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Old 02/05/2009, 11:25 AM   #1
gazrox
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Posi-Trac or Locker?

I need to replace my 2.79 open diff as the innards (ring and pinion, differential, bearings) are completely and utterly destroyed.

So, I'm considering to upgrade to a 3.55 ratio but cannot decide on posi-trac or locker. I am getting different opinions from friends etc. What is the experience from my CS friends?

I'm not a weekend drag racer but want something that is reliable if I get on it now and then. The car has a 302 that has been warmed up a little with a cam, 351 heads, etc and a 3 speed auto C4 with a shift kit. I'm sticking with the 8" rear end.

Gary

Seafoam Green '68 GT/CS
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Old 02/05/2009, 12:39 PM   #2
J_Speegle
 

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Easy - posi
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Old 02/05/2009, 02:44 PM   #3
robert campbell
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Gary,
From a reliability standpoint, a non-posi 8 inch with 3.55 gears will work just great. But from a traction standpoint you will be lacking. A posi will add starting line traction. Even works better in the snow or when you are out “stump jumping”. Just kidding…

Depending on the diameter of your tires, the 3.55 ration will make your engine a lot “busier” at freeway speeds. You may or may not like that if you take long cruises on the freeway. A 3.25 might be better for that. I myself like as low a gear as I can stand and would not hesitate to use a 3.55 ratio. Even without an overdrive. My 67 Fastback has 4.11 gears and I drive down the freeway at 60 no problem. Is it busy?? Yup! Does it hurt it? No.

Let’s talk axles. The weakest part of your 8 inch rear is the stock 28 spline axles. Currie Enterprises offers high strength 28 spline axles that will mate to an 8 inch posi rear end. You may want to consider a better axle if you are like me and like to “hammer” on your car. I don’t beat my cars, but the axles in my cars know what a 5,000 RPM launch feels like. I drive them hard. I have 9 inch posi’s in both my cars with 31 spline axles.

The 8 inch posi with 3.55 gears will work great in your car. Much better acceleration and enhanced traction. If you like to hammer you may consider the axles. I have a few broken axle souvenirs if you want one.

Link to Currie 8 inch stuff

http://www.currieenterprises.com/cestore/8inford.aspx

Rob
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Old 02/05/2009, 03:55 PM   #4
robert campbell
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Gary,
By the way, I converted my GT/CS from 8 inch to 9 inch. The backing plates for the brake drums for the small bearing 9 inch are the same as the 8 inch. So I was able reuse the brakes on my car in the conversion.

Ebay (lots of bad ink lately) has a lot of respected and trusted dealers for Ford 9 inch stuff. You may also find some 8 inch stuff at much lower prices than straight from Currie, Moser, or Strange.

Rob
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Old 02/05/2009, 03:58 PM   #5
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Limited Slip Differentials

Equa-Lock and Traction-Lok is the Ford name for the Chevrolet term Posi-traction or posi-trac for short.

Detroit Lockers were made by Eaton Corporation, I believe, and they make Detroit Lockers, and the Truetrac Locker, I think this one is also known as the 'soft' Locker.

Scott Behncke
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West Coast Classic Cougar A good source for Mustang mechanical parts too.
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Old 02/05/2009, 04:10 PM   #6
robert campbell
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Gary,
Cougar is all over it. The Detroit locker was the pinnacle of rear ends for Fords in the 60’s. Still in use today. They will take more abuse than a 4 pinion or 2 pinion traction lock which is a clutch style posi unit from Ford. The Detroit locker is a ratchet style locker and is much harsher going around a corner. It actually ratchets to “unlock” as it goes around the corner. Very noisy and noticeable inside the car and outside. No mistaking a Detroit locker equipped car parking at you local cruise or car show.

I would recommend a traction lock. It is cheaper and will hold what you want to do. But if you plan on more engine mods and want to race David and his black GT/CS, then step up to the locker!! Or if you want that unmistakable sound of a locker!!

Here are a couple links to a power seller in ebay.

http://cgi.ebay.com/ebaymotors/FORD-...1%7C240%3A1318

http://cgi.ebay.com/ebaymotors/FORD-...1%7C240%3A1318

http://cgi.ebay.com/ebaymotors/FORD-...1%7C240%3A1309

Hope they work

Rob
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Old 02/05/2009, 07:50 PM   #7
gazrox
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ayup, in Saskatchewan that posi-trac will be great for pulling the seeder in the spring!

Thanks for the info - my gut was telling me to go with the posi and not the locker. The thing about this is that while I want the restoration to "look" original, these types of mods can still achieve that until you get behind the wheel.

Unfortunately this wasn't in my budget but I'm finding that I should expect the unexpected. That damn diff didn't make a noise when I drove the car - maybe I was distracted by seeing the road go by through the floorboards!

Gary

Seafoam Green '68 GT/CS
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Old 02/05/2009, 08:40 PM   #8
robert campbell
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Gary,
3.55 ratio 8 inch "open" (non-posi) rear ends were very common in Mustang II cars from 74 to 78. I have found a couple in salvage yards. Very cheap.

Rob
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Old 02/05/2009, 09:02 PM   #9
gazrox
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Thanks Robert,

I might do some snooping around this weekend. Most of the mustangs around here are pretty well stripped but I might stumble across something. There are a few on Ebay as well.

I want to to make sure that I'll be happy with a posi-trac though before I fork out the $$. My 67 has an open diff and it seems to be OK but you don't know what you don't know.

Gary

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Old 02/06/2009, 04:20 AM   #10
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I have a 3.55 Tru Trac - simply awesome behind my midly warmed over 428CJ through a C6

A guy called TJ on ebay sold me the pumpkin with new everything for $500 USD

shaun

68 J/R code special - 2007 Turbo Territory - Mercedes CLK 2008
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Old 02/06/2009, 06:59 AM   #11
gazrox
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I'm goin' nowhere and I'm in a hurry

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Hey Shaun,

your wheels wouldn't happen to be a black CS that was in a mustang show in Mandurah back in '99 or 2000 would it? If it was, then it was the car that inspired me to have one of my own!

PS. I'm a Adelaide/Kalgoorlie boy in case you were wondering why.

Gary

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Old 02/06/2009, 04:25 PM   #12
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Hey Gary ,

No I imported mine from Austin Texas in 2006 - but I do know of the Raven black car you speak of , its still running around WA with new owners.
There are quite a few CS in Oz now , around 15 cars I reckon which is quite significant.
Might have to start a OZ chapter of the CS owners forum !!!!

I am guessing your involved in either the T/sands or Mines up there in Maple leaf country??

Also that Tru Trac is a cool idea for cars under 500hp IMHO - No noise around corners and mechanical lock up when you squirt the juice in.

Shaun

68 J/R code special - 2007 Turbo Territory - Mercedes CLK 2008
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Old 02/06/2009, 07:10 PM   #13
gazrox
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G'day Shaun,

Yep, doing some gold mining here in Saskatchewan.

I had my 67 coupe in Perth. I get a few surprises when I tell people about dodging roos on the highway between Kal. and Perth when driving the mustang! Will be back there one day, but will have the CS restored by then to bring back.

Gary

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