Can someone evaluate this LSD description...

[spalind]

for me? It comes from an "off-road" book I am reading and doing a review on and its definition of an LSD sounds wrong, in fact BACKWARD from how I understand an LSD to work...

"A limited-slip differential works like an open differential--up to a point. When either side-to-side towque difference or wheel speed exceeds a certain point, the differential mechanically locks the two wheel shafts together, sending equal amounts of power to both wheels."

Doesn't a limited slip work in the OPPOSITE fashion?? That it stays LOCKED until sufficent force is applied, at which point it lets go or "slips" to prevent damage?? Thats why I thought that TIGHT LSD's will chirp the tires going around corners as it is not "slipping" and is staying locked through the turn...Also why when you get up on three wheels in an LSD vehicle that one wheel may just sit and spin like an open diff as the LSD is transferring all the torque and power to that one wheel with no traction...Please someone correct ME if I'm wrong or confirm for me that the sentence above is wrong...Thanks....

[DailyPedal]

The statement is correct, at low speed the diff is open on most traditional LSDs. As torque and load increase on the driven axle, force is applied to mechanisms inside of diff that then lock the diff to drive the other axle. Remember there are many different forms of LSDs and some are more positive than others. The clutch protected diffs are quieter and have a degree of slip built in but still turn positive with enough force.

[Michael Pee]

I thought you were talking about LSD the drug....DUH

[spalind]

The statement is correct, at low speed the diff is open on most traditional LSDs. As torque and load increase on the driven axle, force is applied to mechanisms inside of diff that then lock the diff to drive the other axle. Remember there are many different forms of LSDs and some are more positive than others. The clutch protected diffs are quieter and have a degree of slip built in but still turn positive with enough force.

Then why does a "tight"er than normal LSD cause the tires to chirp and why does an LSD NOT lock the axle together in a situation where one tire is off the ground and spinning? Are you sure you are not referring to a mechanically locking differential which is different than an LSD?

[spalind]

Then why does a "tight"er than normal LSD cause the tires to chirp and why does an LSD NOT lock the axle together in a situation where one tire is off the ground and spinning? Are you sure you are not referring to a mechanically locking differential which is different than an LSD?

Ahhh...now I understand...an LSD diff starts open then locks when the wheels start spinning at different speeds, then if enough force is applied becomes open again...I was just imagining that it STARTED locked and then just opened at a certain point of force...thanks!!

[jgbjgb]

To make a LSD "tighter" one must increase the preload and increase the number of clutches.

A LSD driving down a straight road "acts like" an open diff, meaning equal power is being sent to each wheel. Now, when the open diff hits a low friction surface, the power is diverted to the path of least resistance, the spinning wheel, and the other just sits there. With the LSD, with both wheels being "locked" when you hit that low friction surface, power is still being sent to both wheels, UNTIL you overpower the clutches and then they will slip. Hence the name.

With one tire off the ground you should still have power going to the opposite tire because of the preload. Unless you have a Torsen worm gear LSD which has 0 preload.

I am running an Eaton Positraction diff in my rear, set up with 800 lb preload springs and 18 steel clutches. If I coast around a corner my tires do not chirp, if I give it the slightest bit of gas, they chirp. Makes for interesting driving in hard pack snow and ice.

[jgbjgb]

Ahhh...now I understand...an LSD diff starts open then locks when the wheels start spinning at different speeds, then if enough force is applied becomes open again...I was just imagining that it STARTED locked and then just opened at a certain point of force...thanks!!

False.....due to the preload, a LSD DOES start out "locked". Depending on amount of preload determines how strong that "lock" is.

A LSD never "becomes" open, the clutches will be overpowered at some point and will slip.

[jgbjgb]

The statement is correct, at low speed the diff is open on most traditional LSDs. As torque and load increase on the driven axle, force is applied to mechanisms inside of diff that then lock the diff to drive the other axle. Remember there are many different forms of LSDs and some are more positive than others. The clutch protected diffs are quieter and have a degree of slip built in but still turn positive with enough force.

Not really.....because of the built in preload on a clutch LSD, at ANY speed the diff is still "locked".

But since you are not increasing the torque load, as in coasting around a corner, the clutches will be over come very easily and you make the turn without tire chirping.

If you increase the torque load by say, accelerating around the corner, the increased torque load will increase the grip of the clutches and this could lead to tire chirping. Again, it all depends on how "tight" you have your LSD set up.


I have had three different rear end set ups in my truck:

original Ford Traction-Lock
Eaton Posi (standard, 14 Carbon Fiber clutches w/400 lb preload)
Eaton Posi (tuned, 18 steel clutches w/800 lb preload)

Each one tighter than the preceding.

[jgbjgb]

To learn more:

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

www.offroaders.com/tech/limited-slip-lockers-differentials.htm

[Samco Fab]

I see the original article written in the book as backward. I think the author of the original article is thinking of a "Gov. Locker" that works with counterweights and other mysterious gismos that lock both tires together when you get single tire spinup or windup, but normally act as an open diff. I have heard the "Gov Locker" is a pretty weak differential in some of the older GM vehicles that they were used in, and would explode under heavy use. They sound to me like some sort of centrifigual clutch setup.

A clutch style limited slip starts off with a certain amount of preload that you can feel if you lift up one tire and try to rotate the tire while the opposite tire is on the ground. If you put a torque wrench on an axle, most limited slips would have approximately 50 to 200 ft. lbs of preload. I have been told by a LSD manufacturer that testing this torque tells you how worn your LSD clutches are.

A Torson Gleasen (sp??) LSD diff like the Trutrac or the Hummer H1 diff, as mentioned earlier does not seem to have much or any initial pre load, I dont quite know how they work:confused: but they are great diffs that lock up really well if you give them preload from your brakes. I have installed Tru tracs in the front of a few Jeep guys that could not afford an air locker, but did not want a Detroit up front. These Jeep guys can lock up a tire in the air completely with brake preload on the diff. This is also known in the Hummer H1 world as "Brake Throttle Modulation"

[jgbjgb]

Which is exactly how ETC (Electronic Traction Control) works, it is an open diff, when one tire starts spinning faster than the other in a low traction situation, the brake modulates via the ABS system on the spinning wheel and sends power to the non spinning wheel.

Not to be confused with an Eaton Electronic Limited Slip Diff, which is in the Jeep Grand Cherokee, Quadra Drive ll, an open diff, when one wheel spins faster than the other in a low traction situation, an electrical current is sent to the LSD and the clutch pack tightens, in theory it can tighten to 100% lock.

The TorSen (Torque Sensing) LSD uses worm gears, not going to go into the particulars, to send power to the opposites wheel. As stated, the older versions do not have any preload.

Yeah, the G80 Gov-Lock has a history of exploding in extreme engagement.

[loufish]

Yeah, the G80 Gov-Lock has a history of exploding in extreme engagement.

You could tell a guy blew one up by looking at his diff cover...It looked like a small grenade went off inside the diff and the cover had dings going out from the flying pieces...
I've welded up a few that actually tore small holes in the cover..