Rear End Swap
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Rear End Swap
I have a 67 F-100 with a 390 and a fordomatic tranny, and I want to swap out my whole rear end (limited-slip) out for a posi or a locking rear end off of another Ford truck. What would be the best models/years of trucks to look for, and how do I identify a posi/locking differential?
-z
-z
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
What rear axle do you have in it now?
"Positraction" is a GM term referring to their limited slip axles. It's the same thing as a trac-loc. A locking rear end, as far as I know, never came in a factory axle. It's an aftermarket thing only.
An LS rear axle will have an L as the second digit of the axle ratio. For example, a 3.50 LS axle will say 3L50 on the tag.
However, the clutches in a factory LS axle wear out, usually within 100,000 miles. Anything you get from a yard is likely to not work very well.
It's hard to recommend what you should do, because you haven't really said what you use the truck for. An offroad truck has different requirements than a dragstrip truck.
Your best option might be to keep your current rear axle and find an aftermarket LS or locker for it. The first step is figuring out what you have under it now.
"Positraction" is a GM term referring to their limited slip axles. It's the same thing as a trac-loc. A locking rear end, as far as I know, never came in a factory axle. It's an aftermarket thing only.
An LS rear axle will have an L as the second digit of the axle ratio. For example, a 3.50 LS axle will say 3L50 on the tag.
However, the clutches in a factory LS axle wear out, usually within 100,000 miles. Anything you get from a yard is likely to not work very well.
It's hard to recommend what you should do, because you haven't really said what you use the truck for. An offroad truck has different requirements than a dragstrip truck.
Your best option might be to keep your current rear axle and find an aftermarket LS or locker for it. The first step is figuring out what you have under it now.
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Thanks for the reply. Well the rear end is a 3.25 Ford but I'm not sure what size (8" or 9") and I am also not sure what size the axle is (28 or 31). I think I will put a locker in the rear end, but how do I identify the rear housing size and the axle size to get the proper part? The main reason for this is that I get sick and tired of getting 1 wheel stuck in the soft ground and mud on the the property I live on and having all the power going to that wheel, and then the final insult of having to ask my roomate to get me out with his dodge. Also it would be nice If I got power to both wheels instead of one of the wheels spining and the other doing nothing but holding the truck up when I punch it off the line.
-z
-z
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
If it's original, it should be a 9". If it was swapped about, who knows. You'd probably have to pull the 3rd member out and measure the ring gear.
It sounds like a good LS will do the trick for you.
Auburn makes a good one, and also look at Powertrax, they make a no-slip that supposedly installs in your driveway with no special tools. Search here for it - it's been talked about a lot. I've seen them on ebay for about $400 or so.
The 9" sees a LOT of racing application, so there are a ton of aftermarket goodies for it.
It sounds like a good LS will do the trick for you.
Auburn makes a good one, and also look at Powertrax, they make a no-slip that supposedly installs in your driveway with no special tools. Search here for it - it's been talked about a lot. I've seen them on ebay for about $400 or so.
The 9" sees a LOT of racing application, so there are a ton of aftermarket goodies for it.
Laughing Gas
Joined: Jan 2005
Posts: 1,142
Likes: 25
Detroit TrueTrac
Check out the Detroit TrueTrac , it is a torque biasing differental rather than a locker, much smoother operation, feeds power to the wheel with the best traction and uses NO clutches or special friction modifiers. Have one in both ends of an F-350 with over 200K on th clock and never have had any problems.
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