Differential Strength

[Jus Cruisin]

Originally Posted by Mother

I have been using a 1971 Ford Torino 9 inch for many years. The 3.46 ratio with an Auburn ratchet spool has never given up. I check the lash every second year just to be safe. My engine produces 740/ 680 at the finals. No problems.

Backdraft doesn't use Ford 9". All BMW parts. Unless someone has completely scrapped the rear independent suspension for a solid axle Ford.

[dcdoug]

Originally Posted by Bill Bulmer

I just changed from the 3.46 factory open differential to a 3.91 posi, and it is like a different car. All the chugging and bucking from lagging at low rpm's is gone, and I can actually get decent traction when I hit he gas in 1st and 2nd now. I would order the car with the posi if I had it to do again.

Wow. I didn't think any cobras had open rearends. That's hard to imagine.

[spookypt]

The e36 mid case 188 diff in lsd configuration is fine for street and track days. Once you start putting down 500hp at the treads on sticky tyres with 391 or shorter rear end ratios expect trouble. I've broken 6 but have done the easy 750ie pumpkin and cradle conversion at 210mm and 391 and no issues now.

[Xmas]

IMHO the 3.91 is to low. With a redline of 6200, a termed TKO600 and 315/35/17 tires my shift points are 42, 64, 95, 121, 148. At least according to this site: http://fitbodyshop.net/gear/index.php. If there is a lower LSD I would choose that, but you definitely want LSD. If I had bought new, I'd put a Quaife sequential and probably a 3.73, or lower.

[Locohora]

What about the strength of the U-Joint of the drive shaft?
There are different sizes on the market... which size use Backdraft? 1310 or 1330?

[GBowman]

For clarity's sake...I mashed the peddle in 1st from a slow roll and snapped the output flange in half. The diff was (apparently) OK but I switched to a Diffs Online upgraded diff anyway. Jay had already installed the bionic half shafts from the Drive Shaft Shop, I guess the weak link was the flange which was stock. I upgraded to a set of hardened ones which were offensively priced, no problems since.