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What does all this mean

Robliepse

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Im trying to learn more about the rear axle on my car. According to Galen and my broadcast sheet my 1972 GTX came with a D53 Axle ratio of 3.23.1 , D83 size 8.75 Diameter and D91 Sure-Grip and I really think the original rear end is still in the car.

Based on this I have a couple of questions.
How can I tell if this rear end is still in the car?

What does "Sure Grip" mean? What makes it different?

Would 3.23.1 be considered a tall highway gear ratio or a low quick gear?

Last but not least, I've only had this car for about a month and the tires need to be replaced so I've been smoking them up on a regular basis. When I get on it only one of the tires typically spin. Id think with the sure grip that both would lock up. IS there a way to easily check the read end without taking it apart? I kida remember jacking both rear tires off the ground and manually spinning them in different directions which would tell you something.

Thanks for your input
 
Sure grip is Chryslers name for a limited slip differential. Commonly referred to by the gm name posi traction.

Technically 3.00:1 and lower gears (higher numerically) are considered torque gears. Higher gears (lower numerically) are speed gears. 3.23:1 are regarded as a good all around gear.

Yes, if you lift the rear end, put it in neutral and spin a wheel, the other wheel should spin the same direction. If not the sure grip is worn out or it was changed at some point and no longer is a sure grip rear end
 
thanks Rebel, what does it mean if the rear tires spin in opposite directions? I haven't tested mine yet but I remember that opposite direction told you something.
 
If the wheels spin in opposite directions either the limited slip is worn out or it does not have one. Its an open rear.
 
Just a note that on torque sensoring limited center sections will turn opposite ways but once the torque is applied they both spin the same way, it's a newer technology but just in case someone swapped it out it could be that. Had on on my dodge neon srt4 that bugged me but when I did a burn out both tires went up in smoke. But since it's probably the original you should be fine. Either lift the tires off the ground and spin or go do a burn out see if you get two marks or one that's the fun way of finding out
 
To fill in some blanks here: an 8.75" rear will have a drop out center section, like a Ford 9". If you have no bolts on the rear end cover as viewed from the back, you have an 8.75" rear. Somewhere on it should be a small aluminium tag with the gear ratio. Sometimes these get lost but you can still figure out your gear ratio by getting the rear tires in the air and counting the number of revolutions of the axle vs the number of revolutions of the driveshaft. As stated above, a SureGrip is Chrysler's version of a "Posi", limited slip rearend. If you have a SureGrip in working order both wheels will turn in the same direction when spun by hand. The other way to tell would be a two-wheel peel which you say you aren't getting. They can wear out, so you may still have the hardware in there, but its just been spun to death requiring a rebuild or replacement. Do your burnouts without the brake-stand. Back when I was younger, cockier, and faster I would tell my buddies that: if you want to know if you've got limited slip do a burnout and count the black marks, dude. If they said they couldn't do a burnout without the brake I'd be all like, then why do you care whether you got a Posi or not? Such a punk smartass.
 
Thanks Jonnyuma, looks like I need to get the jack out this evening
 
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