open vs limited slip diferentials.

carringb wrote:

ScottG wrote:


The "drag" is so minimal it is inconsequential or non existent - oil separates them and technically they do not touch. When they are not locked up there is nothing holding them back - they just freewheel. Other wise they would wear out quickly.
They do not get engaged until a ratio is met. Not even a little bit and it make no discernible heat.
What makes heat is heavy loading and lots of power - or abuse.

Personally I would never own a truck, especially a 2WD, without some form of LSD. Had one once and got stuck in the most ridiculous places.

Maybe you are confusing various limited slip and locker differentials. The most common LSD is a clutch-pack style. The friction surfaces are always in contact as long as there some pre-load (there usually is, and more can be added by adding extra clutch discs), and friction increases as torque through the differential increases.

I'm not saying anybody should skip on LSD for this reason. I'm just stating that it can add extra heat vs an open diff. I have observed in my vehicle, that curving 2-lane roads increase MY differential temps substantially over the same grade roads without curves.

Bryan,

I think you are right as usual. Looking a little closer, Scott is partially correct too. While both GM and Ford generally still use spring-loaded LS (limited slip) with some constant curvy-road drag, GM apparently does use a more positive locking mechanism in their Eaton G80, which might be an option. I found a good G80 article here that appears knowledgeable.

I suppose either a pin/ramp locking system (never seen one) or the above G80 might not generate excessive clutch-slip heat. The pin/ramp locker does have one other disadvantage identical to the Detroit Locker. The driving wheel is always on the inside of the curve when turning (outside ratchets/freewheels faster). This means that the inside rear tire is trying to turn the rear axle opposite of the desired steering direction which I found a debilitating nuisance in greasy mud. If the G80 truly locks, a similar steering problem could result with the inside tire trying to push the front straight during turns. But the G80 mechanism supposedly allows an axle difference of about 100 rpm pre-engagement which shouldn't affect turns. The G80 also supposedly entirely disengages over 30 mph. Maybe the G80 would not be too bad on highway glare ice if it allows one rear tire to spin as a warning, while the other maintains direction as does an open diff. My Ford Trac Locks sucked.

I don't know what Dodge/Ram uses, but my first guess would be constant spring/bevel gear loading which would heat as you say, and side-slip on ND icy interstates. Maybe Scott can enlighten us which type his truck(s) use(s).

Wes
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