Note: If you’re going to change your back diff liquid yourself, (or you intend on starting the diff up for program) before you allow fluid out, make certain the fill port can be opened. Absolutely nothing worse than letting liquid out and then 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 means that rotational torque is created parallel to the path that the tires must rotate. You don’t have to modify/pivot the path of rotation in the ultimate 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 gear(s) will mesh with the ultimate drive ring gear. In almost all cases the pinion and ring gear could have helical cut tooth just like the rest of the transmission/transaxle. The pinion equipment will be smaller and have a much lower tooth count than the ring gear. This produces the ultimate drive ratio. The band equipment will drive the differential. (Differential procedure will be described in the differential portion of this content) Rotational torque is sent to the front wheels through CV shafts. (CV shafts are generally known as axles)
An open up differential is the most typical type of differential within passenger vehicles today. It is usually a simple (cheap) design that uses 4 gears (sometimes 6), that are known as spider gears, to operate a vehicle the axle shafts but also allow them to rotate at different speeds if required. “Spider gears” is certainly a slang term that is commonly used to describe all the differential gears. There are two various kinds of spider gears, the differential pinion gears and the axle aspect gears. The differential case (not housing) gets rotational torque through the ring gear and uses it to operate a vehicle the differential pin. The differential pinion gears trip upon this pin and so are driven because of it. Rotational torpue is usually then used in the axle aspect gears and out through the CV shafts/axle shafts to the tires. If the vehicle is travelling in a directly line, there is absolutely no differential action and the differential pinion gears will simply drive the axle side gears. If the vehicle enters a convert, the outer wheel must rotate faster than the inside wheel. The differential pinion gears will start to rotate because they drive the axle aspect gears, allowing the outer wheel to speed up and the inside wheel to slow down. This design works well so long as both of the driven 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 as the wheel with traction will not rotate at all. Because the wheel with traction isn’t rotating, the automobile cannot move.
Limited-slip differentials limit the amount of differential action allowed. If one wheel starts spinning excessively faster compared to the other (way more than durring regular cornering), an LSD will limit the rate difference. This is an advantage over a normal open differential design. If one drive wheel looses traction, the LSD action will allow the wheel with traction to get rotational torque and allow the vehicle to move. There are many different designs currently used today. Some work better than others depending 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 others are splined to the differential case. Friction material is used to split up the clutch discs. Springs put strain on the axle part gears which put strain on the clutch. If an axle shaft really wants to spin faster or slower than the differential case, it must conquer 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 resist this action. As the Final wheel drive swiftness difference increases, it turns into harder to get over the clutches. When the vehicle is making a tight turn at low velocity (parking), the clutches provide little 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 most likely require a special type of liquid or some form of additive. If the liquid isn’t changed at the proper intervals, the clutches can become less effective. Leading to little to no LSD action. Fluid change intervals vary between applications. There can be nothing wrong with this design, but keep in mind that they are only as strong as an ordinary open differential.
Solid/spool differentials are mostly found in drag racing. Solid differentials, like the name implies, are totally solid and will not really enable any difference in drive wheel speed. The drive wheels constantly rotate at the same acceleration, even in a change. This is not an issue on a drag race vehicle as drag automobiles are traveling in a directly line 99% of that time period. This may also be an edge for vehicles that are being set-up for drifting. A welded differential is a regular open differential that has acquired the spider gears welded to make a solid differential. Solid differentials are a good modification for vehicles designed for track use. For street use, a LSD option will be advisable over a good differential. Every turn a vehicle takes will cause the axles to wind-up and tire slippage. This is most visible when traveling through a slower turn (parking). The effect is accelerated tire use and also premature axle failure. One big advantage of the solid differential over the other styles is its strength. Since torque is applied right to each axle, there is absolutely no spider gears, which will be the weak point of open differentials.