Popping noise in the rear diff?

[irtySanchez]

Two weeks ago, I had the rear driveshaft balanced and the U-joints replaced. As soon as I installed the driveshaft, there were problems. As soon as I would accelerate (in drive or reverse) there was a distinct pop (like metal on metal). I took the shaft out, had it balanced again and re-checked the U-joints. At the same time, the rear pinion seal was changed on the rear differential. I reinstalled the driveshaft and everything was OK.

Then today, the popping sound (or a thunk) reappeared. The strange thing is it is only in reverse. I do get a slight thunk when I put the EX in drive, but it is much louder when it is put in reverse, usually when I tap the gas.

Here are the facts:

I am pretty sure it is NOT the driveshaft or the u-joints.
I am almost sure that it is coming from the rear end, not the front portion of the drive shaft. the transmission was replaced 3 months ago. The rear brakes were done about 3 weeks ago. The rear diff is definetly full. The slip yoke is definetly greased.

Any ideas? I am really getting frustrated.

Thanks, Brad

 

[Jason_25]

Sounds like rear end backlash. Welcome to the backlash club! I'm the president. My explorer does this because of the locker I have and my BII does this because the L/S is worn out. Sounds like to me when the took the pinion out to change the seal they didn't set the backlash correctly.

 

[irtySanchez]

I was thinking what if I did have limited slip, because I don't think I do, but wasn't sure.

As for the pinion, it wasn't removed. The seal comes out when the companion flange on the front of the rear differential is removed. If the backlash is the problem, how do I adjust it?

 

[jimmiecakes]

Backlash and pinion depth are adjusted i a complex relationship to ensure that the gear teeth of the ring and pinion mesh correctly and without howling. Backlash, measured at the ring gear, should be (here comes the "from memory" part) no more than .010" but, seeing what can happen to diff. repair costs, most people put up with something more than that.

Since yours only happens after you're already in reverse and when you "tense" the powertrain, I'd start with checking the real wheel torque - 85 to 95 ft/lb should suffice. At the same time, make sure that the pinion nut is tight - checking bearing preload is very difficult with the diff fully assembled - but you need to be sure that you don't overdo it on the crush sleeve (maybe just give the nut a little nudge and then road test). You could also take a look for broken spring leaves and loose/damaged u-bolts.

If that doesn't help, it's time to go snooping inside the diff......

 

[FMExplorer]

Quick question...

Was there an occassion to loosen the ubolts on the spring perches? Mine came loose and made the exact noise you are describing...

Jon

 

[irtySanchez]

I have never had an occasion where the U-bolts have been loosened, but there is something loose on one of the leaf springs. This will need some further investigation.

As for adjusting the backlash, I am going to leave this to a professional. I will have them check the rear end for wear and tear, and adjust the backlash at the same time.

One thing I thought of: if the rear end is L/S and I didn't add the friction modifier, could this be the source of the problem?

Thanks everyone who has responded so far!!! You all have been very helpful!!

 

[jimmiecakes]

Tough to describe the sound of improperly nourished positrac plates (a grindy/growly kinda noise)..... this would be apparent usually only when turning a corner.

 

[FireZeus]

My '95 is doing the same thing. It has been doing so for about 6 months now and though its not really getting worse, it is very annoying. For me, it seems to do it more when you accelerate and let off the throttle to coast at about 40 mph. It will do it at almost any speed but 40 seems to be the most dominant. It does come and go too. I am thinking along the lines of the ring and pinion since the frequency of "clunks" between 40 and 55 mph doesn't increase as fast as a ujoint or wheel bearing should.

 

[Jason_25]

Originally posted by FireZeus
My '95 is doing the same thing. It has been doing so for about 6 months now and though its not really getting worse, it is very annoying. For me, it seems to do it more when you accelerate and let off the throttle to coast at about 40 mph. It will do it at almost any speed but 40 seems to be the most dominant. It does come and go too. I am thinking along the lines of the ring and pinion since the frequency of "clunks" between 40 and 55 mph doesn't increase as fast as a ujoint or wheel bearing should.

Yep that's what mine does.