Loud Popping Sound When In 4-Wheel Drive: SOLVED

So, lately, you’ve been hearing a loud popping sound when in 4-wheel drive and you want to know what the possible causes could be. This is not a sound you want to hear when you’re off-roading. This article explains the origin of the strange sound and what method you can use to inspect your drivetrain to isolate the problem irrespective of your vehicle type.

If you hear loud popping sounds coming from underneath your vehicle while in 4-wheel drive mode, it might indicate an issue with your U-joints. Typically, this noise is caused by a faulty u-joint in one of your driveshafts. These components are commonly responsible for generating such loud popping sounds specifically when engaging 4WD.

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 the approximate cost to replace a u-joint on an (SFA) solid front axle 4WD

Loud Popping Sound When In 4-Wheel Drive: U-Joints

As someone passionate about cars and inclined toward do-it-yourself projects, I embody a mix of being a petrolhead and a hands-on enthusiast. Whenever I notice even a slight irregularity in the sound of my 4-wheel drive, I promptly take action and investigate. I believe swift responses are crucial because a minor problem, if ignored, could escalate into a larger issue, leading to an avoidably substantial repair expense.

So, to isolate the loud popping noise you need to get beneath the vehicle and inspect the following components thoroughly:

Component	Description
Front axle u-joint	Connects front axle shafts and allows movement
Rear axle u-joint	Connects rear axle shafts and allows movement
Left wheel u-joint	Connects the left wheel shaft and enables movement
Right wheel u-joint	Connects the right wheel shaft and enables movement
Dripping rust water	Indicates corrosion or rust issues, leading to water leaks
U-Joint rubbers	Flexible components around the u-joint for cushioning
U-Joint grease-nipple	Fitting for applying grease to maintain u-joint lubrication

What indications should you watch out for? You’ll want to spot any notable looseness present in the individual drive shafts, particularly near the U-joint where it connects to the yoke. Excessive play typically manifests as movement ranging between 4 to 6mm in any direction. Grip the driveshaft firmly and apply an upward and downward force. Additionally, move the driveshaft side to side to detect any lateral play.

Ensure the vehicle is parked with the gearbox in neutral. Enhance stability by placing wheel stoppers or wedges behind both the front and rear wheels.

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 they consist of many tiny metal pins inside them. 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 regularly. 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’s function is to be able to inspect and lubricate the u-joints when necessary. This is to allow hanging components 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:

1. Rust water leaking
2. Excessive play in a horizontal direction
3. Excessive play in a vertical direction
4. Cracked or Missing rubber seals
5. Lack of lubrication caused by lack of grease
6. Missing or damaged grease nipples

Any of the above-mentioned symptoms will cause the popping noise you hear once you engage 4WD.

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 my writing this article, the following U-joint combo was available on Amazon:

Option 1 (Moog 269 Super Strength Universal Joint)

Buy a New Moog 269 U-Joint here (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 a compressed double lip design for protection from contaminants

Option 3 (Moog 377 Super Strength Universal Joint)

Buy a New Moog 337 U-Joint Here (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 a 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) Buy a new Spicer Dana30/44 Ujoint Combo (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.

Final Thoughts

Before embarking on an adventure with your reliable 4-wheel drive, conduct essential inspections on your drivetrain system. It’s advisable to perform these checks ideally a week or two before your off-road journey to allow ample time for any required maintenance. Particularly if you frequently navigate through rivers or wet terrains, examine all rubber components for signs of cracking and ensure the seals remain in optimal condition to preserve the crucial grease within.