Piston Slap: Range(r) of Motion, OMGWTF Edition

TTAC Commentator 67dodgeman writes:

Sajeev, I have a question for the Piston Slap expert. My son drives my old ’99 Ford Ranger (extended cab, 4 cyl, manual, 2WD) with roughly 130,000 miles on the odometer. I had new tires put on 5 months back at the Firestone place. Then last week, the anti-lock brakes started acting up. As in heavily manipulating the pedal even during very light braking. I assumed the sensor was fried and pulled the fuse, after which everything worked normally. There was a slight ticking sound from the drive train, so I replaced U-joints. Still ticking, but no other obvious issues.

Then, Friday, the driver’s side rear tire and axle came loose. Luckily he was making a low speed U-turn and the last 6” of axle was still in the housing by time he stopped. We jacked the truck up, pushed the axle back in, and pushed it home (two blocks – very very lucky it happened there and not on I-45). I pulled the differential cover and immediately found the (bleeping) C-clip loose in the housing. The anti-lock sensor works off of teeth on the ring gear (just now figured that out), so I’m assuming that having about half the teeth ground off is the cause of the brake malfunction. The oil appeared original, had that burnt smell, and was full of grit. I’m now in the process of changing the whole assembly with a salvage yard spare due to the gear damage.

My question is – what caused the C-clip to fail? I noticed when pulling the driver’s side tire off the axle that the lug nuts were over-torqued. I put my torque wrench on it and had to dial up to 150 ft-lbs before they would break loose. I’ve had issues with Firestone (and others) over-torqueing wheels in the past. But to pull the axle hard enough to damage the C-clip? Maybe if the brake drum wasn’t squared up properly?

Most of the forum discussions about C-clip failures center on jacked up trucks with over-sized tires. This one is stock. For a plain Jane work/commuting truck, that Ranger has been my best vehicle purchase in the past 25 years. Having an axle fail at 130,000 miles has seriously shattered my faith.

Sajeev Answers:

Funny you mentioned the fear of a Ranger axle failure on the highway, a former co-worker had that problem (2002-ish, 2.3L, 5-speed) on I-10 with less then 100k on the odometer, zero modifications, and no history of heavy duty use. The axle flew out, landed in the grass, and the Ranger slid across the median and screeched to a stop on the other side of the freeway. Nobody was hurt (thank goodness) but it totaled the truck. I called Ford after the owner did the same, but we didn’t hear back from Dearborn. Then I moved on to a new job and new co-workers. Who knows if anything ever happened, but the Detroit 3 are bad about fixing problems once the warranty expires.

Which seems unfair in these situations. Trucks axles have legendary toughness, even small Rangers with zero suspension/wheel modifications. The Ford savvy among us may debate the durability of the Ranger’s 7.5-inch differential, but I’ve seen drag racing Fox Body freaks run 12-second timeslips (consistently) with no problems. They don’t suck as much as the 8.8” fanbois may suggest.

Since the C-clip is connected to the wheels, an over-torqued wheel can affect it. Technically. But it’s a steep jump to assume that cranked-down lug nuts can shave off the ABS exciter teeth, burn the fluid and vibrate the C-clip loose. I’ve never taken apart a differential, because I know better: that’s suited to a professional. So I shouldn’t comment.

But I will. And cry foul: a manufacturing or assembly error at whatever factory produces these axles. Best and Brightest, am I wrong?

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