Goss’ Garage

Modern automatic transmissions can be traced back to nineteen-o-four when the Sturtevant brothers of Boston developed a clunky, inefficient, failure-prone centrifugal gearbox. A crude beginning and nothing like today’s transmissions which shift smoothly, deliver great fuel economy, good performance and exceptional durability.

However, the sophistication of today’s transmissions means repairing or replacing a broken one now costs more than a whole fleet of cars did back in o-four. Transmission repair or replacement can be mind-numbingly expensive these days. To further complicate things long term financing on the vehicle may mean you owe more than your car is worth, so you can’t afford to trade and that means another maxed-out credit line looms.

Although repairs are expensive preventing them is cheap and makes the most sense. Maintenance used to mean dropping the transmission pan, replacing a filter and refilling with fluid. But that was a long time ago. Today, proper service is vastly different because the old method can actually shorten rather than increase the life of today’s transmissions. That’s because the old method didn’t clean anything inside the transmission, and it only replaced about a third of the fluid.

The old process leaves the transmission nearly as dirty as it was before the process began and still filled with two thirds old, oxidized fluid. The problem is that new fluid doesn’t always mix properly with the remaining old dirty fluid. Plus, without any cleaning the new more-detergent fluid softens deposits allowing fine particles to circulate through the transmission causing wear. Some of the dirt particles are so small they pass right through a transmission filter. That is, if yours even has a filter as many now opt for a filter-screen instead. Today, proper transmission service means flushing, which significantly extends transmission life. Unless you feel dirt and varnish is somehow beneficial to mechanical devices, I suggest you flush your transmission.

The most important part of a transmission flush is cleaning the inside of the torque converter. Because the torque converter spins at engine crankshaft speed it tends to act like a centrifuge. In case you don’t know, a centrifuge is a device that spins at high speed and applies centrifugal force to its contents. Its purpose, in a general sense, is to separate fluids of different densities or solids from liquids. In the case of the transmission torque converter the centrifugal motion tends to spin solids out of the fluid and collect them on the inside of the converter housing. If not cleaned away with a flush the solid materials will collect until they reach a point where they can no longer adhere to the inside of the converter housing and begin to circulate through the transmission.

As the dirt circulates through the tiny channels in the valve body, they partially clog some of the small passages that fluid flows through which alters the pressure that controls shifts. This altered pressure might feel great to you because the shifts may be buttery smooth, but buttery smooth often means slippage and slippage means wear on clutches. Wear on clutches means more debris which accumulates in the torque converter, which —- well, you get the picture!

The first step in flushing is adding chemical cleaners followed by running the car to soften and dislodge all the oxidized varnish and dirt built up in the transmission, torque converter, cooler and cooling lines. Then the car is connected to the transmission flush machine which captures and quarantines all the old fluid coming out of the transmission and sends fresh new fluid back into the transmission. In a transmission flush all the bad stuff is quarantined outside the car while in the old method all the bad stuff stays in the transmission. Plus, flushing replaces nearly one hundred percent of the fluid where the old method only replaces a quarter to a third.

When it comes to the fluids in your car there is nothing more beneficial than cleanliness. So, a flush should be done every two to three years or 24,000 to 36,000 miles. Also, contrary to what your dealer may have told you, there is no such thing as a fluid that lasts the life of the vehicle. Nothing lasts forever, all fluids wear out and when the fluid wears out the transmission soon follows.

There is also no such thing as a completely sealed transmission, they can all be flushed with proper adapters. Beware of shops that sell fluid exchanges calling them flushes. A fluid exchange is quick and highly profitable for the shop but a waste of your money. Fluid exchanges can be done in the service lane in about half an hour or less, where a flush requires about an hour and a half. A fluid exchange is done through the filler tube or fill hole and simply siphons some fluid out while simultaneously adding fresh fluid. Much like an old-fashioned drain and refill this process does not change all the fluid and leaves considerable dirty fluid in the transmission.

Beware when it comes to shops that claim all transmission fluids are the same or that they can add a can of goop to a basic fluid to make it magically change into the proper fluid for your vehicle. This is risky at best and deadly to your transmission at worst. The transmission fluid used should have the qualification number of the product required by your car on the container or data sheet. With good preventive maintenance and sensible driving an automatic transmission may well last the life of the vehicle. We have a C5 Vette in the shop today that we have maintained for years with its original transmission and an odometer reading of 189,090 trouble-free miles.

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