XJ40 Limited slip diff
Discussion
I am totaly rebuilding my xj40 xj12. I have all the rear subframe off and stripped and am replacing all bushes/ bearings/ seals etc. I am not sure whether the diff is working properly or not though, and don't want to start stripping it if it is in fact fine! is there any way of doing this? Both driveshafts rotate the same way and feel well and truly locked together as though the diff is totally solid. Certainly I would expect some types of LSDs to do this but being a viscous clutch type (salisbury powr-lok) I thought that they relied on heat in the diff oil to bind the clutch plates plus reacting to the torque input at the propshaft to tighten it up? Being stone cold with no torque through the prop I thought it would act as an open diff? Or is there a fair bit of preload on the diff? I can't turn the driveshafts opposite ways even with a couple of 2 foot bars through the UJs as leverage.
Does anyone know how this type of diff should feel?
Will post some pics up soon!
Does anyone know how this type of diff should feel?
Will post some pics up soon!
That is what they always feel like.
To test if its working, one wheel on the grass verge one wheel on the tarmac, blast off. If you clay where you are with the wheel on the grass spinning, its not working.
(sorry thats not the most fullish tip while the sub-frame is out of the car) But I can assure you that tight feeling and both wheels seemly locked together is what they were like from new.
To test if its working, one wheel on the grass verge one wheel on the tarmac, blast off. If you clay where you are with the wheel on the grass spinning, its not working.
(sorry thats not the most fullish tip while the sub-frame is out of the car) But I can assure you that tight feeling and both wheels seemly locked together is what they were like from new.
Its not heat that makes a viscous diff work its sheer effect in the fluid, you need a torque wrench to check if a viscous is working right, basically you'll need to find out how much torque it takes to turn one shaft a certain distance at a certain speed while the other is stationary, a Workshop manual may have the figures you need.
http://auto.howstuffworks.com/differential5.htm
http://www.youtube.com/watch?v=KUatvj937c8
http://auto.howstuffworks.com/differential5.htm
http://www.youtube.com/watch?v=KUatvj937c8
Edited by popuptoaster on Tuesday 27th October 21:40
Ah thanks guys, all useful info there. I have researched a little further and all makes perfect sense now.
It would appear that mine is working perfectly well, I didn't have any reason to doubt but just wanted to check while it's off. I'm simply going to replace the pinion and output seals, give it a lick of paint, a fresh load of the correct oil and go for gold.
It would appear that mine is working perfectly well, I didn't have any reason to doubt but just wanted to check while it's off. I'm simply going to replace the pinion and output seals, give it a lick of paint, a fresh load of the correct oil and go for gold.
Out of interest how common are LSD's for the XJ40 and will they fit the shafts etc on a non LSD car?
My 3.2 spins the inside wheel really easy at junctions if the road is wet and will also spin up one wheel on a quick launch as it shifts into second so i've been thinking about a slipper.
what cars have them standard? I may be looking at getting a bigger engined one anyway as i've decided i like mine but the 3.2 isnt fast enough so i either buy another one of find a broken 4 litre to whip the engine out of.
My 3.2 spins the inside wheel really easy at junctions if the road is wet and will also spin up one wheel on a quick launch as it shifts into second so i've been thinking about a slipper.
what cars have them standard? I may be looking at getting a bigger engined one anyway as i've decided i like mine but the 3.2 isnt fast enough so i either buy another one of find a broken 4 litre to whip the engine out of.
popuptoaster said:
Out of interest how common are LSD's for the XJ40 and will they fit the shafts etc on a non LSD car?
My 3.2 spins the inside wheel really easy at junctions if the road is wet and will also spin up one wheel on a quick launch as it shifts into second so i've been thinking about a slipper.
what cars have them standard? I may be looking at getting a bigger engined one anyway as i've decided i like mine but the 3.2 isnt fast enough so i either buy another one of find a broken 4 litre to whip the engine out of.
They're reasonably common. You can spot an LSD diff at the breakers by looking for a coloured square on the rear diff housing, if it has a big black X on it it's a Powrlok diff. The issue for you will be whether the ratio is correct - that's another matter altogether. The half shafts are common so no worries there.My 3.2 spins the inside wheel really easy at junctions if the road is wet and will also spin up one wheel on a quick launch as it shifts into second so i've been thinking about a slipper.
what cars have them standard? I may be looking at getting a bigger engined one anyway as i've decided i like mine but the 3.2 isnt fast enough so i either buy another one of find a broken 4 litre to whip the engine out of.
oversteerxj12 said:
As far as I know LSDs were standard on all 4 litre and 6 litre cars, optional on others.
The diff casing and prop and driveshaft flanges are all the same it's just the innards that are different, and as said they are identified by a coloured square sticker with a black cross.
A limited slip differential was standard on 4 litre XJR XJ40s and all but very late 4 litre Daimlers, but cost extra on all other 4 litre XJ40s (even the 4.0S, though many of them have one) unless they have the sports handling pack. 6 litre cars all had a LSD fitted.The diff casing and prop and driveshaft flanges are all the same it's just the innards that are different, and as said they are identified by a coloured square sticker with a black cross.
David
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