Coolers and Contaminants - Transmission Digest

Coolers and Contaminants

Most of us have been battling cooler and contamination issues for years. We may not realize it, nor care to look for it, but it does manage to rear its ugly head. First we need to look at the sources. Mike Steen (technical director at Certified Transmission) has spent considerable time on finding these sources. Along the way, I have found a few as well. Hung valves and stuck governors have plagued us for years. We thought the contaminants came from coolers. We bought flushers and flushed coolers, and the problem went away – well, not quite. We still have problems.

Coolers and Contaminants

TASC Force Tips

Author: Wayne Russell

TASC Force Tips

  • Author: Wayne Russell

Most of us have been battling cooler and contamination issues for years. We may not realize it, nor care to look for it, but it does manage to rear its ugly head.

First we need to look at the sources. Mike Steen (technical director at Certified Transmission) has spent considerable time on finding these sources. Along the way, I have found a few as well. Hung valves and stuck governors have plagued us for years. We thought the contaminants came from coolers. We bought flushers and flushed coolers, and the problem went away – well, not quite. We still have problems. Here is a list of some contaminant sources:

  1. New parts
  2. Coolers
  3. Lube passages (shafts such as in A500/518)
  4. Drums with inner stampings
  5. Passages in cases, pumps and valve bodies that cannot be accessed for cleaning.
  6. Solenoids, EPCs and pressure-switch manifolds
  7. Transmission-fluid handling and storage
  8. Cleaning wipers and abrasives (such as Scotch-Brite)
  9. Work environment
  10. Torque converters (shell-in-shell types such as smooth C6)
  11. Water and coolant.

New bushings, washers, clutches and bands are a source of contaminants. Mike noted that Certified built and dyno-tested a test batch of units with good used parts (no new bushings, washers, clutches and bands) and a batch with all new parts. The builders and testing procedures were the same. Governor problems occurred in the batch with new parts but none in the units with used parts. This was evident when the pans were removed and inspected (more residue with new parts).

Coolers are great filters. Contaminants must get into the cooler by traveling through, or originating from, the torque converter. We bought a big lathe and tooled it to open suspect converters. Since doing this, we have eliminated guessing whether we should re-use or replace a cooler by looking inside the converter.

We have found destroyed planetaries in the pan and found the converter and cooler to be OK. But when you see a “blown converter” or a wiped-out lockup-clutch lining, you’ll seriously wonder how the cooler can be flushed effectively. Impressive flushers are available, but in some instances the cooler must be replaced.

You may have come across Ford vehicles with stand-alone oil-to-air (OTA) coolers. Ford and the cooler manufacturer do not recommend flushing. Contaminants can stay lodged inside a cooler and move deeper into the cooler. Flow testing can’t assure that cooler flow will increase or decrease when the cooler is returned to full use. Engineers who design transmission coolers consider flushing to be a risky practice and believe a new cooler is best.

Cooler flow also affects the operation of lockup in some units. If flow is low (high resistance), the lockup circuit may not perform properly. Clamping pressure can be reduced, and slippage and converter failure can occur. Chrysler FWD units suffer here. Perhaps you can recall early Caravans that had 3-4 transmissions by 100,000 miles. We found that coolers were often the culprit causing early and repeat failures.

Coolers can leak coolant into the transmission-cooler circuit. In small quantity, the water will combine with the sulfur in ATF to make sulfuric acid. We have linked this to rusty transmission parts often found in some GM transmissions such as 4L60-E. If you haven’t seen this, perhaps you have seen a very rusty dipstick. Consider a new cooler or radiator. The in-tank cooler is available from GM. When water finds its way inside a transmission, inspect all parts closely and replace all friction linings and electrical components.

Passages in shafts, pumps, drums, cases and so on are yet another source of contaminants. We cannot get into all the passages because of manufacturing processes (captured passages, plugged with staked balls etc.). A perfect example of a shaft that collects debris is the A500/518 type. You must remove the plug to clean the shaft passage. Often, this plug can’t be re-used and the shaft must be replaced. Fortunately, Sonnax includes this plug in its Sure Cure kits. Remove test plugs and clean out the case passages. What you frequently will find is typical of all the passages, many of which can’t be cleaned effectively. Also, look closely at AX4S/AX4N pump shafts. Debris often is trapped between the tube and passage inside. Don’t overlook new parts.

Drums such as A4LD (4L60/4L60-E, TH 200-R4 etc.), which have a shell-in shell design, can trap debris between the shells. There is little we can do here. Mike cut the welds on some drums and examined the debris, then rewelded the drums and cleaned them as thoroughly as possible. Cutting the welds and examining the “cleaned” drums showed that the cleaning was practically useless. The only solution here is to replace the drum. Mike is working with ultrasonic cleaning, but testing is still in progress.

Electronic parts are another source of contaminants. Many rebuilders replace electronics as standard procedure. Certainly, if the transmission has a lot of wear, metal or miles, strongly consider replacing and not re-using. The electromagnetic fields attract fine metal filings. We have disassembled solenoids, EPCs and PSMs to find metal debris clustered inside. Unfortunately, most electronics can’t be taken apart and serviced.

Is your new fluid clean? You may be surprised. We have bulk ATF that we store in a 275-gallon tank and 55-gallon drums. The storage tank from the distributor, the delivery truck and your storage tanks all can be sources of contamination. We are looking into oil-testing programs and will get our ATF tested at various points where we store and handle ATF. We dyno-test our transmissions and have added non-bypass-type filtration. We fill transmissions through 40-micron and then 10-micron filters. The cooler circuit has a 10-micron filter with Sonnaflow meter and pressure gauges. Since adding these, we get less than 15 hours to the cooler filter. This means we have contaminants coming from ATF and, of course, the transmissions being tested. Better here than in the vehicle, which is why we added these filters.

We all use wipers and abrasive cleaning pads. We work in a dirty environment. Dust, lint and abrasive particles get into the units. Using compressed air to blow off parts sends particles everywhere, including into your work. Care and cleaning are essential. FYI, you can’t see particles much smaller than 40 microns.

Some converters also have hidden places to trap debris. The older C6 smooth shell has an inner shell that the fins lock into. The area between the two shells is a haven for trapped debris. Stators, fins and internal parts frequently must be cleaned by hand. The spray-cabinet cleaner may not get it all. Perhaps you should visit your converter rebuilder and see for yourself.

Remember that after rebuilding, debris remains. The new ATF has fresh detergents, and the cleaning process continues as the transmission returns to normal use. We can find debris in the pan after overhaul (sometimes an alarming amount even though everything is working just fine). This may be residual material from your transmission, cooler and/or converter.

Contaminants cause valves to stick, but with electronics we may not see hung governors. Contaminants often make their way into the lube circuit and can cause premature washer, bushing, planetary-gear or shaft wear. So don’t be fooled by the fact that stuck valves are gone. Contaminants can seriously reduce transmission life.

I hope this information has helped you in some way; it is being shared through many years of experience and failure.

Wayne Russell, president of Russell Auto Inc., Manchester, N.H., is an associate member of the TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.

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