PwrSmoke
Full Access Member
RLDSL is right all the way down the line here, though I do think the Ford Traction Lok is a pretty wimpy piece of hardware (back to that in a minute) What he says about applying some foot brake or parking brake is definitely a great tip and it works for open diffs too. In one of my old Land Rovers I had fitted a turning brake like dune buggies use so I could apply the brakes individually to each of the rear wheels. If the left wheel was spinning, I would brake that wheel and the right would then start pulling. I like using the parking brake (if it applies on the rear wheels) in low speed situations because you are not also increasing the drag (and increasing the amount of traction needed) by applying the front brakes as well.
If you want to hear differential operation in a nutshell, here it is; THE AVERAGE SPEED OF BOTH AXLE SHAFTS IS ALWAYS EQUAL TO THE SPEED OF THE RING GEAR. That means if you are going straight down the road and the ring gear is turning 200 rpm, both shaft are turning at 200 rpm as well... 200+200/2 is 200. When you turn, the inside wheel will slow up and the outside wheel will speed up. The side and spider gears will always make it proportional but the axiom still works: Inside =150 rpm, outside =250 rpm and ring gear is 200. 150+250/2=200. Same thing happens when you have one wheel on ice and the other on dry pavement. Torque will always take the path of least resistance so the tire on ice will spin and the one on pavement will be still. If the ring gear is at 200 rpm, the spinning tire will be at 400 rpm (400+0/2=200). Ok, so then you take that 400 rpm spinning wheel and slow it down to 200 by apply the brake... the other side HAS to speed up to 200 rpm (that or something breaks in the axle) and that grip may be enough to pull you out.
It works on all clutch type limited slips too but what happens is that the limited slip essentially applies some braking force to the spinning wheel and forces the other side to speed up. How much it will or can do that is according to the bias ratio of the unit. A high bias ratio is above 3:1 and a low bias, like most Traction Loks (1.8:1) are under 2.0:1. A high bias LSD unit gets nasty on the street because what works for you in low traction situations works agains you in others.
In a turn, there has to be some biasing side to side to let the outer wheel speed up and the inner to slow down. The LSD tries to resist this. In order to achieve the braking needed for equal traction side to side, the clutch packs are preloaded. In addition, gear separation of the side and spider gears will clamp the clutch plates tighter as well. So in a turn, those clutches need to release smoothly. With a low bias unit, that's pretty easy. With a high bias unit, the braking force in the clutches may exceed tire traction so the tires bark (usually it's the inside tire that is unloaded by weight transfer in a turn). In low traction situations like ice and snow, a high bias unit really bites you in the butt because there isn't enough tire grip to force the diff to bias, so you are operating essentially like a spool. All this is made worse if you apply power because the gear separation forces clamp the clutches even tighter. In ice, a locker is better than a high bias limited slip, because the outer tire (the more loaded one) is able to ratchet ahead mechanically ... so long as you don't apply power, which locks the unit up HARD.
Back to the Traction Lok. Coming from an off-roading background, I tend to dislike any low bias unit because they are so easily overcome by difference in traction side to side. If traction is roughly equal side to side (a muddy road) they are OK, but if you pull off the road and put one tire in the goo and the other is one pavement, that's when the unit is easily overcome and you get trouble. Of course, that's also when you apply the parking brake trick, which you could also do with an open diff. I've found that an LSD with a bias ratio of about 2.5:1 is a perfect combo. Many of the aftermarket units are in that range (Eaton Posi, Auburn HP come to mind). They deliver better performance in low tractions situations but they're not so tight that you run into problems in ice and snow (though you may have some sooner than with the 1.8:1 unit). The best are the gear type LSD, like the TruTrac. This is because they don't have any preload at all, and when you turn, the wheels speed up or slow down as needed with little resistance according to the gearing of the side and element gears in the unit. They to will be more effective when torque is applied but because they don't have preload, they respond well to brake pedal moduataion (that's the term Hummer used to use... Hummer H1s had gear type LSDs at both ends).
Yes, changing the oil, and keeping the right amount of FM in the oil (friction modifier) makes the LSD last longer but with any clutch type LSD, the more you use 'em, that faster they wear out. That means they will wear out quicker in town (lots of turns), or if off road situations, because they are slipping more. Same thing with a manual trans clutch. A guy who always is on the highway may get 200K out of a clutch. Same truck in town might only get 75K. One thing to remember.. a chattering LSD clutch is tearing itself up long term, so keep enough FM in it to prevent that. Some oils have it built in and some high end syns don't always need it because they have such good friction characteristics (that happen to match the parameters of the clutch linings).
If you want to hear differential operation in a nutshell, here it is; THE AVERAGE SPEED OF BOTH AXLE SHAFTS IS ALWAYS EQUAL TO THE SPEED OF THE RING GEAR. That means if you are going straight down the road and the ring gear is turning 200 rpm, both shaft are turning at 200 rpm as well... 200+200/2 is 200. When you turn, the inside wheel will slow up and the outside wheel will speed up. The side and spider gears will always make it proportional but the axiom still works: Inside =150 rpm, outside =250 rpm and ring gear is 200. 150+250/2=200. Same thing happens when you have one wheel on ice and the other on dry pavement. Torque will always take the path of least resistance so the tire on ice will spin and the one on pavement will be still. If the ring gear is at 200 rpm, the spinning tire will be at 400 rpm (400+0/2=200). Ok, so then you take that 400 rpm spinning wheel and slow it down to 200 by apply the brake... the other side HAS to speed up to 200 rpm (that or something breaks in the axle) and that grip may be enough to pull you out.
It works on all clutch type limited slips too but what happens is that the limited slip essentially applies some braking force to the spinning wheel and forces the other side to speed up. How much it will or can do that is according to the bias ratio of the unit. A high bias ratio is above 3:1 and a low bias, like most Traction Loks (1.8:1) are under 2.0:1. A high bias LSD unit gets nasty on the street because what works for you in low traction situations works agains you in others.
In a turn, there has to be some biasing side to side to let the outer wheel speed up and the inner to slow down. The LSD tries to resist this. In order to achieve the braking needed for equal traction side to side, the clutch packs are preloaded. In addition, gear separation of the side and spider gears will clamp the clutch plates tighter as well. So in a turn, those clutches need to release smoothly. With a low bias unit, that's pretty easy. With a high bias unit, the braking force in the clutches may exceed tire traction so the tires bark (usually it's the inside tire that is unloaded by weight transfer in a turn). In low traction situations like ice and snow, a high bias unit really bites you in the butt because there isn't enough tire grip to force the diff to bias, so you are operating essentially like a spool. All this is made worse if you apply power because the gear separation forces clamp the clutches even tighter. In ice, a locker is better than a high bias limited slip, because the outer tire (the more loaded one) is able to ratchet ahead mechanically ... so long as you don't apply power, which locks the unit up HARD.
Back to the Traction Lok. Coming from an off-roading background, I tend to dislike any low bias unit because they are so easily overcome by difference in traction side to side. If traction is roughly equal side to side (a muddy road) they are OK, but if you pull off the road and put one tire in the goo and the other is one pavement, that's when the unit is easily overcome and you get trouble. Of course, that's also when you apply the parking brake trick, which you could also do with an open diff. I've found that an LSD with a bias ratio of about 2.5:1 is a perfect combo. Many of the aftermarket units are in that range (Eaton Posi, Auburn HP come to mind). They deliver better performance in low tractions situations but they're not so tight that you run into problems in ice and snow (though you may have some sooner than with the 1.8:1 unit). The best are the gear type LSD, like the TruTrac. This is because they don't have any preload at all, and when you turn, the wheels speed up or slow down as needed with little resistance according to the gearing of the side and element gears in the unit. They to will be more effective when torque is applied but because they don't have preload, they respond well to brake pedal moduataion (that's the term Hummer used to use... Hummer H1s had gear type LSDs at both ends).
Yes, changing the oil, and keeping the right amount of FM in the oil (friction modifier) makes the LSD last longer but with any clutch type LSD, the more you use 'em, that faster they wear out. That means they will wear out quicker in town (lots of turns), or if off road situations, because they are slipping more. Same thing with a manual trans clutch. A guy who always is on the highway may get 200K out of a clutch. Same truck in town might only get 75K. One thing to remember.. a chattering LSD clutch is tearing itself up long term, so keep enough FM in it to prevent that. Some oils have it built in and some high end syns don't always need it because they have such good friction characteristics (that happen to match the parameters of the clutch linings).
