Identifying Bad Axle Noises

Belly Growl
Problem: Low-pitched growl emitting from the axle at speed. It can sound like tire drone, and you may not notice it at low speeds. Sometimes accompanied by vibration.

Cause: Axleshaft bearing or differential carrier bearing.

Fix: If it’s an axleshaft bearing you may notice the seal leaking beside the bearing due to axleshaft scoring, and you may have diff oil on your brake pads. You need to replace the axleshaft bearing, seal, and possibly the axleshaft. If it’s a carrier bearing it typically requires a total axle rebuild because metal shavings have probably damaged other components in the differential. However, in rare cases if it’s caught early you may get by with just replacing the carrier bearings. Rule of thumb: If the carrier is loose, the axle will probably need to be rebuilt.

Wheel Wobble
Problem: Slower-paced vibration at speed.

Cause: Loose lug nuts or bent axle.

Fix: Look for wheel wobble. If wheel lug nuts are missing the problem is obvious. However, loose lug nuts may not be visible, and you won’t know they’re loose until you get a socket on ’em. Loose lug nuts can damage the wheel and the wheel studs, so inspect both. If the wheels are tight, the axleshaft may be bent. On C-clip–style axleshafts, remove the axleshafts and inspect them for impact marks from the bearings. Look for straight lines on the axleshaft. You should be able to feel these imperfections with your finger or fingernail. If the axleshaft is scored it needs to be replaced. If the vibration is faster-paced check for a bent driveshaft, a bad CV or U-joint, or in rare cases a bent pinion shaft.

Vibration Station
Problem: Consistent chatter; increases to vibration with speed; may change on and off the gas.

Cause: Incorrect pinion angle for driveshaft.

Fix: Besides being annoying, incorrect pinion angle can eventually wipe out pinion bearings and cause U-joints to wear prematurely. Depending on the vehicle and suspension type, there are several solutions, including pinion-correction wedges, adjustable control arms, or rotating the axle to get the correct angle. See “Drivelines and Geometry” elsewhere in this issue.

Gearbox Issues
Problem: Noise that changes significantly or goes away when you shift gears.

Cause: Transmission.

Fix: The key here is to differentiate between axle and transmission noises. Noise in a specific gear or gears is a clear indication that you have an internal transmission failure and the problem is not related to the axle or driveshaft.

Limited-Slip Slip-Up
Problem: Shudder or popping noise while making slow turns, which becomes worse as the axle warms up.

Cause: Limited-slip differential failure.

Fix: Depending on the type, the diff may have seized or have broken clutches, or it may not have the proper additive that many limited-slip diffs require. The fix is to rebuild or replace the limited-slip unit and include the proper additive if required. There may be collateral damage to other components due to metal in the axle, which may necessitate a complete rebuild of the axle.

Whoa, That’s Twisted!
Problem: Can’t remove axleshafts from carrier.

Cause: Axleshaft splines may be twisted.

Fix: You may not even know your axleshaft splines are bent until you try to remove the axleshaft and it won’t release from the carrier. C-clip axles with twisted splines also pose a problem because they first have to be pushed inward to remove the C-clips, and if the splines are bent they may not want to move. To remove the axleshafts you may be able to pound them with a mallet, or you’ll have to torch ’em out. Typically you can reuse the carrier, but the internals (spider gears and sidegear) will have to be replaced. It is also worth noting that axleshafts can crack lengthwise or splinter, which can cause them to be stuck in the carrier or destroy the carrier.

Where To Get Parts
After you’ve determined what’s wrong with your rig’s axle you’ll need parts to fix it, and if you’re like us you’ll want those parts fast and with no hassle. The following companies are all great sources for axle parts, and most stock a huge variety so they can get ’em out to you quick.

4Wheel Parts, www.4wheelparts.com
4x4 Parts.com, www.4x4parts.com
Complete Off Road, www.completeoffroad.com
Dick’s Driveshaft, www.dicksdriveshaftphoenix.com
Just Differentials, www.justdifferentials.com
Motive Gear, www.motivegear.com
Quality Gear, www.qualitygear.com
Randy’s Ring & Pinion, www.ringpinion.com
Summit Racing Equipment, www.summitracing.com
Superior Axle & Gear, www.superioraxlegear.com
West Coast Differentials, www.differentials.com

Axle Glossary
If you’re new to the world of axle guts here’s an overview of the major parts.
Axleshaft: Part of the axle assembly that is turned by the differential side gear and transfers power to the wheel.
Carrier: This mechanism transfers motion from the ring gear to the axleshafts.
Carrier bearings: These are the bearings that the carrier rides on.
C-clip: On some semifloat axles this clip retains the axleshaft in the carrier.
Cross-shaft: A hardened pin that transfers a load from the carrier to the spider gear assembly.
Crush sleeve: Collapsible spacer placed on the pinion to preload the pinion bearings.
Housing: Holds all of the internal differential components and the axleshafts.
Pinion bearings: The bearings that the pinion rides on.
Pinion shaft: A shaft with a small gear that is connected to the driveshaft and meshes with the ring gear.
Ring gear: Bolts to the carrier and is driven by the pinion gear.
Side gear: These fit into the carrier and have internal splines that accept the axleshaft splines.
Spider gear: Also known as differential gears, these install into the carrier and allow one wheel to spin faster than the other.