Is It Worth Installing An Inline Transmission Filter?

You may think that installing an aftermarket inline transmission filter will add unnecessary complexity and expenses to an otherwise functioning rig, and you're probably right. Most automatic gearboxes have built-in screen filters to keep the automatic transmission fluid (ATF) fresh and contaminant free. Messing with the factory transmission lines to retrofit an inline filter may introduce annoying problems like leaks, flow restrictions, and the need for more maintenance than required –- not to mention the costs associated with such a mod.

Then again, the rewards may compensate for the risks. Excess heat is the primary killer of most automatic gearboxes – operating at punishing conditions with low or contaminated fluid is a surefire recipe for overheating, and it's one of the common mistakes that can destroy your automatic transmission. If your car's gearbox is slipping or hesitating to change gears, those symptoms are telltale signs of automatic transmission failure, with most issues stemming from neglect or forcing the gearbox to run on old and degraded fluid.

An inline transmission filter is exactly what it sounds like. It's a filtering medium made of cellulose, metal screens, or magnetic fibers that attaches to the transmission fluid line. You can think of it as a secondary filter for your vehicle's ATF, and there's certainly nothing wrong with keeping the fluid clean if longevity, reduced downtime, and low maintenance costs are what you crave from your workhorse.

Most automatic transmissions have screen or panel filters in the pan with an efficiency of 200 to 100 microns. However, while about 82% of contaminants in automatic transmission fluid are larger than 5 microns, only 15% are bigger than 15 microns. That means a large percentage of contaminates can slip through a standard filter. Of those, around 51% are steel particles, 21% are copper, and around 7% to 11% are aluminum and lead.

If left unchecked (or unfiltered), contaminants in the fluid can harm the internal valves, reducing the efficiency of the gearbox. Moreover, abrasive particles contribute to more wear, internal leakages, and low pressure within the system, which can cause the clutches to slip and hesitate when engaging or disengaging gears.

Prevention is always better than a cure, and installing an inline transmission filter –- especially one with magnets and lower-micron filtering –- can help catch and trap microscopic contaminants before causing long-term damage. Some inline transmission filters are so good that fleet companies have experienced a significant drop in premature gearbox failures and saved hundreds of thousands in repairs and maintenance, all by simply fitting an auxiliary transmission filter.

Inline transmission filters come in many shapes and sizes, but what's more important than size or shape is where to place the filter within the system. If you have a newer rig, installing a secondary filter in the cooler outlet line is preferable. The timing is also important, since it's better to get down and dirty and install that filter while your vehicle is relatively new.

However, if you have an older rig or are running a rebuilt transmission, putting an inline filter on the return line is highly advisable. After doing so, don't forget that your new transmission filter is not maintenance free, and it's not a substitute for periodic fluid changes. It's a stellar idea to inspect and replace the filter every 30,000 to 50,000 miles, and remember to check it more frequently if you do a lot of driving or towing. Most automatic transmissions require servicing every 60,000 to 100,000 miles. Installing an inline transmission filter in vehicles that do a lot of towing and heavy-duty work could be a wise idea.