What's the difference between a "limited slip" and a "Posi"

[reamer]

I just had to take out the Bronco yesterday, Still have some snow/slush on the trails.

Currently it has 3:50 "open" diff's. When stepping on it in the snow, of course it what to pull to one side and then we fishtail, fun in itself but.....

Would installing a LS or Posi help "keep it straight" on acceleration in slippery conditions?

1. So what's the difference LS vs Posi?

2. Would I have to swap out both front and rear Diff's or just do the one in the rear?

Thanks

[Pete Whitstone]

#1 - "Posi" and limited slip are the same thing. Posi-traction is GM's brand name for it, and it kind of became universal, like "Coke" or "Kleenex".

#2 - You can run limited slip in back but not in front, no problem. That's how my truck is set up.

There are many forms of limited slip - clutch & cone, helical worm gear, torsen, detroit locker, and so on. I'm a fan of the helical worm gear or the torsens. Very tough, don't need periodic rebuilding like the clutch & cone style, and don't have the clunkiness of the detroit lockers.

There are also "part time" lockers that are activated by air or electrically, so you can turn them on and off at will.

[Gary Lewis]

#1 - "Posi" and limited slip are the same thing. Posi-traction is GM's brand name for it, and it kind of became universal, like "Coke" or "Kleenex".

#2 - You can run limited slip in back but not in front, no problem. That's how my truck is set up.

There are many forms of limited slip - clutch & cone, helical worm gear, torsen, detroit locker, and so on. I'm a fan of the helical worm gear or the torsens. Very tough, don't need periodic rebuilding like the clutch & cone style, and don't have the clunkiness of the detroit lockers.

There are also "part time" lockers that are activated by air or electrically, so you can turn them on and off at will.

Pete is right.

But a bit more explanation on the front. Ford had a limited-slip option for the front, but fortunately very few bought it. My understanding is that with it when you are under power in slippery conditions you go forward, regardless of how you turn the wheel. In fact, one said "You don't want to send your wife or daughter out in the snow with it." I've not tried it, although I do have an electric locker in front on Big Blue, so if I get out in the snow some day I will just to be able to say "Yep, they were right!"

I have a Detroit TruTrack in the rear of Big Blue and really like it. That's one of the helical-gear style units and I agree with Pete - nothing to rebuild or wear like the clutch packs in others.

However, I will say that it is always watching and will come "in" at the slightest provocation. One day when it had just rained and the oil in the pavement had come to the top it came in as I was turning a corner. That meant both rear tires turned, which caused the rear to step out a bit until I backed off the throttle. Not a big deal, but something to watch out for.

You could go with a selectable locker in the rear, but then you have to know when to engage it, and then both rear wheels turn at the same speed, making cornering more difficult. The TrueTrac takes care of that, automatically.

[85lebaront2]

Pete is right.

But a bit more explanation on the front. Ford had a limited-slip option for the front, but fortunately very few bought it. My understanding is that with it when you are under power in slippery conditions you go forward, regardless of how you turn the wheel. In fact, one said "You don't want to send your wife or daughter out in the snow with it." I've not tried it, although I do have an electric locker in front on Big Blue, so if I get out in the snow some day I will just to be able to say "Yep, they were right!"

I have a Detroit TruTrack in the rear of Big Blue and really like it. That's one of the helical-gear style units and I agree with Pete - nothing to rebuild or wear like the clutch packs in others.

However, I will say that it is always watching and will come "in" at the slightest provocation. One day when it had just rained and the oil in the pavement had come to the top it came in as I was turning a corner. That meant both rear tires turned, which caused the rear to step out a bit until I backed off the throttle. Not a big deal, but something to watch out for.

You could go with a selectable locker in the rear, but then you have to know when to engage it, and then both rear wheels turn at the same speed, making cornering more difficult. The TrueTrac takes care of that, automatically.

You should have driven my Shelby with the Detroit Locker, Shelby's choice for the cars so it could be used on the R models (SCCA and FIA rules regarding allowed changes). It drove the slowest turning wheel in a corner and the outside one unlocked and turned freely. When you straightened out and applied power, the car would shift sideways a bit, make a loud "bang" in the 9" center section. and then got straight.

When a friend and I ran the car in a series of high speed events, we learned that you needed to be sure the front of the car was pointed where you wanted to go, because particularly in 1st or 2nd, the car was going where the hood was pointed once the locker engaged. The fact that that little 289 engine could actually lift the front end enough to get the wheels off the ground in 1st was part of it.

As far as a very stout and extremely reliable unit, it was great, for someone not used to it, it usually scared the devil out of them, particularly if they were driving it.

[Rembrant]

"Posi" in another one of GM's Generic Trademark names, like "Stepside"...lol. Everybody uses the GM term Posi to describe a limited slip the same way everybody uses the word Stepside when talking about Ford's Flareside, or Dodge's Utililine, etc.

[reamer]

"Posi" in another one of GM's Generic Trademark names, like "Stepside"...lol. Everybody uses the GM term Posi to describe a limited slip the same way everybody uses the word Stepside when talking about Ford's Flareside, or Dodge's Utililine, etc.

Sounds like I should just stay with the open, and put the 1000 somewhere else...

I am running the original 302, never re-built and only 20k miles on it (have the documentation on it) And also running good-ole points in the dizzy..

What do ya think of the Edelbrock (I think) true fuel injection system that comes with a new intake and 8 actual injectors?

[Pete Whitstone]

What do ya think of the Edelbrock (I think) true fuel injection system that comes with a new intake and 8 actual injectors?

I'll let you know in a few months, I'm putting a Pro Flow 4 on my 351w. There are tales of unreliability or just plain doesn't work out of the box around around these units. But then I think the same could be said of a lot of aftermarket FI units. We shall see.

[mat in tn]

Sounds like I should just stay with the open, and put the 1000 somewhere else...

I am running the original 302, never re-built and only 20k miles on it (have the documentation on it) And also running good-ole points in the dizzy..

What do ya think of the Edelbrock (I think) true fuel injection system that comes with a new intake and 8 actual injectors?

well first of all let's see what axle you have as the costs and options may vary. sometimes going with a good used unit is a reasonable option.

but how they help is a big variable also. in snow they can help a lot up to the traction breaking point then when they spin, they spin together. same in mud. on dry or pavement, they can work differently. it all depends on traction of the surface. nothing is perfect. I am using the ford traction loc in my build today. the weak point is that they are clutch design, and they can wear out.

in a pinch, you could just apply a "little" parking brake, and that shared resistance will make the open behave like a traction loc. but don't run it that way as there is no heat removing lubrication at the drums as they are brakes after all.

there are three basic design theories on locking the rear wheels together

power goes to least resistance being traction lock or posi traction.

power goes to most resistance being auburn gear cone style.

locker where the stress has to override the face gear plates which are held engaged by heavy springs which reset repeatedly and reengage.

[FuzzFace2]

well first of all let's see what axle you have as the costs and options may vary. sometimes going with a good used unit is a reasonable option.

but how they help is a big variable also. in snow they can help a lot up to the traction breaking point then when they spin, they spin together. same in mud. on dry or pavement, they can work differently. it all depends on traction of the surface. nothing is perfect. I am using the ford traction loc in my build today. the weak point is that they are clutch design, and they can wear out.

in a pinch, you could just apply a "little" parking brake, and that shared resistance will make the open behave like a traction loc. but don't run it that way as there is no heat removing lubrication at the drums as they are brakes after all.

there are three basic design theories on locking the rear wheels together

power goes to least resistance being traction lock or posi traction.

power goes to most resistance being auburn gear cone style.

locker where the stress has to override the face gear plates which are held engaged by heavy springs which reset repeatedly and reengage.

Anything that has "Locker" in it's name is going to "lock" the 2 wheels together under power. When no power they will unlock and the wheels can now turn at different rates.

I have a Detroit locker in the drag car so cant say how it is on the street but if the street car need a carrier it will go in.

I also have a lunch box locker in my 75 factory v8 Gremlin. It replaces the spider gears and lock the axles together under power. As pointed out if wet out it could be a hand full at 92" wheel base if you were not ready for it to come around. I only had to move the car once with snow down, it did not go anywhere even with 2 rear tires turning.

I have had 2 4x4's (86 K5 Blazer & 02 Durango) with factory LS or posi in the rear axle, dont know if they offered it in front? and loved them.

I would lock the front hubs (K5) at first snow and drive as far as I felt safe in 4x2 mode then just move the lever to 4x4 and keep going. The Durango you just turn the knob on the dash.

Neither truck was ever taken off road so cant say how they would do on a trail.

Only thing I can see with a LS / Posi in the short wheel base Bronco is the SWB and it wanting to come around faster like my 92" WB Gremlin other wise I dont see any issues with it.

Dave ----

[mat in tn]

Anything that has "Locker" in it's name is going to "lock" the 2 wheels together under power. When no power they will unlock and the wheels can now turn at different rates.

I have a Detroit locker in the drag car so cant say how it is on the street but if the street car need a carrier it will go in.

I also have a lunch box locker in my 75 factory v8 Gremlin. It replaces the spider gears and lock the axles together under power. As pointed out if wet out it could be a hand full at 92" wheel base if you were not ready for it to come around. I only had to move the car once with snow down, it did not go anywhere even with 2 rear tires turning.

I have had 2 4x4's (86 K5 Blazer & 02 Durango) with factory LS or posi in the rear axle, dont know if they offered it in front? and loved them.

I would lock the front hubs (K5) at first snow and drive as far as I felt safe in 4x2 mode then just move the lever to 4x4 and keep going. The Durango you just turn the knob on the dash.

Neither truck was ever taken off road so cant say how they would do on a trail.

Only thing I can see with a LS / Posi in the short wheel base Bronco is the SWB and it wanting to come around faster like my 92" WB Gremlin other wise I dont see any issues with it.

Dave ----

I found a " mini spool" and just had to try it. it goes in the carrier replacing the spider gears and now the two wheels are bolted together. no give! I kept it in about two weeks. for a flare side wheelbase, it chattered the tires a lot. it was cool for a minute and the kid in me played with it a bit. but when I turned into my subdivision one day and it did a 180 without me trying much, I said that's enough. miss Ann would have freaked out if she were driving. so, dolly is open now.