Jeep Wrangler Knocking Noise When Accelerating – SOLUTION

Jeep Wrangler knocking when accelerating

When taking off from a stationary position, have you noticed a loud knocking noise? Does it only occur when you initially press the gas pedal? Does it make an audible metallic ‘clunk’ when going over bumps? If you are experiencing any of the above mentioned symptoms on your Jeep Wrangler, then this article has the solution.

When your Jeep Wrangler emits a loud metallic knocking noises when accelerating, it can be caused by wear on any of the following components.

  • Driveshaft U-joints
  • Front axle U-joints
  • Engine Mounts
  • Transmission Mounts
  • Loose Shock/Strut Mount

In order to accurately diagnose the problem, we need to eliminate a few possibilities by doing a few simple checks.

Has your suspension been modified recently? Check all Sway bar links after suspension lifts for play. Inspect for a loose control arm bushing in the arms if you have stock LCA (Lower control arms) If you’ve recently been off-roading and knocked a skid plate, this could misalign it, causing it to make contact with your exhaust pipe when you pull off hard. Also make sure all your exhaust clamps are still ok and are properly torqued.  Inspect your frame side rear track bar and make sure its torqued to spec.

If you are 100% sure all of the above-mentioned components are all ok, then we need to look a bit deeper to find the culprit.

Jeep Wrangler Knocking Noise When Accelerating

Let’s look at a few real-word reports and experiences of Jeep Wrangler owners.

User Experience

At a stop light and accelerating or while i am coasting i hear a god awful knocking noise in my rear end.. and i can feel it coming from the rear end. I am hoping to god its not my wheel bearings.. Any idea what it is??

Hey all trying to diagnose a problem I’ve been having, 02 TJ 4.0 5 speed 2 inch spacers on stock suspension and 31″s, when taking off from a dead stop I hear a somewhat loud clunk as if something is loose or has play in it, it only occurs when taking off hard from a dead stop, sounds like it may be coming from the driveshaft or rear, I took a look under there and nothing seems to be out of the ordinary, kind of hard to describe without hearing it for yourself but does anyone have any ideas

Symptoms

Some of the reported symptoms include:

  • Loud clunk noises
  • Mostly when taking off from a dead stop
  • Loose Metallic noises
  • Coming from the rear of the truck
  • Excessive play

Possible Cause

Let’s look at the most likely cause – U-joints

U-Joints

Jeep Wranglers are equipped with 4x Universal Joints. Two are located on the front axle shaft. One is located on the front drive shaft and one on the rear drive shaft towards the rear diff. The rear U-joint connects directly to the rear differential and the front end of that same driveshaft is connected directly to the transfer case.

The front u-joint is located on the front driveshaft and connects directly to the front axle via the front differential.  

The u-joints lets the drive-shaft connect to the diff at an angle and compensates for vertical and lateral movement of the differential while the vehicle is in motion.  

Always ensure you are driving in 2H, which you should be, if you are driving on a high-traction surface with a part-time 4-wheel drive, such as a Wrangler. This mode only engages the rear driveshaft and propels the rear wheels only. The front driveshaft, axle and wheels all just coast along when in 2H mode.  

If the u-joint rubber caps get damaged or wear out, allowing the grease to drain out of u-joint, it will become unlubricated and dry causing the u-joint to fail prematurely. The rubber seal perishes due to old age and all the lubricating grease escapes.

The excess movement that results from play inside the u-joint causes a loud clunking sound under acceleration.

Engine Mounts

A loose engine mount could result in excessive play and vibration only under load and when pulling off. When the engine mount cracks you will hear all sorts of impact noises emitting from the lower part of the engine bay. Sounds such as clunking, knocking, rattling all means the engine is loose at one of the engine mounts.

Transmission Mounts

One thing to keep in mind when it comes to transmission and engine mounts, is that they don’t require a certain amount of miles before they can fail. They are perishable components and designed to last a very long time, however, they have been known to fail or tear, even at low mileage.

A few important questions you need to ask:

1Has your Jeep undergone any extensive frame work recently?
2Have you been involved in an accidents recently, even a light “fender-bender”
3Have you driven any hard off-road tracks in the last few weeks?

Any one of these scenarios can result in a hair-line crack in the rubber mounts, resulting in a slight vibration being felt through the vehicle. The crack might not even be visible from the outside.

The job of the engine and transmission mounts are to secure your vehicle’s engine and transmission to the sub frame. They mounting rubbers are designed to dampen all the vibration into the cabin and absorb vibration and shock, to ensure that the driver and passengers are unable to feel any movement of the motor, detracting from the driving experience and comfort.

Symptoms of a bad transmission mount:

  • Excess vibration while the engine is running.
  • Metallic Knocking or clunking noises when shifting gears.
  • Knocking when shifting gears (Manual Transmission)

Loose axle mount

A loose axle mount could result in a heavy metal on metal clunking noise. This is a rubber bush that could get perished over time and crack resulting on direct metal contact resulting in a clunking noise.

Other items that could result in clunking noises are:

  • Sway-bar link
  • Control arm Bolts
  • Shock mountings

Resources

Driveshaft U-Joints

Axle shaft U-Joints

TJ Wrangler Poly Transmission Mounts

L/R Wrangler Engine Mounts

Conclusion

Knocking and clunking noises on Solid front axles are a common issue. Get underneath your Jeep or get it on a hoist to inspect all bushings and rubber mounts for tears and cracks. Inspect your driveshaft U-joints as well as your axle shafts for excessive play, wear and lack of lubrication.  When replacing rubber mounts, try to avoid poly bushes, since they are a lot harder and don’t dampen vibration very well. Insist on OE MOPAR transmission and motor mounts. Spicer U-joints are recommended.

Jade C.

4-Wheel drives and off-road driving techniques has been my passion for over 20 years. Here we strive to provide the most accurate, up-to-date, information about the functionality, common faults and latest technology built into most 4 Wheel Drives.

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