Trans jumps out of gear

[RoadSailor]

I’m looking for any suggestions to figure out why my transmission jumps out of gear. I’m not finding much of anything in my research so far, so hoping someone here has experienced the issue.

My motorhome is 1995 Fleetwood Pace Arrow built on a 1994 F-53 chassis with a 460 V8. It has 63k miles. Intermittently, the transmission jumps out of gear. After a short time, from nearly immediately up to a couple seconds, it goes back into gear. Based on how high the engine RPMs jump up when this happens, it is more than just the overdrive dropping out. It acts like I suddenly shifted into neutral.

Trans fluid level is within operation range. The oil does not look burnt or dirty.

Occurrence is random. I haven’t been able to isolate the circumstances to make it happen. Sometimes it happens at the beginning of the trip. Sometimes it occurs after driving 5 or 6 hours. Sometimes it’s when raining. Sometimes it’s when the roads are dry. Sometimes it’s when under a “load” (i.e. climbing up an overpass) and sometimes when there’s no load (ex: going down the overpass hill).

This started about 2 years ago. For a long time, it would happen once in the entire trip. It is more frequent now, happening multiple times in the trip. I have found that if I pull over, shut off the engine, then restart, it resolves the issue for a number of hours (usually the rest of that day’s drive). For example, I drove it about 6 hours total yesterday. At 2 hours, it started dropping out. I did my “pull over/kill engine/restart” bandaid. It worked fine the rest of the day.

The intermittent behavior suggests a poor electrical connection somewhere or a failing electronic component. I’m thinking if it was a mechanical issue, it would not be intermittent. Also the “pull over/kill engine/restart” bandaid would have no effect on a mechanical issue.

Has anyone had a trans do this?

Thanks much in advance for any suggestions.

[Mark Kovalsky]

When I saw the title of this thread I *KNEW* this was a mid to late 90's chassis. When I was an engineer at Ford I spent some time researching this very problem.

Replace your MLPS (Manual Lever Position Sensor,) also known as the TRS (Transmission Range Sensor.) It is located on the driver's side of the trans. It is the part with the wiring harness plugged in.

Normally I require reading codes before replacing anything. This is the exception. This fault will never set a code.

Here is what happens. The sensor has a series of resistors. The lever inside makes contact with each additional resistor as it moves through its range. As it wears dirt and debris can build up under the contact. This causes additional resistance which the PCM interprets as the driver moving the shifter from D to N. What do you get with the shifter in N? Nothing! The PCM can't tell if the resistance is wrong or that you really moved the shifter.

The fix is to replace the sensor. It isn't very expensive and not hard to replace.

[RoadSailor]

Thank you so much for your reply! I ordered up a replacement MLPS from Rockauto, which included a new connector for the wiring, and installed it. Installation was easy except for unpinning the wiring from the old plug. I wasn’t able to find any video about installing the new connector, so getting the wires unpinned from the old plug without damaging them was a trail and error exercise. But I did finally win, and finished the installation.
I’m happy to report the truck is now fixed. No jumping into neutral, and it even seems the trans shifts a little “softer” now!
Thanks again for your spot on long distance diagnosis!

[TeJay]

Way to go Mark K. Great diagnosis as usual. Man those years of experience in the transmission world sure have come in handy over the years and especially for many of our forum folks. There's nothing like real world experience to solve some of these issues. Great job and many thanks for your swift reply to the OP.

Usually some of these happen so infrequently most technicians today have never encountered them so they just remove and replace parts until something gets fixed and we know that's all at the cost to the customer. The worst case for the OP would have been for a tech to just recommend a transmission rebuild.