Godti

My buddy drive a mustang with a posi rear end. I want to replace my gears, and I was wondering what was better?? Posi or Limited slip?? And what are the main differences?? Advantages, and Disadvantages??

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Godti
'89 Trans Am (Red)
305 TBI 5spd

merf23

they are the same thing. They provide POSItive traction to both wheels or LIMIT SLIP between both wheels. There are several different designs which all have advantages and disadvantages. The OEM LSDs are very good for all around driving. If you are dragracing or autocrossing the powertrax has some advantages. Any type is an improvement over an open diff IMHO

freeze92

The difference between a "posi" and a "limited slip" are:
"Posi": usually a spool, both rear axles are locked together. When one turns, so does the other one. Usually makes parking difficult, and wears tires rapidly if driven daily. Cheaper than a limited.

"Limited slip": Rear axles locked together with a series of clutches that allow slippage on turns. Makes parking easier than a posi, not as hard on the tires. More expensive.

Most cars are limited slips. People often refer to a limited as a "posi". Spools are used for inline racing (drags). Hope this helps.

MRZ28HO

Wrong freeze92, Posi (as in POSItive TRACTION = Posi-traction = Posi) is GM's trade name for Limited Slip. What you are talking about is a spool. We seriously need an FAQ on this.

freeze92

Oops! I forgot about that. Any way, limited slips are what you want for street use, spools for drags.

scoob8000

they are the same thing.. posi is just gm's trademark for it.. ill second that idea for a faq.. its way too common that people think they are different things, when they are really the same but with a different name

ede

man this comes up a lot. the only differant is the way they're spelled. same thing.

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-=ICON MOTORSPORTS=-

Grim Reaper

I too will third the idea about a faq. I don't know HOW MANY TIMES I have had this very same discussion with my "know-it-all/knows nothing" brother-in-law. Posi (or Posi-traction) IS just GM's trade name for their limited slip. Of course, GM had different TYPES of limited slips.. but they were all called Posi-traction.

Also, Mopar calls (or use to call) their limited slip "Sure Grip". I am not sure what Ford calls theirs.

Vader

Glenn,

I believe they are called "Spin-Resistant", or as the more technically-correct term goes, "The waste-of-iron axle on the waste-of-iron vehicle".

But I hate to get technical all the time.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

zippy

no ford product including mustang has or will ever come with a "posi". posi as mentioned is chevy's name for limiited slip. not for all gm models. safe t track, no slip, etc. all were other names gm used across the board. ford's name for the limited slip used in mustangs is traction lock. and everyone should thank freeze92 for his useless and wrong information. just so helpfull.

Godti

You guys have set me straight on the differences between the two. I was just wondering if anyone recommends a certain rear-end to put into my 89 TA?? Are certain ones stronger than others. Or do I just have to replace the gears?? (I would like to put 3.23 or 3.55 in). How long does it take to do a gear swap??

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Godti
'89 Trans Am (Red)
305 TBI 5spd

Cntrvrsy

Is that really true about POSI being GMs trade name 4 limited slip? If so, does that mean that any rear where both wheels spin in opposite directions when off the ground r OPEN rears?

MRZ28HO

Cntrvrsy, yes, if the tires spin in opposite directions it is an open diff.

Godti, the prefered rear end is a 28 spline. These were found on newer 3rd gens ('88?-present). Also the 9-bolt is stronger than the 10-bolt, although more expensive for rebuilding/parts.

Godti

How would I tell what type of rear end I have?? Would I notice a difference, if I replace the gears and kept my stock engine? Or should I upgrade the engine first?? I have also heard a lot about 3rd gen rear disc brakes suck, is this true?? Or should I look for a rear end with disc brakes?? Or maybe a aftermarket kit??

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Godti
'89 Trans Am (Red)
305 TBI 5spd