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Types of LSD diffs and varios tests


Gaz

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Even open diffs can drive both wheels the same way. It's not until you put load onto them that you can see LSD or not. This is because a little bit of drag friction of the gears inside can cause both wheels to turn same way when not loaded. When you put the load on, the load overcomes the friction and then change speed.

Some LSD's, when you jack one wheel up and turn the flange, it will drive the car off the jack....ie...both wheels trying to drive under load. However early and sometimes cheap LSD's used a clutch pack to distribute the drive....and clutches can slip and/or wear so this is not fullproof.

This would be my best guess at testing for an LSD if anyone cares.

-Get people on each wheel.

-Get a third person on the diff flange

-Turn the diff flange quite smoothly and as fast as you can for quite a while.

-Both wheels should be turning at same speed.

-Then get one person to see if they can stop one wheel.

-The guy turning the flange will have to be strong and keep going, trying to keep the speed constant

- Person on the other wheel should notice his wheel slowing down.

This should work because the one who is trying to stop his wheel, shouldn't be able to because the LSD will sense that that wheel has more grip and will keep the load going to it but the free one will have less load and the LSD should reduce the load going to it

Q. ok i though clutchpack lsd's were good and vicous ones were shit of the locking action ..is there another type im missing>>?

A. Viscous LSDs arnt as efficient as mechanical types. They lose some power. They are way less maintence tho and wont break down as much. Just gotta make sure you change the fluid more. I think they are also smoother.

Clucth type ones often need rebuilding. I think some of the hardout drifters use viscous.

Another type of mechanical diff is a helical LSDs.

There is also differant typs of LSDs. Below stolen from some site.

1.5 Way

Primarily applied during acceleration but also applied slightly during deceleration. Improves drive out of the

corner and increase stability under heavy braking. The benefits are easily harnessed by anyone and this is

perhaps the most effective type of LSD.

2 Way

Increases traction under acceleration and braking but also makes the car less willing to turn. Requires a

chassis set up which promotes easy steering and requires a good driving technique.

Variable LSD

It is possible to adjust the strength of the LSD effect under acceleration and deceleration. It is possible to

make big changes to the handling balance of the car.

Active Yaw Control

Adjusts the amount of torque distributed between the left and right side. By increasing the effect of the AYC a

turning moment i produced enabling the car to turn more effectively. However if the effect is too much the car

can become very oversteery

Q. Jack the car both wheels up one person holds one wheel the other person trys to turn the other. If its hard to slip the LSD is in good shape if its easy its fairly worn if you cant make it slip its awsome.

Not really. if its ever been pulled apart then they can change how much and when the slip would come in etc.

A. If its a clucth type LSD then this MAY work. Lift both wheels of ground and spin one. If the other wheel does not turn or turns the same direction that points to having a clutch type LSD. This would only work on the clutch type LSD.

The Fluid or Viscous uses this test. One wheel turned one direction, then reveresed and turned and then reveresed back again and turned, then the rear should lock up and both wheels turn.

All depends on the type of LSD you have,.

Locked is when the spider gears are welded to the side gears which makes both wheels spin at the same time no matter what.

Q. You dont want this. Why?

A. Because when you go around corners the outer wheel has to travel more than the inner. Therfore the inner wheel will drag (as it HAS to spin at same time as outer) so ya get mad understeer or if you hit the gas mad tail steer

Locked = good for straight line drag racing. If your axles can hold up to it.

Adjusting the breakaway pressure

The breakaway pressure can be adjusted by putting shims between the end of the disk/clutch stack and the case end plate. Putting in a thicker shim increases what is called the "preload" or the initial pressure on the disk/clutch stack. If you have the type with all flat disks and clutches, don't get too carried away with shims, because a little bit will make a big change. If you really intend to do this right, you will need a micrometer or at least a very accurate caliper. Be sure you measure each friction disk and plate separately, and keep notes. If you can't dial in the right breakaway pressure with shims, you can selectively change disks and plates to get the right combination.

Breakaway Pressure

What the heck is "breakaway pressure" anyway? The breakaway pressure is the amount of torque required to make the plates and disks slip. In practice, it is the torque generated between the rear tires when they try to go different distances. If you put a torque wrench on one axle shaft and lock the other one in place, then apply torque, the axle won't move until a certain pressure is reached. Then the axle will start to rotate, showing a constant torque resistance. That's the breakaway pressure. More on how to test this later.

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  • 1 month later...

a weak clutch type lsd can often be checked by having both wheels jacked up and free. turn one wheel lightly and watch if the other one tries to spin the same way or opposite way.. often a weak clutch lsd starts to spin same way but then switches to opposite way. an open diff will immediately try spin in opposite direction. this obviously wont work if your drums are a bit tight! if the wheels keep spinning same way (gearbox in neutral).. chuck it in 1st gear and try again and see how hard it is to spin one wheel before the clutch pack breaks friction and other wheel spins opposite direction. if your clutch type lsd is any good you wont be able to break friction by spinning an axle flange by hand with it in gear or driveshaft clamped to stop it spinning.

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