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Transmission Flushes Are Excellent for Maintenance

Working in automotive for the last 20 years as a technician and service advisor has provided me with a lot of information to share.

Almost all repair facilities recommend transmission services these days. Many consumers wonder about the value of these services and how it relates to their own personal vehicle. Manufacturers vary on recommended time intervals and sometimes the repair facilities do too. The most important rule of thumb is, be sure to do it before 60,000 miles and use a fluid that matches your vehicle make. Fluid specifications can greatly affect your vehicle performance. As you can imagine, the wrong fluid will cause problems. Each repair shop will have their own flush kit providers. Be sure that they have a warranty on the flush. Any reputable shop will.

Changing transmission fluid used to mean removing a pan off of the bottom of the trans and letting whatever fluid that came out to drain into a receptacle. Then a new filter was installed in the pan area. The pan was then reinstalled and new fluid was poured in to mix with whatever old fluid remained in the trans. It wasn't a great service, but it was better than not changing fluid at all.

The new systems are very thorough. They are designed to push fluid throughout the entire system to completely remove old fluid and any particulates from the system. Usually a flush kit will contain a cleaner that will go in first to help remove any varnish. Then fresh fluid is pushed through the system with an additive pack designed to enhance the fluids properties. Fluid is circulated through until all that remains is fresh fluid.

2010 Chevy Impala auto trans


Service Intervals

The frequency of service can vary based on vehicle year, make, model and drivetrain configuration. Believe it or not, the same vehicle may have different engine or trans. Realistically, doing the service more frequently will reap greater benefits. If a vehicle has over 100,000 miles and it has never had a service, then I honestly wouldn't recommend it. The reason is, the buildup of material in the system could have a negative effect when chemical cleaners are run through. Kind of like an artery that has filled up with cholesterol on a sedentary person who suddenly decides to run a mile all out. The material can break loose and clog up in a vital spot and create a lot of damage. The old way is better for an old vehicle that has never been serviced. It's not as good, but it's better than nothing. I recommend doing a service every 30-40,000 miles.

A key factor is the type of fluid used in your transmission. A quick crash course on trans fluid. It is a petroleum based fluid with lots of additives. These additives are relative to the type of trans in the vehicle. Some of the additives are friction modifiers, pour point additives, anti-foaming agents and seal conditioners. There are a lot more than that, but that shows a few to consider.

Transmission types

There are multiple transmission types. A trans is designed to take the energy created by the crankshaft of the engine and direct it to the wheels. Gears on a bicycle give a general feel of why this is important. The smaller gear is easier to turn at low speeds, but is too easy at higher speeds. It will spin fast, but not really get you anywhere until you increase the gear size. Then it takes a lot less turns of the pedal to maintain the same energy thanks to proper gearing. A transmission does this in a variety of ways: Manual, auto, clutchless manual, and cvt. Let's explore these a little.

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manual trans

manual trans

Manual transmission

The manual transmission is the first transmission developed. It consists of a clutch, gears, input and output shafts, and a gear selector. There are a few other components, but we'll keep it simple. Most of us know this as driving a 'stick shift'.

This type of transmission has the most direct mechanical engagement. The fluid is designed to keep things moving freely and smoothly. It is also designed to reduce friction between the gears. Reducing friction reduces heat. Heat is the enemy. Heat is what will destroy the mechanical parts and cause seizing.

cut-away of automatic transmission

cut-away of automatic transmission

Automatic transmission

As you can see, an automatic transmission is built very differently than the manual. It has no clutch and no 'stick'. There is a gear selector in the car that does provide input, but it does not have to be used to select each gear. Once the vehicle is 'in gear', the transmission does the rest based on mechanical and hydraulic conditions. The large turbine looking disc in the front spins with the engine. This is called a torque convertor. Fluid moves through the internal fins and the faster it spins, the more fluid pressure is created. At certain points of pressure, valves in a valve body open or close and different gears are selected. This is a very basic description of it's function, but you can see that the fluid in an auto trans has to do more than just provide lubrication between metal parts. It must pass through the spinning fan-like turbine of the torque convertor without separating or foaming up. The reason is, air compresses more readily under pressure than fluid which would cause problems in the valve body, which in turn causes problems in the shift. Also, air heats up faster under pressure than fluid. Again, too much heat is the enemy of mechanical components. Valves stick, shifts don't occur, engine revs up too high and ultimately, the car just won't go.

Continuously variable transmission


The continuously variable transmission, or CVT, is one of the latest styles of transmissions introduced. It is most commonly paired with a hybrid or electric vehicle. The one illustration above describes pretty well what it does. This type of trans is able to use the cones to create a very wide variety of gear ratios.This type of trans doesn't necessarily shift. The input from the gear selector on this car simply tells a computer which direction to go. It relays this forward, back or park command to the trans and that's it. As speeds increases and rpm's increase, the cones move in. Alternately, when slowing, the cones move out. The fluid in this trans is almost completely there for hydraulic reasons. Very little needs lubrication. Again, fluid must stay in liquid form for accurate pressure. If foaming occurs and heat increases, failure is the end result. Fluid in these are extremely specialized.

When it comes to transmission fluid, there's more than meets the eye.

There are a couple other transmission styles that are versions or hybrids of the transmissions I described. Rather than delving too deeply into the mechanical functions, I want to emphasize the importance of the fluid. In spite of all the differences, the common factors are by-products of fluid breakdown caused by temperature extremes and friction. The by-products can stick to the moving parts which creates varnish. This varnish is sticky when cool and creates higher heat + friction when hot. This is the leading cause of internal mechanical failure. This is the most common cause of transmission problems. Regular maintenance greatly reduces the likelihood of breakdown.

An IMPORTANT note, some chemical supply companies, such as Run-Rite, offer higher mileage warranties on system components. For instance, Run-Rite offers a 240,000 mile warranty if you begin servicing your vehicle with their product at 50,000 miles, then every 30,000 miles thereafter. This warranty will assist in repairing and/or replacing, mechanical component failure, should it occur. To learn more please speak with a Run-Rite rep in your area or take a minute to visit their website at

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