confused about rear end

bodavis100 · May 26, 2011

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.

jlangholzj · May 26, 2011

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

Fstbk · May 26, 2011

Or it could be worn out, need friction modifier etc..?

Are you sure it's a 9?

96 DOHC Cobra · May 26, 2011

Either it's an open rear or a very worn posi. If the rear still has the metal ID tag still bolted to it, it might help figure out what's in it. Otherwise, you'll just have to pull an axle or the whole pumpkin.

65fastbackresto · May 26, 2011

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.

bodavis100 · May 26, 2011

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 · May 27, 2011

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.

2+2GT · May 27, 2011

If the wheels spin easily in opposite directions, it's almost certainly an open rear.

bodavis100 · May 27, 2011

Is that in park or drive? In park they spin opposite but in drive they spin the same direction.

zookeeper · May 27, 2011

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.

bodavis100 · May 28, 2011

In neutral they spin the same way, so I guess it is a posi. Just dont know why I aint seeing two marks. I guess ill try power breaking the car and see if I leave two marks. Thanks for the input guys.

CarMichael Angelo · May 28, 2011

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.

2+2GT · May 28, 2011

madmike1157 said:
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".

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.

danny clemens · May 28, 2011

Well where do ya live. If it ain't too far I'll come by and help you break it in.

bodavis100 · May 28, 2011

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 · May 28, 2011

Ah....

I don`t want to argue either but they should not spin at all in park....

2+2GT · May 28, 2011

bodavis100 said:
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.

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".

bodavis100 · May 28, 2011

Appreciate it. Yeah ive been around chevys mainly (but only bought Fords, weird), that explains sayin posi.

confused about rear end

bodavis100

New Member

jlangholzj

Mustang Master

Fstbk

Member

96 DOHC Cobra

65fastbackresto

Active Member

bodavis100

New Member

65fastbackresto

Active Member

2+2GT

bodavis100

New Member

zookeeper

bodavis100

New Member

CarMichael Angelo

my rearend will smell so minty fresh,

2+2GT

danny clemens

Member

bodavis100

New Member

65fastbackresto

Active Member

2+2GT

bodavis100

New Member

Similar threads

confused about rear end

New Member

Mustang Master

Member

Active Member

New Member

Active Member

New Member

New Member

my rearend will smell so minty fresh,

Member

New Member

Active Member

New Member

Similar threads

Privacy & Transparency

Privacy & Transparency