Читать книгу Chevy Differentials - Jefferson Bryant - Страница 10
ОглавлениеThe disassembly procedure for both Chevy 10- and 12-bolt rear differentials is virtually the same. You do not need to be concerned with getting it out of alignment. As long as you take the proper steps to ensure that the shims go back in the correct location, the entire unit can be disassembled, cleaned, and inspected, with the exception of the pinion gear. In both units the pinion gear uses a crush sleeve to set the preload on the bearings and removing it requires the installation of a new crush sleeve. So, consider this fair warning.
Although other components do not have to be aligned, you need to keep the inner pinion bearing properly aligned. This bearing is pressed on and removing the bearing instantly changes alignment. Don’t remove the bearing unless you are replacing it.
Once the axle shafts have been removed, you can lift the ring gear and carrier out of the center section. Then the carrier disassembly can commence.
You can work with the axle assembly in the vehicle or on the bench. It really doesn’t matter which. There are drawbacks and advantages to both, especially in the set-up phase. Most applications require removing only a few extra bolts to the get the housing out of the vehicle. If you are performing a complete overhaul, taking the housing out of the chassis allows you to clean and paint the housing. However, it’s your decision whether or not to unbolt the axle from the chassis. Here are some of the pros and cons you must consider.
If you have the use of a lift, you can more easily remove the entire housing because you aren’t on your back under the car to complete the procedure. If you do not have a lift, you need to jack up the car and place it on jackstands. Removal is a bit more difficult. However, removing the housing is often the best way to go because it’s much easier to work on the entire housing on a bench or stand rather than still installed in the car.
Limited-Slip or Open Differential?
You need to determine which differential is in your vehicle. One of the most common questions when looking at an axle assembly is, “Do I have a Posi-Traction (limited-slip) or an open carrier?” There are several ways to answer this question. Most gearheads use the common burnout method: Do a burnout, and if you get two black stripes, you have a working Posi-Traction carrier. This doesn’t always work, however. Posi-Traction is a limited-slip design, and over time, the clutches wear out and function essentially as an open carrier.
Another simple test is to jack up the back of the vehicle with the wheels off the ground and the transmission in neutral. Spin the tire and watch which direction the other wheel turns. If it spins in the same direction, it is a Posi. If it spins in the opposite direction, it is an open carrier. Without a load on the clutches, even a worn Posi carrier should function in this manner.
To conclusively determine the type of differential, you can always open the housing and look at the carrier itself. In certain situations, this is the only way to know for sure. Open carriers have four spider gears and a crossbolt. GM Posi units usually have four spider gears, a crossbolt, and a pair of S-shaped springs with a set of four coil springs between two plates in the center of the carrier.
Most axle assembly issues make noise when in operation. Howling, clunking, or banging indicates different issues inside the axle housing. Many signs can tell you that the differential is worn out and may be close to failing. The following is a brief list of signs and their general cause.
Leaks
A small pool of gear oil on the ground by the rear tires or a greasy wheel/tire is a sure sign of a bad axle seal. Often, worn axle bearings cause this condition. You can tell it is gear oil by the color and smell. Gear oil is always dark and it smells horrible. There is nothing else like it.
Don’t just replace the seals, you should go ahead and replace the bearings too. If you ignore this sign, the bearing could lock up, which will also lock up that wheel, destroy the tire, break or bend the axle, and possibly wreck the vehicle.
Groaning or Howling
Two things typically cause these sounds: worn bearings or gears out of mesh. Gears usually howl when they have not been set up correctly. In most cases, this is a result of too little or too much backlash as well as not correctly setting the preload on the pinion bearings. Unfortunately, an incorrectly set up differential will damage the ring-and-pinion gears within a hundred miles or so, and correctly resetting the backlash does not eliminate the howling. If the howling appears after many years of use, a worn or damaged bearing is most likely creating the noise.
Six bearings are installed in GM 10- and 12-bolt rear axle assemblies. Two bearings are in the axle ends, two are in the differential carrier bearings, and two are in the pinion bearings.
Knocking or Banging
Worn bearings or improper gear adjustments most often create these noises. Keep in mind that worn-out U-joints in the driveline can also cause clunking sounds; inspect those first to eliminate that possibility. Does the noise happen when shifting, under a load, or when letting off the gas? The following tests can help you localize the issue. It is best to perform these tests on a clear stretch of road without other vehicles around.
Cruising Speed: When driving the vehicle, accelerate up to a speed over 30 mph and maintain that speed. Listen closely for any kind of noises coming from areas of the vehicle other than the axle assembly. Axle assembly noise is usually not heard at a constant speed, unlike engine, suspension, and transmission noises, which can be mistaken for axle assembly noise.
Varying Speed: Many axle issues become evident when you quickly accelerate and decelerate using the throttle. When you do this test, you are loading and unloading the gears and bearings. Clunking or banging is evidence of worn bearings or seriously worn gears.
Coasting: If you hear a howl or whine when the vehicle is coasting, you most likely have a worn-out pinion bearing.
Worn Bearings
