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Automatic Transmission and Transaxle, Page 3 of 3

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Automatic transmission maintenance

Automatic transmission fluid

Automatic transmission fluids can be broken down into two types, Dexron® III and Ford type F. These fluids are specific to the transmission using them. Don't assume that all Ford vehicles use type F, they don't!

There are the following types of fluids.

  • Dexron® III, sometime referred to as multi purpose ATF. This replaces the old Type A, Suffix A, which was recommended by GM, Chrysler and AMC between 1956-1967. It also supercedes Dexron® and Dexron ® II fluids. Ford vehicles 1977 and later with the C6 transmission or the Jatco transmission in the Granada and Monarch also use this fluid. Ford refers to this fluid as Mercon®, or on older models as type H or CJ where recommended.
  • Type F fluid is recommended by Ford Motor Co. and a few imported manufacturers, and contains certain frictional compounds required for proper operation in these transmissions.

There is not much of a problem here, since the bottles are clearly marked to indicate the type of fluid. If you are in doubt, check your owner's manual. Also, some transmission dipsticks are labeled or stamped with the recommended fluid type.

Checking fluid level
See Figures 17, 18, 19 and 20

Check the transmission fluid level at least every 6,000 miles (9,654 km) or 6 months, whichever comes first. Under extreme usage the fluid should be checked at shorter intervals or if a problem exists.

In most cases the vehicle should be on a level surface, transmission in Park, and the engine running. The fluid should be at normal operating temperature. If the vehicle has been used to haul a trailer or has been on an extended trip, wait half an hour before checking so a correct reading can be measured.

  1. Park the vehicle on a level surface, with the parking brake on. Start the engine and allow to idle for about 15 minutes. Move the transmission through the gears and then back to park.
  2. Remove the dipstick and carefully touch the wet end of the dipstick to see if fluid is cool, warm, or hot. Wipe it clean and then reinsert it firmly. Be sure that it is pushed all the way in. Remove the dipstick again while holding it horizontally.
    1. If fluid is cool (room temperature), the level should be about 1/8 to 3/8 inches (3-10mm) below the add/cold mark.
    2. If fluid is warm, the level should be close to the add mark, either above or below.
    3. If fluid is hot, the level should be at the full/hot mark.
  3. If the level is low, add the appropriate fluid through the dipstick tube. This is easily done with the aid of a funnel. Check the level often as you are filling the transmission. Be extremely careful not to overfill it. Overfilling may cause slippage, seal damage and overheating. Typically, 1 pint (0.473L) of ATF will raise the fluid level from one notch/line to the other.

If the fluid on the dipstick appears discolored (brown or black), or smells burnt, serious transmission troubles (probably due to overheating) should be suspected. The transmission should be inspected by a qualified technician to locate the cause of the burnt fluid.

Figure 17 Remove the dipstick and wipe clean. Reinsert the dipstick all the way. Remove it again and check the fluid level.
Remove the dipstick and wipe clean. Reinsert the dipstick all the way. Remove it again and check the fluid level.

Figure 18 Some dipsticks are hinged (locking into place to seal the guide/filler tube).
 Some dipsticks are hinged (locking into place to seal the guide/filler tube).

Figure 19 The fluid level should be between the ADD and FULL marks depending upon transmission temperature, cold (A) or hot (B). Also, check the appearance of the fluid.
 The fluid level should be between the ADD and FULL marks depending upon transmission temperature. COLD (A) HOT (B) Also, check the appearance of the fluid.

Figure 20 If the level is low, add fluid through the dipstick tube, using a long funnel. Do not mix fluid types and do not overfill.
 If the level is low, add fluid through the dipstick tube, using a long funnel. Do not mix fluid types and do not overfill.

Fluid temperature
See Figure 21

Transmission fluid is designed to last many thousands of miles under normal conditions. However, one of the most important factors affecting the life of the fluid and the transmission is the temperature of the fluid. Overheated fluid forms sludge and particles of carbon that can block the minute passages and lines that circulate the fluid throughout the transmission. This causes the transmission to overheat even more and will lead to eventual failure of the transmission.

Some cars come from the factory with coolers that help with the temperature. The transmission oil flows through the cooler as air flows across the cooler to lower the temperature of the transmission fluid. The coolers can be purchased at any after-market store for most cars. Some cars have warning lights for the transmission that will alert the owner of any maintenance intervals or overheating problems.

Anything that puts a load on the engine can cause the transmission to heat up and speed the deterioration of the fluid. Towing a trailer, idling in traffic and climbing long hills is all hard on a transmission. The accompanying graph illustrates just how much transmission temperature affects the life of transmission components. Fluid that lasts 50,000 miles (80,450 km) at a temperature of 220°F (104°C), will only last half that long if the temperature is consistently 20° higher.

The secret to long transmission life is regular fluid changes and keeping an eye on the condition of the fluid-both temperature and color.

Transmission fluid indications

The appearance and odor of the transmission fluid can give valuable clues to the overall condition of the transmission. Always note the appearance of the fluid when you check the fluid level or change the fluid. Rub a small amount of fluid between your fingers to feel for grit and smell the fluid on the dipstick. 

If the fluid appears: It indicates:
Clear and red colored
  • Normal operation
Discolored (extremely dark red or brownish)or smells burnt
  • Band or clutch pack failure, usually caused by an overheated transmission. Hauling very heavy loads with insufficient power or failure to change the fluid often result in overheating.
  • Do not confuse this appearance with newer fluids that have a darker red color and a strong odor (though not a burnt odor).
Foamy or aerated (light in color and full of bubbles)
  • The level of fluid is too high (gear train is churning fluid).
  • An internal air leak (air is mixing with the fluid). Have the transmission checked professionally
Solid residue in the fluid
  • Defective bands, clutch pack or bearings. Bits of band material or metal abrasives are clinging to the dipstick. Have the transmission checked professionally.
Varnish coating on the dipstick
  • The transmission is overheating.

Figure 21 Transmission temperature indications.
Transmission temperature indications.

Checking for leaks

If the fluid level is consistently low, suspect a leak. The easiest way is to slip a piece of clean newspaper under the vehicle overnight, but this is not always an accurate indication, since some leaks will occur only when the transmission is operating.

Other leaks can be located by driving the vehicle. Wipe the underside of the transmission clean and drive the vehicle for several miles to bring the fluid temperature to normal. Stop the vehicle, shut OFF the engine and look for leakage.

Remember, however, that where the fluid is located may not be the source of the leak. Airflow around the transmission while the vehicle is moving may carry the fluid to some other point.

Servicing the transmission

Aside from changing the fluid and filter and tightening nuts and bolts, repair or overhaul of the automatic transmission should be left to a trained technician. This is because there are special tools needed for inspection (such as hydraulic pressure testers, electronic scan tools for retrieving trouble codes, etc.) and for the repair of the transmissions. Transmissions are heavy and special jacks or hydraulic tables are needed to remove them from the vehicle. In some cases special tools are used to separate the transmission from the engine.

Automatic transmission service intervals

Troubleshooting basic automatic transmission problems

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©1998 W. G. Nichols - Chilton's Easy Car Care