There’s nothing more frustrating than busting a CV off-road. Swapping one out is a messy job at the best of times, but what’s worse is that CV breakages usually happen at the most inconvenient time, like half way up an epic hill climb or while clinging to the side of a rock ledge. So not only is it a pain in the neck to repair, but a busted CV at the wrong time could put you and your passengers in real danger.
That’s exactly why we want to arm you with the info you need to properly bush-proof your CVs. We’ll run you through how they work, what causes most problems, the upgrades available, plus proven driving techniques that’ll get you out of trouble every time.
WHAT MAKES YOUR CVs TICK?
Your CV joint’s job is to transmit drive from the diff to the hub while allowing the wheel to steer left and right and the suspension to move up and down. They’re also somewhat of a fusible link in your drivetrain designed to protect more expensive components, like your diff and gearbox, from sustaining damage when placed under extreme loads.
Most CV breakages happen when the joint is at full stretch, or if a tyre comes crashing back to earth while the engine’s under load, as the shock load shatters the internal cage or cracks the bell. The resulting ‘crunch – clack, clack, clack, clack’ and lack of drive is a dead giveaway that you’ve busted a CV.
BIG TYRES COULD COST YOU MORE CVS
Regardless of if you drive an IFS or solid-axle, fitting larger aggressive tyres increases your chances of snapping a CV. Just like using a longer breaker bar allows you to crack tight nuts and bolts, larger tyres have greater leverage over your driveshaft, increasing the load being placed on the driveline.
Where your old highway terrains would slip and spin, larger off-road tyre bite into the terrain and transfer that torque straight through your CVs. If this happens when the CV is at full lock or the suspension is at full droop, there’s a good chance you’re going to do damage. Your best bet here is to avoid opting for a larger set of tyres than you really need. Anything larger than 32s for IFS rigs and 35s for solid-axle trucks, and you’ll start to find your CV’s working limits.
LIFT KITS WEAKEN CVs
The flatter you can keep your CV angles, the stronger they are and the longer they’ll last, which is why manufacturers align the diff with the wheel so the CV sits as flat as possible from standard.
Fitting a lift kit to a 4WD with IFS increases the angle of the CV, as the wheel is pushed down away from the chassis while the diff remains in the same position. Naturally, this means the CV is working much harder even just punting around town, and it’s much closer to its weakest point off-road. Installing a 2in lift kit in an IFS 4WD is about as far as you want to push things if you don’t wish to sacrifice off-road reliability. Anymore and the CV angle becomes too great, and even the smallest shock loads could snap your CV like a twig.
Bump stops are fitted to the suspension control arms to limit the amount of up and down travel, and therefore the severity of your CV angles. When lifting your independent 4WD, the bump stops will need to be extended to avoid over stressing the suspension and driveline components. It’s much better to limit suspension travel by a couple of inches than have to replace CVs or bent shocks after hitting a pothole off-road. You can also look at fitting a diff drop kit to level out the CV angles, but you’ll need to get it engineered which is often a lot more hassle than it’s worth. Solid-axle 4WD owners don’t have to be as concerned when raising the ride height of their 4WD, because the diff, CV and wheel hub move together as one. So even when taller springs are installed, the CVs remain flat.
GO EASY ON THE LOUD PEDAL
Throttle control is the most effective way to reduce CV breakages. Instead of busting through obstacles at warp speed, aim to roll up over technical obstacles as slowly as possible. This is even more important if you’re tackling an obstacle like a rut or rock step, where you’re constantly lifting wheels. You want to minimise wheel spin as the tyre comes back down to earth, which in turn reduces the shock loads transferred through the driveline.
TYRE PRESSURES ARE MORE IMPORTANT THAN YOU THINK
Most of us know that reducing our tyre pressures off-road helps to increase traction, but did you know it also helps to save your CVs? More traction means you can steadily crawl over obstacles without losing momentum and spinning wheels. This is particularly important when tackling hill climbs and rock steps, where your 4WD is constantly shifting its weight on and off each tyre.
If you do notice it starting to buck all over the place, instead of feeding the gas, gently back off, reassess your line and give it another go in a lower gear. If you’re struggling in low first and can’t go back, you’re better off calling for the winch than you are busting a CV.
GO EASY ON THE STEERING
In steep rocky country, jamming a tyre into a big rock is fairly common. Sometimes the weight of the 4WD can rip the steering wheel from your hands, forcing the front wheels to full lock. In this situation, the worst thing you can do is feed the accelerator and try to drive through it, particularly if you have lockers engaged. If your tyre is jammed up and you hit the go pedal, all of your engine’s torque begins to wind up in the driveline, and if your steering is at full lock, you’re more likely to do damage than you are to drive out.
Having your standard CVs heat-treated will add strength without breaking the bank, but most people invest in heavy-duty chromoly replacements. They’re made from a high-grade 4340 steel (chromium, molybdenum and nickel) and have a thicker bell and cage. Definitely a worthwhile investment if you’re a little go-hung on the loud pedal. Cough – Brenno – Cough.