mainly by the rear quarter panels and some small amount of bracing running under the floor. Over time (with a bit of weight in the boot; created by the rather large custom fuel tank), the metal at the base of the rear pillars will fatigue and start cracking. The options were to reinforce this location or provide additional bracing elsewhere. We eventually (after having the boot strapped-up during one race) dropped a couple of tubes from the top shock mounts to the rear of the boot and created some nice triangulation in the area.
Lights, Fenders and the Monocoque
Lights (as per the 1600) were protected by polycarbonate lenses. The mounts for these deteriorate over time and a few knocks will make using the standard push-in fitment unusable. The best solution using the original lenses was a combination of numerous metal tabs, screws and a fair bit of silicon goop. Unfortunately replacing the things when they get whacked is rather expensive and time consuming. Eventually the units were replaced with a couple of spots mounted horizontally through the radiator support housings. These were relatively cheap, easy to mount and keep mounted, reliable and came complete with polycarbonate lenses. They gave the car a bit of a bug-eyed appearance, but seemed to do the job.
Fenders need to be seriously cut/moulded to fit any decently sized tyre. We were running 31" tyres which required some significant removal of material. Note that where the guard bolts to the floor pan is a weak point. These locations are subject to constant hits and the standard bolts will shear/tear. Somewhat surprisingly, the easiest solution was running large cable ties, which if sheared were easily replaced.
The monocoque in an old offroad car is difficult to work with. Not only is the thing old/rusty but generally the metal has started fatiguing and doesn't require much to actually rip. Particularly prone parts of the monocoque are the upper arm mounts for the rear axle, strut towers (they start folding), engine-bay chassis rails (if you can call them that), and certain sections of the floor pan (particularly the transmission tunnel). Plating is an option, but pretty hard to do without the right gear, plus it takes a while and adds more weight. If possible, run all the suspension, shock, engine, transmission, etc mounts back to some part of the roll-cage. Not only will the car be easier to modify, but it'll last longer.
