I have a ford 9 in my 65 mustang. I was told it was a posi, but when i burn rubber I only see 1 tire mark. I jacked the back up today and when in park the tires spin opposite but when in drive they spin in the same direction. When i do peel out It is the driver tire that leaves a mark. I am just not sure if i have posi or trac lock or neither. Any help will be appreciated, I am new to working on these old cars.
confused about rear end
- Thread starter bodavis100
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jlangholzj
Mustang Master
1 tire = open diff.
look at the tag on the pumpkin if its still there, it will tell you everything. The way a differential works is the reason why in drive they spin the same direction and they spin opposite if you turn one on its own
look at the tag on the pumpkin if its still there, it will tell you everything. The way a differential works is the reason why in drive they spin the same direction and they spin opposite if you turn one on its own
65fastbackresto
Active Member
Got a pic of it?
If it has a small indention on the bottom of the housing, like where your jack would sit under it, its an 8 inch rear. I`d be kinda surprised if it was a 9 inch under there to be honest, unless someone raced that car in the past or something.
If it has a small indention on the bottom of the housing, like where your jack would sit under it, its an 8 inch rear. I`d be kinda surprised if it was a 9 inch under there to be honest, unless someone raced that car in the past or something.
Yeah it was built for the strip mainly. It has subframe connecters, tubbed, and a built 351w etc. I know by looking at the bottom bolts that it is a 9, like the guy told me it was. Everything was new in the car, but the guy got cancer and it sat up for about 10 years or so, it doesnt seem like it would be worn out. The car is still being broke back in from sittin so long. I was hopeing that maybe its a kink that will work itself out or maybe even that it doesn have the right fluid in the rear.
65fastbackresto
Active Member
I have a 8 inch positrack.
With it on jack stands when I spin one tire the other tire spins the same direction. If you think the rear may be still good and just needs broke in, go to a vacant parking lot and just turn the car around several times (steering wheel lock to lock both ways) in each direction, maybe that`ll loosen things up for you.
With it on jack stands when I spin one tire the other tire spins the same direction. If you think the rear may be still good and just needs broke in, go to a vacant parking lot and just turn the car around several times (steering wheel lock to lock both ways) in each direction, maybe that`ll loosen things up for you.
zookeeper
Founding Member
With the engine running, and powering the rear wheels, you can't tell anything. Shut the engine off, put the trans in neutral and spin one wheel by hand. If the other rotates the opposite way, it's not a limited slip.
Power braking will not tell you anything different than standing on the gas pedal will. It is not a posi unit, and is simply a standard open diff.
If by some chance there are worn out clutches in a T lock diff, then yes, you have a posi. Regardless though, a worn out posi will ALWAYS be a worn out posi. There is nothing that you can do to "break it in".
It's already broke.
If by some chance there are worn out clutches in a T lock diff, then yes, you have a posi. Regardless though, a worn out posi will ALWAYS be a worn out posi. There is nothing that you can do to "break it in".
It's already broke.
True. A newly rebuilt Traction-Lok is stiff, "breaking it in" makes it work more easily.
If the wheels turn easily in opposite directions forward or backward, on the ground, off the ground, it doesn't matter, it's either massively worn out, or it's a conventional diff.
Why is this so hard to accept? Many big-block cars, even Shelbys had a conventional diff.
I aint arguin with anybody on if its a posi or not. All I'm tryin to figure out is if when jacked up do i put the car in neutral or leave in park to to check the direction of the spinning tires. I just thought it was weird that mine spin opposite in park but in the same direction when in drive/neutral. I have heard conflicting things on if you test it in park or in neutral.
65fastbackresto
Active Member
The direction doesn't matter. Any difference between forward or backward is due to brake shoes dragging.
If the wheels can easily turn opposite directions under any circumstances at all, IT AIN'T A LIMITED SLIP DIFFERENTIAL. Reverse, drive, park, neutral, doesn't matter. If at any time the wheels turn opposite, it's a conventional "open" rear.
PS- Unless it's a Chevy, it's not a "posi". Positraction™ is a General Motors trademark. The Ford equivalent is Traction-Lok™. The generic industrial term is "limited slip".
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