While I've done my share of automatic transmission work, I've never really been a big fan of it. I even did transmissions as a specialty for awhile, but I never enjoyed working with fibers, steels, snap rings and spool valves as much as the computers, wiring, spark plugs and sensors of the driveability area. Admittedly, when electronics invaded transmissions, they became a bit more interesting. It's not that the money is any better in driveability/automotive electronics. But it takes a special kind of a person to enjoy doing automatic transmissions. A transmission technician worth his or her salt in a busy shop can take home some astounding paychecks at the end of the week. But we all know that takes a tech with the right stuff and even more true grit than Rooster Cogburn to hammer out a living working on transmissions day after day. You've got to love it or leave it.
DEAD IN ITS TRACKS
The first transmission I ever rebuilt was a 727 TorqueFlite, and as I was carefully disassembling it and laying the parts out on the bench, a older tech who had done some transmissions work came by and removed one of the inner lip seals to inspect it while my back was turned. Because I hadn't removed a seal from that slot, I didn't think to put a new seal back in there. We all know it's best to keep our hands off somebody else's work, particularly when so many parts and critical steps are involved.
This month's vehicle was a high-mileage Dodge Dakota that came in on the hook because the transmission would barely pull out of its tracks in forward gear; it responded a little better in reverse, but it was still no prizewinner. This 42RH unit is basically a modified 904 Torqueflite (32RH) with an overdrive compounder unit outfitted with an additional planetary gear set, which replaces the extension housing and provides a fourth gear ratio of 0.69-to-1 to boost the fuel economy at road speeds. I gave the Dakota job to Josh and Red, two of my students, who both had practical mechanical experience but no real internal transmission experience to speak of beyond fluid and filter changes.
The transmission was full of dark, smelly fluid. A quick pressure test at idle showed that it had enough line pressure to apply the clutches, but with the fluid in the shape it was in, a pan snatch was the smartest next step. The pan was loaded with glitter and a dark fluid residue, and the magnet was nice and fuzzy with metal pieces.
MOVING TO THE BENCH
A couple hours later, Josh and Red had the transmission spread out across the bench in all its glory, and there was nary a burned clutch or hard seal in sight. As a matter of fact, all the internal hard parts, including the disassembled pump, looked just as pristine as the clutches, with the exception that there were metal particles of various sizes everywhere. It was one of those confusing situations that left these burgeoning techs wondering what the heck was going on and what they needed to replace in order to get this problem taken care of. In other words, a "pizza box" repair wasn't going to straighten this one out. There was only one place left to look.
Taking the front clutch housing with its turbine shaft, I went to the torque converter and found the problem. Engaging the turbine shaft in its splines, I found that the turbine had welded itself to the impeller. Among other things, a loose transmission filter or damaged filter seal can pull air into the fluid supply and cause a failure like this, because the resulting air bubbles always find their way to the center of the converter when it's spinning, and that's the part of the torque converter that needs lubrication the most.
This filter wasn't loose, but it was evident that the Dakota would need a replacement torque converter, and while we were in there, we might as well replace the gaskets and seals. We also needed to take the time to clean the valve body and the governor (the 42RE electronic version of this transmission doesn't have one). Because the fluid leaves the torque converter in an unfiltered stream and goes to the transmission cooler in the radiator, it was a foregone conclusion that the cooler would be loaded with metal as well.
When the metal comes from somewhere besides the torque converter, it's a good idea to flush the converter as well if you have the equipment or replace it, because getting all the metal flotsam out of the converter is nearly impossible. In those cases, including this Dakota, it's wise to either replace the radiator, or if cost is an issue, take the contaminated cooler out of the loop and install a good quality external transmission cooler. In an attempt to contain the cost of this job, it was nay decision to take a chance on having the students flush the transmission cooler and lines with denatured alcohol and transmission fluid and install an inline filter in the cooler return line near the radiator. The inline filter is actually an authorized repair on Ford vehicles.
BACK ON THE ROAD ... BRIEFLY
On reinstallation, there was a problem with the replacement torque converter: Three of the flywheel bolt holes would line up but the fourth one was about one-half of a hole off--no matter which way the converter was turned or which holes were used for which bosses. I called the vendor, and he knew right away what the problem was. He had sent us an incorrect converter, and when he sent the right one, it fit like a charm. It was surprising that a wrong converter could be so nearly the same as the right one.
Josh figured he had done a good job flushing the transmission cooler, so he chose not to install the inline filter on the return line. As his instructor, I let him make the decision, figuring he would either be lucky or he'd learn a hard lesson. After all, that fine paper filter Chrysler has used for so many years might just do the job.
Test driving the Dodge revealed a smoothly operating transmission, but the 3.9L engine had a seriously annoying misfire under load that made it feel like there were machine guns mounted on the fenders. I secured the customer's approval, and we went after the skip.
We found worn plugs and a plug wire boot that was leaking spark, so I ordered a set of plugs and a single lead from a local parts supplier, only to find that it only partially corrected the concern. Another leaking spark plug wire goaded us into replacing the whole set of wires, which initially seemed to make a big difference in the performance of the truck, but then the skip returned but with different qualifies. Not only would the engine misfire under load, but it would misfire intermittently at idle. Nothing was evident on the oscilloscope to indicate the cause of the intermittent idle misfire. This was getting personal, and in the interest of putting the Dakota back into the wind, I wasn't about to take it lying down. In chasing this anomaly, I rapidly drew a number of conclusions:
A. The #2 cylinder was the guilty party. It was the one that made no difference when the spark was shorted away and the skip was present.
B. Allowing the spark to jump to the plug, I noticed that spark was always popping, even when the misfire was underway.
C. The injector on cylinder #2 was clicking away, even during the misfire.
D. The Dakota was outfitted with a returnless fuel system.
E. The fuel gauge showed less than an eighth of a tank of gas, but it was above empty.
Drawing on past experience, I remembered a late '90s Dodge van I had encountered a few years earlier with basically the same fuel system and the same concern. Having been slapped around royally by the van, I took notice of the fact that the #2 injector was at the highest point on the fuel rail on that side of the engine; any air bubbles that entered the rail from a cavitating or air-sucking fuel pump would tend to gather at the mouth of the #2 injector, much the way aerated fluid gathers at the center of a torque converter. The cheapest and smartest thing to do was add a couple gallons of gas, which we did. That fixed the skip, as I figured it would. Another test drive was in order.
CAT'S ON THE ROOF
Josh came back from his test drive with a long face. The transmission was hung in high gear. I smiled inwardly. The inline filter would have been a good idea. However, when he pulled the pan again, we found all three filter screws loose. Somebody had finger-tightened the filter screws and both students thought the other student had torqued them. A lesson learned, but that wasn't the worst of it: In the pan, we found more metal filings and tiny needle bearings from the overdrive piston thrust bearing.
To make a long story short, when Josh disassembled the transmission the second time, he found that he had mistakenly installed the thrust bearing backwards, and the paper-thin, super-brittle races had shattered, allowing the whole bearing to cross up and come apart.