Limited slip and locking differentials
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==Introduction== | ==Introduction== | ||
| − | A limited slip differential is a means to apply power to the ground when traction is limited, by sensing which wheel has traction and applying force to it, while maintaining the wheel speeds to be different when turning instead of only to the wheel that is without traction like how an open | + | A limited slip differential (or "diff") is a means to apply power to the ground when traction is limited, by sensing which wheel has traction and applying force to it, while maintaining the wheel speeds to be different when turning instead of only to the wheel that is without traction like how an open diff works. |
==How to tell an open differential from a limited slip differential (LSD)== | ==How to tell an open differential from a limited slip differential (LSD)== | ||
| − | Under normal conditions if the rear wheels are lifted off the ground and one of these wheels is rotated, an '''open''' | + | Under normal conditions if the rear wheels are lifted off the ground and one of these wheels is rotated, an '''open''' diff will allow the rear wheels rotate in ''opposite'' directions. A '''limited slip''' (or "posi") diff will allow both wheels to rotate in the ''same'' direction, and it will be very difficult to hold one wheel from rotating while the other wheel is being turned. But- a damaged ''open'' diff or a diff that has been converted by using a spool or mini spool, or a diff that has had the spider gears welded (an old school, dangerous "backyard" method to get two-wheel traction all the time) will ALSO allow both wheels to rotate in the same direction. Conversely, a LSD with a bent housing, worn clutches, or galled pinion gears and/or cross shaft may not allow both wheels to rotate in the same direction with the rear wheels off the ground. Ironically, the way many open diffs get that kind of damage is from extended spinning of the single driven wheel. |
| − | Having both rear wheels spin under acceleration is not a positive indication of having a LSD. Under certain circumstances- like when rear wheel traction is identical for both rear tires- an open diff can behave like a LSD. | + | Having both rear wheels spin under acceleration ''is not'' a positive indication of having a LSD. Under certain circumstances- like when rear wheel traction is identical for both rear tires- an open diff can behave like a LSD. |
| − | In some isolated cases like the second generation Pontiac Trans Am, a 10-bolt 8.5" corporate LSD rearend was standard equipment, so they will (except cars specifically ordered with an open rearend) | + | In some isolated cases like the second generation Pontiac Trans Am, a 10-bolt 8.5" corporate LSD rearend was standard equipment, so they will have a LSD if it's original (except cars specifically ordered with an open rearend). |
| − | So, checking | + | So, checking whether a differential is limited slip or not isn't as simple as jacking up the rear of the car and turning the wheels, or seeing if both wheels spin when you hammer it. The only way to be 100% certain of what type of differential is in the rearend is to remove the cover (like in the case of a Salisbury-type rearend) or drop the center section (Hotchkiss-type rearend) and look to see what's inside. |
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Rearend housings will often have codes stamped into the axle tube or center section (depending on make and type of rearend) that can be decoded to give the gear ratio, manufacturer, date of manufacture, LSD or open, etc. Some rearends can be identified as to type by the casting numbers (raised numbers cast into the metal, not stamped), because some rearends use different housings for open and LSD differentials. | Rearend housings will often have codes stamped into the axle tube or center section (depending on make and type of rearend) that can be decoded to give the gear ratio, manufacturer, date of manufacture, LSD or open, etc. Some rearends can be identified as to type by the casting numbers (raised numbers cast into the metal, not stamped), because some rearends use different housings for open and LSD differentials. | ||
| − | Many | + | Many LSD rearends carried tags having info pertaining to the ratio and to use limited slip lube only- a good indicator that the rearend was a posi originally, but of course the rearend or diff could have been changed during the life of the vehicle. |
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Depending on the type and application, there may be some slip allowed, i.e. the two wheels are not connected to one another directly, like in the case of the viscous, clutch, and cone types. In other cases (like the locking-type differentials), the wheels are directly linked while in the locked position. | Depending on the type and application, there may be some slip allowed, i.e. the two wheels are not connected to one another directly, like in the case of the viscous, clutch, and cone types. In other cases (like the locking-type differentials), the wheels are directly linked while in the locked position. | ||
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| + | ==="Lunchbox" locker=== | ||
| + | The lunchbox locker, or "drop-in" locker is a type of automatic locker that replaces the side (axle) gears and spider (pinion) gears (in some/most types) of a diff. The pinion gears referred to '''here''' are NOT the same as the pinion gear that meshes with the ring gear. Instead, they're the smaller gears in the center of the diff that allows the two wheels to rotate at different speeds when turning, etc. | ||
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| + | A lunchbox locker is relatively easy to install, mainly because the original backlash and preload settings are not disturbed during the installation. | ||
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| + | The lunchbox locker will only be as strong as the original carrier and rearend housing. | ||
==Spools== | ==Spools== | ||
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| − | |[[File:Spool.jpg|thumb| | + | |[[File:Spool.jpg|thumb|250px|center|Spool]] |
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