majordad

Had the misfortune to inadvertantly test my Limited Slip Diferential by getting stuck in mud. The front left wheel and the right rear wheel spun while i did not move. The wheels were up to the rims in mud and I used 4wd hi and lo to some engage the other wheels, but no luck. I read somewhere that if you jammed the brake, the other wheel would catch, but that didn't work either. Any ideas???
Thanks in advance

Chillimau

My understanding was to lightly apply the parking brake to get the limited slip to catch... :-

Do you like the Westin bars? I am thinking about them for my truck. The 4" Putco looks really good, but too much $$.

Gary

majordad

If you are going to get the WEstins, get the Platinum series which is chrome over stainless. They will not rust out. it took 1 hour to install by myself. They are great, especially because i need them to step into truck.

I did try to step lightly on brake and then just became frustrated and slammed them, but they still did not catch. Those two tire kept on spinning.

Winr

with limited slip you should not have to apply the E brake, that is for when you Don't have limited slip. If your limited slip is working correctly it should suply the same amount of power to both rear wheels. The only time it will slip is when you havbe equil amount of traction going around turns. Thats haow they have worked for years. Just drove an '03 with limited slip abd worked as just described. Is it possible yours is'nt working or is'nt there ???

Berak

A limited slip differntial cannot supply the same amount of torque to both wheels. A locking differential is the only type that can. Typically a limited slip differential will offer some percentage of the torque to the wheel that has good traction. I've read that is typically 20% of what the slipping wheel would get. Applying the e-brake can offer more torque because it causes the wheel that is spinning to see more resistance (and take more torque to spin), thus the wheel with good traction will also have more torque.

doug

just to be precise, here, a locking diff doesn't guarentee equal power to both wheels, it only guarentees that the two wheels move together. I tend to agree with Winr -- it sounds like you don't have LS at all, or the clutches are worn such that it doesn't work any more.

I'm thinking that an electric actuated locker would be cool on the front diff. that, and a working LS on the rear and you'd get yourself so far into the mud that nobody could get you out . can you add a locker to the AA axles?

majordad

Thanks for the feed back. I remember paying for the Limited Slip so i guess its there. I wouldn't know how to check for it. There isn't a E-Brake or Jake Brake on the truck. As was described to me by the dealer, it transfers power from the wheel that slips to the wheel that grips. The hubs are always locked on the axles because it is always turning, so there isn't any slipping of spindles. I hope this clarifies the conditions.
Still do not understand the why's to the power throughput to the wheels...

erics76

You may want to open the diff and make sure there is a LS for sure. I know a few years ago, a few jeeps slipped out without a LS when the window sticker said they had it.

Crabjoe

A Limited Slip diff will not transfer power from the wheels that slip to the wheels that grip. The waya limited slip works is that if allows drive shaft to power both wheels. But because of a clutch to keep your axle from binding, it will loss power is the traction is not equal or close to equal. Look at it this way, if your making a turn on pavement and stomp on the gas, one of 2 thing will happen, either the inside wheel will spin because all the power is going there or both wheels will spin causing you to fishtail. There is a 3rd option but it only occures if your clutch is burned up. That is the outside wheel will spin. Reguardless, if your stuck and only one of the wheels on the rear axle gets power, apply the break lightly to even out the traction. The brakes will usually allow for power to get to both wheels. I hope I made sense. BTW, if you rutted out the mud and got high centered, you ain't gettin out without a tug from someone else.

erics76

My LS is a POS too, and I know it's got one. I've done the parking brake thing, and it works to some extent. The problem, I think, has to do with the diesel's massive ammount of torque. I don't think the clutches can handle the power and let the diff slip. I had a gas dodge, and it's LS was tight. I guess the only true fix is to pony up the $$ and get a detroit or a selective locker.

doug

[quote author=majordad link=board=20;threadid=18269;start=0#msg171270 date=1060639332]
Thanks for the feed back. I remember paying for the Limited Slip so i guess its there. I wouldn't know how to check for it. There isn't a E-Brake or Jake Brake on the truck. As was described to me by the dealer, it transfers power from the wheel that slips to the wheel that grips. The hubs are always locked on the axles because it is always turning, so there isn't any slipping of spindles. I hope this clarifies the conditions.
Still do not understand the why's to the power throughput to the wheels...
[/quote]

Winr's reference to an "E brake" is the "emergency brake" I believe. The exhaust brake, such as those made by Jacobs, are commonly refered to as an "e-brake", and would have zero effect on how the differential applies power.

as for checking your LS - I think you just did. But this would be a good opportunity to make a personal appointment with your dealer service manager and ask what you are to expect from this LS axle. tell him what happend, and ask him to help you set your expectations, and how to test it.

thinking about this more, deep mud is a pretty severe test for the LS. it could be that you were so burried in mud that the LS clutches were just not applying enough torque to the gripping wheel to break it loose. the LS clutches do have limits and maybe you found them. If Berak's 20% rule is accurate, then clearly the LS axle won't help you when you are in the really deep stuff. Only a locker will help there.

for purposes of understanding the axle operation, think in tems of "force". Like when you lean up against a wall, you apply a force to it. but you apply no power to the wall because the wall doesn't move. Well, similarly, the LS clutches detect a spinning wheel and then they start "leaning on the other wheel" -- they engage to apply a turning/twisting force (torque) to the gripping wheel. I'm just being precise here, in the physics and mathematical sense -- because the term "power" has a particular meaning and requries that the wheel moves (spin). So before it spins, the power is zero to the gripping wheel, and what the LS clutches do is apply spinning force which we call torque. if the force is not enough to spin the wheel, then its just like you leaning on the wall -- force applied but no power because nothing moved.

maybe your LS clutches were indeed applying force (torque) to your stationary wheel but the available force (torque) wasn't enough to spin the tire.

people often miss the fact that in an offroad situation, a 4x4 truck is really only 2 wheel drive -- one front wheel and one rear wheel. Thats when both diffs are "open" (no limited slip or locking going on). Now, when you add LS to the rear you have an improvement over 2 wheel drive but you dont' even have three wheel drive -- remember only a portion of the engine's torque can be transfered from the slipping wheel to the gripping wheel.

Now then if you put in a real locker in your rear axle, then the two rear wheels do not have any differential at all --they are locked together as if there were a solid shaft between them. Then you would have true, 3 wheel drive (2 rear wheels always grip, one front wheel always grips).

Here's how to visualze that fact that when two wheels are locked together, they don't apply the same power to the ground: imagine you are climbing a hill and the right tire is on pavement and the left tire is in really shallow mud (not anything deep -- just a slick surface). A locking axle will guarentee that the left tire won't spin, but that left tire won't be pulling much either --- because it can spin no faster than the gripping wheel. the right tire is doing most of the work but the left wheel contributes whatever traction it can.

What a locker does (and the LS attempts to do) is allow that left tire to contribute something instead of just spinning there doing nothing to move your truck. only the LS can only apply a portion of the available twisting force (torque) to that gripping wheel and if that is not sufficient to break the tire loose or move the truck, then you're still stuck, wanting to blame the LS diff for not doing its job. when really you were expecting it to behave like a locker which it is not.

Berak

Well written Doug. Most people think the LS should act like a locker and are shocked to find themselves in a position where one rear tire is spinning and the other isn't moving. By e-brake we are taling emergency brake in this context.

A locker does provide that both tires always receive the same torque.

I got the 20% figure for limited slips from the HowStuffWorks.com website which has some good information on things like this.

NC_Mog

You don't have to open the diff to determine if you have a LS. Just chock to front wheels, jack up the rear axle (both tires in the air), put the transfer case in neutral and rotate one wheel by hand. If it has a LS, the other will rotate in the same direction. If it has an open diff, the other will rotate in the opposite direction.

bulabula

majordad, I had the same thing happen to me last winter when I ventured out into 21" of snow on a grassy field trying to pull out a chevy 1500 4x4 p/u that was stuck in the snow. Same two wheels were spinning. I verified it by stepping out of the truck with it in gear and looking at them spin. Touching the brakes etc didn't help either. Glad I had a shovel with me. Yep, I've got AS too. I'd hate to think they were worn out at 3000 miles. Remember, they're only "limited slip", not lockers.

I made it out ok, but never did pull the other guy out. He was an Army MP getting ready to ship out for the war and wanted to play in the snow with the kids before he left. He called one of his buddies with the keys to a 5-ton 4x4 Army truck to rescue him.

BTW, I've also got the chrome over SS Westin bars.

doug

[quote author=Berak link=board=20;threadid=18269;start=0#msg171338 date=1060651539]
A locker does provide that both tires always receive the same torque.
[/quote]

yes I know what you mean. So don't take what I'm about to say as a disagreement 'cause I believe you and I are on the same page -- this is just little more precision physics :P

technically speaking, both tires do not receive the same torque -- if they did, then that would mean they would have to contact the ground with the same traction, which of course is a situation of no interest because the locker is not needed. Certainly when that is the case (equal traction to each tire), then absolutely they do receive the same torque --50/50 split as delivered by the engine. But then an open diff would do just fine, then ;D

Anyway, (for the locked axle case), when the left tire's traction to the road is less than that of the right side tire, the left side tire cannot transfer as much resisting force from the road back to the engine. In short, this tire can't "push back" on the engine, so the engine cannot deliver the same torque to it. The tire that pushes back the most (resists the engine) is the one that gets the most torque.

the beauty of the locker is that it guarentees that the tire on the slickest surface will never break loose and spin, thereby loosing friction to the road. it maximizes traction to the ground for each tire and optimizes the ability of the road to "push back" on a pair of tires without regard to which tire has the best traction at the moment. In short, it maximizes torque to the ground for the combination of two tires.

this of course assumes that the driver doesn't slip the tires