Back on the Bench - April - 2021

New is Not Always Good

…Once on the bench and disassembled, all we found was burnt forward clutches, everything else looked ok…

My co-worker recently built a 5R110W, followed all the normal procedures to protect it from the common pump failure, along with new pistons, clutches, bushings, and a new OE pressure control solenoid. After installation, he took it out for a test drive, and everything worked like it was supposed to. The vehicle was delivered to the customer, who later brought it back for the ten-day checkup.

The customer stated they couldn’t be happier, and that it never shifted better, and would leave a positive review on our website. There were no codes stored and no leaks; everything was good to go. It should last another hundred thousand miles or more, or so we thought. The customer called in about a week later, saying that the vehicle quit moving. Our first thought was that there was a pressure problem and maybe the pump broke. We thought that losing movement in both directions would definitely point to something along those lines. When the vehicle arrived, the fluid had a burnt odor to it, so we dropped the pan. We found clutch material stuck in the filter, so we removed the transmission for inspection.

Once on the bench and disassembled, all we found were burnt forward clutches; everything else looked ok. We were convinced it had to be a pressure-related issue, so we began exploring the possible causes of pressure loss. The fluid level was checked before the removal, so we crossed that off the list. The pump gears and body were in excellent condition, and though the filter had some debris in it, it was not restricted enough to prevent the transmission from pulling up enough fluid to build pressure. The solenoid body and screen plate also appeared to be in good condition, leaving us with either a solenoid problem or a command issue from the computer.

Since the solenoid had been replaced and was working, this left us concerned that it might be a computer failure. We decided to repair the transmission and check the line pressure and command after installation. The transmission wouldn’t even wiggle a tire, and the pressure was around 23 psi (figure 1). The needle would barely move, no matter what the throttle angle. The command on the scan tool looked good, so I leaned towards a computer issue more and more. We still had one test left. We needed to check the amperage on the wire to the solenoid from the computer (figure 2).

We attached an amp clamp to the solenoid command wire to check the amperage to the solenoid. We found that the amperage on the wire matched the amperage on the scan tool (figure 3), though the pressure was still low. This left the pressure control solenoid on our list of possible causes. We dismissed this at first since it was new OE, but all roads pointed there. We replaced the solenoid and rechecked line pressure. The pressure was in specifications and responding with the throttle. The transmission was now engaging in both forward and reverse. On the test drive, the transmission shifted like new again. The vehicle was delivered to the customer and is still out there working several weeks later. A wise man once told me, all new means is that it Never Ever Worked.

I take a lot of pride in my work. When one that I built shows back up at my door, I tend to get a bit frustrated and start wondering what I missed or left out. Though I sometimes tend to assume that those new parts I replaced are not the problem during the diagnostic process, I still recommend doing all the steps before replacing parts. When a transmission comes back to your door, and you’re doing your diagnostic routine, keep in mind that even though the parts are new, they will not always prevent the transmission from ending up back on the bench. Be sure to view WE GOT A FIX FOR THAT to the left of this article!