Posi Rear end

[ArtBBQ]

My 71 Mach 1 M code has a open diff rear end. I'm thinking about converting it to a positraction.

Got the 9-in rear end in this one.

Those one tire burnouts are kind of lame.

Has anybody done it before and if so what's the difficulty on a 10 scale?

What brand and type of posi did you install ? I'm looking at the Duragrip limited slip Trac loc

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[Don C]

Not that difficult, if you have the right tools and carefully follow the instructions in the shop manual. Read the details in the shop manual before you start to find out what tools and supplies you will need, before you start on it. The carrier is quite heavy, so you'll need to be prepared to handle it when you remove it from the housing. If you do it with the axle in the car, and are doing it by yourself, a fixture that mounts to a floor jack and bolts to the pinion bearing retainer will really help. It's easy to loose control of it and it's heavy enough to break bones.

 

[ArtBBQ]

Not that difficult, if you have the right tools and carefully follow the instructions in the shop manual. Read the details in the shop manual before you start to find out what tools and supplies you will need, before you start on it. The carrier is quite heavy, so you'll need to be prepared to handle it when you remove it from the housing. If you do it with the axle in the car, and are doing it by yourself, a fixture that mounts to a floor jack and bolts to the pinion bearing retainer will really help. It's easy to loose control of it and it's heavy enough to break bones.

I talked to a friend of mine about doing this one. He suggested I take the axle out of the car and bring it over to his house to do it on the bench. He's got the tools in the setup to do this one.Yeah the thought of that axle housing falling and breaking arms legs etc doesn't sound fun.

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[Kilgon]

Trac loc weighs about 85 lbs.  As Don C said try to use your jack or get some help in removing it.  Don't know if you have a lift or not so that will make a difference in how hard or easy of a job it will be. While you are in there I would replace the outer axle bearings and seals also.  

 

[Stanglover]

While I know what you mean, I hate it when someone refers to a Ford rear end as a "Positrac". That's a GM term.

I had mine converted this spring as my Mach 1 had an open 3.25:1. I kept the ratio and only had the "Traction-Loc" installed. As my original intent was just to have the axle checked over and add new  bearings, seals and gear oil, but the guy who did it (rear axles is all he does) had a new Tration-Loc 28 spline in stock, bought in for someone who never came for it, so I was offered it for a price I couldn't refuse. Job done. After a couple hundred miles break in, what a difference, but you'll need to adjust your driving a bit as it can get a bit squirrely!! As for gear ratios, if money was no object, I would have gone for a 3.50:1 for a bit more get-up-and-go and still have pretty good mileage.

A friend has a Torino with a 429 transplanted into it and it needed a stronger rear end. He opted for a Tru-Trac and loves it, so there's another option for you.

Also, don't forget that it is suggested NOT to use synthetic oil in rear axles. (I know that'll get some comments) I like Valvoline 80W90 gear oil and you MUST add a friction modifier with a Traction-Loc. I bought Ford friction modifier from the dealership, but be warned, it stinks to high heaven, so don't get any one you!!

 

[Bentworker]

I’ve set up several sets of gears.  The Ford 9” is one of the easiest.  About the only special tools you will need are a 1/4” drive beam or dial type inch pound torque wrench, dial indicator and base, and a press.  Some good pattern paint is needed too.  I have a tube of the yellow acdelco stuff and it is fantastic.

As for what limited slip to use consider a torque biasing type like a Detroit Truetrac or a Quaife.  They have no clutches to wear.  You use regular gear oil with them.  
 

 

[tony-muscle]

I have an Eaton Truetrack with 3.5 ratio and 31 splines. It is awesome! I bought the unit all assembled from Strange so I just had to pull the old one and get the new one in. Pretty easy to do it alone with the help of a jack. As suggested, it is a good time to replace bearings and seals. In my case I also got Strange's 31 spline shafts with bearing and o-rings (no seals). You may not need to upgrade to 31 splines if you are planing on leaving the engine stock.

 

[ArtBBQ]

While I know what you mean, I hate it when someone refers to a Ford rear end as a "Positrac". That's a GM term.
I had mine converted this spring as my Mach 1 had an open 3.25:1. I kept the ratio and only had the "Traction-Loc" installed. As my original intent was just to have the axle checked over and add new  bearings, seals and gear oil, but the guy who did it (rear axles is all he does) had a new Tration-Loc 28 spline in stock, bought in for someone who never came for it, so I was offered it for a price I couldn't refuse. Job done. After a couple hundred miles break in, what a difference, but you'll need to adjust your driving a bit as it can get a bit squirrely!! As for gear ratios, if money was no object, I would have gone for a 3.50:1 for a bit more get-up-and-go and still have pretty good mileage.
A friend has a Torino with a 429 transplanted into it and it needed a stronger rear end. He opted for a Tru-Trac and loves it, so there's another option for you.
Also, don't forget that it is suggested NOT to use synthetic oil in rear axles. (I know that'll get some comments) I like Valvoline 80W90 gear oil and you MUST add a friction modifier with a Traction-Loc. I bought Ford friction modifier from the dealership, but be warned, it stinks to high heaven, so don't get any one you!!

The previous owner of my car put in the 350 gear set. why they didn't set it up with a locker type rear end while they had it apart is beyond me?


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[ArtBBQ]

I’ve set up several sets of gears.  The Ford 9” is one of the easiest.  About the only special tools you will need are a 1/4” drive beam or dial type inch pound torque wrench, dial indicator and base, and a press.  Some good pattern paint is needed too.  I have a tube of the yellow acdelco stuff and it is fantastic.

As for what limited slip to use consider a torque biasing type like a Detroit Truetrac or a Quaife.  They have no clutches to wear.  You use regular gear oil with them.  
 

The reading I did they prefered the clutch type because they're rebuildable. Is that just a selling point or is that a legit thing?

 

[Bentworker]

I never heard the argument that a clutch type is better because it is rebuildable.  The fact that you don’t have to rebuild the torque biasing type is normally seen as a positive.  
 

https://www.kmpdrivetrain.com/differentials/torsen-vs-plated-limited-slip-differential/

 

[Carolina_Mountain_Mustangs]

Our local rebuild shop will back up the NO SYNTHETIC. He has a massive pile of burnt gears and bearings he does all the warranty service work for several new car dealers. He agrees worst thing ever done. 
On the gears. If you have never driven a traction loc or any type of locking rear you will soon know how those loose control doing their burn outs showing out. It takes practice to know how to let off at the right time. You for sure probably do not want a Detroit Locker. 
My friend that drag races just took out a 35 spline 9" Moser large 3,250" carrier bearings. Would be pretty much unbreakable. No gear set he will take $500. 

 

[Don C]

After you take it out once, you'll find the benefit of not having to rebuild it. Clutches never seemed to last very long for me, for some reason.

 

[Stanglover]

The previous owner of my car put in the 350 gear set. why they didn't set it up with a locker type rear end while they had it apart is beyond me?


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Well, look at it this way, you have a perfect ratio for street and occasional strip use imo. So, adding a limited slip whatever you choose, will be good. But yes why did that guy not spend the extra cash and do it right ,once. 

 

[Tnfastbk]

I had a detroit locker and hated it. Took it out for a trutrac and love it. I guess it depends on what you want to do with the car. But for me and driving a lot the detoit locker was not the way to go.  To many curves around here. Here is a short read on the differences.

https://www.currieenterprises.com/differential-options-explained

 

[Stanglover]

I had a detroit locker and hated it. Took it out for a trutrac and love it. I guess it depends on what you want to do with the car. But for me and driving a lot the detoit locker was not the way to go.  To many curves around here. Here is a short read on the differences.

https://www.currieenterprises.com/differential-options-explained

Great info there, explains it in a very simple way even I can understand. Thanks