The Word On The Street - January/February - 2016

They Said It Couldn’t Be Done

I was doing some research at a local shop one day while they were working on a late model Toyota Camry equipped with a 2.5L, 4-cylinder engine and a U760E transmission. The transmission was slipping on takeoff and the fluid was burnt.

They pulled the unit, disassembled it, and there it was: The C1 forward/C2 direct drum was black. At the time, the molded piston for the U760E C1 forward clutch wasn’t available; the only piston available was for a U660E that fits behind the 3.5L V6 engine.

Why was the U660E piston available but not the U760E? Because the U660E was failing a lot because the molded C1 forward piston was failing. That increased the demand for the piston so it was more popular to produce.

The shop had a U660E core, so we took it apart to examine the C1 forward/C2 direct drum assembly. Unfortunately it was nothing like the U760E. Rats; we thought we’d get lucky and be able to use it, since they had a new piston for that unit.

Figure 2

This was a typical, end-of-the-week customer who wants his car back for the weekend. So, while the shop was calling around for a U760E forward drum or a rebuildable core, I took a closer look at the two drum assemblies sitting side by side on the bench.

The first thing I noticed was the corrugated area on the U760E and the upper windows and corrugations on the U660E C2 apply sleeve. These corrugated areas and the upper window openings are what the input speed sensor monitors to develop the input speed signal to the ECM. So I counted the slots and windows: There was the same number of corrugated slots on the U760E as there were windows and corrugated slots on the U660E.

I measured the corrugated slots and window openings with a caliper and discovered they matched. Then I measured the outside diameters of both assemblies; they matched too (figure 1).

Next, I placed the two C2 apply sleeves on top of each other; as you can see, they matched up quite well (figure 2). The only other difference I could find between the two assemblies was the U660E C2 apply sleeve was a bit taller than the U760E apply sleeve (figure 3).

With so many similarities, I decided to try to install the U660E drum assembly in the U760E case (figure 4). I needed to see if the longer apply sleeve would hit anything inside the U760E. Turns out there was plenty of room for the taller U660E sleeve. When I showed this to the rebuilder and shop owner they looked at me as though I were from another planet.

I convinced them to give it a try; the only issue that concerned me was that we might get an input speed sensor code. But if my measurements were correct, the swap should work without any issues. The other benefit of using the U660E forward/direct drum assembly is the U660E drum holds three clutches instead of the two in the U760E drum.

When the unit was installed it shifted fine on the lift, but the check engine light came on and the transmission went into failsafe. We connected a scan tool and read the codes: the only code was P0717 — no signal from the input speed sensor. “Damn,” I thought to myself. “My measurements were dead on; it should have worked.

The shop owner wanted to pull the unit back out but I stopped them. I wanted to put an oscilloscope on the input speed sensor to see what type of signal, if any, it was creating. The oscilloscope showed no signal at all; the sensor should have created some signal, even if it was weak or incorrect.

We had another speed sensor from the U660E core, so I figured, why not? Both sensors measured the same and the part numbers were the same for both units. We swapped the sensors and, sure enough, the input speed signal looked fine on the scope and the scan tool data. Once we cleared the code, the unit shifted like new and the code didn’t return. Job done!

If you are going to swap the drum, it’s always best to replace the U760E drum (two clutches) with the U660E drum (three clutches) because the additional clutch provides more load capacity, but they’ll work either way.

There are times when a vehicle just has to go and you can’t find the parts to get it finished on time. That’s when it’s so important to have a clear understanding of how the systems in the transmission work; that understanding is what can open new doors — and provide new solutions — for you and your customers.