Posi question...

[gpadilla1071]

OK I've been searching around how posi traction works but I'm a little confused... Some of the threads here said that to lift your car and if the wheel moves the opposite from the other in not posi trac... my car does that, but when I do a burn out, how come both tires leave a nice mark on the pavement? What gives? Thanks.

German

 

[Steve V]

That's the corerect test and I can't give an explanation why you get two rubber marks. Somebody will straight us out!:tongue:

 

[gpadilla1071]

I kept researching and some of the guys say that I need to put the car in neutral and move the wheels. Although I haven't done that, I think that's the reason why the wheels were moving in opposite directions. I've been doing with the car in the park position... I'll try this weekend with the car in neutral... we'll see how it goes. Thanks.

Steve, what are you up this weekend? Still working on the motor?...

 

[Steve V]

See Virginia Area

 

[Hyboost]

OK I've been searching around how posi traction works but I'm a little confused... Some of the threads here said that to lift your car and if the wheel moves the opposite from the other in not posi trac... my car does that, but when I do a burn out, how come both tires leave a nice mark on the pavement? What gives? Thanks.

German

No, put it in park, & have both rear wheels off the ground, they shouldnt turn at all, if you put a TON of force, you might get it to turn a little bit if its a posi. If its an open type, with both rear tires in the air & the car in park. Turn either wheel forward and the other will spin backwards. As for why you leave 2 marks, either it
it is a posi or you were on a very level road, both rear tires in the same shape with the same amount of air pressure in them & getting the same amount of traction with them. If you tried spinning the tires around a right turn and only the right tire spins, it is a open type. You could try this making a left turn but sometimes both will spin because or the direction of the driveshaft. The torque is always biased to the left, putting more weight on the left tire during accell, which is why the right rear tire will usualy will spin with a "open" or non posi unit .

 

[gpadilla1071]

No, put it in park, & have both rear wheels off the ground, they shouldnt turn at all, if you put a TON of force, you might get it to turn a little bit if its a posi. If its an open type, with both rear tires in the air & the car in park. Turn either wheel forward and the other will spin backwards. As for why you leave 2 marks, either it
it is a posi or you were on a very level road, both rear tires in the same shape with the same amount of air pressure in them & getting the same amount of traction with them. If you tried spinning the tires around a right turn and only the right tire spins, it is a open type. You could try this making a left turn but sometimes both will spin because or the direction of the driveshaft. The torque is always biased to the left, putting more weight on the left tire during accell, which is why the right rear tire will usualy will spin with a "open" or non posi unit .

Icepicker,

I found a thread in which it saids to put the car in neutral, once I did that the tires moved in the same direction... I also, did it the way you suggest, which is in the park position, both tires moved in oppsite directions... So, my question is, is it Posi or open?

Thanks,

German

 

[bnewsom]

That should mean it is a posi. But how much effort is it taking to turn the tire when it is in park. If it takes little effort, your clutches are worn out.
Bob

 

[gpadilla1071]

That should mean it is a posi. But how much effort is it taking to turn the tire when it is in park. If it takes little effort, your clutches are worn out.
Bob

It takes some effort, you really have to use some muscle, but good point... maybe I should be looking into buying one the future... Thanks.

German

 

[waddell87]

If you can turn your wheels in park, what the heck is holding you parked on a steep hill? If your e brake isn't on and your tires not turned. I know that you can bust your kingpin by doing that but, noway can I turn my wheels in park if its off the ground.. I do have posi but have had non posi units too

I would think to test in nuetral would make more sense, seeing the tranny has nothing to do with the posi unit or clutch packs.
just my o2. thks

 

[bnewsom]

We are talking with rear wheels off the ground with the trans in park to keep the pinion from turning. In a car without a posi, you can easily turn one wheel and the other will turn the opposite direction. If the car has a clutch type positive traction in good condition, you will have great difficulty turning a wheel by hand if you can turn it at all. The easier it is to turn, the weaker the clutch and/or spring is. Still the best way to tell is remove the cover. I bought a "posi" rear without pulling the cover. It was good and tight - could not break it loose. Got it home, pulled the cover and found welded sun gears. Glad I checked it out before it was put in. I had a Vega back in the day with a healthy 283/4 speed and an open rear end. On a hard launch it would leave 2 black marks about 10 feet and it was gone. I guess it just transfered the weight to where it was needed. So pull the cover so you'll know.
Bob

 

[bison]

Even in an open differential one tire has to slip before it will burn. If they both have equal traction it will still spin both at the same time. Do you think the posi unit in a rear is going to compensate for the tremendous torque load in a heavily modified car? The posi is primarily for the burnout. After that the goal is to plant both tires hard. The equal traction is what keeps the wheels from spinning not the posi. The torque available at the axle is enough at WOT to overcome any posi unit.

 

[bnewsom]

Do you think the posi unit in a rear is going to compensate for the tremendous torque load in a heavily modified car?

Of course not, but then why bother with a spool if you can always plant them evenly. I've seen many a "peg leg" leave a single black mark a mile long and take forever doing it. A posi is a good compromise between an open rear and a spool for a street driven car. But who said a posi would compensate for tremendous torque of a heavily modified car anyway? I was just trying to help the guy to find out if he had a posi or not. Gosh....
Bob

 

[gpadilla1071]

Of course not, but then why bother with a spool if you can always plant them evenly. I've seen many a "peg leg" leave a single black mark a mile long and take forever doing it. A posi is a good compromise between an open rear and a spool for a street driven car. But who said a posi would compensate for tremendous torque of a heavily modified car anyway? I was just trying to help the guy to find out if he had a posi or not. Gosh....
Bob

LOL. Thanks Bnewsom. I must say this forum is awesome!!:biggrin:

 

[bison]

Of course not, but then why bother with a spool if you can always plant them evenly. I've seen many a "peg leg" leave a single black mark a mile long and take forever doing it. A posi is a good compromise between an open rear and a spool for a street driven car. But who said a posi would compensate for tremendous torque of a heavily modified car anyway? I was just trying to help the guy to find out if he had a posi or not. Gosh....
Bob

I wasnt flaming anyone. Just stating the function. Drag racers run spools because they are the strongest option for a center section and they keep the axle speed the same on both axles at all times.

 

[Hyboost]

Icepicker,

I found a thread in which it saids to put the car in neutral, once I did that the tires moved in the same direction... I also, did it the way you suggest, which is in the park position, both tires moved in oppsite directions... So, my question is, is it Posi or open?

Thanks,

German

From what you stated above, you have a open type diff.

Again, all procedures are with the car in PARK

1) Jack up so both rear wheels are off the ground.

2) Shift the car into PARK. Make sure parking brake is OFF!

3)Turn the driver side wheel forward at least 1 full rev while watching what the passenger side tire is does.

4) If the passenger side starts spinning backwards, you have a open diff OR a completely shot posi unit.

5) If you can't turn the driver side tire forward 1 complete rev fairly easily, it is most likely a posi unit

6) The reason both tires spun forward when in neutral is that the driveshaft started spinning when you rotated the wheel.

7) The only other option is that someone might have installed an aftermarket "locker" style carrier & not a posi. They both do basicly the same thing but a posi uses a clutch pack to lock the wheels while a locker unit has cones or gears to lock the wheels. A posi has a smoother engagement where the locker unit, although very heavy duty, most are noisy and rough when they engage. Pull the diff cover to know for sure. Also a good idea to do this as general maintaince so you can inspect ring & pinion and fluid condition. Make sure theres no metal in gear oil which could mean worn bearings and or ring & pinion.

 

[Hyboost]

If you can turn your wheels in park, what the heck is holding you parked on a steep hill? If your e brake isn't on and your tires not turned. I know that you can bust your kingpin by doing that but, noway can I turn my wheels in park if its off the ground.. I do have posi but have had non posi units too

I would think to test in nuetral would make more sense, seeing the tranny has nothing to do with the posi unit or clutch packs.
just my o2. thks

Bust a kingpin? A kingpin has nothing to do with a diff in any way. Kingpins take the place of ball joints. Do you mean the parking pawl that is located inside the transmission that helps prevent a car with an automatic transmission from rolling??
Anyhoot,
Think about it. If you have vehicle with a non posi unit in park, now the driveshaft is locked, the diff pinion flange is not turning, with both wheels off the ground, one is going to spin forward while the other spins backwards. Now let the car down, how is the car going to roll? Remember one tire forward & the other backward??? Now, If the car is in Neutral, both wheels will spin freely because now you have the driveshaft spinning, allowing the pinion flange to turn freely.

 

[t-topflyer]

YouTube - 20% grade G80

YouTube - How a Eaton G80 locker works

 

[waddell87]

Bust a kingpin? A kingpin has nothing to do with a diff in any way. Kingpins take the place of ball joints. Do you mean the parking pawl that is located inside the transmission that helps prevent a car with an automatic transmission from rolling??
Anyhoot,
Think about it. If you have vehicle with a non posi unit in park, now the driveshaft is locked, the diff pinion flange is not turning, with both wheels off the ground, one is going to spin forward while the other spins backwards. Now let the car down, how is the car going to roll? Remember one tire forward & the other backward??? Now, If the car is in Neutral, both wheels will spin freely because now you have the driveshaft spinning, allowing the pinion flange to turn freely.

I see.. said the Blind man..Yes I was talking the parking pawl and I wasnt referring to it to the dif but with regards to movement of everything while in park..thanks for clarifying, tips

 

[GDNF2ET]

Just look at the trunk sticker and see if there is a G80 listed..If there is , its a posi..