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View Full Version : I Need POSI.....



tbirdsc357
09-16-2004, 10:54 AM
I have that stupid one wheel spinning crap and I need to get both wheels getting power. What's the best/cheepest way of doing this?

Ford? Auburn? 28 teeth? 31 teeth? Is limited slip the same as POSI trac?

BlueThunder90
09-16-2004, 10:56 AM
Steve, looks like I'll be switching my rear end diff and axles but not till the winter....if that's something you'd be interested in. :)

Peterdroy66
09-16-2004, 10:59 AM
Steve, looks like I'll be switching my rear end diff and axles but not till the winter....if that's something you'd be interested in. :)
Steve
The cost adds up when you're not lookin...
Used Posi pumpkin $100
Used Aluminum Case $100 us + ship (optional)
Used gears $100 us
Setup the gears $250
Pumpkin swap $250
I don't want to add it up
PR

SkunkWorks
09-16-2004, 11:25 AM
Just get a rebuild clutch pack kit for the rear and have someone rebuild it for ya.

lazybird4pt6
09-16-2004, 07:27 PM
Grab a coffee, this won't be short.

What you have in your car comes in:
'94-95 SC's with Traction Assist
ALL '94-97 LX's

It's Ford's ever-useless "open" differential. For any performance applications it's pretty much useless. The only way you can get both wheels to spin is when you feed it a ton of power, and even then it's only partially doing a decent job getting it to both wheels. YOU, along with many others, already know this.

The other differential Ford placed in the MN-12's is the Trac-Loc equipped unit. It's their proprietary version of "Posi-traction", or limited slip. Far superior to transferring power to both rear wheels when compared to the "open" differential. However, it still lacks giving you "absolute" transfer to both wheels - this is due to the somewhat "soft" spring used to expand against both halves of the clutch packs.

Now let's talk aftermarket. Auburn will easily be the first name that comes to mind to many. Again, it's very similar in design to the Trac-Loc unit in terms of it's workings, but it offers several MAJOR advantages. Ford uses a "plate style" clutch. Imagine a flat disc with friction material on both sides - hey, just like a clutch! What Auburn does is they take this flat disc and make it a cone shape. This conical friction now also has a larger surface area (VERY important when more power transfer is desired!). Add to this a "stiffer" SET of springs (Auburn uses 4 smaller springs to increase pressure and do so more evenly) and - voila! For all intents and purposes it's nearly impossible to build a Ford Trac-Loc differential to possess the same amount power transfer to both wheels when compared against an Auburn, or most other differentials.

There may, or may not be, other options (Detroit style locker, Eaton, Powertrax) but there is one extremely (!!!!!) important thing to realize with our cars - they're NOT a Mustang (or any other Ford solid-rear-axle car). You MUST use a differential that has a groove in the spider gears inside the differential to accept the c-clip on the end of our half-shaft! Failure to do so will eventually result in a car the winds up in a gaurdrail.

History class is over. ;)

Options? Several.

1) swap with a Trac-Loc - sure. You could upgrade your stock unit to a Trac-Loc equipped one by simply replacing the open with the Trac-Loc. Simple, somewhat effective, relatively inexpensive and it'll "do the job". ONLY the differential, as opposed to the entire carrier, needs to be swapped!

2) swap with an Auburn - do I REALLY need to sell you on this? I haven't already? Okay - look at your last runs...... now think longevity. My Capri has run the same Auburn for 7 years (okay, it's really only like four) and has had TONS of abusive driving put through it (drag racing, drag racing and drag racing, a bunch of donuts - which are REALLY bad for diffs - and more drag racing) and it still "holds" very well.

3) spool - track-only cars need apply.

Hope that helps.

Jason Wild
09-16-2004, 10:09 PM
Steve you might want to give Bill A call he might be wating to part with his auburn. I'm not to sure I'm in the same boat my diff is on it's way out.

SkunkWorks
09-16-2004, 11:08 PM
Did his car not come Stock with Track Lock??

fast Ed
09-16-2004, 11:14 PM
Nope, 94 - 95 auto. trans SC cars were equipped with the electronic traction control tied into the ABS. No traction-lock on those cars.

cheers,
Ed N.

SkunkWorks
09-16-2004, 11:39 PM
oh, ****, thats very very gay...

lazybird4pt6
09-16-2004, 11:47 PM
Yeah, even the LX crowd isn't subject to that kind of torment.

Sorry, Steve. But, hey, your car is faster than mine :D

for now.

So, how many bottles have you gone through, hmmmmm?

tbirdsc357
10-18-2004, 10:30 AM
Options? Several.

2) swap with an Auburn - do I REALLY need to sell you on this? I haven't already? Okay - look at your last runs...... now think longevity. My Capri has run the same Auburn for 7 years (okay, it's really only like four) and has had TONS of abusive driving put through it (drag racing, drag racing and drag racing, a bunch of donuts - which are REALLY bad for diffs - and more drag racing) and it still "holds" very well.

Hope that helps.

Okay.....now the Auburn Pro is supposedly better than the Auburn HP, is it worth the extra $100US. I trying to keep the costs down. However, if it's way better than the regular diff, I don't mind paying the extra.

Also, the Auburn will fit into my current pumpkin that's on the car correct??

Thoughts?

tbirdsc357
10-18-2004, 10:35 AM
Auburn Pro - $585 CAD Shipped + Duty :rolleyes:
Auburn HP - $495 CAD Shipped + Duty :rolleyes:

Add $250 for Installation

Pro - $835.00 CAD
HP - $745.00 CAD

Superbird281
10-18-2004, 12:11 PM
There's only one way to go...
1. Get an Auburn Pro
2. Have John Goodman in Newmarket install it

Cheap? No, but how much do you value your life and you car's reliability? I had my Grand Marquis' differential grenade on me while drivng and it ain't fun to have your rear end lock up and skid to a halt in the middle of traffic. $900 rebuild and it still makes noise. FORD LSDs SUCK.

tbirdsc357
10-18-2004, 12:14 PM
I'm leaning towards the Pro more and more........John did my gears a few years back, so I would go back to him for this job.

HoseHead
10-18-2004, 12:24 PM
a Trac-Loc unit from a parted 89-93 auto SC or any 5Spd SC? Swap is cheap and easy. Unless you're racing, the factory Trac-Loc should be more than adequate.

I have a '93 5Spd and the previous owner swapped in a 3.27 set from the factory 2.73. Trac-Loc units of course. I use the car daily and find 3.27 really steep and rarely use 1st gear. I am considering swapping back to 2.73. It's a more docile ratio for my particular application. It would also help save re-surfacing intersections with my P-zeros.............

Saw two T-Birds for sale this weekend. I will take some digiphotos and post. One is a 94-95 LX, looks clean from afar and the other is a '91 SC Auto in behind a rice rocket modification shop. It's punched and looks like the engine is gone, but other pieces may be valuable. More to follow...Cheers.

SeanMatteson
10-18-2004, 01:20 PM
Steve,

You might want to contact Bill McNeil in regards to his Auburn Pro diff. Now that he's scaled the car back to near stock, he might not be needing it anymore. Perhaps he'd be willing to part with it. I think it currently has 2.73's installed, so those would need to be swapped out, but you may get some savings over buying brand new. They haven't even been in his car a year, and I don't think he made it to the track more than twice with it installed.

...Just a thought.

Cheers,

Sean

tbirdsc357
10-18-2004, 01:28 PM
a Trac-Loc unit from a parted 89-93 auto SC or any 5Spd SC? Swap is cheap and easy. Unless you're racing, the factory Trac-Loc should be more than adequate.

Cheers.

I am planning to use this car more at the track so a stock trac loc unit might not be the way to go. If i'm going to do it, I might as well do it properly. Besides, the stock swap are not as cheep to do either. I would want to have the trac loc rebuilt and have new braeings and seals installed......thay way I don't have to go back in there after 6 months. Sooooo, based on that:

pumpkin - 100
rebuild trac loc kit- 90
Seals/Bearings kit - 150
rebuild Labour - 100
Install (swap pumpkin) + swap my 3:55 gears - 200

Total = $640.00

I can get an Auburn HP installed for $764.00. For $124 I am getting a much better unit.


If there are any flaws in my analysis please point them out. :)

tbirdsc357
10-18-2004, 01:29 PM
Steve,

You might want to contact Bill McNeil in regards to his Auburn Pro diff. Now that he's scaled the car back to near stock, he might not be needing it anymore. Perhaps he'd be willing to part with it. I think it currently has 2.73's installed, so those would need to be swapped out, but you may get some savings over buying brand new. They haven't even been in his car a year, and I don't think he made it to the track more than twice with it installed.

...Just a thought.

Cheers,

Sean

I'll email him. Thanks.

Blown_347_SC
10-18-2004, 01:31 PM
Something to keep in mind is that Eaton diff's are rebuildable....

kiwikiwikiwi
10-18-2004, 02:48 PM
I have a powertrax locker with street or strip springs :)

tbirdsc357
10-18-2004, 03:38 PM
I have a powertrax locker with street or strip springs :)

Scott,

never heard of them......price? Did it fit without any problems? How do you like it?

MercsSC
10-18-2004, 07:34 PM
The buck is worth near 80 cents http://www.sccoa.com/forums/images/smilies/tongue.gif .....US...... But halloween coming and I have a pumpkin with 3:27 if needed ...dave

coolhand
10-18-2004, 10:07 PM
For those of us not blessed with an abundance of smarts about gears, this months mustangandfords has an article that even I can understand. Its not on the website yet, but here is a link to the site anyway.
http://mustangandfords.com/

Bill McNeil
10-19-2004, 12:38 AM
Steve,

I'm interested in selling my Auburn unit.

It has about 5,000km on it, with a fresh complete rebuild.

I paid $550 for the unit, $200 for rebuild parts, and $200 for the actual rebuild process from the guy that Wayne always recommends in Newmarket.

Someone should be able to help you install it. It isn't that bad. (Andrew) :p

Let me know if you are interested. Won't be until spring though.

tbirdsc357
10-19-2004, 12:36 PM
Steve,

I'm interested in selling my Auburn unit.

It has about 5,000km on it, with a fresh complete rebuild.

I paid $550 for the unit, $200 for rebuild parts, and $200 for the actual rebuild process from the guy that Wayne always recommends in Newmarket.

Someone should be able to help you install it. It isn't that bad. (Andrew) :p

Let me know if you are interested. Won't be until spring though.

Bill, I sent you a PM.....all I would need is the Auburn unit itself, my car had the new bearings, seals and 3:55 gears installed maybe 4000kms ago.

Paul93SC
10-19-2004, 03:53 PM
While I agree the Auburn PRO is the best as far as strength, you might not like the increased gear whine some folks complain about. The standard Auburn is good enough for any SC around here.

As much as people like to say the OEM limited-slip is junk, that too is an exaggeration. It does well enough on it's own for our power levels.


The other differential Ford placed in the MN-12's is the Trac-Loc equipped unit. It's their proprietary version of "Posi-traction", or limited slip. Far superior to transferring power to both rear wheels when compared to the "open" differential. However, it still lacks giving you "absolute" transfer to both wheels - this is due to the somewhat "soft" spring used to expand against both halves of the clutch packs.

Well, not even the Auburn PRO gives "absolute" power transfer... only a locker will do that. Mine was (well, still is) decent with regard to equal power transfer to the wheels under WOT (as evidenced by the black marks left on the ground :) ), and it's got 260,000 kms on it!

The pre-load spring is an often-misunderstood part. It is there to provide some torque to both wheels under very light loads. The stronger this spring, the quicker your clutch plates will wear out over time.

Consider how the differential operates. When you turn a corner, you cause the clutch plates to slip against each other. Most times in this scenario you aren't applying much power and don't need the 'limited slip' benefit. This 'slippage' is just wearing the clutches out when not needed.

The pre-load spring does not play a role under heavy loads. When significant power is applied to the pinion gears, they force the side gears outward (lateral thrust). The side gears are stacked on the clutch plates and this is the primary force that engages the clutches. Just wanted to clear that up.

Andrew, I have something for you... call me.

SeanMatteson
10-19-2004, 06:48 PM
...Interesting, Paul.

I wonder why Kurt K. decided to run the heavier spring from the F150's?! Maybe he's confused?

Cheers,

Sean

Greg Coleman
10-20-2004, 07:32 AM
Steve I believe your car is an auto right? Nickey's 94 is and Paddy put some sort of a possi in the rear with 373's and I find it to much on the highway but perfect around town so my question to you is how do you find the 355's as I think that is what Nickey's car needs.I know one thing when it was running if you stood on her both wheels spun.

Peterdroy66
10-20-2004, 09:05 AM
Steve I believe your car is an auto right? Nickey's 94 is and Paddy put some sort of a possi in the rear with 373's and I find it to much on the highway but perfect around town so my question to you is how do you find the 355's as I think that is what Nickey's car needs.I know one thing when it was running if you stood on her both wheels spun.

Greg
I have put the 3:55's in my 95 with OEM posi in the aluminum Mk diff case.
My main goal was to get posi into the 95, the 3:55's and aluminum case were a matter of "while you're at it"...
Obviously having posi back is just SOOOOO much better!!!!
However switching to 3:55s I am not as overjoyed with. Yes its quicker, but not a whole lot to notice, combined with a less "relaxed" low RPM cruising feeling on the highway. Also it appears that I have dropped highway MPG by about 2-3 MPG. It might be better for economy in the city, but very hard to tell just too many variables, the loose nut behind the steering wheel kind of influences this...
PR

tbirdsc357
10-20-2004, 09:33 AM
Steve I believe your car is an auto right? Nickey's 94 is and Paddy put some sort of a possi in the rear with 373's and I find it to much on the highway but perfect around town so my question to you is how do you find the 355's as I think that is what Nickey's car needs.I know one thing when it was running if you stood on her both wheels spun.

Greg, I really like the 3:55's in my car. I think the 3:73 gears that you have in there right now is a bit too much. Don't know if you are planning on taking that 95 to the track but with 3:73's you are going to have major wheel spin.

The gears that I have right are a perfect balance.....IMO.

Paul93SC
10-20-2004, 02:59 PM
I wonder why Kurt K. decided to run the heavier spring from the F150's?

I have no idea Sean... that makes no sense to me unless his car is mostly a "track use only" type, or he's not concerned with slightly accelerated wear over time (emphasis on "slight: it's not going to wear significantly faster than the OEM version).

Our OEM limited slip differentials don't work too well unless the pinion gears are getting some resistance from both axles. When both side gears resist being turned, the pinion gears try and "slip between" the side gears (for lack of a better term) and they end up trying to force the side gears apart in order to do that (due to the angle of the teeth on the gears themselves; this is what actually creates this side-thrust force).

The side gears slide on the axle shaft splines, and since they are stacked on top of the clutch plates, this side-thrust forces them to compress the clutch plates. Both clutches are part of the carrier which drives the pinion gears, so if both side gears are locked to the carrier, you have effectively locked both axles together.

The amount of lock-up is directly proportional to the thrust being applied to the clutch plates... in other words the harder you accelerate, the more thrust you apply to the differential clutches.

Now if one tire were, say, on a slick sheet of ice, there may not be enough resistance to create any amount of side-thrust, and it would perform no better than an open differential. In order to provide some power to both wheels under these conditions, a certain amount of clutch plate pre-load force is needed and this is provided by that spring.

(*Note: some people refer to pinion gears as spider gears)