Universal joint failure causes horror accident…the tell-tale signs your u-joint is about to fail

ByIsaac BoberNovember 11, 2019
3 MINUTE READ
Universal joint failure causes horror accident…the tell-tale signs your u-joint is about to fail

A recent Facebook post showing a horror crash because of a universal joint failure is a timely reminder for four-wheelers to give their rigs some TLC.

Unsealed 4X4 reached out to Jose Hernendez after he posted photos of his friend’s mangled vehicle.  It had flipped four times after the double Cardan universal joint had fallen out and caught against the road. The driver was lucky to have walked away with just a “broken sternum and scalped head,” according to Jose. The poor old short-wheelbase GQ Patrol was, as you can see, a complete write-off.

With permission from Jose, we’ve shared the photos of his friend’s accident, and we wish him a speedy recovery. With the Christmas holidays fast approaching we thought it timely that we remind four-wheelers to keep an ear out for a u-joint on its way out.

First up, let’s take a quick look at what a universal joint is. A u-joint (or uni-joint) is a way of connecting two straight rods and is designed to compensate for any difference in height between the transmission and the rear axle. There’s one at each end of the driveshaft, allowing the shaft to ‘bend’ as it turns. A double Cardan joint is essentially two universal joints mounted back to back; the second Cardan joint will cancel out any jerks in the first one and act as a CV joint. Essentially, u-joints help to remove jerkiness from the drive shaft’s rotation.

But when they fail, well, you can see from the photo above what can happen. So, what should you be looking out for to avoid u-joint failure?

The first thing is a squeak or squealing noise. You’ll likely hear this when driving both forwards and in reverse but only at low speeds, this noise is a tell-tale sign the bearing(s) in the u-joint are on the way out. See, while they’re greased from the factory, because the bearings on a u-joint tend to spin only in one direction, the grease can be forced out causing the bearing to become dry. Take your vehicle to your mechanic to have the bearings re-greased. That said, most uni-joints have a grease nipple, and if you’ve got a grease gun and are handy on the tools, you can regrease them yourself.

If you ignore the squealing bearings or fail to notice them, you’ll likely then hear a clunking noise. The bearings have stopped doing their job properly and are allowing too much movement because they’ve got insufficient grease; the clunk will be heard when you change from Drive into Reverse, or as you take up the clutch in first gear – this is the slack in the u-joint being taken up, with the slack getting worse every time you take off (it’s a slippery downhill slope from here).

Ignore those two noises and you’ll then get vibration at speed. The buggered bearings are allowing too much movement of the driveshaft. If this is left to continue then you’ll start causing damage to other parts of your vehicle, like your gearbox. Transmission fluid leaks are a sign your u-joint is literally on its last legs, as the more movement allowed around the joints, the more the tail-shaft yolk (the part that connects the u-joint to the output shaft on your gearbox) can move around, and this can and will damage the output shaft seal, allowing gearbox oil or Automatic Transmission Fluid (ATF) to leak out. Ignore this one and there’s a good chance the u-joint will fail completely and fall out like it did in the photograph above and cause a potentially fatal accident.

Where a uni-joint failing can cause serious issues and potentially an accident, is if the front uni-joint lets go of the rear tail shaft (for argument’s sake), the front of the tail shaft can drop on to the ground, while still being connected to your rear diff, and dig in to the bitumen or track. Think of it like pole-vaulting your four-wheel drive – obviously not ideal. Either it’ll tear your rear diff clean out, or make your whole rig do a front flip crossed with a barrel roll.

Unfortunately, heavily modified vehicles cause havoc with u-joints, whether that be through big lifts increasing angles on the uni-joints from your transfer case to your diff, or engine power boosts causing stresses on the u-joint it wasn’t designed to handle. Similarly, fitting bigger tyres can cause premature wear and tear on u-joints, as can aggressive off-roading or when towing heavy loads. Don’t get us wrong, we’re all for modifying our rigs, it just means we’ve gotta spend more time under them keeping them running right.

If you’ve modified your vehicle, make sure you get the u-joints checked to ensure the angles are still correct. If they’re out of alignment, then a visit to your mechanic is essential. Universal joint failure has never been a good thing for anyone, and you don’t want a simple bit of maintenance destroying your pride and joy.