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noise from the rear end when making right turns has me worried. just changed the fluid, that didn't seem to help. ( i used Mobil 1 syn. 75-90, should i have done that?) rear end is all stock, and i hope replies aren't " it's the damn axle bearing" , but i have that feeling! thanks!
 

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Dump the Mobil and use a good dyno oil.
Add some GM posi additive.
That vibration you're feeling is probably the clutch packs growling.
 

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I would try using the GM posi additive first, just because it's a pain to drain and refill the rear end. If that doesn't work, then I would try another lube, WITH the GM posi additive. If THAT doesn't work, well, then I dunno....
 

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i would change the synthetic out of there. Unless it came that way from the factory i would stay with the dyno oil. My new Eaton unit even stated that if i used synthetic that my warrenty would be void. My dad recently serviced his rearend on his 00 GMC Z71(came with dyno oil) with 275,000 miles, they put synthetic in and a week later it went out. The GM posi additive is a must no matter what fluid you go with though.
 

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The problem with synth's is that they don't cling to the gear sets the way dyno does.
That leads to premature wear.
Get the dyno back in it. :)
 

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Boost Sux my Wallet
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I concur. Run only dino in the rear.
Had to replace the posi in my 86 when I first got it, and the Eaton had a label that stated " Use of synthetic oils will hamper clutch operation"

My cocktail of choice in both of my GN's rears is:

Valvoline 75w 90 dino
1 bottle Lucas oil stabilizer dino
1 Bottle either GM or Kw limited slip additive (the KW is usaually available atthe parts houses in a blue tube)

I been running this blend for over 6 years and it works.

Folks are gonna chime in and say the lucas gets foamy and turns white due to some test.

As many miles/beatings (50 plus k miles) as I have put on the rearends it would have gave up now if the lucas was as bad as "they" say.
 

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turbo nasty said:
I concur. Run only dino in the rear.
Had to replace the posi in my 86 when I first got it, and the Eaton had a label that stated " Use of synthetic oils will hamper clutch operation"

My cocktail of choice in both of my GN's rears is:

Valvoline 75w 90 dino
1 bottle Lucas oil stabilizer dino
1 Bottle either GM or Kw limited slip additive (the KW is usaually available atthe parts houses in a blue tube)

I been running this blend for over 6 years and it works.

Folks are gonna chime in and say the lucas gets foamy and turns white due to some test.

As many miles/beatings (50 plus k miles) as I have put on the rearends it would have gave up now if the lucas was as bad as "they" say.
That "test" was flawed.
The oil was not at operating tempurature. :)
 

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Older--but Getting Wiser
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wh1-t said:
( i used Mobil 1 syn. 75-90, should i have done that?)
You're on the right track==NO, you should NOT have done the synthetic thing--stay with the Dino/factory GM-type stuff
 

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Why have one ?
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most of the on the shelf Dino oils for posi rears have the addative aleady in now . I recently redid mine with Castrol and no GM addidtive was required . so you can save yourself a few dollars . :)
 
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