Yup, thats not a straight 90W though. Its "good enough" for most people, but not me. Seems like cars using the 90W DiaQueen experience the fewest amount of failures.

 

I'm not trying to start a war here.

I mentioned the oil because it was the last thing I changed.

History of the car is this...

Bought with 30k miles.
Changed oil at 30k miles with mobil 1 and filter.
Replaced brake pads and ss clutch line, and removed clutch restrictor pill at 30,500 miles.
changed transmission fluid to amsoil at 30,500 miles. Was over all very happy becuase it made the crunch I feel between 2nd and 3rd better.
launched 3-4 times largely because I wanted to test the 2 step out and see how it works.
32k wife smokes the clutch at 7k rpm at the top of my driveway and I revoke her driving privileges. I drive the car the rest of the day and have no problems.
33k changed oil again using mobil 1 and filter.
33,500 miles replaced diff and transfer case oils with amsoil notice no change other then slightly more whine coming from transfer case(at least I think that what it is). I would like to state that I am fine with a little more noise coming from my car as long as it's in top working order.
~34,000 miles I hear a wierd noise while coming out of my garage and notice a "chatter" from the rear of my car, but by the time I'm up and out of my drive way it seems gone.
34,500 miles I'm noticing the "chatter" every time I come from a stop and am making a turn.

Car hasn't been launched or abused since the diff/transfer case oil change. I'm not holding the amsoil responsible for anything But that was the last thing I know to of changed before the problem. I have a very limited understanding of how diff's work and what's happening to my car right now and am having a friend come over to help figure out what it is. The car could of had 30k miles of abuse before I got it, and by draining the oil in the diff or transfer case who knows what I could of stirred up/loosened. There was plenty of metal on all the magnetic drain plugs. I after the transmission change went ok, I just assumed that was normal for evo drive train parts.

I will report back with the solution once I verify what ever the problem is and verify a fix for anybody else with a similar problem in the future.

 

Well, I switched out the fluid to oem. I've been driving it for about a week now and the shudder is all gone. It took a day or two for it to completely subside.

Anybody who is experiencing shudder shortly after changing their diff/tcase oil to amsoil I suggest switching it back to oem, preferably as quick as possible.

If you run amsoil and have no problems. Congrats!
I know of several people who run it who post on this forum. And it was largely off of their recomendations that I used it originally.

When I changed it out there was some very fine silver particulate attached to the plug and in the drain pan.

I'm not blaming any of this on amsoil or claiming it as an inferior product. Just stating that I had problems after I switched to using it. Could be I'm noticing a problem the oem fluid covers up for all I know.

 

I remember driving I-80 in my rear drive Trans Am. I had recently change the rear differential oil. I saw a ramp I wanted to take and turned the steering wheel. The car continued straight down the road past the ramp. Now, that was a bit of a surprise. At the next ramp I cranked the wheel hard and heard a loud snap from the rear of the car. Then the steering was fine. What was going on?

The new oil, even though it was advertised as for limited slip, didn't have enough limited slip lubricant in it and the highway driving had spun the oil out of the clutch pack. So, the clutch plates were locked until I put enough pressure on them to break them free. A little GM limited slip additive and all was fine.

This is an extreme case of the problem you were having.

 

Did the Amsoil you used have an LSD additive in it? With Redline, they sell 75-90 with and without the additive, so you are covered whether you have a clutch type rear diff (like an Evo) or a helical gear rear (like a Camaro or Miata).

 

I used this

http://www.amsoil.com/catalog.aspx?code=SVGQT-EA

I got it after filling out the information on there site asking what type of car you drive, and after reading some posts about what other people had used.

Some one mentioned adding an additive to it, but at that point I'd just as soon use the oem stuff.

 

35 dollars? what vendor has this for 35 dollars??

 

what about lsd friction additive or anything like that? I use severe gear but i always add in a little lsd additive.

I do run a new rear diff unit tho - cusco 1.5 way

 

The Rear diff needs some sort of clutch type LSD additive. This is why people use DiaQueen because it has that clutch type LSD additive in the fluid. I used Redline shock proof in the rear diff and my car was acting like yours. I switch back to DiaQueen and it went away. I’m not sure if Amsoil has an additive for Clutch type LSD’s

 

how would you know if your rear diff is going out? because whenever im driving and from 3rd gear to 5th gear and when i hit a the gas, im hearing a roaring noise from the rear of my evo.