7.5 in. rear end 'clunk'

[fourhigh]

My '85 Bronc with a 302, C4, original (well over 100,000 miles of course) 7.5 inch rear end has developed a 'clunk', mainly under acceleration.
Kind of strange, when I was driving it (made it home, driven slowly, it's been here since) it is not a constant noise,
sounds like something sliding, and then the 'clunk', maybe every 100 feet or so. I pulled the diff. cover, and drained the oil, it looked good, and nothing metallic that I could see. No teeth missing, retaining bolts are tight. U-joints seem fine, very little, if any, play in the driveshaft or axles
each side. I put the diff cover back on with 4 or 5 bolts just snugged, jacked it up and put it in drive, with my neighbor here, it did it twice, he
felt it with his hand on the cover, but it did not do it again. Guess I will double check the bottom of the inside of the diff housing tomorrow after work. The sun is starting to set too soon too early already, I ran out of daylight. Gonna be 4 wheel drive weather soon. Gotta get it figured out.
Any thoughts ? I appreciate it.
fourhigh

 

[fourhigh]

Sorry, this probably should have been put in the 'axles' section, I apologize,
I didn't think about it until I posted it...

 

[Uncle Gump]

I moved your post to the axle forum.

Is this a Trac Lok diff? Maybe you have some sticky clutches.

Usually when you have a diff problem... it is pretty clear when you take the cover off. Were there any metal bits in the bottom?

 

[fourhigh]

Thank You Gump,
I would have to do some tag research, but I think it's just a standard 7.5. Headed off to
work in a bit, working close to home, back before dark to investigate internal
housing closer. Will update later on today. I appreciate the help !

 

[dvdswan]

I would also check the rear suspension components for loose nuts/bolts, broken springs, loose shocks, etc.

 

[Curious Hound]

Can you make it happen by turning the drive shaft by hand with the rear on Jackstands?

Another thing to try would be to remove the drive shaft and put it in drive and see if it happens. Could be a transmission issue.

 

[Uncle Gump]

Can you make it happen by turning the drive shaft by hand with the rear on Jackson's?

Another thing to try would be to remove the drive shaft and put it in drive and see if it happens. Could be a transmission issue.

thats a BUNCH of Jackson's

 

[Curious Hound]

thats a BUNCH of Jackson's

View attachment 67574

Dang spellchecker!

They should make spellchecker for motor heads. There are a lot of automotive terms that get autocorrected.

 

[pjtoledo]

when it's on Jackson's stands apply the parking brake, then give it a try in F/R
a quick look at the brakes wouldn't hurt.
and don't be afraid to whack parts with a rubber or wooden mallet.

 

[fourhigh]

Thanks Guys,
I appreciate all of the suggestions. As soon as I got home from work,
I jacked it up again, placed jack stands and removed the cover. Absolutely
no signs of any metallic bad things in the bottom of the housing. All bolts tight.
No noise when I rotated driveshaft by hand, I noticed there was a little bit of
play in the gears when spinning it one direction to the other.
I then started it and put it in drive. It never did make the 'clunk' noise, forward or reverse....
Kind of wondering if it will only be doing it when it is rolling with resistance except
for last night jacked up, when it did it twice with my neighbor here. Gotta apologize,
describing the noise is tough to replicate on the web, I understand only so much help can be offered.
It's just an unusual situation that has me baffled.
B.T.W., according to the wealth of knowledge that the tech library is, my axle code 42 is an open 7.5" 3.45 ratio.
Thank You all.
fourhigh

 

[cbxer55]

I recently had my axle rebuilt by a friend's shop while they were installing 4.10s, also a 7.5 open. It was making some noise on sharp turns. Ends up the spider gears were worn some. Not horribly, but the edges were pretty well rounded. Friend said, "You can sell the 3.73 ring and pinion, but don't sell the spiders". Since the rebuild, no more noise on hard turns.