Whats the diff?
 

You know nothing jon snow :)...... actually no I know nothing at all about diffs...
What is a LSD (other then the drug), or Open diff? I kinda put 2 and 2 together and figured welded diff is both wheels spinning the exact same no matter what, but idk what the rest of them are.. and which is best for low HP daily driving?:confused:

LSD is a Limited Slip Differential. This means both wheels put power to the ground at the same time just like a "welded differential" as you mention. However when going around a curve, the inside tire turns slower than the outside, therefore there must be some mechanical way to allow one side to slip a little as not to bind the thing up. The limited slip gear housing has a set of spring loaded clutches and spider gears that will allow one side to slip a bit on the fly.

Solid axle (welded as you call them) are NOT for street use. I've only seen these on dragsters when turning is not part of the normal operation.

Regular differentials are more common. But only one wheel gets the power.

I prefer the LSD's any day.

Watch this video and it will all make sense.. https://www.youtube.com/watch?v=yYAw79386WI It's old but a very good visual explanation.

so thats why when i put my trans back up and had the rear of the car jacked up only the passanger wheel was spinning? and the driver side was only faintly moving? but in reverse only the passanger wheel was spinning?:confused:
Im sorry im still trying to learn these things.

https://en.m.wikipedia.org/wiki/Differential_(mechanical_device)

If the other wheel is spinning the opposite direction, you have either an open differential or a LSD that is severely worn.

As DG mentions, welded / locked differentials are not for street use. In addition to tire wear and break-away in cornering, there is a safety issue: if you lose traction entirely to one side, the other side will snap the car around in a heartbeat. Dangerous.