I have a 69 Cutlass with a 3.23 rear. When up in the air and the wheels are turned they both go the same direction. I had figured it was a posi rear but when I leave a trail of rubber on the road it is just the DS. This would make me think it's a limited slip rear. Is there a way to know for sure. I assume a posi would leave two trails of rubber I assume.

Steve

 

Limited slip and posi are the same both wheels should leave marks unless it’s worn out. Only way to know for sure is to open the cover.

 

As said, posi-traction and limited slip are the same thing just different marketing names.

An open diff can have both wheels turn the same direction when checked as you did, it just depends upon how much friction there is at the wheels. If the wheels can "freewheel" very easily and the gear mesh inside the diff has more friction than the wheels have, then the wheels turn instead of the gears in the diff turning. Try again but have someone put a hand on one wheel to see if it continues to try to turn or if it can be stopped very easily.

This could still be a limited slip diff with severely worn clutches, so as said pulling the cover is the sure way to determine what's in there.

 

Anti-Spin was Oldsmobiles name for it I believe. All the same thing.

 

If you lift one tire off the ground w/ the trans in neutral (parking brake released), it should take > 100 ft-lbs of torque to turn that tire if the posi / LSD is working correctly. If it spins easily (<20 ft-lbs), you likely have an open rear. In between its a worn out posi.

 

I thought limited slip shifted traction to the other wheel if one began to spin on ice or snow? I will see how many lbs of torque it takes to turn.
thanks,

Steve

 

Usually the passenger side tire is the one that goes up in smoke. If you put air bags in the rear springs and isolate the air lines side to side you can adjust preload to where the “peg-leg” will spin both tires.

Having said that, the only way to be sure is to remove the diff cover and inspect things. The carrier could be worn, and need rebuilt

 

The clutch style limited slip units have friction clutches that connect the axle shafts to the carrier, so both wheel are driven the same amount. There is no transfer of traction from one side to the other, but if one wheel loses traction on snow/ice the other wheel will keep the vehicle moving, assuming it has traction.

 

Sorry, couldn't resist.

 

Okay, so I lifted the PS side put it in neutral and started to torque the lug nut, gradually increasing to 100# no slip, did the same on the other side, 100# no movement. Hum, I checked the tire pressure, 35 on the DS and 25 on the PS side. Equaled them out and had to wait for a dry day and took it out, found a quiet private place and punched it. Two nice trails of rubber!!!!! Yay, what a relief. I had just checked the tires a month or so back so I will need to stay on top of it. Thanks to all for the suggestions.

Steve

 

Look for the two-letter code on the passenger side axle housing. If you have the "O" type differential, and unless someone has completely changed out the gearing, you should be able to find a two-letter code of "SF" (drum brakes) or S7 (disc brakes) with anti-spin. The two-letter code is usually facing directly forward or directly aft on that passenger side axle housing. It might be upside down and buried under years of dirt, grime and perhaps some rust, but you should be able to find it.

Randy C.

 

[QUOTE=dragline;1257225]Sorry, couldn't resist.

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QUOTE

Good stuff!

 

So I cleaned up the PS axel and could not find any #s. It is a 3.23 Posi rear for sure. Would those #s on it confirm if it is an Olds rear and possibly original? A PO did many performance improvements so I'm not sure if it is even an Olds rear. Any help is appreciated.
Steve

 

That's a Pontiac 10 bolt rear end according to monzaz on the JD Race forum:

http://forum.jdrace.com/viewtopic.php?t=500

 

Yes. Here's the decal that is on the trunk lid of the '73 Custom Cruiser I owned until a few years ago. The OP's Cutlass was probably born with a sticker similar to this on its trunk lid.

 

Wow, thanks for the info. I'll look into it.

Steve

 

casting number on center section 9799100 denotes it is a Pontiac 8.2 rear

 

Is that considered a good rear? If he swapped the entire rear would that effect the brakes as far as ordering parts for repairs?

Steve

 

According to monzaz in the link I posted above it's a strong rear and the brakes are the same:


Post by monzaz » Mon Apr 24, 2017 8:19 pm
oK YOU HAVE A 1969 Pontiac 10 bolt 8.2 rear end
Axles are 28 spline bolt in - it is not original to the Chevelle BUT can be a very good candidate for better power in a 10 bolt rear.
the date is September 18 1969 housing (I 18 9 ) was not a (I188) ity is Letter I (month) and number 18 DAY and Year 9
gear ratio is a 2.56 freeway flyer gear NON POSI
You can fit any ratio you want in the rear ...NEW posi and 3.55 gears will fit right in.

We sell all the parts for it or you can go else where too.
Axle bearings will be seal and bolt in from the housing end flanges.
This rear will take the same brakes as your 12 or 10 bolt Chevelle rear also. 9.5 x 2

U-joint will be slightly bigger than a Chevy also again more strength. ALL Buick Olds and Pontiacs got bigger yokes than the Chevys.

 

So it is definitely a 3.23 posi rear. Any idea why someone would put in a Pontiac rear as opposed to just changing gears? Is this better than if that had been done?

Steve

 

It is a whole lot easier to swap rearends than it is to install new ring and pinion gears. Since around 1980 I have swapped entire rears in my cars 6 or 7 times vs installing gears only one time.

 

And I guess getting a Pontiac rear is common and an easy fit?

Steve

 

It's a direct fit so if the car originally had say a 2.56 rear, then it would be an easy way to get a much better rear gear and posi.

As far as being common, that would depend upon what was available in a given area at a given time over the past 50 years. The rearends are interchangeable between all 68-72 A-bodies, which would be any of the vehicles below:

Buick Skylark, Gran Sport
Chevrolet Chevelle, Malibu, Monte Carlo, El Camino
Oldsmobile Cutlass, 442, F-85
Pontiac LeMans, Tempest, GTO, Gran Prix

 

I believe this works the same as the Electronic locking differential on my 2014 F250.

 

No, not quite. A locking differential, whether it is activated by an electrical solenoid, by cables, by pressurized air, or by inertia, creates a solid mechanical lockup between the axle shafts. There is no differential action and both tires will turn the same amount, even if one is off the ground. This is why there is a caution that it is not to be used on dry pavement.