Amsoil in my Eaton posi

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Since my Eaton posi had a propensity to fry pretty much any gear oil I put in there, I decided to try Amsoil Severe Duty 75W-90W. Eaton recommends petrol based oil with 2-3 tubes of friction modifier. I lost count how many different brands of oil and modifier I tried, but severe chattering would return after less than 1K miles. Amsoil ended up sending me 75W-140W instead of what I ordered, but I decided to try it anyway. The chattering is barely noticable now...even without friction modifier. We'll see how it does once I get some miles on it. If it worsens, I'll try Amsoil's friction modifier. If that doesn't fix it, I'm throwing out the posi and getting a Truetrac.
 
I had good luck with Mobile 1 and no modifer. I found there was very little holding power in the diff with any friction modifier in there. I'm talking less than 100 ftlbs. Did you have your diff rebuilt to different specs or is it an oem frpp unit?
 
95blklsc said:
I had good luck with Mobile 1 and no modifer. I found there was very little holding power in the diff with any friction modifier in there. I'm talking less than 100 ftlbs. Did you have your diff rebuilt to different specs or is it an oem frpp unit?
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You've got an Eaton? I know the traction-loks don't have an issue with chattering. I was told that the Corvette guys (Eaton is OEM) complain about it a lot.

I had mine rebuilt...though I'm not sure what spec they used. I just told the shop I wanted an Eaton posi with stock gearing. They did the rest.
 
Mine is a OEM ford LSD that came with the FRPP 3.73 diff a few years back. I'm not sure if it's eaton or not. I can't say I'm overly impressed with it's side to side holding ability, but I don't get chattering.
 
I use the Amsoil SVT severe gear 75w-110 in my 03 cobra spec trac-loc. This was the oil recommended to me for my 4.30 gear application by Amsoil techs. No chattering at all, didn't have to add friction modifier.
 
95blklsc said:
Mine is a OEM ford LSD that came with the FRPP 3.73 diff a few years back. I'm not sure if it's eaton or not. I can't say I'm overly impressed with it's side to side holding ability, but I don't get chattering.
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From what I understand, GM uses Eaton as OEM, but Ford doesn't. The drivetrain shop guy told me that he has the Eaton posi in his truck, and that in fact the Eaton posi was really designed for trucks and towing applications. For this reason, vehicles with lighter rear-ends tend to experience chattering. I would think that the posi could be loosened up via adjustment, but I don't know enough about them.

My situation is the opposite - side-to-side holding is good, but I've got (had) chattering.
 
Yea it might make sense to slowly add friction modifier every weekend until your chattering goes away. I'm talking maybe a 1/4 tube at a time.
 
Well, still getting the chattering.

I just ordered Amsoil limited slip additive. If that doesn't work, bye-bye posi.
 
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