A popular answer for transmission problems from inexperienced mechanics or do it yourselfers is a service or flush of the transmission. This article explains why that could end up costing you more money for transmission repairs.
Transmission Servicing: Will a Service or Flush Solve Your Transmission/Gearbox Problems?
Are you having problems with your vehicle’s transmission? When was the last time the gearbox was serviced? If you’re like most people, it’s probably been a while. For some reason, transmission or gearbox maintenance is neglected by most people until a repair is needed. If your vehicle is exhibiting problems with shifting or engagements, a service or fluid flush is not the answer.
What is a Transmission Service?
A service is when the automatic transmission fluid (ATF) and filter is changed. Most transmissions have a serviceable filter, but some cars like Honda, don’t have a filter that is accessible for maintenance. In the case of vehicles that do not have an accessible filter, a simple “drain and fill” is all that is required for proper servicing. This is a preventative maintenance that ensures proper function by keeping the ATF fresh.
Some vehicle manufacturers list service intervals at every 30,000 miles, some every 100,000 miles, and there are some manufacturers that claim their transmissions will never need servicing. I find these high mileage service intervals are risky. The high pressures and temperatures that ATF is exposed to during normal operation will break down the fluid’s conditioning and lubricating properties, and can lead to premature mechanical failures. To be safe, a transmission should be serviced once a year for gearboxes that use non synthetic ATF and once every two years for vehicles that use synthetic automatic transmission fluid. This is a rule that applies to all vehicles. If you’re not sure what type of ATF your vehicle uses, consult your owners manual or qualified mechanic.
What is a Transmission Flush?
A flush is when a technician hooks a machine to the transmission’s cooler lines and replaces all of the fluid with new ATF. Is this better than a regular service? My 17+ years of experience, along with several vehicle manufacturers, and respected technicians say no. The argument for a flush verses a regular service is, when performing a regular service on an automatic transmission, only one third of the fluid is actually replaced whereas a flush replaces 100% of the ATF. Sure, changing 100% of the fluid sounds better than replacing only a third, but the fact is automatic transmissions don’t need 100% of the fluid changed.
Transmissions are sealed units; they don’t have anything that is fed to them. Engines feed off gasoline to run. That burnt gasoline produces byproducts that engine oil traps and delivers to the filter. Because of these byproducts, engine oil will become contaminated, and must be changed frequently. With the gearbox being sealed, there are no outside materials that can break down the ATF and clog filters. Performing the basic 1/3 service is sufficient for proper maintenance. Think of it like your cup of coffee at a restaurant; the waitress (mechanic) periodically tops off your coffee (ATF) to keep it hot and fresh. The main difference is ATF has to be “poured” out to make room for the fresh fluid. How crazy would it be for your waitress to grab your cup, throw all your coffee away, and then charge you full price for a refill?
Honda of North America actually warns against flushing Honda and Acura transmissions. A direct quote from Honda bulletin HSN0206-07 states, “Flush systems haven’t demonstrated an improvement in vehicle performance or reliability.”
But my Transmission is Acting Up and I’ve Never Serviced it.
If maintenance has been neglected, now is not the time to pay $100 for a regular service or up to $300 for a flush. The transmission needs to be diagnosed by a specialist to see what is causing the shifting or engagement problems. Malfunctioning components like solenoids or sensors will cause gearbox problems, and can be replaced during services that require oil pan removal. If the transmission is serviced before it is properly diagnosed, you may have to pay double the labor for replacing the part that could have been accessed during the initial service. If an internal failure that requires a rebuild or overhaul is causing the problem, a service or fluid change will be a waste of money that cannot be recouped during the repair.
Following a service schedule for transmission fluid maintenance is the best thing you can do to avoid costly repairs. If shifting or engagement problems do happen, have your vehicle diagnosed by a certified transmission specialist, or you could just be throwing your money away.
