From 2004 to 2006, the Mazda RX8 used a 4-speed, fully electronic transmission from JATCO called the JR405E. Mazda calls it the RC4A-EL transmission. Approximately 48,000 of these cars using this transmission were sold in the U.S. Around the world, it has had a bit longer of a life. In fact it was used in the Chevrolet Colorado from 2004 to 2011. Here in the U.S., the 4L60E transmission was used. I don’t know how many of these 48,000 are still on the road today, but every once in a while we get a call on this transmission. And the rare times this transmission shows up on your door step, it’s good to have some information so you can diagnose and repair the vehicle.
|Want more ? Enjoy a free subscription to Motor Age magazine to get the latest news in service repair. Click here to start you subscription today.|
ENTER CODE : ART30 AT CHECKOUT
A good place to start is with a simple component application chart as seen in Figure 1. The location of the clutch assemblies inside the transmission are provided in Figure 2. The application chart also provides solenoid and pressure switch activity which we will go over further in this article. But for now, a quick look at the application chart in Figure 1 shows how the Low clutch is on for 1st, 2nd, and 3rd gear and releases in 4th. When a shift into 2nd takes place, the 2-4 brake is applied. This makes the 1-2 shift transition non-synchronous in that no timing is involved in releasing one clutch and applying another.
But the 2-3 and 3-4 shifts are another story; they are synchronous. The 2-4 brake releases while the High clutch is applied for a shift into 3rd. The Low clutch releases while the 2-4 brake applies for a 3-4 shift. This is essential to observe, as there are significant additions to diagnosing harsh synchronous shifts as opposed to a non-synchronous shift.
Characteristically, with a non-synchronous shift, you would need to consider pressure control, accumulator control, cushion plates, clutch clearances or band travel, orifice controlling check balls and fluid to friction compatibility. The same could be said for synchronous shifts with the addition of computer calculated adaptations for clutch release and apply timing control and temperature. Depending on the type transmission involved, this also might include counter balance pistons.
The RC4A-EL utilizes this strategy with the Low (Figure 3) and High (Figure 4) clutch assembly. They refer to this as a centrifugal balance system. It replaces the conventional piston check ball. Centrifugal head oil pressure generated during clutch drum rotation is used to prevent clutch drag-engagement and to stabilize piston pressure during full rotation.
To take this a little deeper, you would need to determine what solenoids and regulating valves are involved in the specific shift transition giving troubles. This also includes bushings and sealing rings that are in play. When it comes to the RC4A-EL, there are pressure switches involved, particularly the 2-4 clutch pressure switch and the High clutch pressure switch (Figure 5). Without exhausting all the variables, there still remains quite a laundry list of items to consider when fighting harsh or slipping shifts; especially synchronous shifts.