Patrolman
March 31st, 2009, 08:48 PM
Found this in the December issue of Off-Road Adventures (free mag from 4 Wheel Parts). This has been pasted from their site:
E-BRAKE LOCKER
I was told that if I set my parking brake just about half-way that it almost locks the rear end and aids traction. Is this tip true?
Jeff Young Orange County, CA
Well, it’s not true that it turns your axle into a “locker,” but it does help a little, especially if you already have a limited slip. The first rule of differential operation is that the average of the two wheel speeds will always equal ring gear speed. That applies just as much as when the vehicle is going straight, turning or stuck with one wheel spinning. Let’s say the ring gear is at 100 rpms for all the following examples. Going straight, the ring gear and both wheels are all at the same speed (100+100/2=100). In a turn, one wheel speeds up and the other slows down but if you average them, they are still equal (125+75/2=100). With one wheel on a rock and the other in goo, the spinning wheel will spin at twice the ring gear speed but averaged by two wheels, the rule still applies (200/2=100). The other differential constant is that torque takes the path of least resistance and flows to the tire with the least traction. The limited slip type diff works on the principle that if you apply some braking to that low traction tire it has to transfer some torque to the other side. Most limited slips do that with clutches splined to each axle to supply that braking force. If you slow that 200 rpm spinning tire from the example above to 150 rpm, then the other tire will now have 50 rpms more(and some torque) to play with. That’s what the parking brake does, it slows the loose tire down and helps transfer some torque to the other side. This works especially well with low bias (loose) factory style limited slips, when the difference in traction side to side exceeds the built in braking action of the clutches. The partially applied parking brake augments it. Back in the “old days” ‘wheelers would separate the two parking brake cables and put a handle on each. If the right wheel started to spin, they’d pull up on that handle and slow the wheel down, transferring some torque to the other side. Obviously, applying the parking brake will have limited effects and should be done only short term, but it’s a timetested trick that works. It does NOT work on true lockers, only open diffs and limited slips.
E-BRAKE LOCKER
I was told that if I set my parking brake just about half-way that it almost locks the rear end and aids traction. Is this tip true?
Jeff Young Orange County, CA
Well, it’s not true that it turns your axle into a “locker,” but it does help a little, especially if you already have a limited slip. The first rule of differential operation is that the average of the two wheel speeds will always equal ring gear speed. That applies just as much as when the vehicle is going straight, turning or stuck with one wheel spinning. Let’s say the ring gear is at 100 rpms for all the following examples. Going straight, the ring gear and both wheels are all at the same speed (100+100/2=100). In a turn, one wheel speeds up and the other slows down but if you average them, they are still equal (125+75/2=100). With one wheel on a rock and the other in goo, the spinning wheel will spin at twice the ring gear speed but averaged by two wheels, the rule still applies (200/2=100). The other differential constant is that torque takes the path of least resistance and flows to the tire with the least traction. The limited slip type diff works on the principle that if you apply some braking to that low traction tire it has to transfer some torque to the other side. Most limited slips do that with clutches splined to each axle to supply that braking force. If you slow that 200 rpm spinning tire from the example above to 150 rpm, then the other tire will now have 50 rpms more(and some torque) to play with. That’s what the parking brake does, it slows the loose tire down and helps transfer some torque to the other side. This works especially well with low bias (loose) factory style limited slips, when the difference in traction side to side exceeds the built in braking action of the clutches. The partially applied parking brake augments it. Back in the “old days” ‘wheelers would separate the two parking brake cables and put a handle on each. If the right wheel started to spin, they’d pull up on that handle and slow the wheel down, transferring some torque to the other side. Obviously, applying the parking brake will have limited effects and should be done only short term, but it’s a timetested trick that works. It does NOT work on true lockers, only open diffs and limited slips.