Originally Posted by Peder_y2k
LSD's and locking diffs are only good where one rear wheel slips, and the other on good traction. Like when one wheel moves off pavement while the other remains on pavement. Also helpful on steep wet inclines. But that's simply my 55 years of experience.
I would sort of agree with this but I think it does understate the capabilities of a good LSD or locker. There are numerous styles of both and all function a bit differently.
Most think of an LSD as the normal type we all had in the past. They are simple spring loaded clutches tying the two side of the differential together. They can be setup to be not, lightly, or tightly engaged in regular driving. Both wheels will drive more or less on less slippery depending on how tight they are. Tighter means locked more tightly on turns and more likely fishtailing for instance on slippery surfaces. Putting power on in a turn will often make the inside tire squeal or chirp a bit. They are not capable in most cases of being able to transfer all the power to wheel that has traction, however, as the clutches don't hold that tight.
There are helical gear LSDs also that use no clutches, just two sets of helical gears. When a power per side difference is seen, the slowest turning side gains more power. They can also be set tight or loose to be mostly unengaged or just a bit snug so less likely to fishtail on slippery stuff unless power is going on. Once they get to the speed difference to start to lock, more power tightens them very quickly with more power. I have one in my 96 Buick Roadmaster and it is seamless in normal driving unless I get on the power in a tight turn, then it chirps the inside rear tire.
Lockers come in two main styles plus the oddball GM Govlock setup. Full time lockers are just that, they are locked all the time except when turning forces on good traction surfaces generates enough force to make them ratchet. They are killers on slippery surfaces and nearly impossible to keep in a straight line. Manual lockers use either electric or compressed air to lock to two sides together only when you tell them to. They are great in all conditions as they don't ever lock unless you want them locked. The Govlock is a full locker that runs in unlocked mode until you get 100-200 rpm difference in wheel speed then locks solid but will unlock with enough force difference just like a full time locker. They also unlock above about 20 mph no matter how much speed difference so much safer that way. They are great, but have had some reliability, especially in the under 10.5" ring gear lower capacity axles.
My choice for a class B would a electrically operated manual locker first, then a Govlock, then a helical gear LSD, then a clutch type LSD. Of course there are lots of other opinions on all of this.