Gear Box and Drivetrain
>Gear boxes. Gear boxes go bad due to low gear oil ( not too common find but not impossible ), but mainly improper shifting, causing gears to grind. Grinding gears will result in grinded gear teeth, sticking gears, premature wear and tare on needle bearings, main bearings, shafts, destroyed Synchromeshs ( these are used to slow the spinning gear down during shifting ), causing stiff shifting, sticking shifting or jumping out of gear.
Due to the amount of internal parts the gear box can be very noisy. Worn clutch pressure plates, clutch friction plates, bad Flywheel and clutch release bearings will also create noise. Bearings squeal during shift, friction plate slips because its worn or the pressure plate surface is worn. They become bad by high mileage/hours, hot dogging it. Ridding the clutch. This will result in possible slippage, noise, gas mileage loss or power loss because the friction plate slips at certain speed ( the engine is revving for 50kmh. but that trans is turning for 35Kmh because the clutch friction plate is slipping between the clutch pressure plate and fly wheel ).
* How dose a clutch do all that? Easy.
*You press the clutch pedal, this moves a slave cylinder, moves a clutch fork, and presses the release bearing, that slide and press force against the diaphragm spring on the presser plate ( that detail many finger object in the center the bearing attaches to ) that is pressing force back, which release the squeeze pressure from the friction disc. This assemble is attached to the fly wheel on the back of the engine that the starter uses to turn the engine over to start the car. so it is always spinning.
*So the bearing is spinning holding force and getting hot, gear is shifted which stops the clutch because the gearbox is “In Gear”, releasing the clutch pedal to reapply the squeeze pressure to the clutch friction plate cause a brief slip because it has to move a 10,000 pound car, and then full engagement and off the car drives away normally. So with all that neat stuff, yeah it could be destroyed. Race cars and drag cars are made for heavy shifting and beating on, not a factory available to the public car.
>Differential. Differential makes noises when driven with low gear oil. Similar to the gearbox. Also you can heat up bearing, the ring gear, pinion and spider gears. This is usually a result of hot dogging the car by over spinning the tires, but low gear oil will also get the same result but takes longer, just hot dogging the car is faster or instant. This will result in possible Noise, premature wear and tare stress on drive axles.
*It’s not a engine, how dose it get low gear oil? On the top of the case is a breather line or cap. It is to relieve pressure out of the gear case when it gets hot from normal driving condition. When this gets plugged, pressure can’t ventilate out. So it builds enough and forces its way out through the axle seal or gasket. Now it is leaking as it is used until there is not enough gear oil to leak out. Now your problems began if they haven’t already…
>CVC Drive axles on the modern car uses CVC joints. This is so it can pivot up and down and turn right and left in front wheel drive cars, and on rear wheel cars to be able to sit on a angle and pivot up and down. When they go bad, they have play, once they have play, they can be noisy too. Front drive axles get louder because they have to pivot not only for up and down but a harder pivot for turning left and right. This is why they get louder when they turn and quieter when they are straight.
During turning, the joint is binding and popping under the stress of the road condition and the power out put to the wheels as well as the shifting weight of the car. They go bad for one very popular reason. The rubber boot that covers the joint either tears, cracks or comes off from their seal ridge. Causing road dirt, water and the environment to ruin the grease and make the bearings rub against each other causing friction.
Rubber boots fail from age or a improper tow. Because the tow truck driver used hooks that pressed against the boot instead of the correct tie down attachment, or the wheel took a direct hit and this compressed the drive axle CVC joint in a manner it is not design to do. This will result in possible noise for rear wheel drive cars, and front wheel drive cars noise, and louder noise during turning and binding.
*The rear wheels? Yeah the rear wheels. Some cars use independent suspension. So the Differential is fixed to the body. Sport cars use this system for better handling and power in turns and a better alignment for the drive shaft to the Differential. Torque loss is possible on a drive shaft that is fitted on a car with a Differential that moves as part of the rear suspension. Because your diverting power to the first cross and roller, than making it turn on a angle to the next, and then turn on another angle to get to the Differential. During this process the cross and rollers are under the most load of stress of the power travel. But if you have a fixed Differential using independent suspension, Then the torque transfer is better and the cross and rollers have less load stress, which is now placed in the CVC joint were it can handle it better.
*If the wheel took a direct hit, the wheel and suspension damage will be present regardless front or rear.
>Drive Shaft. When drive shafts go bad because the use a cross roller style bearings at each end. This allows pivoting in rear wheel drive cars, so the shaft can move up and down when going over bumps. With out effecting the gear box. Drive shafts go bad due to lack of grease to the cross and roller, or When they receive a direct hit some place on the drive train causing it to bend or compress the cross and roller bearings in a manner they are not design for, abuse, Or due to Mileage/hours. When they go bad they make a clicking noise, the worse they get, more the risk of the cross and roller risks of breaking and ejecting the drive shaft.
*On some cars that have drive shafts you will see a small plate bolted to the body just under the drive shaft. This is a emergency catch, if the cross and roller fails, and under a load they tend to fail badly, this catch plate is suppose to prevent the drive shaft from ejecting from under the car. The out come is very aggressive, Your talking about a sudden release of power in a single blow.
*It is ideal when changing oil to grease the cross and rollers beside the front suspension by filling through the grease zerks/plugs. When pupping grease into a grease zerk on a cross and roller, what your looking for is what happen when the grease starts to seep past the seal, nothing or did it shift, and if it shift how bad. Also can you make the shaft shift by wiggling it? This is important because it is a sign of worn bearings, the more the worst. Using inspection mode would be simulating this action.