AX4S/AX4N - No Go/No Charge - Transmission Digest

AX4S/AX4N – No Go/No Charge

With their fingers crossed and the cooler-return line still in the bucket, they start the car up. The cooler line makes a little pop, a spit, some foamy fluid then, lo and behold, a nice clean steady stream of fluid comes out of the line. Mission accomplished. The converter has charge. After the cooler line is re-connected, the trans is topped off, road tested and everything works perfectly. End of story you say. Not quite yet. The question that remains is what did we do to correct whatever was wrong with the unit? We did not find anything to point a finger at as to the cause of the problem.

AX4S/AX4N - No Go/No Charge

Shift Pointers

Author: Gerald Campbell

Shift Pointers

  • Author: Gerald Campbell

OK, so the story goes something like this. Once upon a time an R&R technician finishes turning all the nuts and bolts on his Taurus, and satisfied that the installation is complete, he lowers the vehicle to begin filling the unit with the appropriate fluid.

The trans has just been overhauled or exchanged with a fresh one off of the shelf. He is quite confident everything will work fine because the technician that put this one together always has had a near impeccable track record. Comebacks or “no goes” have been virtually nonexistent when this builder puts them together. Why would this one be any different? We’ve never had any problem with these vehicles in the past.

This R&R tech is no slouch either. He knows enough to dump 4 or 5 quarts of fluid into the unit before the key is even turned. The car is started and the tech immediately begins to add another 5 or 6 quarts as the engine is running. Satisfied that he is getting close to the factory fill requirement he wipes the dipstick clean and feeds it in to the tube to get an idea of how much more fluid may be needed. (He doesn’t want to overfill it either. He’s had his ear chewed on for that before!) Much to his disbelief, the trans fluid is so high on the stick that he is thankful it didn’t run out when he removed the funnel. Anyhow, no harm done, no mess yet. “We’ll just lift her off of the ground and run her through the gears to charge all of the clutch packs and servos. Then we can check it again.”

So, he climbs behind the wheel, puts his foot on the brake and places the shifter in D, then manual 2, then 1. Hmmm – nothing. All right, then let’s try reverse – nothing. What the – Well you know what was said so I won’t repeat it. At this point he calls the builder over to check it out. Together they recheck the linkages etc. Everything seems to be in order, but the level is still too high on the dipstick even though a total of 10 quarts was all that was added. Bone dry; this unit requires almost 12 quarts. So what’s going on here?

Out come the oil pressure gauges. (Everyone has a set of these, right?) When the line pressure is checked, it is found to be within the normal range at an idle. How can this be? If it’s so high on the dipstick, then it would seem as though we’re not picking up any fluid. There’s no more than 10 quarts of fluid in this unit. How can you have good line pressure if you are not pulling any oil? Obviously the pump is turning. Seems strange, don’t you think?

Being very thorough, this builder decides to make one last check before making the call to yank it out for a re-¬inspection. Upon disconnecting the lower cooler line and placing it in to a clean bucket it is discovered that there is no fluid coming through when the engine is running. This would lead us to believe that the cooler may be plugged. But not so fast. Let’s pull the top line first to see if there is any fluid coming out of the transmission going to the oil cooler. Hmmm, no oil out of the top line either. Now we definitely have a problem with this unit.

It’s late Friday afternoon, the boss already has called the customer to come and pick up their car, and they are on their way to the shop. Unless we can rectify this situation quickly, ain’t nobody going to be happy!

Knowing that the problem is not likely to be with the converter itself, both technicians decide to pull the side cover and valve body off to check for a mis-aligned or incorrect gasket. Maybe there’s a hole that didn’t get punched through the gasket. Who knows?

Once the control valve is on the bench all these possibilities are checked and everything seems to be in order. The valve body is inspected meticulously, with particular attention being paid to the converter regulator and bypass valves. Again, all the valves are free, no problem is found here. Even the round steel sleeve that’s pressed in to the valve body is not found to be loose, and the feed hole in the sleeve is still perfectly aligned with the passage in the control valve casting.

Next, remembering a TSB that he had once seen, the builder decides to check the pump shaft for blocked or incorrectly connected passages (see figure 1). Again, everything is as it should be. (Did I mention that these people were thorough?)

Realizing that he’s running out of options, the builder is ready to make the call to yank the unit back out again. Maybe something was damaged or mis-assembled with the stator, turbine shaft rings, or a feed hole plugged. But as a last ditch effort, these techs decide to bring the bulk oil pump gun over to the vehicle and placing the tip of the gun in the open end of the turbine shaft that’s exposed with the pump shaft removed, they pump as much fluid as they can in to the converter through the turbine shaft. The pump shaft is dipped in fluid to coat the rings. The valve body and oil pump are re¬assembled and carefully installed back in to the unit again for one last shot at getting the customer on their way by the weekend.

With their fingers crossed and the cooler-return line still in the bucket, they start the car up. The cooler line makes a little pop, a spit, some foamy fluid then, lo and behold, a nice clean steady stream of fluid comes out of the line. Mission accomplished. The converter has charge. After the cooler line is re-connected, the trans is topped off, road tested and everything works perfectly. End of story you say. Not quite yet. The question that remains is what did we do to correct whatever was wrong with the unit? We did not find anything to point a finger at as to the cause of the problem.

Chapter 2: (I promise this chapter will be short and sweet) OK, so John (the R&R tech) and Jeff (the builder) are cleaning their tools and putting things away at the end of the day. John turns to Jeff and says “Hey man, what do you think was wrong with that thing?”

Jeff turns to John and says “Listen; did you dump 2 or 3 quarts of fluid in to that converter to soak that converter clutch? You know we should be doing that with all of these units.”

Hesitantly John replies “Ah, no, but I’ve never had to do that before. Besides, we’ve never had this happen to us before. Why?”

“Well,” Jeff says, “we had it happen today and the only thing that we did any different was to pump oil through the turbine shaft into the converter to prime it. Then it worked. What do you think?”

The moral of the story: PRIME THAT SUCKER!!!!

And no, this is not a fairy tale! Only the names have been changed to protect the not so innocent.

Gerald Campbell is a technical consultant for the Automatic Transmission Service Group (ATSG) and a frequent contributor to Transmission Digest.

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