# Noise From Auburn Posi Unit



## 68Resto-mod (Nov 10, 2009)

I have a stock 3.55 Auburn cone type posi unit in my 68. It is the only part of this car that I did not restore or replace. All I did with it was to drain the old gear oil and replaced it with Amsoil Severe Gear 75W-90. I did not add their “Slip Lock” additive. 

I am just finishing a 7 year restoration and have started road testing to work out the bugs. At first, I would get the expected chatter when turning. I also got a “clunking” sound when going from forward to reverse and back etc. (straight line, no turns). After as few test drives and tight turns, the chatter when turning went away.

Here is the issue: I am still getting a “clunk” from the rear carrier area when accelerating and decelerating. It is most noticeable at low speeds because road and engine noise are lower. Also note that this not during turns, it is straight line driving. I can duplicate the noise with the car parked, in first gear, engine off and I manually rock the car forward and back. It sounds like the clutch cones are snapping across their friction surface as if there was bit of free-play somewhere.

All “U” joints are new, outer wheel bearings are new, pinion input shaft and seal are new and I was very careful not to over-crush the existing crush collar.

Does anyone have an idea what might be causing this?:banghead:


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## ALKYGTO (Mar 29, 2010)

If I had to hazard a guess I would say excessive backlash between the ring and pinion. Could be worn gear set or pinion bearing. 

Jack the rear up on jack stands and with the car in park see how much you can rotate the rear tires back and forth and listen for noise. Watch the pinion as you do this so you can see absolutely how much backlash you have.


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## Goat Roper (Oct 28, 2014)

Not a big fan of Amzoil, I used it in my new Dodge truck in the early 90's and it destroyed the LS rear end and every seal in it.
Engine, pinions and axles all leaked like sieves, my buddy and I both converted our trucks to it at the same time and the same thing happened to him.
Dealer was no help the truck was still under warranty but I was told it was my fault for using it.
No way I would ever use it again.


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## 68Resto-mod (Nov 10, 2009)

Alky

There could very well be excessive backlash or a worn gear. I have also read that the pin or pins that hold the planetary gears can ware the hole in the carrier case oval. 

I think I am performing the same test by leaving the car on the ground, in 1st gear and rocking the car back and forth. When I rock it gently, it sounds like normal gear lash. But when I push harder, you can hear the cone clutches "chirp" a fraction of an inch. I can almost hear the tensioning springs "ring" when it happens. The entire axel housing shudders. 

I may have to pop the rear cover off the housing and observe the gears and carrier assembly during the same test.

Roper
I have read many mixed conversations regarding Amzoil. It may not be right for the Auburn type posi. If all else looks good inside the housing, I will try good old GM gear lube with additive. Hay, it worked for the first 46years!

Thanks guys
Lance


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## Pinion head (Jan 3, 2015)

put the car up on some good jack stands, or preferably up on a lift. Remove the ubolts and carefully swing the the rear of the driveshaft aside where the yoke does not come out of the transmission and leak everywhere. With a thick leather glove grab the pinion flange and violently rock it fore and aft. this takes somes strength, do you feel any to a fro of the pinion? 

If the pinion seal is leaking, there's is a good chance the pinion is loose. The pinion becoming loose is not an easy, tighten the nut up deal, or a pull the pinion nut, washer, pinion flange, and replace the seal and pinion flange deal. The pinion head needs to be at the exact .001 depth that it was originally set up at. Another way you can ck to see what's going on with the ring and pinion, is pull the rear cover, drain the r/e grease, is there any glitter in it? next, rock the ring gear on the pinion. Set up correctly, the backlash should be around .008. Even a 300K mile properly functioning differential in a very abused tow vehicle can be that tight after doing nothing other than changing r/e grease over the years. if you have access to a magnetic base dial indicator, you can measure the backlash at 3 points around the ring gear. untouched, a backlash of .008-.012 would not throw up a red flag to me. If the backlash is in the high teens to .050 range, you have serious problems. On long time gears, one can note a pattern, when the tolerances are loose, the ring gear rocks on the pinion and both wear abnormally and the entire ring gear tooth shows contact. 

Having picked up the pieces of a bunch of blown up Pontiac 8.2 rears, what has destroyed many of them is the pinion getting loose and eventually the pinion getting in a bind with the ring gear. Usually this happens when the car is being slowed down from speed, to stop and the pinion slightly shifts along the bore of the two pinion bearings. this shifting should not occur. The relatively small pinion (think 3.55's, 3.90's, 4.33's) then gets in a bind and the result is a few broken teeth on the ring and pinion.


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## Pinion head (Jan 3, 2015)

Last question, till can get on late tonight, this rear, someone has been into and installed an Auburn posi carrier? Or it has the original cone type posi carrier?


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## 68Resto-mod (Nov 10, 2009)

Pinion
GREAT INFO!

It is (or should be) an original Pontiac posi unit. I may be calling it the wrong name. 

Pinion play front-to-back should be tight. I replaced the seal myself. I followed the service manual to the letter. I punch marked the nut and counted the thread turns coming off. I replaced the seal and counted the turns back on to equal the turns off plus a fraction of an inch (whatever the book said) to just seat against the crush collar.

I am going to start with adding “Slip Lock” additive and see if the problem clears. If not, I will dive deeper with some of the tests you and Alky have mentioned.
Thanks again


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## geeteeohguy (Feb 2, 2008)

What OPH said. You most likely have a back lash problem. Easy to check with a guage. You can even ballpark it without one....jack out the rear and turn the driveshaft by hand back and forth and you can feel it if it's excessive.....I once had broken several of the ring gear bolts on an 8.2 and it had about 1/4" backlash....you could _really _feel it.


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## chuckha62 (Apr 5, 2010)

While I can't improve on the info you got from Pinionhead, I can add that on deceleration a loose pinion will allow the pinion to run way too deep and the differential will have a distinct whine to it.


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## 69Goatee (Aug 14, 2009)

I have an auburn diff in my GTO also. I used the high dollar parts store additive and had noise. The instructions I have call for Ford factory additive, so I replaced the diff lube and added the Ford stuff. I haven't had noise since.


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