well me and my friends were doing some burnouts for a video we are making and i was doing my burn-out and i noticed both tires were smoking and i left 2 tire marks! i thought that without posi only one would spin? i'm hoping that someone who owned the car before switched 2 posi because when i ran the vin it said i should have 2.73 no posi. thanks guys

 

Its possible. If there is equal "lack of traction" to both wheels, then both can turn. Its common for it to happen on wet roads or in the grass or sand, but I suppose it could happen on pavement under the right conditions.

 

Mine used to with the open rear. When I would launch, I would turn a little to the left and/or run more pressure in the left rear tire.

 

Yep, it can defintely happen. My 85 was a bonafide one legger, but i left a few sets of dual marks. Only a few out of hundreds, but when the stars were aligned just right. Actually had gto do with traction lik the other guy said.

 

good ole peg leg

 

Yeah it's possible. If you not sure if someone swapped a posi in or not, just left the rear, put the car in nuetral and spin one of the tires. If the other tire spins the same way, you have a posi. If it spins the other direction, you have a one legger and were lucky to have both spin.

 

this would only happen if you had a locker,or a spool.


gary

 

if you think both tires can spin with equal amounts of (or lack of ) traction......

think about what happens when the car is jacked up....that is the most perfectly equal lack of traction possible....no turn the pinion (driveshaft).....what happens? both tires spin in opposite directions....because thats how an open diff works.

Thereby, if you are spinning a tire doing a burnout one wheel will sit still because the rest of the diff will rotate around that side gear.

if both tires spin? i dunno, unless its not an open diff it should be mechanically impossible. because any resistance or load placed on one wheel in relationship to the other wheel will cause the diff to rotate around the wheel that has more grip, and spin the one with less grip.

 

yes its pretty easy to spin 2 tires with 1 leggers ya just need equal loss of traction as pretty much everyone has pointed out
quote:
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Originally posted by CraZ-28
Yeah it's possible. If you not sure if someone swapped a posi in or not, just left the rear, put the car in nuetral and spin one of the tires. If the other tire spins the same way, you have a posi. If it spins the other direction, you have a one legger and were lucky to have both spin.
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this would only happen if you had a locker,or a spool.


gary
.... yeah locker, spool, or a properly functioning posi...

 

Nope, can't be done. Didn't you guys watch 'My cousin Vinnie'? That is the whole reason they got off.

Seriously though, I don't think it is possible to lay rubber with both if you have a single legger.

 

k thanks guys i will have to try that neutral thing.

 

pull the inspection plate and look!!!! and change the fluid while you are at it!

 

A normal posi that works will spin the other tire the same direction when you spin one.

Ben

 

i have seen none posi's lay some rubber on the street but then went right back to the one leg monster...

 

yes i agree,what i was trying to say is that this method isnt true for all types of posi's.I always thought that method to be true also.My dad worked in a junkyard for years,and he corrected me,as he always does.now he doesnt knw about late model cars,but when it comes to anything pre '80,hes a guru.

Gary

 

lockers and spools arnt types of posi's....as far as i know that method would work for all posi's, meaning gm limited slip rear ends

 

that had a part to do with it but it was because of an independant rear suspension mainly that their car did not have.that is the true reason why they got off.

 

"I don't think it is possible to lay rubber with both if you have a single legger"
Done this many times, and seen it done. An air bag in the right rear spring will also help. If you want to test a working posi without opening up the case, put the right rear in some water, and the left rear on dry clean pavement--see if they both spin.
If the traction on each tire is equal, the power will be divided equal. If traction is unequal, power will follow the path of least resistance. FYI, when you spin-up a one-wheeled-wonder, actual wheel speed is 2x the speedo reading.

 

you guys seem to have some problems understanding physics. once again, if traction is equal on both tires in a non-posi diff only one tire will spin still.

try it yourself....jack the car up and turn the pinion, either one wheel will turn or both will turn in opposite directions. even with a posi.....if you jack the car up and turn one wheel the other wheel will spin the opposite way. If you turn the PINION both wheels will sping....thats how posi works....it alows the wheels to turn independantly when there is a differntial in speed between the wheels.

 

I have to testify that i have seen the one leggers lay two stripes before can't explain why but I have seen it happen.

 

Another way to check it would be to jack up only one rear wheel. Leave the other one on the ground and leave the car in neutral. On an open diff. you will be able to turn the wheel that is off the ground, and the driveshaft will, in turn, (no pun intended) spin. If you have a posi you won't be able to rotate the wheel that's off the ground, even if you climb under the car and try to turn the driveshaft. With a posi, in any experice I've had (swapped a 3:23 posi into my 69 GTO in place of the original 2:56 open carrier) with a posi if both wheels are off the ground and you rotate one the other one WILL rotate in the SAME direction. There is a clutch mechanism in the carrier which locks the two axles together unless there is enough difference between traction to hold one tire and allow the other to spin. For the GTO the GM manual says that it would require applying 400 ft. lbs. of torque (I believe that's the number) to turn one wheel if the other was on the ground (like in the test I described above). In other words 400 ft. lbs. of torque to overcome the posi clutch. It is also very possible to leave "posi marks" from an open diff. I've done it several times in my TA with an open 3:73 rear end. Once was from a 20-30 mph rolling start in 3rd gear (with the new motor and tranny ). Sorry for rambling on so much, but I hope I've been able to explain some of this a little better, if I missed something or said something drastically wrong please correct me. But if traction is exactly equal for both tires on an open rear end they can and will often both spin.

-Paul

 

if you spin one wheel on a posi the pinion gear turns as well and the other will spin in the same direction unless there is something wrong with the posi.. your explination seems to make sense but if you turn the right pass side wheel the pinion gear will turn with it..

 

I'm confused a little on that one. Are you talking about with a posi? Because with a posi if both wheels are off the ground and you turn either one the pinion should turn as well as the other wheel turning in the same direction as the one you're turning. It shouldn't matter from pass. side to driver's side. Any time one of the wheels, or both of the wheels for that matter, turns the pinion will turn, because when one wheel/axle turns it turns the differential carrier, which turns the pinion, in a posi the wheels/axles are joined together by the clutch in the carrier, which will keep them both turning the same, unless a force is strong enough to make the clutch slip. I just don't quite understand why you talk about the pass. side wheel turning the pinion gear if the driver's side didn't? Maybe I just misunderstood?

-Paul

 

yeah i guess i did word that really bad.. i just read it and got confused myself.. lol reason i said pass side is becasue im not really sure if the pinion gear would turn if you turned the drivers side wheel on a open rear.. never tried it.. but i know it does turn the pinion if u turn the pass side on an open rear.. i am quite positive with a posi that if you have the wheels off the ground and turn one wheel it will turn the pinion and the other wheel will turn in the same direction regardless of which wheel you spin though... in your first post u said that they would spin in opposite directions.. now u just explained why they wouldnt turn in opposite directions.."Any time one of the wheels, or both of the wheels for that matter, turns the pinion will turn, because when one wheel/axle turns it turns the differential carrier, which turns the pinion, in a posi the wheels/axles are joined together by the clutch in the carrier, which will keep them both turning the same, unless a force is strong enough to make the clutch slip." in ur first post u said that turning a wheel off the ground wont work but turning the pinion will... but if you turn one wheel you turn the pinion so the other wheel will also turn the same way.. damn im startin to confuse myself here lol

 

I have a 2.73 open and I have spun both tires in some gravel does that count??

 

Sorry to confuse, I didn't mean to lol in my original post I said

In saying that I guess I worded it kind of confusing, but I meant that you won't be able to turn anything if it's a posi and one wheel is on the ground, unless you can apply enough force to make the posi clutch slip. Did that make more sense? lol But the main point is that a posi locks the wheels (axles actually) together by using a clutch in the carrier, whereas an open diff. doesn't have that clutching mechanism. However, if traction is equal both wheels can and will spin with an open diff. It's happend before and I've seen it happen, and I'm sure it'll happen again! There are even instances when I've heard people refer to a rear end as "posi-ing up" which is just to say that one wheel started to spin and then traction evened out and then both wheels started spinning and the car left "posi marks". Did that make a little more sense? Please stop me if I'm going way off track or getting really confusing lol

-Paul

 

oops i was mixin up with 383 said with what u said.. n got it all confused. lol

 

Haha, no worries 89, happens to the best of us

 

I have heard of open diffs getting so tosted that both tires will spin. And I have heard of posi's getting so tosted that only one wheel will spin. Of corse both instances are shortly before the rears frag.

 

it also depends greatly on the type of posi it is.

I have a locker in my car, and you absolutely can overcome the force to unlock it and turn the wheels in different directions or only turn one wheel. quite easily i might add.

the cone clutch posi in a 9-bolt works alot differently than a clutch type does as well.

its alot different mechanism however.

 

oh ya, and if it took 400ft/lbs of torque to cause the posi clutches to allow the slower wheel to let go, posi diffs would work like spools most of the time. It would take alot of cornering force to produce that kind of a difference

 

All I can tell ya about that is that it's what's written in the factory GM shop manual for the 1969 Pontiac GTO. I didn't make it up at all. And 400 ft lbs doesn't really seem to be all that much when you think about the forces going on with the car. What I'm confused about is if it's so easy to overcome the clutch or locker mechanism, why bother with it at all?? I always thought the point of a posi or locker was so that you would be putting power to the ground through both rear wheels? So if it's easy to break the posi or locker connection and only spin one wheel, why is it worth bothering with?

Don't mean to flame at all, just getting really confused...

-Paul

 

ah see, a locker is a horse of a different color, it isnt a posi, but is it a type of limited slip

 

because it doesnt do that when your going straight.....when the car is pointed straight the axles are locked together like a spool....there is no differential action whatsoever. However in the locker i have the more street friendly power trax......slight variations in wheel speed are enough to unlock the faster turning axle in cornering, making it function like a posi, but have the rock solid, impossible to wear function of a spool in a straight line.

there is a center piece with teeth on it, and 2 side pieces (1 on each axle) which replace the side gears.....the 2 side pieces mesh with the teeth on the center section creating one solid rotating mass. but when there is a differential in wheel speed, either side can unlock itself accordingly. (this is a gross over simplification, but you get the idea)

its absolutely impossible for both wheels to NOT spin when going straight......unless something is broken. and they are really hard to break, i snapped an axle off inside one and it was fine.

 

negative on that one good buddy....


an LSD (limited slip differential) is a designation of a posi differentials....and there are several different types.

a locker, however, is not one of them. A locker is basically a NO SLIP differential, as it does not allow any freewheeling in a straight line what so ever.

 

OK, well that's pretty much what I thought from the beginning, guess we all have to go around in circles before we figure this stuff out haha. It is still possible for a posi or even your PowerTrax street locker (which I am seriously considering purchasing, btw ) to spin only one tire off the line, if the conditions were right, just as it is possible for an open diff. to light up both tires on takeoff, if conditions are right. Anyway, sorry for going around and around about this so much, hope I didn't get too annoying lol

-Paul

 

Actually, a posi(limited slip) can only spin one weel, but this should only happen if it is worn out(clutches). A locker will always spin both in a straight line. I believe that if you are on the gas decent they tend to spin both even around corners which could take some getting used to also. Limited slip units are supposed to be slightly more street friendly but if you get something like the powertrax that 383 has it shouldnt be to bad on the street.

Also, are you sure it didnt say 40 ft lbs instead of 400 in that manual? I know that my information on the borg warner posi for thirdgens says that if it takes less that 35 ft lbs then the posi needs to be rebuilt or replaced so I would think that 40 sounds closer to what it should be.

Ben

 

the only conditions that would allow a locker to spin the tires launching in a straight line would be if it was broken.....

if the ratchets werent locked up when you pulled to the line (very possible) as soon as you hit the throttle and the wheels start to turn, it will immediatly lock both wheels together no matter what.

and as momar said, my locker isnt bad on the street but its not for the faint of hard....as under hard acceleration it will try to lock up both wheels even while cornering. this can be kind of scary to the novice. once you get used to it though its cool, and it scares the hell out of everyone else.

its really loud when it does that (makes loud snapping noise) and the rear of the car jerks slightly hehe.

 

383 backinblack then pleeaase explain to me why my non posi having v-6 fieros would light both tires at almost any given time what you have to contend with on most rear wheel drive cars that my fiero or anything with a tranverse mount engine doesn`t is that engine torque drive the left rear into the pavement and attempts to lift the right rear off the pavement and that is why an open diff will only spin one tire so yes with an equal lack of traction you can spin both tires on an open diff

 

Man, could you try to please use some punctuation? I am not trying to be rude, but it is kind of hard to tell where one sentence should end and another shoud start if it even is more than one sentence.

Anyway, I honestly dont know how they do the whole transverse thing, but I do think that some front wheel drive cars will spin both tires. As far as the fiero goes, I had one for a short period. It was a 84 w/ 2.8. That thing did some mean donuts. You would go into one and it would just swing you all around.

Ben

 

Ok guys, thanks I understand how it all works a lot better now....all this time I had some wrong ideas about the whole thing. I am pretty sure it says 400 ft. lbs. in that manual though, but I am going to be home for spring break in a month or so and I will check to be sure that I didn't read it wrong in one of my more crosseyed moments lol I know that I couldn't ever manage to break it loose by hand (trying to turn one wheel w/ the other one on the ground. But the physics of how the posi works (at least the way I understand them now) could be the reason for that. I'll check it though Thanks again guys!!

-Paul

 

Yes, I would be interested in knowing what that actually says. Also, just so you know I dont think I could turn one of my wheels with the other on the ground with my bw 9 bolt and it is the one that says that it should be at least 35 ft lbs. If I could it would take a lot.

Ben

 

I've actually laid quite a few dual tire marks with a known open differental. Takes some power to do it. The best I can offer for an explanation is that perhaps the interal friction under the high loads creates a posi effect. The clutches in a posi just help this along. I could see under stress that the spyder and side gears on simple washers could begin to grab. Whatever the explanation, I have seen it with my own eyes quite a few times.

On the subject of ft-lbs to turn over a posi, I believe the GM spec is 35 ft-lbs with one tire chocked. This is continuous rotation, not break away torque. So maybe the spec was 40ft-lbs and you are remembering an extra zero. If they try to account for the axle under a load the torque to slip the posi could be significantly higher. Remember the preload in the clutches just gets things started, its up to the force on the side gears to finish the job.