what should come out of a diff?
Discussion
I was talking with an engineer friend of mine over the weekend and he was telling me about the oil change he'd just done on the differential of his Jag XJ12 (late 1980s vintage, Limited slip diff). I had always imnagined that diff oil would remain quite clean in operation, given that there are no combustion processes for it to get close to, but my friend said his oil was black when it came out (30k miles since last change) and the diff sump plug (which is magnetic) had a small "xmass tree" of fine metallic (graphite?) powder stuck to it. He sadi there were no lumps of metal, aside from one pice which he described as like a chip off a tooth.
I said it sounded like his LSD was shagged, but he reckons its all normal for clutch pack type LSDs.
Is he correct? And if he is, what does have to come out of your diff sump plug before you should be alarmed??
andy
I said it sounded like his LSD was shagged, but he reckons its all normal for clutch pack type LSDs.
Is he correct? And if he is, what does have to come out of your diff sump plug before you should be alarmed??
andy
andymadmak said:
I was talking with an engineer friend of mine over the weekend and he was telling me about the oil change he'd just done on the differential of his Jag XJ12 (late 1980s vintage, Limited slip diff). I had always imnagined that diff oil would remain quite clean in operation, given that there are no combustion processes for it to get close to, but my friend said his oil was black when it came out (30k miles since last change) and the diff sump plug (which is magnetic) had a small "xmass tree" of fine metallic (graphite?) powder stuck to it. He sadi there were no lumps of metal, aside from one pice which he described as like a chip off a tooth.
I said it sounded like his LSD was shagged, but he reckons its all normal for clutch pack type LSDs.
Is he correct? And if he is, what does have to come out of your diff sump plug before you should be alarmed??
andy
ive seen this on XJS'S in the past when i use'd to work on them,it's not uncommon,just drive it till the diff gets noisey.
It's got to be ferrous to stick to the magnet so it's not graphite.
The "chip off a tooth" sounds..... shall I say less than ideal.
I've yet to do an oil change on my powerlocker and will no doubt be shocked by what I find! I'd say if it doesn't make any rumbling/humming/vibrating noise I'd stick it back in and worry about it another day BUT that's just what I'd do. Maybe someone who has worked on the internals of an LSD will comment soon? I read recently that a silvery metallic sparkle to the drained oil is normal. Don't know if that's true or not tho.
Are you as startled by my lack of knowledge as I am?
The "chip off a tooth" sounds..... shall I say less than ideal.
I've yet to do an oil change on my powerlocker and will no doubt be shocked by what I find! I'd say if it doesn't make any rumbling/humming/vibrating noise I'd stick it back in and worry about it another day BUT that's just what I'd do. Maybe someone who has worked on the internals of an LSD will comment soon? I read recently that a silvery metallic sparkle to the drained oil is normal. Don't know if that's true or not tho.
Are you as startled by my lack of knowledge as I am?
All sounds normal to me, as the bearings and gear set wear they give off tiny fragments of ferrous metal, the magnet is just doing it's job of keeping them out of the oil.
The oil has to cope with extreme pressures between the teeth of the gearset, that heats it up and will discolour it after a while.
The oil has to cope with extreme pressures between the teeth of the gearset, that heats it up and will discolour it after a while.
andymadmak said:
I was talking with an engineer friend of mine over the weekend and he was telling me about the oil change he'd just done on the differential of his Jag XJ12 (late 1980s vintage, Limited slip diff). I had always imnagined that diff oil would remain quite clean in operation, given that there are no combustion processes for it to get close to, but my friend said his oil was black when it came out (30k miles since last change) and the diff sump plug (which is magnetic) had a small "xmass tree" of fine metallic (graphite?) powder stuck to it. He sadi there were no lumps of metal, aside from one pice which he described as like a chip off a tooth.
I said it sounded like his LSD was shagged, but he reckons its all normal for clutch pack type LSDs.
Is he correct? And if he is, what does have to come out of your diff sump plug before you should be alarmed??
andy
All diffs will get darkened oil if heated up, and an XJ12 has inboard brakes so it does see some heat.
As far as seeing metallic particles, the ring gear and pinion will shed metal, and you will also get some very small shavings from the plates.
The plates do have a darkened plated surface (I'm pretty sure phosphated to hold oil) and as the oil gets older it will be coloured by the plating.
I don't think there is anything wrong with the diff, my recommendation would be to use a synthetic limited slip diff oil, if you get chatter when turning you can buy a special additive that fixes the chattering without massively affecting effectiveness.
andymadmak said:
I was talking with an engineer friend of mine over the weekend and he was telling me about the oil change he'd just done on the differential of his Jag XJ12 (late 1980s vintage, Limited slip diff). I had always imnagined that diff oil would remain quite clean in operation, given that there are no combustion processes for it to get close to, but my friend said his oil was black when it came out (30k miles since last change) and the diff sump plug (which is magnetic) had a small "xmass tree" of fine metallic (graphite?) powder stuck to it. He sadi there were no lumps of metal, aside from one pice which he described as like a chip off a tooth.
I said it sounded like his LSD was shagged, but he reckons its all normal for clutch pack type LSDs.
Is he correct? And if he is, what does have to come out of your diff sump plug before you should be alarmed??
andy
If a tooth is chipped it will be noisey and will only get worse.
Stop being so soft the lot of ya!
Had to swap a diff in a bobtail rangie in a competition at the weekend and the fluid which came out was a mixture of black, green and brown.
Change it regularly and it will clean out all those little fillings which build up. As long as it is just oil in there, should be ok. It gets interesting when you get water in there and then block the breather. The water boils and the steam can't escape. It then lets go in a stupendous fashion!
Had to swap a diff in a bobtail rangie in a competition at the weekend and the fluid which came out was a mixture of black, green and brown.
Change it regularly and it will clean out all those little fillings which build up. As long as it is just oil in there, should be ok. It gets interesting when you get water in there and then block the breather. The water boils and the steam can't escape. It then lets go in a stupendous fashion!
Deltafox said:
torsen diffs,They're useless
Ill be sure to pass on your criticisms to the pioneers of 4 wheel drive who still use them in their vehicles.
You're welcome. Audi use them because they are cheap, not because they are good. To get things in perspective a Torsen costs about 17 quid over an open diff and a plate diff is about 20.
In the Impreza vs EVO technical war, where performance actually counts, a pressure controlled plate diff is the component of choice. You can get most of the way there with ramps and pawls. Viscous diffs also have merits, as do variants like the BTR Hydratrak, as used in TVRs etc.
Having driven all of them I'd use an ecu controlled pressure plate system if my budget wasn't limited, but in a vehicle programme where the drivers will settle for acceptable I can understand Audi's choice of Torsen. At least it is better for the enthusiast than the FWD based Haldex system.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff