Editing Limited slip and locking differentials

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==Normal operation==
Under normal conditions if the rear wheels are lifted off the ground, an '''open''' differential will rotate the rear wheels in ''opposite'' directions. A '''limited slip''' (aka "posi" or "LSD") will rotate both wheels in the ''same'' direction, and it will be very difficult to hold one tire from rotating while the other wheel is being turned. But a damaged open diff or a diff that has been converted by using a spool or mini spool, or a diff that has had the spider gears welded (an old, dangerous "back yard" method to get two-wheel traction all the time) will ALSO allow both wheels to rotate in the same direction. Conversely, a LSD with bent axle tubes, worn clutches, or a galled pinion gears and/or cross shaft may not allow both wheels to rotate in the same direction with the rear wheels off the ground.

Having both rear wheels spin under acceleration is not a positive indication of having a LSD. Under certain circumstances like when rear wheel traction is identical for both rear tires, an open diff can behave like a LSD. 
 
So, checking for a differential being limited slip is not as simple as jacking up the rear of the car and turning the wheels. The only way to be 100% certain of what type of differential is in the rearend is to remove the cover or drop the center section (like in the case of a Salisbury rearend) and look inside.

{|
|[[File:Open diff.jpg|thumb|center|300px|Open differential]]
|[[File:Auburn limited slip differential.jpg|thumb|center|300px|Auburn limited slip differential]]
|}

==Other cues==
Rearend housings will often have codes stamped into the axle tube or center section (depending on make and type of rearend) that can be decoded to give the gear ratio, manufacturer, date of manufacture, LSD or open, etc. Some rearends can be identified as to type by the casting numbers (raised numbers cast into the metal, not stamped), because some rearends use different housings for open and LSD differentials.

Many posi rearends carried tags with info pertaining to the ratio and type of diff lube to use. This included tags that state to use limited slip lube only- a good indicator that the rearend was a posi originally, but of course this could have been changed during the life of the vehicle.
{|
|[[File:Lsdlube tag.jpg|thumb|center|300px|Posi lube tag]]

|}

==Resources==
*[http://www.crankshaftcoalition.com/wiki/Gear_ratio_check Gear ratio check]

[[Category:Rearend]]
[[Category:Good articles]]