By far the most common problem I come across when repairing 5HP24s is the failure of the axial bearing between the B-clutch hub and the C-clutch drum



which allows axial movement in the input shaft assembly leading to the O-ring seal on the A-clutch to split



When the fluid is cold, the oil pump is able to keep up with the leakage through the seal so the transmission operates normally. After around 20 minutes of running though, once the fluid is up to temperature, the reduced viscosity of the fluid means that the leakage is so high that the pump can no longer maintain pressure on the A-clutch and it slips.

The A-clutch is used in 1st, 2nd, 3rd & 4th gears so the transmission controller has no option other than to engage 5th (usually with a bang, because it doesn’t have an accumulator to damp the engagement) and flag the transmission failsafe message. The A-clutch isn’t used in reverse.

When the transmission cools down it functions perfectly again and then the whole cycle repeats. Do you think that this might be the same problem that you are experiencing? Might it be 5th gear that your transmission is engaging when it flags the failsafe message rather than 4th?

You could easily test the PTC sensor, which is built into the electrical wiring loom, just using a multimeter rather than risk spending money on parts that you don’t need which could be put towards a rebuild





The temperature signal is transmitted via pins 13 and 14 on the electrical connector at the back of the main casing, and the resistance between the pins should follow this characteristic :



Phil