How can you tell the difference between a Sierra LSD diff and normal diff. The diff i have has disc brakes but unfortunetly i didn't find out what model sierra it came off

If you turn the input/propshaft flange both output/driveshaft flanges turn in the same direction on a LSD, if they turn in different directions normal open diff. Sierra 4x4 seems to be best option when LSD hunting for 7" monting unit (connects the most common Sierra driveshafts. Larger 7.5" mounting on Granada/Cossie.

Zetec, is this an absolute rule? I noticed yesterday that both my drive flanges turn in the same direction when I turn the propshaft. My diff came from a 2 litre 1991 Sierra GLX, which should be a standard diff (it is 3.62 ratio, says so on an alloy tag)

John

That's what my Mum always says so it must be true. I'm sure someone will be along in a min with a more indepth answer any minute now, but like I say sure that is they easy way to tell.

Yep Zetec is right....proof is in the dumping of the clutch and leaving TWO black lines outside the neighbours house instead of one perhaps if you are lucky!

in the interests of controversy, i would raise doubts about that myself. Obviously when wheel spinning off the line only one wheel must turn, but why should the other wheel want to turn backwards? surely the best way to test LSD is to see what resistance there is to turning the two OUTPUTS against each other?

maybe, with a non LSD, one drive shaft might stay still when you turn the input, but for it to go backward then the other would have to go faster to compensate, which doesnt seem right.

im off to jack up my back end anyway, soon find out! and if they do spin opposite ways, i'll cut the diff up to find out why, cos it cant be like i think it is inside!!

All IMHO of course, and i'll point out ive never held a bare diff before.

As a PS, if you turn one output shaft one way and the other output shaft the other, at the same rate, the input shaft wont turn at all.

Much of what you have been told is correct but just to remove some of the confusion --

(1) Ordindary Diff (or knackered LSD)

Hold the input flange turn one output shaft the other will turn backwards. Also if you hold one output shaft while turning the input the input you are not holding should turn twice as fast note you should feel little ressistance on the shaft you are holding.

(2) LSD (Ford Viscous)
Turn the input shaft and both output shafts should turn in the same direction, if you try to hold one output shaft while turning the input you should feel ressistance.