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Discussion Starter #1
So I took the Elky out for Thanksgiving to visit family. While I was down I decided to swing by the beach, been a while. Well I decided to spin the ole tires in the sand and have a little fun. I noticed in the rear view I had 2 marks in the sand, for both tires. I did not know I had a limited slip or posi rear end. Is there a way to tell which one I have? I do not have the build sheet and the sticker in the passenger side door is gone. Below are the cowl tag numbers, not sure if it is on there or not.

78 1aw80 R 026137
TR 74v a52 15l 15u
10a 020184
 

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Deputy Director Region 18 Participating Member
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..well, you can jack up one side of the car,make sure the front tire are blocked, and put the cruck in netrual and spin the rear tire by hand, if it turns,then, it's a "peg-leg",if it don't turn by hand and it's stops, it's a posi, Also, look for this tag on the rear diff.:dontknow:


:bigups:
 

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Yup sure fire way is to spin
 

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corect me if im wrong but opposite directions means its a standard Limited slip diff. Posi would have both spinning in the same direction/locking up.

if it was an open diff i think just that one side would spin and not both.
 

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Deputy Director Region 6
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corect me if im wrong but opposite directions means its a standard Limited slip diff. Posi would have both spinning in the same direction/locking up.

if it was an open diff i think just that one side would spin and not both.
Limited slip & Posi is the same thing !!!!
Different words same meaning !
I think GM says Limited slip & Ford says positive traction
 

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Acting Director, Region 13
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Maybe I was seeing things at the beach, I jacked up the car and spun the tires and they spun in opposite directions....
Opposite direction means it is an open rear end. Posi they both spin the same direction and would have to be in neutral to spin if off the ground.

Tim
 

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Deputy Director, Region 1
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my 78 does that in the snow. after a few seconds of one tire spinning the other will start spinning too. but jack it up and turn one and the other turns the opposite way so ....open rear but why both spin?
 

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The open carrier CAN spin both tires. It depends on the traction of both tires. It will apply power to the tire with the least amount of traction. Conceivably if both have equal traction, the differentials internal gears can stand still and power is then applied to both tires.
 

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Now there is a difference between limited slip, posi, then locked. I have a locker in mine. Put one tire on ice, and the other on drive pavement, both will spin. It will for the most part drive like a standard diff., until you but the power to it. I love it, but have to learn to drive it in the rain all over again.
 

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The limited slip in the 7.5 rearends actually has a governor inside. When 1 wheel spins A certain percent faster than the other wheel the governor actuates a cam and locks up the clutch plates. So it will act like an open rearend jacked up and spinning by hand. If you take the cover off it's pretty obvious if you have one. They a pretty fragile and break a lot.
 

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Discussion Starter #18
What I thought rear ends were before:

Posi - both tires have same power to them at all times
Limited Slip - One tire has power unless it starts slipping then half the power is sent to the other tire for support
Open - Just one tire has power regardless of traction

Thanks for the info on the rear end. I do not plan on this car to be a speedster so I think the open rear end should be fine.
 

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Posi and limited slip are both the same thing.

Standard rear end "Peg leg", both back wheels always propel the car but the power goes to the wheel that spins the fastest. So if one side spins out, all the power goes to that wheel.. That's why the standard rear end is a better set up as far as handling and braking go. They turn bends so much smoother then the clutch set up... But the posi is best for drag racing and snow..
 
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