8 3/4 Rear End Noise

Now that I have gotten my Cuda back on the road (after being restored) and have put a few hundred miles on it I am now noticing a noise coming from the rear end.

The noise only happens when I make a right hand turn and it seems to happen only when the car seems to be swaying to the drivers side. It does not make the noise when I make a left hand turn and it does not always make the noise when I turn right (only sometimes).

The noise sounds like it is coming either from the 3rd member or the drivers side axel near the driver side rear wheel, hard to tell. The noise sounds like a clunking sound that seems to repeat while making the right hand turn but once the car straightens out it goes away. Again it only does it every so often.

Some background on the rear end. It is an 8 3/4 with 3.91 gears, sure grip. I had a rebuilt 3rd member (3rd member by Dr. Diff) put in the car 8 years ago and never had any issues or noise. This year the rear end was dis-assembled, cleaned, and painted as part of the restoration. The only things changed to it where the old original style bearings where replaced because the where worn and all the gaskets and seals were replaced. The other thing to note is that the bearings were replaced with a set of Dr. Diff green bearings.

I'm not sure what is causing this noise but I suspect either something was not re-assembed correctly or something is now out of adjustment. I'm kinda bummed because I suspect whatever it is the rearend will have to come apart to address this and after a full year of restoring this car I am flat out sick of working on it. Nevertheless it is what it is and I need to suck it up and get it fixed.

I know some of you folks here on the board know what this issue is so I need some advise on what to do to trouble shoot and fix this.

-Thanks

There is a very (very) small amount of play in and out with the green bearings on my Satellite.
Check for wear marks and make sure there's no contact between the drum and backing plate.
Only other thing I can think of is does it have a posi additive in it???

Could the "clunking" be from clutch pack binding and releasing in the turn? Did you add friction modifier to the rear end lube???

Agree. When the diff was reassembled and the gear lube replaced, did you use the special limited slip additive? If not this could easily cause the noise.

Thanks for the feedback guys.

I embarrassed to say i did not know I needed to use any kind of limited slip additive. I just added gear oil to the rear end.

Is their a particular kind/brand of limited slip additive that I need?

Go to the ford Dealer and get the ford racing friction modifier, very good stuff. Its like 6 bucks a bottle.

If it is only happening on 1 side I would check the axle bearing on that side. If the rear was run after it was built and the only change since then were greenies then I think it's pretty easy to figure out what is making he noise. The bearing might have been damaged when it was being installed ?

What kind of sure grip does it have ?

It is a 489 case with 3.91 gears that I purchased from Dr. Diff. Unfortunately I don't know what type of sure grip it is.

Also, do I need to drain the gear oil out of the 3rd member and then put in the friction additive and then put new gear oil back in?

Another question; did you put the axle seals in the rear end tubes?

You do not have to remove the 3rd member. You only need to remove about 5-6 ounces of gear oil. You can do that a few different ways.

I had a shop do the restoration and assembly on the rear end so I assume the bearings, seals, etc where installed correctly. I have worked with enough shops to know that this is not always the case but as of this moment I believe they re-assembled the rear end correctly until I learn differently.

Agree the additive is a good place to start. The GM spec stuff Autozone sells has worked fine for me. As mentioned, suck a few ounces of lube out of the rear and put the additive in. No need to drain it.

You will have to drive a little to get the additive mixed and worked into the clutch packs to see if it helps.

NAPA and Advance carry Trans-X Posi-Trac Limited Slip Gear Oil Additive. It's been a good additive for me.

is it neccessary to drain out several ounces? I wouldn't think several more would cause an issue (foaming)

No, it's not. As long as the additive will fit. In the case of the Ford additve, we're only talking 4 ounces.

Alright. thanks bro

The reason I asked about the axle seals is you are supposed to run them with the green bearings. The green bearings are a sealed bearing that contain their own grease, it is possible for the gear oil to wash the bearings out if the seals are not in place, at least that is what I was told.

As far as the suregrip lube is concerned. Like pacnorthcuda said if it fits, it doesn't need to be drained at all. Also you can jack up the right side of the axle so it is leaning a little bit to the left to give you a little extra room. or vice versa, I am trying to remember which side the fill plug is on. Use jack stands and be safe.

Jeff

The reason I asked about the axle seals is you are supposed to run them with the green bearings. The green bearings are a sealed bearing that contain their own grease, it is possible for the gear oil to wash the bearings out if the seals are not in place, at least that is what I was told.

As far as the suregrip lube is concerned. Like pacnorthcuda said if it fits, it doesn't need to be drained at all. Also you can jack up the right side of the axle so it is leaning a little bit to the left to give you a little extra room. or vice versa, I am trying to remember which side the fill plug is on. Use jack stands and be safe.

Jeff

Did they take the center spacer out of the diff when they switched to green bearings?

If clutches, how is the clunking only on one side? Axel to short or to long? One question, does it lurch or jerk when you hear the noise? My sure grip was new and did the clunk-jerk both ways, put additive in then did continuous hard turns left and right, got in faster that way. Personally I wouldn't use the green bearings on any street car, hard to beat factory stuff.