One Legger, Posi, or Limited Slip

[Paso76GMCstepper]

OK Guys how do I tell. Its a 76 GMC k15 4X4. When I get on it in the mud both rear tires light up. It seems to be posi. How can I tell please.

[784X4GUY]

I really have never heard the difference between a limited slip and a posi. I always thought that it was a limited slip untill it kicked into posi? I also need some light put on this situation for me please...Later Mike

[ocbaud]

posi and limited slip are the same thing

yes it sounds like you have a posi unit

[784X4GUY]

Oh I got ya ocbaud thanks for clearing it up for me...Later Mike

[ocbaud]

Originally Posted by 784X4GUY

Oh I got ya ocbaud thanks for clearing it up for me...Later Mike

i have a friend who argues back and forth with me about it.
he has it in his mind that with a limited slip diff. only 1 tires spins.

i've printed out 5 pages of info on every type of diff. and he still doesnt believe me

[784X4GUY]

Yeah what I thought was when one tire started to spin the diff sensed it and applied power to both wheels...Later Mike

[ocbaud]

Originally Posted by 784X4GUY

Yeah what I thought was when one tire started to spin the diff sensed it and applied power to both wheels...Later Mike

yeap, thats exactly right

[MylilBowTie]

What way do the tires spin with the rear lifted and tires not touching the ground? Same direction or different? Open rear ends have more tendency to act as a limited slip, posi rear would in snow and mud even though they are not.

[Paso76GMCstepper]

OK Guys thanks for the info. If its posi it would be harder to break the rear end loose right.

Thanks for the info.

[magnethead]

technically. you would have more grip, so likely so.

Actually, there's 4 types of axles: Open, limited slip (1/2 turn slip), posi, and lincoln.

if you think you have a posi, check that somebody didn't put a lincoln locker in it.

[Russell]

Best way is to lift the axle up and spin a tire, if the other spins in the same direction, then it is a posi / limited slip / lincon locker, if it spins the other way, its an open diff

[magnethead]

thats the easiest way to explain it right thar.

[RockHQ]

Posi, or Positraction, is just a brand name for a limited slip locker (IE Eaton Positraction, Dana Trac-Loc, Ford Traction loc). Of similar design are cone type limited slip clutch action differentials like the Auburn, Mopar Sure-Grip (Either Dana Power Lok clutch type or Borg Warner cone type depending on year/aplication). There are lots more "posi" type, or clutch action differentials, too many to list, but those should be the most common ones for american vehicles.

In addition to those there's a whole slew of different mechanical lockers but that's besides the point.

[magnethead]

but a true posi is what drag racing uses, along with most ATVs- a solid axle from side to side with the ring/pinion connected.

[ocbaud]

Originally Posted by magnethead

but a true posi is what drag racing uses, along with most ATVs- a solid axle from side to side with the ring/pinion connected.

no, thats a spool

[pastorjimk]

My 2 Cents (for what it's worth)

An open rear end will deliver power to both wheels while they have the same amount of traction (i.e. in the mud/snow) but once one of them grips the other one will spin. If you raise the rear end completely off the ground and turn one tire the other will spin in the opposite direction.

A Posi unit typically has a clutch pack and springs which locks both rear wheels causing them to both turn in the same direction while off the ground. They will allow one wheel to slip a little for going around corners but they will break loose at about 20-35 ft-lbs so that you don't snap an axel. In the old days (and for racing applications) they used to weld open rear ends forcing them to be posi...no give...no slip...lots of broken axels.

A limited slip unit is very similar to a posi but has a locking device that causes the diff. to lock the wheels (similar to welding but not as perminent) if one of the wheels breaks loose (20-35 ft-lbs) and rotates approx. 6 rotations or at a certain rpm of the axel. Limited slip rear ends have caused some people problems because they get in a bind and the guy just floors it before the diff. has a chance to "lock" then it locks in at a very high rpm and comes appart!

For what it's worth...BTW the tech data may be off somewhat as I don't have any books in front of me, this is from memory and much of it is from talking to guys that rebuild them when guys like us break them...

[ocbaud]

anyways, with my new gears AND eaton posi, if its wet outside and i floor it under 50mph, i will go sideways....

just cant race in the rain

[RockHQ]

A posi is a brand name for a limited slip differential. It's not a design of it's own, it's a brand name just like Coca-Cola, Pepsi etc are the same thing with a little different flavour. I listed some of the more common clutch type limited slip differentials in my previous post. Limited slip differentials allow some wheelspin if enough torque is applied.

Like Eric said a spool is a direct coupling of the driveshafts to the ring gear carrier. Either a mini-spool which replaces the spider gears, or a full spool which replaces the whole carrier. This is what true drag racers use to transfer equal torque to the driving wheels. These are not posi's.

Then there are mechanical lockers which can either be selectable (electric like the Eaton E-locker, pneumatic like the ARB Air Locker or cable actuated like the Ox Trax locker), self-engaging like the Tractech Detroit Locker, GM Gov-lok, PowerTrax Lock-Right/No-Slip, Aussie Locker etc. Other variations of these are the Zexel-TorSen locker and Detroit TrueTrac. These are lockers, not limited slips. These provide 100% torque to both axle shafts when they are engaged.

[Captkaos]

RockHQ is dead on correct. This has been discussed WAY to much in the past and everyone seems to think 'posi', or Positraction as it is called, is something it isn't. It is JUST a name GM assigned to their differentials that are not open.
There is only 3 types of Differentials (not axles): Open, limited, and locked. There are variations of the limited and locked on how they achieve their results, but there are only 3 types. A spool is not a differential as it doesn't differentiate in speed. It permanently locks both axles together.

BTW a Lincoln Locker is an open differential with the spider gears welded together. It isn't something you install.

[magnethead]

Originally Posted by magnethead

but a true posi is what drag racing uses, along with most ATVs- a solid axle from side to side with the ring/pinion connected.

Originally Posted by ocbaud

no, thats a spool

I meant a solid axle- my go-cart has one. no spool, no gears what so ever, sprocket mounts to a key slot and the axle is 34 inches of pure solid steel 1" in diameter. wish i had a pic. I havent blown the axle in 2 pieces yet turning, but you'd think it would with 22x11-8 tires on each side of it. If my host was up, i'd post a pic.

[1FaastC10]

Originally Posted by magnethead

I meant a solid axle- my go-cart has one. no spool, no gears what so ever, sprocket mounts to a key slot and the axle is 34 inches of pure solid steel 1" in diameter. wish i had a pic. I havent blown the axle in 2 pieces yet turning, but you'd think it would with 22x11-8 tires on each side of it. If my host was up, i'd post a pic.

and i'm sure with a go cart you're makin mad horsepower too. probably pushin 6hp and 38 ft/lb, arent ya.

[magnethead]

lol. 12 HP and enough torque to do what i like doing...which is smoke the living **** out of the torque convertor belt (i'm on the 3rd throttle cable in 3 years, 5th belt in 1 year, 2nd axle in the time i've owned the cart, and replaced the dual stamped axle bearings with dual stamped and dual cast iron bearings from blowing the old ones to pieces- how i wound up replacing the axle).

[Captkaos]

Go-carts are WAY different than a vehicle. You only have 1 gear, cars/trucks can have up to 6. Still, drag racers use spools.

[1985K10]

Most limited slip diffs have a tag bolted to a cover screw or the filler
plug itself.

I forget if my 70 Chevelle is posi or not, so i check with a heavy right foot.

[784X4GUY]

I have seen go carts out here in phoenix, And one of them that I seen had a 125cc motor on it and had a 6 speed with it. And trust me that thing flat hauls ass...Later Mike