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Old 02-19-2012, 07:34 PM
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Eaton Posi Noises

Rear end had 410 gears and master rebuild kit installed in 10 bolt GM in May 2011 by reputable shop. It has an 8.5 carrier with Eaton posi. I added the appropriate type/amout of gear oil with additive and drove the car around town. I know posi units chatter etc when turning etc., and mine does as expected. But, when I drive say 40-50 miles, the rear end gets to operating temp and then begins to make like growling and snap noises. It does it when turning but also makes the sames noise when going straight slowly but only when it has been driven for about 45-60 minutes and its "warmed up".

No noises of any type BEFORE it has reached "operating temp" Once "hot", stopping and then starting causes it to snap and clunk (technical terms, I know) and it just sounds like hell. It should not do this!! Everything is fine until it heats up then all hell breaks loose. Gear oil and additive are new. Gears, axles and Eaton posi are new. The whole shebang (the car) only has about 500 miles of test drives. No hard launches or extended driving at freeway speed yet. Ideas??

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Old 02-19-2012, 08:07 PM
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I'd take it back quick!
They may have set the Gear clearances, Pinion preload etc.. too tight. When it heats up the clearances get smaller/tighter.
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Old 02-19-2012, 11:56 PM
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That makes sense (finally). Sadly the shop is over 100 miles from my home. Can I continue to drive the car assuming that your idea is correct?

Thanks for your fast reply. Nice '64 by the way.
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Old 02-20-2012, 08:20 AM
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I'd be careful driving it. Not only for safety's sake; (which is the most important) but, the shop that did the work may not be willing to cover all the damage that may ensue due to the car being driven after you noticed said problems.

Big Gear Head (Freddie) on this forum and others seems to do a lot of these, you may want to PM him as he doesn't visit this forum often anymore. He may have some insight as to questions you should ask the shop and things to look for. Im sure others here will have some insight as well
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Old 02-20-2012, 05:38 PM
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Check pinion and make sure there is no in and out play or is excessive tight. Remove rear cover and inspect for any signs of breakage.If there's NO sign's of breakage do a clean and refill of the diff. Use your choice of oil and a good additive. DO NOT use oil that states.." NO ADDITIVE NEEDED".

How are the rear tire's? Does one tire have more wear than the other?
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Old 02-21-2012, 12:32 AM
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I'll go out on a limb here from my experiences...if anything was loose,tight,not set up right,mis-adjusted..too much backlash-not enough wouldn't take 50 miles of driving for it to come to light... just a road test around the block would...if something is not right,the rear end will let you know real quick that its not happy,trust me..diff bearings don't tighten up after they get hot...if that was the case,every motor and trans would sieze up after an hour of driving...It's a fact that Eaton sells a lot of posi units...I will say it would also be a fact that Eaton WOULD NOT sell a lot of posi units if they chattered going around corners...if it wasn't re-worked after it came out of the box,it shouldn't chatter....I'm not by any means saying that this is your problem, but I will say this from my ''I've made this mistake before'' archives....If POSI LUBE, not regular gear lube, AND a posi lube additive[I've sometimes used 2 bottles] is not used... depending on the type,and brand, of unit,... chattering,crunching,and other noises associated with the posi plates, not liking the lube[lower vs. higher friction characteristics of the different lubes],will occur...and it takes miles of driving for this to come to light,it doesn't happen during a road test.In my case,I used non-posi lube w/ posi lube additive,and thats what I experienced a side note,the last dana 60 posi unit I installed came with a tag that stated ''do not use SYNTHETIC posi lube''....I thought that was odd...just sayin,this all might not apply to your case,but I've had a similier scenerio happen to me,and from customers alike. It would be nice if it was that simple in your case.

Last edited by rick 427; 02-21-2012 at 12:40 AM.
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