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Note: If you’re likely to change your rear diff liquid yourself, (or you plan on starting the diff up for assistance) before you allow fluid out, make sure the fill port could be opened. Absolutely nothing worse than letting liquid out and having no way of getting new fluid back.
FWD final drives are extremely simple in comparison to RWD set-ups. Almost all FWD engines are transverse installed, which implies that rotational torque is created parallel to the path that the tires must rotate. There is no need to change/pivot the path of rotation in the final drive. The ultimate drive pinion equipment will sit on the end of the output shaft. (multiple output shafts and pinion gears are possible) The pinion gear(s) will mesh with the ultimate drive ring gear. In almost all situations the pinion and ring gear could have helical cut teeth just like the remaining transmission/transaxle. The pinion equipment will be smaller and have a much lower tooth count than the ring gear. This produces the final drive ratio. The band equipment will drive the differential. (Final wheel drive differential operation will be explained in the differential section of this article) Rotational torque is sent to the front tires through CV shafts. (CV shafts are commonly referred to as axles)
An open differential is the most common type of differential within passenger vehicles today. It is definitely a very simple (cheap) design that uses 4 gears (sometimes 6), that are referred to as spider gears, to drive the axle shafts but also permit them to rotate at different speeds if required. “Spider gears” is a slang term that is commonly used to spell it out all the differential gears. There are two different types of spider gears, the differential pinion gears and the axle side gears. The differential case (not housing) gets rotational torque through the ring equipment and uses it to operate a vehicle the differential pin. The differential pinion gears trip on this pin and so are driven by it. Rotational torpue is 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 absolutely no differential action and the differential pinion gears only will drive the axle aspect gears. If the vehicle enters a switch, the outer wheel must rotate quicker than the inside wheel. The differential pinion gears will start to rotate as they drive the axle side gears, allowing the external wheel to speed up and the inside wheel to decelerate. This design works well so long as both of the powered wheels possess traction. If one wheel doesn’t have enough traction, rotational torque will follow the path of least level of resistance and the wheel with small traction will spin as the wheel with traction will not rotate at all. Because the wheel with traction is not rotating, the automobile cannot move.
Limited-slip differentials limit the quantity of differential actions allowed. If one wheel starts spinning excessively faster compared to the other (more so than durring normal cornering), an LSD will limit the rate difference. This is an advantage over a regular open differential design. If one drive wheel looses traction, the LSD action allows the wheel with traction to get rotational torque and invite the vehicle to move. There are several different designs currently in use today. Some work better than others based on the application.
Clutch style LSDs are based on a open up differential design. They possess a separate clutch pack on each of the axle part gears or axle shafts within the final drive housing. Clutch discs sit down between your 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 separate the clutch discs. Springs place pressure on the axle aspect gears which put pressure on the clutch. If an axle shaft wants to spin faster or slower than the differential case, it must overcome the clutch to do so. If one axle shaft attempts to rotate faster than the differential case then the other will attempt to rotate slower. Both clutches will withstand this action. As the rate difference increases, it turns into harder to overcome the clutches. When the automobile is making a tight turn at low velocity (parking), the clutches offer little level of resistance. When one drive wheel looses traction and all of the torque goes to that wheel, the clutches resistance becomes much more obvious and the wheel with traction will rotate at (close to) the rate of the differential case. This kind of differential will most likely require a special type of liquid or some type of additive. If the liquid isn’t changed at the correct intervals, the clutches may become less effective. Resulting in little to no LSD action. Fluid change intervals vary between applications. There is usually nothing wrong with this style, but remember that they are just as strong as an ordinary open differential.
Solid/spool differentials are mostly used in drag racing. Solid differentials, like the name implies, are completely solid and will not really enable any difference in drive wheel acceleration. The drive wheels at all times rotate at the same acceleration, even in a switch. This is not a concern on a drag race vehicle as drag vehicles are generating in a straight line 99% of the time. This may also be an advantage for cars that are getting set-up for drifting. A welded differential is a regular open differential which has experienced the spider gears welded to create a solid differential. Solid differentials certainly are a good modification for vehicles made for track use. For street make use of, a LSD option will be advisable over a solid differential. Every switch a vehicle takes will cause the axles to wind-up and tire slippage. This is most obvious when driving through a slower turn (parking). The effect is accelerated tire wear in addition to premature axle failure. One big benefit of the solid differential over the other styles is its strength. Since torque is applied right to each axle, there is no spider gears, which are the weak point of open differentials.