So you’ve been hearing a loud popping noise coming from your 4WDs drivetrain lately and you want to know what the possible causes could be. This article explains the origin of the strange sound and what method you can use to inspect your drivetrain to isolate the problem.
Loud popping sounds emitting from below your vehicle while in 4-wheel drive mode could be one of four different components. This is usually a worn-out u-joint from either your front or rear driveshafts. These components are most likely to could cause a loud popping sound when in 4WD.
Apart from the popping sound, you might also experience vibrations felt directly below the driver’s seat, clicking noises, or combinations of the three effects. The following section of this article will cover the trouble-shooting process in more detail, the function of the u-joint, as well as approximate cost to replace a u-joint on an (SFA) solid front axle 4WD
If you would like to know more about u-joint and how to troubleshoot the popping noise, continue reading.
What is that loud popping noise?
I’m a bit of a mixture between a petrol-head and a DIY kind of guy. With that being said, as soon as I hear something sound slightly off with my 4-wheel drive, I immediately investigate. I think it’s important to react immediately since a small issue, if left unattended for too long, could have a serious knock-on effect, resulting in an unnecessarily huge repair bill.
So back to the popping sound, in order to isolate the problem, you need to get beneath the vehicle and inspect the following components thoroughly:
- Front axle u-joint
- Rear axle u-joint
- Left wheel u-joint
- Right wheel u-joint
- Dripping rust water
- U-Joint rubbers
- U-Joint grease-nipple
What signs are you looking for?
Well, you want to identify any excessive play found between the individual drive-shafts, close to the u-joint where it joins the yoke. Excessive play can be anywhere between 4-6mm of movement in any direction. Grab a firm hold of the driveshaft and give it a firm upward and downward tug. Also, jerk the drive-shaft back and forth to check for any lateral play.
Always ensure the vehicle is parked with the gearbox in neutral. Place wheel stoppers or wedges behind the front and rear wheels for extra support.
Check the front U-joints
If you have a solid front axle, such as a jeep wrangler, you want to inspect the front wheel u-joints as well. Jack the wheel up slightly and grab a firm hold of the wheel and give it a few firm tugs in horizontal and vertical directions. This will isolate any play on the u-joints.
Rear axle
Carry out the same exercise you did with the rear, as you did with the front axles. Again, you want to identify any excessive play found between the rear drive-shafts, close to the u-joint. A worn or damaged u-joint will manifest itself with a metal on metal knocking or clunking sound when you change gears on a manual 4-wheel drive. You could also experience severe vibrations at speeds of 60km and upwards. This is because the u-joint is not rotating in a balanced fashion any longer and your driveshaft always needs to be balanced since it rotates at thousands of revolutions per minute.
Same as before on the front drive-shaft, give it a few firm tugs and shakes to check for any play. Also, rotate the driveshaft and repeat the exercise. There are 4 parts to the u-joint, sort of like a fat cross. This means you need to do the test, rotate 90 degrees, and repeat. This will cover all 4 joints.
U-joint rubbers
The main function of the u-joint is to lock in and seal all the grease necessary to lubricate and cool the u-joint. If the rubber seal is missing or cracked, all the grease will seep out, resulting in a dry u-joint. Because the u-joint is one of the lowest components of a 4-wheel drive, it is especially vulnerable to grit, grime, and dust. Once any small foreign objects enter and contaminate the u-joint, it’s just a matter of time before you can expect failure.
Dripping Rust water
This is another tell-tale sign that you have a damaged u-joint seal and possibly a rusting u-joint. The u-joint consists of a square-type body with 4 rotating joints and removable caps on each corner. These caps can be opened and greased since it consists of many tiny metal pins inside it. These pins need constant lubrication since they rotate at thousands of RPMs per minute, allowing the driveshaft to rotate and swivel simultaneously. Good lubrication is necessary to prevent overheating, excessive heat build-up, and finally failure.
Because the u-joint is one of the lowest components of the drive-train system, it is easily exposed to water, moisture, dust, and grime on a regular basis. It is, therefore, very important to regularly inspect your drivetrain components for wear and tear before and after each off-road outing.
Grease Nipple Damage
The grease nipple function is to be able to inspect and lubricate the u-joints when necessary. This is to alow hanging component and very vulnerable, especially when off-roading. If the nipple somehow gets bashed off, all the grease from inside the u-joint can leak out, causing accelerated wear and tear and eventually the clunking and popping sounds.
How to identify the faulty U-Joint
As previously mentioned, a faulty u-joint could display any of the following characteristics:
- Rust water leaking
- Excessive play in a horizontal direction
- Excessive play in a vertical direction
- Cracked or Missing rubber seals
- Lack of lubrication caused by lack of grease
- Missing or damaged grease nipples
Any of the above-mentioned symptoms will cause the popping noise you hear once you engage 4WD.
What is the function of a U-joint?
The purpose of the u-joint is to allow the driveshaft to rotate and swivel at the same time. This is done at an angle since the height of the transfer box and the front and rear axles are not the same, the u-joint allows the driveshaft to rotate at that angle safely. It also allows the front and rear axles to flex when off-road without disconnecting the driveshaft from the axles. If the vehicle has an extreme lift kit and aggressive suspension upgrade, there is an increased risk of the yoke slipping out of the axle when doing extreme off-road that requires full flex.
The approximate cost to replace a U-Joint
So now that we’ve isolated the possible cause of the popping sound and how to identify a faulty or dry u-joint, your next question will naturally be, how much does a new u-joint cost?
I’ve listed 3 u-joint options with various
price ranges.
At the time of me writing this article, the following u-joint combo was available
on amazon:
Option 1 (Moog 269 Super Strength Universal Joint)
Sells for $10,55 on Amazon
Features include
- A few of its features include:
- Super Strength alloy steel crosses for higher torque and horsepower
- Eliminates grease passages in the cross for maximum strength in high torque applications
- Exclusive MICRO SHIELD coating resists corrosion that may weaken the cross
- Needle bearings and snap rings sourced from OE supplier
- Nitrile rubber grease seals have compressed double lip design for protection from contaminants
Option 3 (Moog 377 Super Strength Universal Joint)
Sells for $16,34 on Amazon
Features include:
- Super Strength alloy steel crosses for higher torque and horsepower
- Flush lube fitting in the bearing cap for added strength
- Exclusive MICRO SHIELD coating resists corrosion that may weaken the cross
- Needle bearings and snap rings sourced from OE supplier
- Nitrile rubber grease seals have compressed double lip design for protection from contaminants
Option 3 (Spicer Dana 30/44 Heavy Duty Axle U-Joint Combo – Includes Pair of Spicer 5-760X Axle U-Joints)
Sells for $47.04 US Dollars. On Amazon
Features Include:
- O.E.M Replacement
- Heavy Duty Forged Cross with Inside Snap Ring.
- Perma-lube Improved Seals For Long Service Life.
- Cup Size= 1.188in / Snap Ring To Snap Ring= 2.188in.
Resources
Buy a new Spicer Dana30/44 Ujoint Combo (Amazon)
Buy a New Moog 337 U-Joint Here (Amazon)
Buy a New Moog 269 U-Joint here (Amazon)
Buy a Kryptonite Upper and Lower Ball-Joint package deal here (Amazon)
Conclusion
Before you venture into the unknown with your trusty 4-wheel drive, do the necessary checks on your drivetrain system first. This should preferably be done at least a week or two prior to you going off-road to buy some time to carry out any necessary repairs. If you often drive through rivers and on wet surfaces, you want to check all rubbers for cracks and ensure all seals are still in good working condition to lock that valuable grease in.