BACKYARD MECHANIC: Smallest movement can create a loud clunk

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This article was published 19/11/2010 (5444 days ago), so information in it may no longer be current.

QUESTION: I purchased this 1999 Dodge Ram 2wd truck a year ago. It has about 120,000 km on it with a 318 auto. Soon after purchase, I replaced the four shocks. Subsequently, I hear a distinct loud clunk from the rear axle suspension. It is not a driveline issue since it’s associated with suspension flex. It may have been there before, though the previous owner said he never heard it.

I have been unsuccessful at remedying this with new clips on the axles and new bearings and seals. My mechanic checked the suspension bushings and the new shocks he installed without locating the problem. He could induce the problem (somewhat) by pulling on the wheel when the truck was on his lift — a hand on either side of the tire alternating pushing and pulling. That’s why the clips were replaced. He said the spider gears were worn within tolerances. I welcome suggested solutions.

ANSWER: Suspension/axle noises can be caused by surprisingly very little movement in a part. If suspension bushings are not broken, allowing the rear axle housing to move, you should still check the torque on all suspension bolts. Even the smallest movement can create a loud clunk.

Worn rear axle side gears can also cause a clunk. It would appear your mechanic has perhaps already checked this, but if the noise can be created by pulling on the tire, I would check it again. The side gears ride inside the differential housing and support the inner end of the axle shaft. As you drive over a bump, the load decreases and increases on the axle shaft, causing it to move the side gear up and down. Any wear on the side gear bearing surface or inside the differential case where the side gear fits will cause a clunk.

A third possible source of the clunk, and one I often run across, is a binding slip yoke on the driveshaft. Depending on the wheelbase of your truck, you can have three different designs of driveshaft. The one-piece design can have the slip joint on the driveshaft itself just behind the front universal joint or the slip joint may be part of the transmission output shaft and front yoke assembly. Two-piece driveshafts have a slip yoke by the centre universal joint. If this slip yoke binds, it will suddenly move when the suspension flexes and creates a loud clunk. Lubricate the slip yoke with wheel bearing or chassis grease to prevent binding.

QUESTION: I have a 2006 Jeep TJ with a four-litre engine and a standard transmission. Recently, a clicking noise started whenever I depressed the clutch pedal (about halfway down). The transmission shop told me I needed a new clutch. They replaced the clutch, pressure plate, throwout bearing and resurfaced the flywheel. For approximately two weeks everything worked fine. Then the next few times I put the clutch in, that all-too-familiar clicking sound was back. The clicking only lasted for approximately 20 shifts, I heard a slightly louder click, then no more clicks.

Since then when I pull away in first gear there is a shudder/jumping/slipping. All other gear shifts are fine. I have noticed the shuddering is far more pronounced in the morning after the Jeep sits all night, and disappears after driving for a while. There is no difference in the shuddering if it is in two- or four-wheel drive. I would appreciate your help on the matter before I bring the vehicle back to the transmission shop. There was no shuddering problem before the new clutch was installed.

ANSWER: The original noise may have come from a faulty throwout bearing, pressure plate linkage or clutch disc torsional spring. The return of the noise accompanied by a shudder on launch would indicate to me a problem with the pressure plate, perhaps a broken part that is creating uneven clamping forces.

You should get this back to the shop that did the work so they can diagnose it. I think the problem is in the clutch, but without disassembling it to see the parts, it could be any of the parts that originally caused the noise. This will have to come apart again.

Jim Kerr is an experienced mechanic, instructor and member of the Automobile Journalists’ Association of Canada.

kerr.jim@sasktel.net