Note: If you are going to change your rear diff liquid yourself, (or you intend on opening the diff up for program) before you allow fluid out, make sure the fill port can be opened. Absolutely nothing worse than letting liquid out and having no way of getting new fluid back.
FWD final drives are very simple in comparison to RWD set-ups. Almost all FWD engines are transverse installed, which implies that rotational torque is established parallel to the direction that the tires must rotate. You don’t have to alter/pivot the direction of rotation in the final drive. The final drive pinion equipment will sit on the end of the output shaft. (multiple output shafts and pinion gears are possible) The pinion equipment(s) will mesh with the ultimate drive ring gear. In almost all cases the pinion and ring gear could have helical cut the teeth just like the rest of the transmission/transaxle. The pinion equipment will be smaller and have a much lower tooth count Final wheel drive compared to the ring gear. This produces the ultimate drive ratio. The ring gear will drive the differential. (Differential operation will be explained in the differential portion of this content) Rotational torque is sent to the front tires through CV shafts. (CV shafts are generally known as axles)
An open differential is the most common type of differential found in passenger cars and trucks today. It is definitely a simple (cheap) style that uses 4 gears (sometimes 6), that are referred to as spider gears, to drive the axle shafts but also allow them to rotate at different speeds if required. “Spider gears” is a slang term that is commonly used to describe all the differential gears. There are two different types of spider gears, the differential pinion gears and the axle aspect gears. The differential case (not casing) receives rotational torque through the ring equipment and uses it to drive the differential pin. The differential pinion gears trip on this pin and so are driven because of it. Rotational torpue is definitely then used in the axle side gears and out through the CV shafts/axle shafts to the wheels. If the vehicle is travelling in a directly line, there is no differential action and the differential pinion gears only will drive the axle part gears. If the automobile enters a turn, the outer wheel must rotate faster than the inside wheel. The differential pinion gears will begin to rotate as they drive the axle side gears, allowing the external wheel to increase and the inside wheel to slow down. This design is effective provided that both of the powered wheels have traction. If one wheel does not have enough traction, rotational torque will follow the path of least resistance and the wheel with small traction will spin while the wheel with traction will not rotate at all. Because the wheel with traction is not rotating, the vehicle cannot move.
Limited-slip differentials limit the amount of differential action allowed. If one wheel starts spinning excessively faster compared to the other (more so than durring regular cornering), an LSD will limit the acceleration difference. This is an advantage over a regular open differential design. If one drive wheel looses traction, the LSD action will allow the wheel with traction to obtain rotational torque and allow the vehicle to move. There are several different designs currently in use today. Some are better than others based on the application.
Clutch style LSDs derive from a open differential design. They possess a separate clutch pack on each one of the axle side gears or axle shafts within the final drive housing. Clutch discs sit between the axle shafts’ splines and the differential case. Half of the discs are splined to the axle shaft and the others are splined to the differential case. Friction material is used to split up the clutch discs. Springs place strain on the axle aspect gears which put strain on the clutch. If an axle shaft really wants to spin faster or slower than the differential case, it must get over the clutch to take action. If one axle shaft attempts to rotate faster than the differential case then your other will attempt to rotate slower. Both clutches will withstand this step. As the speed difference increases, it becomes harder to get over the clutches. When the automobile is making a good turn at low acceleration (parking), the clutches provide little level of resistance. When one drive wheel looses traction and all the torque goes to that wheel, the clutches resistance becomes a lot more apparent and the wheel with traction will rotate at (close to) the rate of the differential case. This type of differential will likely require a special type of liquid or some type of additive. If the fluid isn’t changed at the correct intervals, the clutches can become less effective. Leading to small to no LSD action. Fluid change intervals differ between applications. There is certainly nothing incorrect with this style, but keep in mind that they are only as strong as an ordinary open differential.
Solid/spool differentials are mostly used in drag racing. Solid differentials, like the name implies, are totally solid and will not enable any difference in drive wheel velocity. The drive wheels usually rotate at the same swiftness, even in a switch. This is not a concern on a drag race vehicle as drag automobiles are generating in a straight line 99% of that time period. This can also be an advantage for cars that are being set-up for drifting. A welded differential is a regular open differential which has had the spider gears welded to create a solid differential. Solid differentials are a good modification for vehicles created for track use. For street use, a LSD option will be advisable over a good differential. Every change a vehicle takes will cause the axles to wind-up and tire slippage. This is most visible when generating through a gradual turn (parking). The effect is accelerated tire use along with premature axle failure. One big benefit of the solid differential over the other types is its strength. Since torque is applied right to each axle, there is absolutely no spider gears, which will be the weak spot of open differentials.