Rick's Free Auto Repair Advice

Transmission service

When and where should you get transmission service?

Neglecting routine transmission service is the #1 cause of costly transmission failure. Transmission fluid lubricates internal parts yet contains a friction modifier to allow clutches and spacer steel plates to slip slightly but stick together and rotate as a unit when pressure reaches a set amount. Those properties may sound mutually exclusive—lubricating  yet allowing parts to stick together, but automatic transmission fluid (ATF) does both very well.

In addition to those properties, transmission fluid must also be compatible with internal seal materials like O-rings, gaskets, seals, and wire insulation and plastic parts. ATF must operate at extremely low winter temperatures and high summer temperatures. They also include anti-oxidation and corrosion additives, as well as dispersants, varnish reducers, anti-foaming agents and shear resistance products.

Over time, the additives and the fluid break down, causing clutches and internal parts to overheat and wear faster. If neglected, ATF eventually loses it’s ability to lubricate, causing irreversible transmission failure. On disassembly, failed transmission components are coated with a dark brown varnish colored substance that’s evidence of fluid breakdown.

What causes transmission fluid breakdown?

Heat is the #1 enemy of transmission fluid. Most transmission service, transmssion coolervehicles are equipped with an external transmission fluid cooler mounted inside the radiator. Strange as it sounds, the hot coolant in the radiator is actually cooler than the transmission fluid. But severe usage can cause ATF to heat up to a point where it simply can’t be cooled enough by the radiator. Here’s what contributes to excessive heat and fluid breakdown:

• Hauling a trailer
• Hauling heavy loads or driving at highway speeds with a roof-top carrier
• Mountain driving
•Aggressive driving with full load downshifts, high speeds

• Extended driving at high altitudes or in desert conditions.

What is transmission service?

Transmission service involves removing and replacing all or a portion of the old transmission fluid as well as the transmission filter (where the filter is field replaceable). Some car makers recommend a transmission fluid flush service where the technician connects a flush machine to the transmission cooler lines and push fresh fluid into the transmission while draining the worn out fluid. In cases where car makers recommend a transmission flush service, the flushing machine must meet the car maker’s specifications for maximum flush pressures and flow rates. Flushing a transmission with an unapproved flushing machine can damage delicate internal seals, causing internal and external leaks after the service is complete. Those leaks can result in total transmission failure.

Other car makers specifically warn against transmission flushing and instead recommend just a partial fluid drain and filter replacement. In those cases, the technician removes a transmission pan drain bolt or the entire drain pan and allows the transmission to drain while they replace the transmission filter. This is referred to as a “drain and fill” procedure. Draining the transmission by removing the drain bolt or the pan removes between a third to half of the transmission fluid.  The car makers recommending this procedure feel that periodically changing a portion of the transmission fluid is safer than flush machines that rely on pressure to purge the old fluid.

Some transmission fluid flushing machine manufacturers recommend adding a cleaning solvent to the procedure. No car maker recommends or authorizes the introduction of cleaning solvents and you should avoid any shop that advocates this.

If your car maker recommends fluid flushing service, make sure the shop uses the authorized flushing machine to avoid seal damage and leaks.

Scams to avoid when purchasing transmission service

Using a cheaper transmission fluid

Modern transmission fluids are expensive, some costing over $8 per quart. A typical automatic transmission holds over 12 quarts of fluid and requires almost 16 quarts to do a proper flush service. Yet some shops advertise transmission fluid flushing services for as little as $149. At $8/quart, their materials cost comes to $128. Since the entire procedure takes about an hour, there’s simply no way a shop can make money on a $149 flush. So how do they do it?

Simple. They use an inexpensive generic fluid transmission servicethat costs about $1.50/quart and add a bottle of friction modifier at the end of the procedure to bring the lower quality fluid to the right lubrication/friction level.  This is referred to as “Top Treating,” and is not authorized by any car maker. Filling with a low quality fluid and top treating with a friction modifier will cause premature transmission wear and harsh shifts.

Using a multipurpose fluid

In years past, car makers used a single transmission fluid for all their transmissions—Dexron for GM vehicles, Mercon for Ford vehicles, ATF+4 for Chrysler vehicles, etc. However, as transmissions have become more complicated, car makers have refined their fluids to match the design characteristics of a specific transmission. As a result, it’s critical to use the specific fluid recommended for each transmission. The proliferation of specialized formulas has caused a huge inventory problem for shop—they simply can’t stock the 30 or more different types of transmission fluids required to service every type of transmission.

Transmission fluid manufacturers have responded to this problem by developing multipurpose fluids that claim to the requirements of many different transmissions. The product labels state they are “Suitable for use in X, Y and Z transmissions.” None of these multipurpose products are approved by car makers. Worse yet, when comparing the car makers fluid specifications, experts have discovered that the multi-purpose transmission fluids can’t possible work well in different transmissions because the individual fluid specifications are mutually exclusive.

In other words, the correct fluid for your transmission must be the proper viscosity, have the exact friction modifiers, seal compatibility and additive package. Avoid any shop that claims their multi-purpose transmission fluid is right for your car.

How often should you service your transmission?

If you believe the sales agents and quick-lube shops, you should replace your transmission fluid every time they recommend it. In other words, they’ll recommend a transmission fluid change every time you come in for an oil change. Or, they’ll recommend a fluid change at “industry average” intervals like; every 30,000 or 60,000 miles. But there are NO industry transmission fluid change averages.

Some transmissions run hotter than others and require transmission fluid changes every 30,000 miles while a different transmission can go 100,000 miles between changes. Don’t rely on the recommendation of an oil change shop. Instead refer to your owner’s manual or maintenance guide.

Where should you go for transmission service?

Dealer service departments are must use authorized flush machines and are required to use only the factory recommended fluids. Dealer labor rates are higher than independent shops, but transmission service only takes about one hour, so the price difference between dealer labor and independent shop labor should only cost an extra $30 dollars.

Independent shops that specialize in your make will be most likely stock the correct transmission fluid and use factory authorized equipment. Double check with the shop to make sure they use the recommended fluid, not a multi-purpose fluid.

Avoid chain operated general repair and transmission shops. Chain operated repair shops often buy cheap fluid in bulk and use it for all transmissions, regardless of the factory recommendations. These shops of also more likely to top treat after using a cheap fluid.

©, 2017 Rick Muscoplat






Posted on by Rick Muscoplat


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