I have a complete rear end that came with my truck when I bought it. It's laying on a pallet right now. How can I determine if it is a posi rear end or not. Thanks in advance.
get some one to hold one wheel or brake drum and see if you can turn the other one. If its a posi you wont be able to. If its not a posi you will be able to turn one side with out the other side turning and the drive shaft yoke will turn.
When I did that to my rear we could not hold but when we took the 3rd member out, it was not a posi.. (accord to the tread I post earlier in the week..)
If it's a Ford 8' or 9' it had a tag on it from the factory. L in the number means locker(posi) for example3L50 would be a 3.50 ratio with posi,
there are some GM rearends with a govlock "posi" that only engages when one wheel spins faster than the other. and some old Danas had no springs on the clutches, they only engage when loaded. So take your time figuring it out....if it's a rear with a removeable cover, pull it and take a looksee.
I was under the impression that posi units take a different lube and are identified with a tag from the factory. Is this not true?
"posi" is not a very descriptive term. Differnt sorts of differntials will respond differntly to the above tests. "Posi" is just an abbreviation for the GM "Posi-Traction" Limited slip rear ends. There are a whole lot of other types of rears out there. Generally, if you can spin one wheel independent of the other, thats not a good sign - but not always. Best bet is to take it apart and see if there is anything funny attached to the spider gears.
i'm convinced that the only way to tell is to crack it open. I thought I had a posi, turned out I had a inner gear broken jammed until it didn't turn...
Pull the cover, should look like these if it is "posi" Limited Slip, clutch types, Lockers are often all thought of as "posi", but really only refer to GM Positive Traction Clutch type from what little I know of it. Anyway, a stadard spider gear on a one legger should look like this.
pics..helpful... here's a govlock in it's normal pose (broken): and here is a normal open differential:
some gm posi's can have "Z" shaped springs too. A buddy had a 79 camaro with that type of posi, first time I had seen one like that.
most gm rears are stamped on the front of the rh tube. this code can be decifered w/a hollander interchange. a good place to start although you cant be shur till you pull the cover.
I was shown by a guy at a wrecking yard, he had a early ford van on its side and needed a brake drum, so he too a huge cheeter bar and socket on the top wheel lugs then stood on the bottom tire and when he jerked the cheeter bar and lug wrench it slammed him into the van and on the ground soon after, Said wow its a posi. I think thats the correct way!
Don't subscribe to the "turning one wheel" test, especially if the rear has been sitting for a long time. I bought a 3.31 posi 12 bolt out of a '67 El Camino cheap one time because the owner turned one wheel and the other didn't turn, so he ***umed it was an open rear end. The oil had drained off of the clutches from sitting, and it didn't have any posi action in that condition.
if the rear has been sitting the drums are ususally locked up so learn the type of rear youre looking at and pull the cover. if its a ford 8 or 9 inch, do not just break off the tab from the factory, they always seem to break right off at the point where the L should be and you cant read it. take the nut off.
That just does not make sense...the posi in the 12 bolt works by having four big*** springs pushing the side gears outward, compressing the posi clutches. With our without oil, you cannot turn just one wheel if the posi is there, and not broken, unless maybe a side gear is stripped or an axle is broken or splines stripped. But your point about making sure to pull the cover and look is a good one!
It might not make sense on paper, but it was installed with nothing more than fresh oil and posi additive and worked fine. Like the bumble bee, I guess it was too stupid to know that it couldn't fly!
Actually, that happened to my buddy with the camaro. We opened the rearend up to put in fluid, and saw the springs, and figured out it was a posi. Previously, it had normal oil in it, and acted exactly like a open rear, one-wheel burnouts and all. He put posi rated oil in it, and it started acting like a tight posi is supposed to. I beleive the posi type oil has an adative that allows the clutches to grab right, but I don't know for sure.
again: that just does not make sense...sorry.... Maybe there was something else going on that you weren't aware of? (btw, once the scientists began to carefully study how bees fly, instead of making false ***umptions, it's no longer "impossible"....)
This one don't p*** the common sense test either - posi-additive is designed to allow the clutches to slip, reducing noise & chatter. Road racers restricted to stock clutch-type limited slip diffs actually leave the additive out so it will grab more.... Your clutches will actually last longer w/o the additive.
Well, that's how it went down. It was a pretty decent 79 camaro that had been garaged for 5yrs. My buddy ran his cars hard, one of the first things he did was lay rubber. It was one wheel burnouts, I was there. The rear started to make noise after a while, so he decided to change out the fluid to crutch it up until he could sell it. He worked at a garage at the time, we had it on a lift so it was easy to deal with. Yanked the cover, and there was these funky "Z" shaped springs on each side of the diff, and we reconized it as a posi. He put in posi type oil after that. A while later I went for a ride, it was a completely different car. The posi worked extremely well, it was quite a difference. I don't claim to be an expert on diffs or oil, but that's what went down.
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