Noisy 8 3/4 Differential

[DJCUDA]

Hi All, I had my 8 3/4 489 Diff overhauled in my 74 Cuda just after the new year, I purchased a new 3.23:1 crown wheel and pinion as well as a master overhaul kit from Summit Racing, they supplied me Yukon products. After the overhaul the car was driven and immediately there was a whirring noise coming from the diff, on acceleration, deceleration and cruise speed, the longer we drove the car the worse it got. The company engaged to do the overhaul removed the diff once more only to find metal particles in the housing, a reading was done on the crownwheel and pinion only to find perfect readings. It was eventualy worked out that there was no hardening on the gears. Another set of gears and ovehaul kit was purchased and installed installed only to find a whirring noise once more, nothing like the original though, it is just a slight whirring noise, the diff was removed once more there was no metal particles in the housing, so a reading was done on the gears only to find perfect marks with probably a 2 thou differerance 180 degrees apart. Its got us baffled as to what is causing this. Has anyone experienced this before or is there something missing in the setup, any info would be greatly appreciated.

Thanks.

 

[john-9]

--- what was the pinion bearing preload set at --with new bearings it should have been 20-25 in/lbs rotating -- if preload was not set properly the pinion gear will not run true to the ring gear
--- gear pattern may be off due to incorrect pinion depth locating shim selection -- but without pictures of the pattern,, we have no way of telling if pinion shim selection was right or even close -- have a pattern check run and get some pics.
--- make sure there was enough preload on the carrier bearings
-- make sure to break in the gears and bearings properly.

 

[DJCUDA]

I believe the setup was correct, check the photos of the markings.

 

[john-9]

drive pattern looks good ,, but a little high (towards heel of tooth) try adding .003 to the pinion shim and take another pattern check --
--- what was the pinion bearing pre-load set at .
--- what was the backlash set to.

 

[DJCUDA]

Not sure about the pinion pre load or backlash I will find out from the Diff Specialist and let you know, thanks for you replys also.

 

[Steve340]

What are the axle bearings like?
They can make some hard to track noises.
Could be the photo but the pattern looks a little odd. Not very uniform.

 

[DJCUDA]

New Green style wheel bearings have been fitted, the noise is not constant like wheel bearings would make, the noise changes by accelerating and decelerating, under acceleration minimal noise, deceleration and cruise the noise is there but changes. Not sure about the pattern I will ask about that when I speak to the Diff Specialist next week.

 

[Steve340]

From the info supplied it does sound like you have a problem with the crown wheel and pinion set.
I used a Nitro gear set and it has been good.
The pattern with a little load applied should be consistent.

 

[DJCUDA]

I have to admit its got the Diff Specialist beat at this stage! I'm sure he will reslove it, but for the meantime I'm not able to drive the car and our cruising time is almost over, we have just gone from Summer to Autumn and the crappy wet days seem to be here early!!.

 

[DJCUDA]

Just an update on my diff. After the 4th set of gears (first set had no hardening) there is still a noise on decelleration, once again the tooth reading is perfect with 1" thou runout. This would have to be the most puzzling diff ever! Last resort is to have the housing checked for straightness, there is nothing left to do, axles have been checked, axle bearings are new, and new bearings throughout the diff. Just wondering if anyone has had such an issue and found the housing to be a problem?

 

[john-9]

Just an update on my diff. After the 4th set of gears (first set had no hardening) there is still a noise on decelleration, once again the tooth reading is perfect with 1" thou runout. This would have to be the most puzzling diff ever! Last resort is to have the housing checked for straightness, there is nothing left to do, axles have been checked, axle bearings are new, and new bearings throughout the diff. Just wondering if anyone has had such an issue and found the housing to be a problem?

i find it hard to believe that a gear set got out of the factory without going thru heat treating and now you are on your 4th set with the same noise issue -- something is wrong with the set up
this sounds like incorrect preload on the pinion bearings and as i stated in my other post try adding .003 shim to bring the pattern down a bit --- did you ever find out what the pinion bearing pre-load was set at -- it should be 20-25 in/lbs rotating with new bearings --- if the fellow setting up the gears can't tell you what he set the preload at find someone else.

 

[moparleo]

Installer problem.............

 

[DJCUDA]

Well, we finally got this diff noise sorted.
But before that and after the last set of gears fitted, we decided to have the housing checked, it was bent 3/4", it was straightend up and fitted back in, the teeth readings were checked once more and as John-9 advised it was shimmed to bring the pattern down a little with a preload tension of 25 in/lbs rotating, (it was set close to this preload tension each time). We were confident this time the noise was gone, but it didn't lets us down, the noise was still there. We were ready to replace the whole rear end with a brand new drum to drum assembly, until it was decided to salvage the original factory fitted gears and try them, because they didn't look bad in the first place (we originally decided to replace them because it was a cheaper option than lapping them in as this is quite expensive) we ended up having them lapped in, they were noisy in the laping machine, but after they were lapped in they went quiet. The diff was set up again, with near perfect marks on the teeth reading, fitted into the car and finally quiet as a mouse. I'm not sure what to say other than if you can salvage your factory fitted stuff then do so, this has been an exhausting excercise, I didn't lose hope as I had confidence in the company doing the work, they are one of most reputable diff companies here in Adelaide, plus he is a friend of mine!
Thanks to everyone that commented.