Shift Pointers
- Subject: Incorrect installation of oil strainer in valve body
- Unit: Toyota U341F
- Essential Reading: Rebuilder, Diagnostician
- Author: Richard Graham, ATSG
No Reverse, 2-3 Neutral and No Overdrive
In rebuilding today’s transmissions one has to be very careful with the small parts that come in these valve bodies, such as checkballs, solenoid filters, springs and relief valves. These small parts might seem insignificant, but they play a vital role in the function of the transmission. Many rebuilders dread rebuilding valve bodies with all these intricate parts that are so easily misplaced or lost. On the 50-42LE found in many Volvo, Daewoo and Saab vehicles, if the valve-body filters are installed incorrectly they can cause problems such as no reverse or lockup issues.
This article is about a 2003 Toyota Matrix with a U341F, an all-wheel-drive transmission also found in the Pontiac Vibe. The vehicle came into the shop with a noise and no reverse. Upon teardown the technician discovered that the planetary was blown and that the low/reverse clutches were burned and the piston was destroyed. With these findings, the technician realized the reason for the no-reverse condition and the noise.
The technician then ordered a new planetary and an overhaul rebuilding kit and proceeded to rebuild the transmission. After rebuilding and installation, this vehicle still had no reverse (déjà-vu). The vehicle would shift through the gears from first to fourth on the lift, but on a road test it shifted first to second and then to neutral.
The technician returned to the shop in the emergency mode, removed the rear cover and discovered that the direct and reverse drum was burned. He then placed a call to the ATSG tech line for help.
I happened to take the call, and we went through different diagnostic checks as to the reason for this dilemma. After a few days of diagnosing with the tech on the line, to no avail, I told him I would stop by his shop and personally assist him with this problem. We went through the unit and I could not find a reason for his no-reverse condition. Not being one to give up easily, I told the technician that the problem had to be in the transmission – somewhere.
I hooked a pressure gauge to the main line tap, and what came next was surprising and hard to believe. There was zero pressure on the main line tap, and even with the gauge disconnected no fluid flowed from the tap. I checked the pressure for the reverse clutches, but with the same results.
The valve body was my next check. Upon opening the valve body I started to verify the checkball locations (see Figure 1), looking for stuck valves, and then I noticed something that did not look correct. I lifted the separator plate from the valve body and discovered a filter blocking a hole in the plate. The filter in question sits in a channel in the valve body with two holes in the separator plate just above that valve-body channel (see Figure 2). I set the plate over the channel and discovered that if fluid pressure entered one hole and the other hole was blocked by the filter, the fluid had nowhere to escape; it was trapped. With the filter installed upside down, oil to the manual valve was blocked (see Figure 3). This is why no oil was present at the end-cover pressure ports.
I turned the filter over and noticed a shoulder that fits into the plate (see Figure 4). When the filter is installed this way, it allows fluid to enter one feed hole, get filtered and then exit to feed the reverse and direct clutch pack. Figures 5 and 6, respectively, show incorrect and correct installation of the filter. After rebuilding and installation of the valve body, our problem was solved, because the car was now able to engage in reverse. This made the shop’s owner, the rebuilder and the customer all happy and satisfied.
Special thanks to Stephan and Jorge Lopez of Advance Transmission in Malvern, N.Y., who helped make this article possible.
