open vs limited slip diferentials.
I have read about differentials overheating. Is this a problem 'almost' exclusive to limited slip? My new vehicle will be used a great amount of time on steep 2 lane winding mountain roads. I woul...
Forum Discussion
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LS constant clutches are an economical compromise. I had several small work trucks with this cheesy option. Like all LS, the traction can be somewhat improved by dragging brakes which can transfer some torque even from a wheel in the air. Their disadvantages are fast clutch wear during hard pulls, and poor directional traction in slippery surface conditions... until the clutches wear out. They tend to slide both wheels frustratingly sideways on muddy slopes for instance, whereas an open diff at least goes straight. Or slide both wheels sideways on highway ice at the worst possible moments. Curves, uphills. Freaky.
For the above reason they are never pro-recommended on a front steering axle, and quite marginal on rear axles on slick ice or wet greasy mud roads. There will be those that claim Limited Slip handle good on slick surfaces, but they lack the full experience and frankly don't know what they are talking about. Again, the diffs are cheap, though.
The cheap flat-clutch limited slip diffs do drag, and heat, anytime the wheels run at different speeds because most are spring pre-loaded against one another all the time, oily or not. In addition for all other types, climbing a long hill around curves is much worse because the diff does dissipate even more friction-heat as the clutches are wedged exceptionally tighter because of the extra wheel torque required to go up a hill... as opposed to low required torque on easy level road, going slow, or with the wind. They can wedge tight either by the spider pinion shaft tightening on ramps, or more commonly by the bevel shape of the side gears and pinions forcing the side gears out tight against the clutch pack.
The flat-type LS clutches wear out soonest, but are easier and cheapest to replace. Auburn cone-type LS clutches hold more differentiational torque, but don't last any longer and are expensive and difficult to replace. The term "limited slip" is a misnomer. They should be called "limited traction" because all LS are purposely designed to slip one wheel under high different traction demand like bottomless sand, deep mud or "door-handle" snow, especially when towing.
Air lockers handle as safely, and cool, as an open diff when turned off and have a positive lock when needed. The downside is that an onboard compressor and plumbing hoses are needed, and one of these several weak links will fail, probably sooner than later. The newer Eaton electric locker is simpler and more reliable and achieves exactly the same traction in the end. Electric is my overall pick.
Torsen diffs supposedly handle well enough to be on a front axle, but I would still prefer a positive electric locker. They work purely because of multi-gear-train friction and have no clutches to wear out. The diff is called a torque-biasing type, but the basic limited slip principle is that it is easy for a spur gear to turn a worm gear, but, in terms of tooth friction, hard for the 2nd worm gear to, in turn, drive a spur gear. This multi-gear-train "biasing" friction, along with some claimed case/gear friction, increases exponentially with rpm if one wheel begins to slip, so they respond best of all to slight brake pressure causing a substancial transfer of torque from any useless airborne wheels. Their life expectancy, without clutches, is as good as an open diff. They are most expensive, but stock on many exotic sports cars and the finest off-road vehicles, such as the US military HMMWV (Humvee).
The last common diff locker is the tried and proven Detroit Locker. It is locked all the time except it allows the fastest wheel to ratchet forward if necessary. They work, but are noisy. I had this type on a one ton dually truck with Mud & Snow tires. It tended to slip sideways on muddy sidehills also, as the ratchet is tighter than typical greasy traction. On rainy days both wheels usually slipped simultaneously and the rear end moved sideways a couple of feet at a crack or the truck would understeer terribly while turning as the inside wheel had all the traction.
The best, and cheapest addition to emergency traction is chains.
Wes
...
LS constant clutches are an economical compromise. I had several small work trucks with this cheesy option. Like all LS, the traction can be somewhat improved by dragging brakes which can transfer some torque even from a wheel in the air. Their disadvantages are fast clutch wear during hard pulls, and poor directional traction in slippery surface conditions... until the clutches wear out. They tend to slide both wheels frustratingly sideways on muddy slopes for instance, whereas an open diff at least goes straight. Or slide both wheels sideways on highway ice at the worst possible moments. Curves, uphills. Freaky.
For the above reason they are never pro-recommended on a front steering axle, and quite marginal on rear axles on slick ice or wet greasy mud roads. There will be those that claim Limited Slip handle good on slick surfaces, but they lack the full experience and frankly don't know what they are talking about. Again, the diffs are cheap, though.
The cheap flat-clutch limited slip diffs do drag, and heat, anytime the wheels run at different speeds because most are spring pre-loaded against one another all the time, oily or not. In addition for all other types, climbing a long hill around curves is much worse because the diff does dissipate even more friction-heat as the clutches are wedged exceptionally tighter because of the extra wheel torque required to go up a hill... as opposed to low required torque on easy level road, going slow, or with the wind. They can wedge tight either by the spider pinion shaft tightening on ramps, or more commonly by the bevel shape of the side gears and pinions forcing the side gears out tight against the clutch pack.
The flat-type LS clutches wear out soonest, but are easier and cheapest to replace. Auburn cone-type LS clutches hold more differentiational torque, but don't last any longer and are expensive and difficult to replace. The term "limited slip" is a misnomer. They should be called "limited traction" because all LS are purposely designed to slip one wheel under high different traction demand like bottomless sand, deep mud or "door-handle" snow, especially when towing.
Air lockers handle as safely, and cool, as an open diff when turned off and have a positive lock when needed. The downside is that an onboard compressor and plumbing hoses are needed, and one of these several weak links will fail, probably sooner than later. The newer Eaton electric locker is simpler and more reliable and achieves exactly the same traction in the end. Electric is my overall pick.
Torsen diffs supposedly handle well enough to be on a front axle, but I would still prefer a positive electric locker. They work purely because of multi-gear-train friction and have no clutches to wear out. The diff is called a torque-biasing type, but the basic limited slip principle is that it is easy for a spur gear to turn a worm gear, but, in terms of tooth friction, hard for the 2nd worm gear to, in turn, drive a spur gear. This multi-gear-train "biasing" friction, along with some claimed case/gear friction, increases exponentially with rpm if one wheel begins to slip, so they respond best of all to slight brake pressure causing a substancial transfer of torque from any useless airborne wheels. Their life expectancy, without clutches, is as good as an open diff. They are most expensive, but stock on many exotic sports cars and the finest off-road vehicles, such as the US military HMMWV (Humvee).
The last common diff locker is the tried and proven Detroit Locker. It is locked all the time except it allows the fastest wheel to ratchet forward if necessary. They work, but are noisy. I had this type on a one ton dually truck with Mud & Snow tires. It tended to slip sideways on muddy sidehills also, as the ratchet is tighter than typical greasy traction. On rainy days both wheels usually slipped simultaneously and the rear end moved sideways a couple of feet at a crack or the truck would understeer terribly while turning as the inside wheel had all the traction.
The best, and cheapest addition to emergency traction is chains.
Wes
...
