Limited Slip Diff on T56 Transmission

[REY 427]

I'm looking to upgrade my current rear end to a limited slip. What ratio and lock % should I go with? I'm running a T56 transmission.

[Cashburn]

Which T-56 do you have?

[REY 427]

Originally Posted by Cashburn

Which T-56 do you have?

Tremec T56. According to my build sheet. I bought the car used with a couple thousand miles.

[Grey 65]

Originally Posted by REY 427

I'm looking to upgrade my current rear end to a limited slip. What ratio and lock % should I go with? I'm running a T56 transmission.

This would depend on what your end goal is. Top Speed, 1/4 mile, autocross, road racing, good mpg's, etc, etc...

Also it would be good to know what gear ratio you have in the car now and what the O.D. is of the rear tires.

With all of this information educated suggestions can be made. Without this information It would be like me asking you what my truck is worth without providing any information other than I have a truck for sale.

[spdbrake]

On your current diff's aft cover is a metal tag. If it starts with an "S" you already have a LSD.
The number that follows is the Ratio. Useful for determining if you want to go up or down rpm wise on the new Diff.
http://images.forum-auto.com/mesimag...71/IMG0760.jpg

[hawk 325]

I have a T56 in my cobra, the rear tires are 26" and the rear ratio is 3.25

[xb-60]

Originally Posted by REY 427

I'm looking to upgrade my current rear end to a limited slip. What ratio and lock % should I go with? I'm running a T56 transmission.

Try punching figures into the Superformance gearing calculator:
Second Strike Gearing Calculator

That's a great way to settle on gear ratios / rear end ratios / tyre sizes

Cheers,
Glen

[pm125]

If you have a T-56 that reverse is all the way to the right and up. What model is that. I know its not a T-56 magnum.

[Cashburn]

There are several different T-56 Magnums or is it a standard T-56?

Application Part # Engine Torque Capacity
(lb-ft.) Includes
Housing Clutch Type Speedo Type Spline Count
Input / Output Gear Ratios
1st 2nd 3rd 4th 5th 6th Rev

GM TUET11009 LS 700 No Hyd Mech/Elec 26 / 31 2.66 1.78 1.30 1.00 .80 .63 2.90
GM TUET11012 LS 700 No Hyd Mech/Elec 26 / 31 2.97 2.10 1.46 1.00 .74 .50 2.90
Ford TUET11010 Modular 700 No Mech Mech/Elec 26 / 31 2.66 1.78 1.30 1.00 .80 .63 2.90
Ford TUET11011 Modular 700 No Mech Mech/Elec 26 / 31 2.97 2.10 1.46 1.00 .74 .50 2.90

[REY 427]

Originally Posted by spdbrake

On your current diff's aft cover is a metal tag. If it starts with an "S" you already have a LSD.
The number that follows is the Ratio. Useful for determining if you want to go up or down rpm wise on the new Diff.
http://images.forum-auto.com/mesimag...71/IMG0760.jpg

Here's a picture of my diff tag. Not sure if you can make out all the numbers since it's been painted.
IMG_9134 by Rey Lorenzo, on Flickr

[spdbrake]

Can't make out the numbers to the left. If you can take Scotchbrite and lightly scuff it to remove the sheen, then shine the flashlight from the right side at an oblique angle to show the relief. Turn off the flash on your camera.

[REY 427]

Originally Posted by spdbrake

Can't make out the numbers to the left. If you can take Scotchbrite and lightly scuff it to remove the sheen, then shine the flashlight from the right side at an oblique angle to show the relief. Turn off the flash on your camera.

This is the best I could do. I know I don't have a limited slip. On hard launches it appears that only the passenger side tire is the one that spins, leaving one tire mark. Wish I knew which T56 Backdraft put in my car. Unfortunately I can't find any info in the build book.
IMG_9147 by Rey Lorenzo, on Flickr

[REY 427]

If Backdraft's website reflects what they put in the cars they build, I assume this is the transmission they put in mine.
https://www.backdraftparts.com/produ...26-spline.html

[Gaz64]

Can you note the engine rpm in 4th gear at 60mph and then in 6th gear at the same speed?

If the engine rpm in 6th is half of 4th gear, drops from say 3000 rpm to 1500 rpm, you have a .50 6th gear.

[mln385]

Originally Posted by REY 427

Here's a picture of my diff tag. Not sure if you can make out all the numbers since it's been painted.
IMG_9134 by Rey Lorenzo, on Flickr

09 3 46 which should be an open differential with the standard 3:46 gear ratio.

[Grey 65]

I vote for 3.91 gears and 60% lock.....

[REY 427]

Originally Posted by mln385

09 3 46 which should be an open differential with the standard 3:46 gear ratio.

Thanks for clearing that up. I had a feeling that's what I was looking at.

[REY 427]

Originally Posted by xb-60

Try punching figures into the Superformance gearing calculator:
Second Strike Gearing Calculator

That's a great way to settle on gear ratios / rear end ratios / tyre sizes

Cheers,
Glen

Thanks for pointing me to this website. I've played around with it for a bit and I think I'm leaning towards 3.91 gearing. This is the one I may be buying. Not sure if 25% lock would be fine or if I should go up to 40%.

BMW E36 3.91 LSD POSI DIFFERENTIAL LIMITED 325I M3 25 LOCK UP BACKDRAFT COBRA | eBay

[Cashburn]

Originally Posted by Grey 65

I vote for 3.91 gears and 60% lock.....

I've been told 40% is the most you want on the street. But again, I was told this I have not directly experienced it.

3.73 works pretty good with the 6 speed. If it's the .8 .6 OD unit. But 3.91 is usable here too.

[joyridin']

I have a 3.7 rear with a .54 ratio for 6th. It seems to be a great ration for both cruising through town and on the highway when you get it in 5th or 6th gear. 4th works great for city streets at between 35-45 mph.