I have a 1994 E350 28’ motorhome, 460 engine, auto trans, with 31,000 miles. On a 5000 plus mile trip out west a couple months ago, the trans started slipping out of high gear occasionally, ABS light began coming on intermittently and cruise control was intermittent as well. When I would stop for gas/cut the engine, it would stop, then without warning it would do it again. Also of note, when the speedometer gets between 55 and 65, it begins to bounce a little and there it's a bit noisy – not quite a grinding noise, but noisy. It will level out past 65 and stop bouncing. Trans fluid is at level and looks fresh and pink. I changed the VSS on the rear diff and it was great for about 50 miles, now seems to be getting worse – ABS light stays on and now trans hunts gears more often, not just in high gear. Took the diff cover off and the tone ring looked good – about 6 teeth were burred and I knocked the burrs off with sand paper, reinstalled cover and refilled with fresh gear oil. Test drove, still does it… maybe worse. I bought the VSS at the corner auto parts store, just bought a new one at the Ford place but haven’t installed yet, but pretty skeptical it will fix the issue. Have read on the web guys with the exact issue, and they have gone so far as to have the trans rebuilt – and they still have the issue. Seems to be common on the 1994 E350’s. Any ideas? Thanks!<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>

 

The transmission would be OK.
The problem is in the circuit between the dash and the rear end.
I would clean the VSS that you took out first and put it back in if you did not brake it as very seldom if ever do they go bad.
More than likely bad bearings or tone ring in the rear end.
You can unplug the PSOM and the ABS plug and run it up to about 30mph on jack stands and check the voltage or frequency coming from the rear end at the ABS test plug. A scope also helps out a lot looking at the AC signal.

 

Before you rebuild the trans let me tell you that I am 99.9% sure that the problem is NOT in the transmission. The PCM is getting bad data and making bad decisions based on that data.

Since you have speedo and ABS issues I suspect that's where the problem lies. The PCM uses vehicle speed to determine what gear the trans should be in at any given time. If it sees the speed drop it may determine that the trans should downshift. Changing the transmission won't make a bit of difference to this.

I would install the Ford VSS. You already have the part and it is a very easy job. My confidence that this will fix the problem is low, but I have heard of this type of problem from aftermarket speed sensors, so it's worth trying.

If that doesn't do it the next most logical step is to check the wiring. While a visual inspection won't hurt, it won't find 95% of wiring problems. To check the wiring you need a wiring diagram (I don't have one) and a meter. You need to check both wires for continuity, short to power, and short to ground.

Sometimes just running new wires and abandoning the old ones will eliminate the problem even if you don't find anything obviously wrong with the wiring.

If there is no problem found there the next place to look is the PSOM module. This is on the back of the instrument panel and converts the pulses from the VSS into a vehicle speed. They have been known to be a common problem. I don't know of a good way to check it, but someone else might.

The other possible way that the trans can slip out of high gear is a bad TRS (Transmission Range Sensor.) It can also be called the MLPS (Manual Lever Position Sensor) or NSS (Neutral Safety Switch.) Whatever you call it, it is located on the driver's side of the trans where the shift cable attaches. It is the part with a wiring harness attached.

There isn't a good way to test it on your truck. Changing it might fix the problem, but it certainly won't do anything to help the ABS or speedo problem. It's about a $40 part and 10-15 minutes to change.

 

Update: first, thanks for the info guys. Very helpful. Well, this evening I put the Ford VSS in and didn't even get out of the driveway and the abs lite came on so I didn't test drive. With the Ford VSS in, I also changed out the neutral safety switch. Fired it up... No abs light. Took it up the road, 5 or so miles... Got up to speed 60-65 mph... Went though the gears... Ran like a champ. I'm cautiously optimistic. Headed to Knoxville this weekend (for some football), its about a 2.5 hr drive one way so I'll report back and see how it goes. Again, really appreciate the feedback

 

Good luck rickwhis, hope that does it. A thought I had was possible corrosion build up between the VSS and the diff housing, pushing the sensor away from the ring. I admit I have not seen it happen on trucks yet, but have seen it on the Ford Contour.

 

The neutral safety switch has nothing to do with the abs lite or the speedometer.

 

Ok, here's the report on the trip. I put about 150-200 miles on it this weekend. The roads and speeds varied from interstate speeds to winding back roads and up and down mointains. The trans shifted flawlessly. Solid and smooth the whole way. I think it ran cooler and got better gas mileage as well. Makes sense since the trans wasn't dropping in and out of gear causing the engine to rev over and over. The ABS lite stayed on the entire trip, but really, that's a minor issue as long as the trans issue is better. I have a 99 F250, 7.3 power stroke with 161k miles and the abs lite has been on for the 5 years, so no big deal. Thanks for the help guys. Hopefully this puts that issue to bed.