Play in rear end

[Rifter_Chevy]

Ok i know that title sounded bad but i think i have a serious problem.

My truck makes on hell of a loud thumping/clunking sound when i put it into reverse, and then another really loud thumping/clunking when put back into drive after moving in reverse.

I had a buddy drive it back and forth while i watched from underneath(yay for hanging from the frame while someone drives your truck around a parking lot) and found that the sound is 100% no doubt in my mind coming from inside the rear diff.

The issue is there is 2-3" of play in the driveshaft BEFORE the tires start to move. For example say i was going forward, then i stop, then i put it into reverse, the thump comes because the driveshaft and pinion move really really fast for those 2-3" of play then makes hard contact with the gears inside the diff and then tires start to move and makes a really loud thumping sound.

How do i fix this? is this backlash related or pinion depth related?

EDIT to add, truck is a 4x4, doesnt do when 4x4 is engaged im assuming because my front diff stops rear shaft from closing that 2-3" of play. Also it is a 14 bolt Full floater rear end.

[78 Chevyrado]

I don't know exactly what would cause that, and still run at all.

Check your axle shafts under the wheel hub caps and make sure they are bolted down tight and havent slipped. if thats fine, pull the cover and see whats wrong.

I don't know what would give it that much slop and still function at all. Maybe the carrier bearings are loose, or the pinion itself has worked lose. can you grab the pinion and move it sided to side OR in and out? just grab the driveshaft and try to move it.

either way the covers gotta come off, now im curious.

Good luck!

[motornut]

try with the back wheels off the ground in N
wiggle/turn the shaft and each wheel may help confirm it's not U joint ...and safer

[Rifter_Chevy]

Originally Posted by 78 Chevyrado

I don't know exactly what would cause that, and still run at all.

Check your axle shafts under the wheel hub caps and make sure they are bolted down tight and havent slipped. if thats fine, pull the cover and see whats wrong.

I don't know what would give it that much slop and still function at all. Maybe the carrier bearings are loose, or the pinion itself has worked lose. can you grab the pinion and move it sided to side OR in and out? just grab the driveshaft and try to move it.

either way the covers gotta come off, now im curious.

Good luck!

Axles are tight on the hubs.

Driveshaft moves about 45 degrees in either direction when its parked, I can grab it and move it a quarter turn in either direction before contact with the gears. Thats the problem, thats whats causing the noise when i go from drive to reverse it takes 45 degrees before the driveshaft is connecting to the gears and moving the tires. U joints are good i checked them already it was my first thought.

Pinion does not move at all, side to side or in and out.

All my local guys are telling me its a backlash issue or loose carrier bearings.

Im going to a buddies tommorow to try and fix the backlash as its easy to do on a 14 bolt. Failing that he has a dana 70 sitting around he will sell me and ill swap it into the truck, its got different gears so i wont have 4x4 till i regear it but it will get me rolling for now.

Thanks for the inut guys.

[INSIDIOUS '86]

dont drive it, something may be loose inside and if you drive it it can get caught in your ring and pinion gear making a very spendy fix, my buddys truck did that and he drove it and the rear end grenaded and locked up

[makman1297]

I had a HO72 in rear end in my 72 3/4 ton it was the same way, i repalced the diff in that one with a different one, just unbolts. When i looked over the old one the ring and pinion looked good, but all the bearings had alot play in them and i guess that is what did it.

[Goldfinger]

U-joints probably

[Rogue_Alphonse]

I've had the yoke or pinion bolt [whatever you call it] come loose and it did something very similar, but this was on a 10-bolt GovLoc. I'd give that a look-see.

I jacked mine off the ground and ran it in gear and as soon as I pushed the clutch in, the driveshaft and yoke moved in and out.