Limited-slip indentification

[Willy G]

Thanks to all of you on answering my past questions, and I have a new question. I need to know if I have a "limited-slip" rear end and of course if you can tell me how I can find out.

In the past, on older cars, I have always done the (raise the car up, spin a wheel, both turn same direction is a yes, one wheel spins opposite is a no) but I was told this is not realiable. As you can imagine I did not buy the car new and am wondering if doing the "limited-slip" or posi-trac will effect performance. I currently have the main portion of a posi but would like to know what I have and if limited-slip would be better. Thanks all

68 2K
Seattle

[nomadtrash]

Posi-trac is just a name like Turbo-hydromatic or hydroboost. It should not be confused as a special type of differential. There are a few basic designs of limited slip differentials. The roadster unit is a clutch type limited slip. It has plates and clutches that tie the axles together. Spring pressure on the plates and clutches determine how much torque is required to spin one axle more than the other. The advantage of this type of limited slip is that they provide equal amount of power to both axles all the time. A disadvantage is that they chatter and also promote understeer. Another type of limited slip is a torque biasing design. It uses gears. It is fairly difficult to describe but works off the concept that you cannot drive a worm gear backwards. This type of differential only drives one wheel at a time. The instant that one wheel has less traction the differential puts all the power to the wheel with more traction. The advantage is that you don't have the chattering and understeer. The disadvantage is that you only have one drive wheel. You never get the traction of both wheels at the same time. Anther design is a viscous coupler. It is similar to the torque converter in an automatic transmission. Each axle has a fan on the end that are submerged in fluid. When one fan turns it causes the fluid to turn and then the fluid drives the other fan. These units allow a lot of slippage. There is also a locker which uses a ratcheting mechanism and springs. Torque on the pinion causes the ratchet to engage. When off the throttle the ratchet disengages. When the ratchet it engaged the axles are locked together. This can cause a lot of understeer. It also causes handling problems when the axles lock and unlock. It can be adjusted with different springs to allow earlier or later engagement and disengagement. They make a lot of racket too.

The Roadster has two types of limited slips available. There is a clutch type and a locker. To tell if you have a locker you can hold one wheel steady while turning the other one. That will cause a ratcheting sound. On the clutch type you can jack up one side but leave the other on the ground. With the car in neutral you should not be able to turn the wheel off the ground. You can also raise both wheels and whith it out of gear both wheels should turn the same direction. If it is in gear then you shouldn't be able to turn one wheel.