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Old 04-22-2009, 12:35 AM   #1
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Default Differential question

So, a little while ago I was gathering info to prepare myself for swapping my 1.6 differential from my car to my dad's automatic 97' and then his 1.8 diff from his to mine, plus installing MMR UHMV diff bushings at this time. I began the project today, and have made good progress but will have to finish tomorrow as I was told that the axle nuts were 32mm and so I borrowed a 32 from my buddy and when I went to pull the axles, I found they are much smaller than 32.. maybe 28 or so so I will be finishing tomorrow.
This left me time to ask a question about something that seems very curious to me.
The 97' Auto is said to be an open unit. My 1.6 has an open diff as well. With both car's rears in the air, I rotated my rear wheel and the wheels spin in opposite directions. When I do this with the 97', they spin in the same direction. By the differential spotter's guide and other diff faq's on miata.net I have determined that the diff in the 97 completely fits what should be in the auto - and thus should be an open, so why does my open spin the wheels in oposite directions and the 97' auto spin in the same...?
This article in the miata.net garage: VLSD Torsen says that to test if a VLSD is good, spin the drive shaft while the rear tires are in the air (and its in nuetral of course) and they should spin the same direction, and that an open diff should spin them in oposites... but the 97' auto is supposed to be an open plus I don't even think the later models had a VLSD option... so what gives?

Thanks
-Ryan
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Old 04-22-2009, 12:39 AM   #2
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my '93 viscous spun both wheels in the same direction, and the cheapo '97 open I put in spun them in opposite directions, as I believe it should. If I recall correctly, this is not always an accurate test. I may be wrong, but some LSD might need a load to begin to lock up the wheels, but dont' quote me on this.

Sounds like that '97 might be an LSD though. Either you get a stronger diff or you get a limited slip stronger diff, sounds like a win win to me.
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Old 04-22-2009, 12:42 AM   #3
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true, I can't lose I guess! .. it just is unsettling to not actually know. I guess once I finally get the axle nuts off and pull the axles I can shine a light into the diff and see for sure what it is.
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Old 04-22-2009, 10:11 AM   #4
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with rear in air, have someone hold the passenger side while you try to spin the driver...
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Old 04-22-2009, 10:31 AM   #5
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Quote:
Originally Posted by Braineack View Post
with rear in air, have someone hold the passenger side while you try to spin the driver...
The driver weighs close to 200#, what do I spin him with?
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Old 04-22-2009, 11:00 AM   #6
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a really long stick?
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