Shift Pointers
- Subject: Loss of reverse after replacement of forward planets
- Unit: 5R110W
- Essential Reading: Rebuilder, Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
Have you ever built a unit that went out running absolutely fantastic but came back with a problem only a month or two later? Maybe you were so good to that transmission that it was missing you and wanted to come back for a visit!
So it went for Trent at Acadiana Transmissions in Louisiana with a 5R110W that needed forward planets, a common failure this unit has. It left the shop after the repairs working like new, only to come back a little over a month later with a problem it never had before. The most-obvious problem was a loss of reverse, but in forward it felt as if it had 4th and then lost 4th. It seemed to have shifted three times but then it shifted only twice. Here is why it was hard to tell.
This unit is actually a six-speed transmission but uses only five gears at any given time. When it is cold (5º F or below) the unit will shift 1-2-3-4-6. When it warms up it shifts 1-2-3-5-6. If you look at the application chart in Figure 1 you will see that the direct clutches are used in reverse, fifth and sixth. If these clutches cannot apply, you can see now why a loss of reverse is obvious but forward may be a bit more difficult to describe. You also may have noticed that fourth gear has a slightly higher ratio than fifth but not enough that you can feel it by the seat of your pants. Overdrive is sixth gear, which when the unit is working correctly is used in both the cold and hot shift modes.
What happened to Trent is that the sleeve on the center support walked, causing a loss of direct-clutch apply oil as you can see in figures 2 and 3. So why did the sleeve walk? That’s easy – Mr. 5R110W missed Trent. He wanted to come back for another visit! So Trent gave him an upgrade by replacing the center support with a new one, and he is still out roaming the streets to this day.
