i ahve a 1985 POntiac T/A..........like the title says i dont know what i have every once in a while ill posi other than that i dont know..... i do think i m low on rear fluid though.. how can i tell with out getting underneath... i believe i am low because my rear is soaked at the bottom and prolly has the original gasket..... back to posi or not is there anyway to tell besides etting the car on a lift....

 

take a look under it and tell me how many bolts are on the cover

 

if i m not mistaken its a 10 bolt

 

then all the parts you need are for a gm 10 bolt with a 7.5 or 7.6 i dont remember right off the top of my head

 

you probably have an open rear, do both tires spin? if so then you have a posi/lsd(they are the same)

 

You can do the fun test and powerbrake to see if you are spinning both tires. Some will tell you this is inconclusive testing, but it was good enough for me! I later pulled the cover off to change gear fluid to find that it was a Posi, and this is the only "true" way to find out.

Also, you can jack the rear of the car up so the tires are off the ground, and stick the car in Neutral. Now, if the tires spin freely and independantly of one another, you have an open rear. If you spin the right tire and the left tire spins with it, and you stop the left tire and the right tire stops, as if the two were locked...hello posi. Do this with the car off.

 

ok when i powerbrake it spins one tire but every now and then if i step on it hardand take a turn both wheels will spin and sometimes when theychirp i hear my left side chirp... and i know it cant be just my left because my right is bald..... and if its a 9 bolt then what??

 

check your rpos(assuming that your rear end is stock that is) and if you have the g80 option it is posi/lsd.

 

it shouldnt be a 9 bolt, either 10 or 12, unless someone has put a ford rear end under there. is there any bolts on the other side of the rear end towards where the drive shaft goes. if you do your powerbrake, you will get smoke from both tires if its a posi or a lsd, you will have to jack it up to determine from a posi or lsd then, if you are just burning the right side then you have a open one

 

A 9-bolt is a factory 3rd gen rear, built by Borg Warner for GM. GM never put a 12-bolt in a 3rd gen. - a 9" is a Ford diff, which many people are up-grading to aftermarket.
- being an 85, it is probably a 10 bolt. Yes a 7.5, GM never put the 8.5's in a 3rd gen. - The only way to know for sure is to pull the cover and look. If it's been leaking, you need to pull the cover and re-seal/change fluid anyhow, so just pull it.
this doesn't work either. Torsion type posi units(factory zexel, detroit true-trac...) will spin opposite when unloaded. They only power both tires when shocked or loaded hard from the pinion/ds. - that said, unless it's been changed, an 85 would not have had a torsional.
probably either not a posi/lsd, or worn out.
- bottom line, pull the cover....

 

is it a drum rear? if it is i would be willing to bet that it is an open rearend. if it is a disc brake rear id be willing to bet it is a limited slip. just some guesses.
kent

 

probably either not a posi/lsd, or worn out.
- bottom line, pull the cover....[/quote]


not sure what you mean

 

posi/lsd are the same thing, just different name
- if you only spin one wheel while brake holding it is either not a posi or its worn out and no longer "locks up"
- pull the diff cover and look at the carrier. probably is due a fluid change anyhow....

 

[QUOTE=Shagwell] A 9-bolt is a factory 3rd gen rear, built by Borg Warner for GM. I am sorry i have never seen a 9 bolt rear end that isnt a ford.

[QUOTE=Shagwell]posi/lsd are the same thing, just different name.
Sorry but no they are not the same thing, a posi doesnt allow a wheel to freewheel around a corner, a lsd does. try having a lsd and go fast around a highway section, one that isnt a hard turn like an exit ramp,but one you have to turn pretty hard. now take that same turn in a posi, you will notice a difference, you wont be able to corner as hard

 

[QUOTE=thirdgenlover][QUOTE=Shagwell] A 9-bolt is a factory 3rd gen rear, built by Borg Warner for GM. I am sorry i have never seen a 9 bolt rear end that isnt a ford.


Via Wiki

"In the 1950's and 1960's many manufacturers began to apply brand names to their LSD units. The most famous of these was Chevrolet's "Positraction". Since then, Positraction (often shortened to "positrac" or merely "posi") has become a genericized trademark for LSDs.

Other factory names for LSD's include

Pontiac: Safe-T-Track

Ford: Equa-Lock and Trac-Lok

American Motors Corporation: Twin-Grip

Mopar: Sure Grip

Ferrari: E-Diff"

 

okay when i pull the cover how do i know its posi, i dont know what a posi unit looks like or lsd..... tell me something to look for by the way thanx for all te help guys

 

if you have a open rear you will see four small gears (you may have to rotate the assy by turning the tire) in the center section these are your spider gears if you cant see these gears or see some springs in there then you have a posi

 

a posi will allow one tire to slow around a corner, although under power they will not allow "freewheel". - As many other have stated, in this thread and in others, posi, limited slip, etc.. are all just brand respective names for the same thing. - "posi", or "positive-traction" differentials are basically just a re-designed open diff in which clutches are used to engage both axles thus limiting slippage. The manufacturer's use clutches so that the diff can slip under conditions such as cornering, thus keeping the vehicle tire/user-friendly.
- A locker or spool are the only type of carriers that won't dis-engage under power around a corner.

 

9 bolt = Borg Warner rear used by GM
9 inch = Ford rear used by Ford

 

pic

There's a pic of my 10 bolt rear, and the posi unit inside it. Apparently this is an Auburn 2 series carrier. The springs inside there are the dead giveaway it's a posi unit. If it's totally open, just a big gaping wound in there, then it's an open diff.

 

Do what Shagwell and others have said. Open the diff and look. Done.

 

its not just a 9 inch, it has 9 bolts too, but on the other side of the carrier

 

A 9" doesn't have 9 bolts; and a 9-bolt doesn't have a 9" ring gear. The 9-bolt ring is 7¾" to be exact. And as far as I'm aware, Ford has never used a 9-bolt in anything at all, EVER.

thirdgenlover, for the time being, you should do more reading and less answering of posts. You're misinformed about the whole subject at hand. You need to put all that other drivel out of your head, and listen and learn, and not argue. Start by reading blyth's post, because it's accurate, but none of yours are.

Meanwhile, to move on past the misinformation argument and answer the original question, the ONLY WAY to know accurately whether a rear is a posi or not and also what gears it is (which is invariably the next question), is to take off the cover and look. Count the teeth on the ring and the pinion; or, find on the edge of the pinion where the count is stamped. It'll say something like "41:15", which would be 2.73 (41 divided by 15) or "37:9" which would be 4.11. If you don't know what a posi looks like, or aren't sure what the pieces in there are, then take a pic and post it here, and we'll tell you - ACCURATELY - what it is.

 

thank you every body.... you have all helped me out very much... one other question whats everybody's views on spools????????????

 

If you have a drag only car, put a spool in it.

If you use the car for regular transportation around town, you'll get sick of the spool pretty quick. (Handling suffers, rear tires squeak around every little turn and wear much faster.)

A posi (limited slip diff) is the only choice for a regularly driven street car.

 

even with aftermarket axles, a spool on decent tires will cause excessive wear/breakage in a daily driver street car. - Factory axles need not apply, especially the earlier/smaller 26 spline.
- I highly recommend the detroit true-trac, or a factory zexel torsional type posi. - Very driver friendly under normal conditions, because it will act like an open diff. When aggressively powered/shocked it will basically lock down, fully powering both tires.

- and yes, a 9" is a ford rear, named so because of the 9" diameter ring gear. A 9-bolt is a GM rear, named so because it has 9 bolts holding the cover on. Ford named for gear size, Gm named for bolts. Ya didn't think the Ford 8.8 had 8.8 bolts in the cover did ya?-

 

Although with some of the GM rears the bolt count doesn't definitively identify the rear. There are 7.5"/7.625", 8.5", and even two different 8.2" 10 bolt rears, none of which have parts that will interchange with the others.

Of course only the 7.5"/7.625" 10 bolts ever came from the factory on thirdgens.

 

we have already established that shagwell, on one wants to hear you repeat it again. 85t/a if i mis lead you in any way i am sorry

 

Look man, don't get upset because you got schooled on this subject. Everything Shagwell has shared is 100% accurate. The point of these forums is to share info. You gave completely inaccurate info and people called you on it. I don't recall anyone being disrespectful to you, although it certainly would have been appropriote. Just learn from this thread, and try to refrain from giving info that you are unfamiliar with. No offense intended, I just hate recieving inaccurate information.

 

hey i powerebraked hard today becausei wanted to se it a posi was worn out so what i did was park half in a stone drive half on the road and i hit it hard and they both spun just like a posi........ now my question will an open rear doo that????/

 

mine does that 2

 

Yes, sometimes.

 

sometimes yes, especially on gravel/dirt/etc. - When there is equally zero grip it could easily spin both tires.

 

Man, you can go out and do these experiments all day, but nobody will know for sure until you get under the car and pull the rear cover off the axle.

My pegleg acts like a posi anytime I'm going straight or turning left, but not turning right.

I have braved the axleial darkness, lifted the cover and seen the spiders.

 

- that's what i'm talking about!

 

He's right, I recently picked up a posi disk rear axle outta an 83 T/A, but what I didn't know is that the rear end is 9-Bolts, not 10, meaning it's a Borg-Warner. I looked at 4 T/A's & they all had 10 bolt housings.

I didn't see this listed above, so sorry if I missed it, here's a little tip to help find your rear end is open or posi. Jack the car up, leave it in park & spin one of the tires, open carrier rear ends will spin the other tire in the oposite direction then the tire you are spining & posi rears, shouldn't spin at all unless the car is outta park & which case will both spin in the same direction.

Joe

 

about a week ago i changed my rims and every since ive had posi in da rain and on dry asphalt ive try getting the right wheel to spin by itself like it used to by puting the wheel in the dirt and the other on asphalt and the both still spin its weird did something brake? or the clutches working again

 

yes, it was mentioned, and I shot it down(not trying to be offensive, just informative). This doesn't work for later-model(or aftermarket) torsional posi's. The torsional units will spin opposite if turned via the tire, they only spin both in the proper direction if powered(shocked/agressively) from the pinion.
we can all guess till the end of time, pull the cover.