I have bought quite a few "low-mileage one-owner unmodified" cars. Usually from pensioners, who probably stretched out service intervals, so changed the fluids when I got them home. Often the diff oil was foul looking and smelling. Now since diff oil is high viscosity, it trickles out slowly at the end. I imagine a bit of sludge stays in the bottom of the housing. Next time, I will pour a litre of kerosene or diesel into the diff, in the hope it moves some crap. Since these are a mixture of alkanes, I cannot see them doing any harm. Any thoughts? Maybe follow up with a bit of engine oil to get rid of the flush.
BTW these were all RWD cars, with hypoid gears, which is more stressful to the lubricant.
I'm intrigued why you would think a pensioner would be *less* likely to service their vehicles at proper intervals, whereas my perception and experience would be diametrically opposed to that POV.
+1. The EP oil used in hypoid diffs is normally a bit smelly. It normally stays much cleaner than engine oil owing to the more benign environment. If you are regularly finding degraded oil that is probably associated with water ingress from the seals.
Are you talking about modern vehicles, or things from the Austin 7 / Ford Popular generation?
I've bought two in my time - both at (proper) auction - and were excellent value. At least you know exactly what you're buying - unlike the same car bought by a used car dealer, given a valet, clocked, and sold on with a
LS430 has an open diff. Quite useless luxury barge.
BMW M's have plated diffs. Older "sports" had LSD as an option but not if they have traction control. But most have E-diff, it's an open diff and traction control. An open diff always splits the torque equally between the axles. If one wheel spins, the other only gets the torque that the spinning wheel is using. The excess power goes into accelerating the spinning wheel and the engine. The spinning wheel is braked by the traction control and the diff sends the same torque to the other wheel that still (had) grip.
AMG LSD is an option. Anyone buying one that doesn't tick the box for the AMG performance package don't get. And if you want a diff oil cooler that needs a tick for "track" package. (Diff oil cooler was standard on Nissan 200SX, even with open diff!)
Diffs with clutch plates use a cam that when a shaft moves relative to the body (with crown wheel), loads the clutch on that side to lock it to the body. Only a diff with clutch packs makes crud from plate wear that contaminates the diff oil. Very few LSD diffs are the type with clutch plates. When the plates need changing (30-50K miles if given some) the oil gets changed as well.
GKN have an all metal cone clutch design.
Viscous LSD have a sealed viscous unit. Locks at a slip rate set by viscous fluid. Uses regular diff oil and need no changes.
Torsen limited slip diffs have a worm gear on each output shaft which can't be driven "backwards". Normal drive is though "locked" worm wheel to the worm gear. If one shaft tries to spin faster (outside wheel in a turn) it transmits torque though it's worm gear to the worm wheel and then though spur gears to the locked worm drive of the other shaft. Uses normal diff oil.
Quaife limited slip diff have helical spur gears, there is a pack of Beleville washers between the 2 output shafts, these bias the diff and it can send 5x the grip-less 1/2 shaft's torque to the other 1/2 shaft. Doesn't actually lock. Put one wheel on ball bearings, rollers or sheet ice and the torque at the other wheel is 5x nothing = nothing. Use normal diff oil.
Not convinced of the need for a LSD on most. They can be positively dangerous on a RWD in the wet. Traction control is a better half way house, and likely cheaper and more reliable.
Apparently that model does not have an LSD, but does have traction control. But, the car could hardly be called useless under any reasonable definition of the word. Extreme quality of build and reliability coupled with an incredible turn of speed, plus shed-loads of safety and comfort.
My Dad frightened me by pulling out of my side road very quickly in an RSTurbo, the FWD LSD took him straight up the pavement, he held it all together and carried on (I was in the passenger seat)
His party trick in the Frazer Nash was to turn it round in its own length with the non differential chain RWD
Thing is there are very few RWD cars indeed incapable of a full belt takeoff on a decent surface without an LSD, unless being stupid with the clutch. Autos obviously even more so. So it comes down to a poorer surface or pulling away on a corner. And in the hands of many, a RWD car with an LSD will go sideways when it looses adhesion - and often with little warning.
Yeeehaa! Turn into the "skid", when it's pointing in the desired direction, lift off, let go wheel, it will self centre, grab hold of wheel and floor it.
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