How do diffs work

Post by **Matt** » Fri Mar 24, 2006 7:01 pm

Hi guys

I think I know how most bits of minors work, but could anyone explain to me how differentials work?

Cheers

Post by **moggyminor16** » Fri Mar 24, 2006 7:33 pm

right a simple why is
the drive comes from teh engine to teh gearbox transported by the prop shaft then to the diff
the drive must be passed throw a 90 degre angle to the wheels but there the problem will start if it was a straight drive to teh wheels at 90 degre then one wheel will wear faster than other or snap teh drive shaft .there for in the diff it helps to take the power to one side mopre than the other depending on which way you are truning .say if you go right the right whell will need to rotate slower than the left side so teh diff will give more power or drive to the left then tyhe right .
i hope you can under stand this it is simple when tou look at it but when you talkabout limited slip diff it gets better but we can save that for a rainy day
mm16

Post by **chickenjohn** » Fri Mar 24, 2006 7:41 pm

It works by "planet gears" on their own shaft rotating around, and thereby walking around, the "sun gears" inside the diff. This allows one axle to turn faster than the other.

Its really difficult to explain in words- best to see an animation or better still, take a diff apart and have a play- all will then be clear!!

Post by **Onne** » Fri Mar 24, 2006 7:45 pm

this might make it a tad clearer

Post by **bmcecosse** » Fri Mar 24, 2006 9:03 pm

I made my first 'diff' with a Meccano Gears set on Christmas Day when I was 10 !! All becomes clear - excellent teaching tool. Still readily available on ebay.

Post by **Onne** » Fri Mar 24, 2006 9:06 pm

I learnt it with Lego! If you have a solid axle (1 piece) you can't steer.

Diff locks do have their advantage in terrain though

Post by **bmcecosse** » Fri Mar 24, 2006 9:12 pm

My autocross Mini had a welded up diff - can't beat that for traction.

Post by **Tris** » Fri Mar 24, 2006 9:13 pm

Yeh learnt about that with the land rover was confusing at the time but you can't live without a diff lock on serious terrain.. you get stuck it turns out

Post by **minor_hickup** » Fri Mar 24, 2006 10:29 pm

Thats whats great about the old landys, although the central diff isnt locked it doesnt allow drive to only one side, so acts like a locking diff. I was never keen on the Range rovers viscous coupling device. I remember my dad and i taking his series II out with him in a range, while he was much faster, but i had to pull him out of mud twice

Post by **Packedup** » Fri Mar 24, 2006 11:08 pm

http://auto.howstuffworks.com/differential3.htm

Sort of makes sense.

Though I still think it's the diff pixies turning the shafts at different speeds, and the whine is them complaining when they've been starved of their diet of gloopy oil...

Post by **Cam** » Sat Mar 25, 2006 12:19 am

Don't be daft. Pixies are far too big. It's Imps in the diff!

Post by **bigginger** » Sat Mar 25, 2006 12:30 am

Matt, get hold of some Meccano or the new fangled clever Lego amd build one - all will become clear

Post by **Peetee** » Sat Mar 25, 2006 10:34 pm

To understand how it works you have to understand that the wheels exert a resistance on the differential. A constant speed is a constant resistance and any change in speed becomes an altered resistance.
When the car starts off the propshaft shaft rotates the crown wheel. The two driveshafts exert the same resistance on the planet gears within the crownwheel so the crownwheel rotates them together. As soon as the resistance on one wheel changes (turning a corner for example effectively slows or resists the inside wheel) the planet gears move independantly of and within the crownwheel.
If you were to see a diff moving while a car was driving down a straight road the planet gears would appear to have no useful purpose - over designed even. If the car was turning a tight bend the planet gears would be whiring away at a great rate of knots.

Post by **bmcecosse** » Sun Mar 26, 2006 12:07 pm

Which is why it is NOT a great idea if stuck in snow/mud to keep one wheel spinning like mad!

Post by **Matt** » Sun Mar 26, 2006 1:27 pm

Thanks guys

I *probably* have a knackered diff so I think I shall take it apart in the summer....

Post by **lowedb** » Mon Mar 27, 2006 1:33 pm

Thats whats great about the old landys, although the central diff isnt locked it doesnt allow drive to only one side, so acts like a locking diff.

Not quite sure what you mean.

Old Old landies didn't have a centre diff at all. They had a 2/4 wheel drive selection.
Prior to the viscous coupling, Landies / Rangies / Discos had a lockable centre diff. I assume this is what you mean However there is still an inherent wekaness that the front / rear diffs won't lock. There are lots of aftermarket options to resolve this though.

I was never clear on the function of the viscous coupling diff. My understanding was that it allowed a small amount of slip, but locked up if too much slip was detected (mechanically I assume, there was no electrical control).

Many centre diffs now use a system known as a Torsen diff, which is mechanical but prevents all the power going front or rear, because of some special gearing rather like worm gears. I've had it explained to me and even had a look at one out of a gearbox, but it still seems a bit like magic! Any comments Ray?