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Transmission Facts

Automatic transmissions normally operate under stressful conditions. This is a direct result of friction, heat, and load. An automatic transmission that is extensively used for towing is put under maximum stress, heat, and wear. There are some modifications that can be made to improve the towing performance of the automatic transmission. Few people think about it but transmission fluid is actually a basic component of an automatic transmission. Its main functions are to act as a hydraulic fluid that transmits pressure, as a viscous coupling fluid in a torque converter, as a lubricant and to provide friction attenuation in bands and clutches for smooth shifting.

Planetary Gearset

The planetary gear train will make the gear shift transition without having to disengage the engine from the drive wheel, like that of a clutch in a manual transmission. How does a planetary gearset operate? Let's see if we can translate this into some layman's terminology:

When the ring gear is held and the sun gear is rotated, the planet gears will walk around the sun gear, then rotate the planet carrier in the same direction as the sun gear but at a much slower speed than the sun gear due to a major gear reduction. When the sun gear is held and the ring gear is rotated, the planet gears will walk around the sun gear at a somewhat slower speed than the ring gear. This is called minor gear reduction. By holding the planet carrier and driving the sun gear, the ring gear is turned in the opposite direction (reverse and gear reduction). Direct drive can be achieved by locking any two elements of the planetary gearset together.

Clutches

The clutches that are used in automatic transmissions are smaller than those used in manual transmissions. Also, the clutches used in an automatic transmission use multiple friction plates. When they are stacked together in a sandwiched sequence, they are known as clutch packs. The friction plates are constructed from an asbestos material. These friction plates are attached to a single driving member while the steel plates are attached to the outer shell driving member. When the clutch piston is activated, it will apply force and squeeze the sandwich of plates together. The clutch applies pressure and the two members become locked together. When the piston releases force, the clutch return springs will force the piston up, allowing the plates to freely rotate and release the two members from each other.

Spotting problems before they get worse:

Watch for leaks or stains under the car

If there is a persistent red oil leak that you are sure is coming from your car, you should have your shop check to see if it is coming from the transmission or possibly from your power steering system (most power steering systems also use transmission fluid and leaks can appear on the ground in roughly the same areas as transmission leaks.) If all you see is a few drops on the ground, you may be able to postpone repairs as long as you check your fluid level often (but check with your technician to be sure). If transmission fluid levels go down below minimum levels serious damage can occur (the same advice goes for power steering leaks as well.)

Check fluid for color and odor:

Most manufacturers require that you check transmission fluid levels when the vehicle is running and on level ground. Pull the transmission dipstick out and check the fluid for color and odor. Transmission fluid is a transparent red oil that looks like cherry syrup. If the fluid is cloudy or muddy, or it has a burnt smell, you should have it checked by your technician who will most likely advise you to have a transmission service. Changing the fluid and filter.

Be sensitive to new noises and vibrations and shift behavior:

A modern transmission should shift smoothly and quietly under light acceleration. Heavier acceleration should produce firmer shifts at higher speeds. If shift points are erratic or you hear noises when shifting, you should have it checked out immediately. Whining noises coming from the floor board are also causes for concern. If caught early, many problems can be resolved without costly transmission overhauls. Even if you feel you can't afford repairs at this time, you should at least have it checked. The technician may be able to give you some hints on what to do and not to do to prolong the transmission life until you can afford the repair.
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