Shift Pointers
- Author: Pete Luban, ATSG Technical Supervisor
Pump/case mismatch causes fluid loss through filler tube on JR403E
Lately on the phone lines, we’ve had a rash of calls concerning transmission fluid spewing out the filler tube on trucks equipped with the JR403E Electromatic transmission once the transmission reaches operating temperature.
Technicians spend a lot of diagnostic time checking cooler flow, making sure that lockup doesn’t quit working and determining whether the pump is causing cavitation because it’s bad.
Well, the transmission cooler is not the problem. Lockup does not quit working. The pump is not bad; however, it might not be the right one for the case you are using.
If you look at Figure 1, you will see that the vent tube is on the driver side of the case. This is an early case. In Figure 2, the pump surface in the vent-tube area is smooth; this is an early case. Figure 3 shows the area of the case where it mounts. This area is cast in such a manner that there is no provision for a vent tube; you will see why soon.
In Figure 4, you can see that the vent tube is on the passenger side of the case, the opposite of the early case. This is a late case. In Figure 5, the pump mating surface in the area of the vent tube has channels cast into it; this is a late case.
In Figure 6 a rubber vent hose is routed from the vent tube to the area of the case where it mounts. Figure 7 shows where the rubber vent hose ends. The mount area has provisions for a vent tube in that location; this is a LATE case.
Now, to the pump. I said earlier that the pump itself is not bad, but it could be the wrong one for the case you’re using. Look closely at the early and late pump assemblies in Figure 8. There is a difference.
See the difference? Take a look at the pump assembly in Figure 9, noting the area that’s highlighted. See how it’s recessed? This is an early pump. Now take a look at the pump assembly in Figure 10. See how the highlighted area is raised and that it has a couple of air bleed holes. This is a late pump.
So, what this all comes down to is pieces and parts; in other words, the parts are not compatible with each other. So if you have an Electromatic that’s spewing fluid, and all the other items that can cause this complaint check out, maybe you have mismatched the pump and case. I hope this removes some of the mystery behind this problem that’s plaguing a number of you out there.
Many thanks to Rolando Farradas of Rainbow Transmission in Hialeah, Fla., for helping to clear up this mystery and for providing the parts and pieces necessary to produce this article.
