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Author Topic: Posi-trac Diff  (Read 4596 times)

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  • Message Board Member but not a NFTAC Club Member
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  • Posts: 5
Posi-trac Diff
« on: May 07, 2007, 06:28:23 AM »
On our '83 Trans Am (38,000 miles) we can hear a noise from the rear (diff? I think) when we back up or roll forward in a straight line at slow speed.  It's a combination of clicking and groaning.  Is this normal?  The car drives great.  The only other noise is a little bit of a whine when the overdrive kicks in, but no obvious howls or clunks from the diff when letting up or punching it.

I checked and added gear oil and additive to the differential, with no change.  We just had brakes redone, in case a caliper/pad was dragging, no change.  Should I just turn up the radio and wait for something to happen?


  • Firebird & Trans Am Club Tech Staff
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  • Posts: 110
Re: Posi-Traction Differential // ( Limited-Slip Rear Axle )
« Reply #1 on: May 07, 2007, 10:35:59 PM »

Clicking and groaning is not normal! // And Jam'en the box ( The stereo) won't help!

If you think the noise is coming from the Rear End hear are some possible causes see bellow:

1.Bearings// Bad bearings generally produce more of a rough growl or grating sound, rather then the whine typical of gear noise.
Bearing noise frequently “wow-wows” at bearing rpm, indicating a defective pinion or rear axle case side bearing; but sometimes this noise can easily be confused with rear wheel bearing noise.
You must inspect and replace as required.

2. Rear Wheel Bearings // A rough rear wheel bearing produces noise; witch continues with the car costing at low speeds and when the transmission is in neutral, the noise may diminish some by gentle braking, also with the rear wheels off the ground; ( Rear Axle Supported by Jack Stands ) and transmission set in neutral, spin the rear wheels by hand whilelistening at the hubs for evidence of rough (noise) at the wheel bearing.

3. Knock At Low Speeds // Knock at low speed can be caused by worn universal joints or a side gear hub counterbore in the case worn oversized.
Inspect and replace universal joints or case and side gear as needed.

And finally if you determine the noise is coming from your Transmission in either case it’s about time to pay a little visit too your friendly Trans-Doctor in your local area.

                                                                         Hope This Helps.  ;D

                                                                                               Justin K.
« Last Edit: May 07, 2007, 10:54:27 PM by T/A JLK »
I am a NFTAC, Member and I was at one time an auto mechanic working for a local GM dealer here in my home town back in the mid-to late '80's now  I currently enjoy working on my own Pontiac's especially on my '85 T/A // making maintenance repairs, repairs, modifications and performance modifications I also enjoy meeting and /or talking to other Firebird & T/A owners an get into technical debates;hopefully just as long as the debate's doesn't go into a to heated argument.

National Firebird and Trans Am Club Message Board

Re: Posi-Traction Differential // ( Limited-Slip Rear Axle )
« Reply #1 on: May 07, 2007, 10:35:59 PM »


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