Micro Cleaning - Transmission Digest

Micro Cleaning

Cleaning’s not technical, right? You take a little soap and water and scrub and wash, scrub and wash some more, rinse, and the part’s clean. Or maybe you use some solvent, different chemical cleaners to get the really hard stuff and get it looking like new, so clean you can eat from it.

TASC Force Tips

  • Author: Mike Steen, Certified Transmission

Cleaning’s not technical, right? You take a little soap and water and scrub and wash, scrub and wash some more, rinse, and the part’s clean. Or maybe you use some solvent, different chemical cleaners to get the really hard stuff and get it looking like new, so clean you can eat from it.

Well, before grabbing a fork and starting to chow down, you might want to take a closer look. After doing the math, I found to my surprise that the things you can’t see can hurt you as much as the things you can. Seriously, if you looked at everyday items under a microscope, you’d have second thoughts about eating from a clean plate.

So how can the things you can’t see hurt you?

First, a quick science lesson. The smallest particle the naked eye can see clearly measures 40 microns. A grain of table salt measures 100 microns. A human hair is 40 to 70 microns. We’re talking small: One micron equals 0.000039 (39 one-millionths) inch.

The typical clearance between a valve and the valve-body bore is 0.0015-0.0005 inch. I think you can see where I’m going with this. Valve clearance – at most – is equal to 38.1 microns, which is still too small to see, but a particle of that size theoretically is large enough to stop a valve. Yes, one 38.1-micron particle probably won’t stop a valve, but there’s never just one. There are usually millions of them, and unless they’re all grouped together you can’t see them.

The ISO cleanliness code has a range that corresponds to the number of particles – 4, 6 and 14 microns – per milliliter of fluid. A test of new oil from a barrel turned up 2,440 particles larger than 15 microns in one milliliter of fluid (one tablespoon equals 14.78 milliliters).

But here’s the real kicker. Typical transmission filters will block particles of 60 to 150 microns, depending on the transmission. If the filter blocks particles any smaller than 60 microns, transmission fluid doesn’t flow well, especially in cold temperatures. Manufacturers could develop filters that catch smaller particles, but they also have to contend with cost and size restrictions from the vehicle manufacturers.

Years of research have proved that contaminants are everywhere, and transmissions are no exception. When a transmission fails, it leaves behind contamination. Contaminants tend to collect where there is little flow, just like in a river where all the driftwood collects along the sides in corners and bends, usually tangled and packed tightly. In the transmission, contaminants are carried through the oil passages and pack up in corners and grooves, hiding in every nook and cranny.

Contaminants can get into the transmission not only from the original failure but also from the remanufacturing process. For example, consider new friction material. The clutches and bands we buy from suppliers can be covered with loose particles of friction material. The OE manufacturers require these clutch manufacturers to keep the friction dust to a specified minimum or they will refuse the product. Contamination could be lurking in a piece of cardboard from the box your overhaul kit came in, or a piece of aluminum oxide from an abrasive pad.

Do you know whether the fluid you buy is clean? We require our supplier to filter the fluid it delivers to us through a 10-micron filter. Then, before it’s pumped to the test stands, it’s filtered again through a 3-micron filter. From each test stand it’s filtered twice from the sump through two more filters and again when it exits the torque converter. After all this we’ve come to realize that the test stands not only test the transmissions but also are an integral part of the cleaning process.

Doing sediment testing on a percentage of our finished product allows us to monitor how clean the process is. This involves disassembling the transmission, rinsing it and collecting any sediment, then measuring and charting it. We then can develop an upper control limit and always try to improve.

I never guessed that the saying “You can never be clean enough” was actually true. Knowing all this, at least we know what we’re up against.

The TASC Force (Technical Automotive Specialties Committee) is a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.

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