Rear End Play

[John-T-53]

I've got an all-original 1/2 ton 4:10 rear end with new brakes and no major leaks, but noticed some clunking when going between forward and reverse. Sometimes when starting from a stop in first, there's a "ping" from the rear as the truck starts moving.

When I had the filler plug off last, I looked in there with a flash light, while moving the companion flange back and forth (driveshaft removed). I could see the ring and pinion clearly. There was quite some free play back and forth with the flange, like a few degrees of rotation, but the ring and pinion were engaged good with no visible excessive backlash between the teeth. The teeth wear pattern looked excellent.

The axle nuts at the wheels are tight, and the keyways and pins are tight...what else could be loose? I'd be hard pressed to believe its the axle splines. Do the diferential side and pinion gears ever wear out? I've never spun a wheel while I've had this truck, but the fluid has gotten low here and there with the former leaky pinion seal.

Looking at the shop manual, taking the differential case apart looks like a b*tch...it says to heat it with a torch and use a special tool to unscrew the case cap. Ugh...

[Dave72dt]

It's possible to have a pinion brg going bad and creating that clunk and ping. Usually a clunk in the driveline indicates a bad U-joint. Check those first. easier and cheaper that a rear diff repair. Also look for loose wheels.

[JBNeal]

I agree that the clunking noise usually indicates u-joints that are worn. Worn differential bearings would cause a growling noise when driving in high gear. Also, with both wheels off the ground and the transmission in low gear, turning either of the rear wheels would produce a slapping noise in the differential case if the bearings were worn out. Alternatively, doing this with good bearings would produce a clicking noise.

[Young Ed]

I had a clunk in my pickup. Happened when switching from forward to reverse too. Even though I thought the drums were tight enough they werent. Spec is minimum 160 ft lbs. I'd double check them.

[John-T-53]

The U-joints are good, the drums are tight, and the rear end seems quiet on the highway...although I can't really hear anything above the noise of the truck at 50 mph.

I jacked up one side and jiggled the wheel. The axle bearings seem to be slightly clunky, as I could hear them even when rocking the wheel 2" back and forth. The inner seals are shot, so they're only being lubricated with gear oil right now.

But the play is definitely the rear end, somewhere. With the driveshaft disconnected and both wheels on the ground, the ring gear can go forward and backward quite a bit (around 3/8" to 1/2") before hitting a stop.

[Dave72dt]

Theoretically you've reduced the number or parts that could be bad. Ring gear to pinion clearance typically set in thousandths and you say that is good. Ring gear connected to the gear carrier. Carrier has 4 gears inside, 2 splined loosely to the axles and 2 that ride on a pin. Is that pin worn excessively, either where the gears ride or loose in the carrier or evenbroken? Lots of gear lash clearances add up. Here's another possibility. Worn spring hanger bushings. Changing direction with spring wrap causing noise?

[JBNeal]

I dang near forgot about this li'l nugget: while in high gear on level grade, alternate stomping the throttle and letting all the way off. If the differential bearings are worn, not only with the chassis jerk to & fro, but it will make a clunky racket as all the associated parts bounce about in that case. This can be a dangerous maneuver if ya slide outta yer seating position, as I did when trying this on a D250 CTD ten years ago. The rear end on that old diesel had so much slop in it & the engine had so much torque that I durn near got wedged between the driver seat, the steering wheel & the floorboard.

[Dodgeb4ya]

"Ping" usually is caused by dried up u-joints. The driveshaft needs to be out and the joints manipulated by hand to feel for binding.

Maybe the trans brake drum nut?