GO
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| posted on 4/2/04 at 10:11 AM |
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testing diffs
whats the easiest way to test the strength of a diff off the car?
For an open diff, if you spin both outputs in opposite directions they'll turn quite happily and the input will remain (pretty much) stationary.
And if you turn them both in the same direction the input will spin.
For an LSD, is it the opposite, so if you spin both outputs in opposite directions - should the input spin. And if you turn them both in the same
direction the input remains stationary??
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Bob C
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| posted on 4/2/04 at 10:41 AM |
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strength of diff - you can't really test this without breaking it...... Your diff will be off a much heavier car so don't worry about
it!
testing LSD - there are at least 3 sorts of LSD & they behave differently. All diffs must do the outputs in opposite directions = input stationary
thing, but it's to some degree harder to do with an LSD. The LSBs I know about are viscous, clutch or gear(torsen, ATB) type. The viscous type I
know are tested by applying a torque to the output with the input locked & seeing how long it takes to rotate a turn (lifted from a mazda workshop
manual) The other sorts do the "locking up" thing when provoked but I don't know how you provoke it - I suspect it will change from
type to type. I'm sure you'll get more info from other forum members.
Cheers
Bob C
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craig1410
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| posted on 4/2/04 at 01:10 PM |
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Go,
quote:
And if you turn them both in the same direction the input remains stationary??
Come on mate, think about this for a minute, if you turn both output in the same direction then this is like your car rolling along normally.
Wouldn't you therefore expect the input shaft to be turning too?  (Unless it's broken of course)
What you probably meant was that if you turn one output with the other output and input free to rotate and the other output turns in the opposite
direction then it is an open diff.
If you turn one output and the other one turns in the same direction then it's an LSD.
The input shaft tends not to turn on an open diff when you do this because due to the dif ratio, the path of least resistance for the torque you are
applying by hand is via the other output shaft. The input shaft will tend to move a little bit but not much. On the LSD, however, if you turn one
output then the other output AND the input shaft will turn.
Hopefully this helps,
Craig.
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GO
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| posted on 4/2/04 at 01:35 PM |
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Craig,
yeah, it didn't seem quite right but I got the thought from the fact that testing the diff on the car, turn one wheel the other turns the same
way - and thinking about it there's nothing to stop the input turning as well (unless its in gear). Whereas for an open diff, being in gear wont
make an difference. Er, think I made sense to myself then.
However, still thinking... it is a different situation to the car rolling along normally, in this case its the input driving the output, not the
output driving the input - which doesn't necessarily automatically follow.
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craig1410
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| posted on 4/2/04 at 09:24 PM |
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Go,
Regarding your last comment, I think you will find that no matter whether the outputs are driving the inputs or vice versa, the ratio of their
rotational speeds will be the same and equal to the diff ratio (assuming that both outputs are going at the same speed).
The point I was making is that IF the outputs are both turning in the same direction then the input shaft MUST be turning and cannot be stationary
unless the diff is well and truly knackered (ie. the pinion or crownwheel is stripped.)
Even though it is a limited slip diff, this does not mean that the pinion is in some way disconnected from the crownwheel, it is just that the two
output shafts are linked together via a mechanism which ensures that the two do not rotate at significantly different speeds.
Cheers,
Craig.
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