If you compare oil filter systems used in automatic transmissions from 50 years ago to present-day, you won’t see many changes until just the past few years. Common were “boulder-catching” screens or coarse filter pads mounted in the pan, with efficiencies of 100-150 microns. Pan filters are a bit better today, catching particles in the 70-80 micron range. A more important development has been the high-efficiency spin–on or cartridge filters used on some of the newest automatics found in light trucks and RVs. However, there remain many older rigs or vehicles with newer transmissions that are not so well equipped. Here’s a little 411 on filtration that should help you decide whether yours needs improvement or not.
The Down and Dirty
John G. Eleftherakis and Ibrahim Khalil are not household names, but since the 1980s, they have tested hundreds of transmissions and analyzed thousands of oil samples. These two engineers broke ATF contamination into two categories: Type I and Type II.
Type I is created during manufacturing. Type II is formed during normal break-in and wear and tear. After about 70,000 miles without an oil change, the ATF is a slurry of Type I and II debris, containing approximately 263 milligrams per liter (mg/l) of contaminants that is 90 percent metallic. The particles range in sizes from 5 to 80
microns, about 82 percent of them larger than 5 microns. Most of that passes through the average filter. It can cause sticky valves, cumulative wear and internal leakage. When 100 mg/l was added to the fluid during a test, it took only 750 hours (about 40,000 miles of driving) to seriously degrade transmission operation.
Improved Filtration
An automatic needs a high volume of oil flow and the technology to do that economically and in a small space is only just now available. If your rig’s automatic has a spin-on filter, it’s likely within the efficiency range of a premium engine oil filter or a hydraulic filter.
Changing the fluid does eliminate the buildup of contamination and that’s always a viable method. On the downside, you are often tossing the baby out with the bathwater. The ATF itself is fine, just loaded with more contaminants than you would like. Plus, contamination levels will rise and fall according to how long it’s been since the last change. What’s more, a fluid change is more difficult on modern transmissions because torque converter drains are largely a thing of the past. Without them, you can only drain 30-40 percent of the oil. A more complete change can be done via the cooler lines but there are caveats to that which we don’t have space to detail here.
The easy path to clean ATF is a filter in one of the cooler lines. A certain percentage of the hot torque converter oil is shuttled off to oil coolers and the returned oil is used for lubrication. Just about any cooler line filter is beneficial, including an engine oil filter or a hydraulic filter on a universal base, but there are specialty filter kits, two of which we were able to test. The finer the filtration the better, but filter flow must match the maximum cooler flow of the trans (typically 2-6 gallons per minute in light trucks). The most important feature is a bypass valve so that if the filter ever plugs, full lubricant flow will continue.
Generally, an add-on filter is installed in the return line between the cooler and the trans. Debris likes to settle in coolers, but it can decide to move at any time. On a new truck, it’s important to get the filter on right away to eliminate Type 1 debris and catch the Type II break-in material. On a used truck, you can install the filter at any time.
If you ever have a trans rebuilt, installing a cooler line filter becomes even more important as problems with Type 1 and Type II break-in debris are more common, as well as the possibility of debris from the previous failure lurking in the lines and coolers. If the tranny shop doesn’t install a cooler line filter as part of the job (many do), you should.
Clean Fluid
The filter close-up sections provide more information about the effects of transmission filtration on oil cleanliness. The longer a filtration system is in place, the cleaner the ATF will get until it levels out at the maximum efficiency of the filter. That usually happens in less than 5,000 miles, according to our sources at Racor. It’s then maintained at that level, even as the trans produces more wear debris.
Eleftherakis and Khalil determined that between the built-in Type 1 and Type II contaminants from break-in, the average new transmission will generate 75 percent of its lifetime contaminants in the first 5,000 miles. That’s a great clue and can be interpreted a couple of ways. Either you need to change that fluid early to get the contaminants out or start filtering better early.
In their 1998 SAE (Society of Automotive Engineers) paper, “Optimizing Automatic Transmission Filtration,” Eleftherakis and Khalil opined that no more than 25 mg/l of contaminants should be allowed to remain in a transmission lubricant and less 10 mg/l practically ensures no trouble due to particulates. A rough calculation by Blackstone Labs indicates both of our test trucks are now well below 10 mg/l. On top of that, oxidation levels are reduced so the oil will last longer in service. Longer trans life and fewer oil changes are a net plus, and will give you peace of mind and in your wallet.
Magnefine
Magnefine packs a lot of capability into a small package. Looking like an oversized fuel filter, it was developed in Australia. The OEMs used them primarily with warranty remanufactured transmissions; and they are currently being used by a major OEM as a power steering filter.
Magnefine comes in two forms, a discardable filter or one with a serviceable billet aluminum housing. Within both is a 35 micron (nominal) filter with approximately 49 square inches of media. A strong magnet with a flow director is mounted at the inlet end to catch ferrous material before the oil passes through the filter media. It has a bypass valve, comes with 5/16-, 3/8- or 1/2-inch fittings and can be installed into cooler hoses. Maximum flow rate is approximately 7 gpm for the 5/16-inch filter (the larger filters flow more). Given that more than 50 percent of transmission wear metals are ferrous, and the magnet will catch virtually all of it, according to the manufacturer, overall efficiency is more than the filter element rating alone would indicate. Recommended change interval is 30,000 miles. It may not be the most efficient filter in our group, but given its low cost and ease of installation, it’s certainly something to consider for those with tight budgets. It delivered a lot of cleaning, dropping the oil two ISO codes in 2,200 miles.
The Magnefine can also function as a power steering filter, a system that usually has no filtration at all. When installed on the low-pressure return line, the Magnefine will continuously filter the power steering fluid. Filtered, this fluid should add significant life to the system, especially rack and pinion systems that are more sensitive to particulate matter. We tested Magnefines on the power steering of two trucks, a 2005 F-150 (rack & pinion) for 552 miles and an 1986 F-250 diesel (recirculating ball) for 289 miles. In the F-150 the ISO code dropped from 20/17/12 to 17/15/12 and in the F-250 diesel it dropped from a grungy 21/18/14 to 18/16/13 (For more information and details about ISO Oil Cleanliness Standards and Ratings, see web exclusive content More Transmission Filter Tech at stg.trailerlife.com).
Magnefine Test Results
’05 Ford F-150HD 4×4, 4R75E Automatic
Beginning ISO Code 15/14/12
Ending ISO Code 13/12/9
Elapsed Miles 2,269
Micron Actual Particle Counts
Size >2 Begin/End 533/101
Size >5 Begin/End 197/37
Size >10 Begin/End 55/10
Size >15 Begin/End 21/4
Size >25 Begin/End 5/0
Size >50 Begin/End 0/0
Size >100 Begin/End 0/0
Racor LFS 22825
The Racor name is well known in diesel truck and RV circles for fuel filtration, but its parent company, Parker Filtration, is a player in every part of the filtration game. Racor’s LFS transmission filter kits stemmed from customer demand, mostly in the commercial light- and medium-duty truck markets. Shuttle vans, ambulances, delivery vans, etc., are all based on light- and medium-duty platforms and when operated in the stop and go, 24/7 environment of a working truck, trans failures are a big expense and so is maintenance. The Racor LFS kits were designed to save money in both areas.
The Racor LFS transmission filter kit uses a highly efficient synthetic media, spin-on filter with 7-micron nominal and 10-micron absolute ratings. It flows 8 gallons per minute and has a built-in bypass valve. The kit comes with the filter, filter base, bracket and fittings. With 234 square inches of media, it has a very large capacity to carry dirt. While the recommended service interval is listed by Racor at 30,000 in severe use, it seems likely it could go much farther in light-duty trucks. Optional to the basic kit are hoses in various lengths and fitting attachments.
The Racor dropped the ATF in our 1986 F-250 test vehicle a full ISO code in a very short period of time. It’s the most efficient filter in our group by a large margin and a very well-built filter. Since it’s designed for medium-duty use, it would be a very robust system in light-duty use.
Racor LFS Test Results
’86 Ford F-250 HD, C-6 Automatic
Beginning ISO Code 16/15/13
Ending ISO Code 15/14/11
Elapsed Miles 423
Micron Actual Particle Counts
Size: >2 Begin/End: 1046/358
Size: >5 Begin/End: 387/132
Size: >10 Begin/End: 108/37
Size: >15 Begin/End: 41/14
Size: >25 Begin/End: 9/3
Size: >50 Begin/End: 0/0
Size: >100 Begin/End: 0/0
BD Diesel Performance
BD makes spin-on transmission filter kits ideal for many trucks used in recreational towing applications. The kits vary according to application, but the base and filter remain the same. The base contains a built-in bypass valve that is robust and precise. The Luberfiner filter, built by Champion Labs, is rated at 25 microns absolute, 10 microns nominal. It’s a very large filter, with 325 square inches of a cellulose/synthetic blend media and has a very high-flow rate of 20 gpm. Because it has so much media it likely could be used for an extended period.
We were not able to test this setup, but given the filter specifications we would expect it to perform at about the same level as the Magnefine. BD recommends a 50,000-mile light-duty change interval, a 30,000-mile severe-duty interval and 3,000 miles for a new or rebuilt transmission.
Sources
Blackstone Labs www.blackstone-labs.com, 260-744-2380
SAE International www.sae.org, 877-606-7323
Magnefine Boss Products USA www.bossproductsusa.com
Racor www.parker.com/racor, 800-344-3286
BD Performance www.dieselperformance.com, 800-887-5030
