Alright, here's the deal. I just threw my new Motorcraft speed sensor in, and checked the fluid level while I was down there. Fluid level was perfect, and the fluid looked to be in good condition.

I test drove it immediately after. The entire time, it shifted much better than with the old VSS. I was actually quite amazed by that. I had no idea how poorly and inconsistently my truck was shifting until I got the new one in. All shifts are now as expected and exactly on cue.

The speedometer reflects the speed accurately until I hit approximately 50 mph, at which point it starts doing a slow, smooth wobble that covers +/- 1mph. This wobble continues, which covers an ever increasing amount of mph as my speed increases, growing to about +/- 2.5 mph at around 65. Somewhere around 65, it then starts violently bouncing, covering about +/- 10-20 mph.

I can post a video tomorrow if it would help you guys.

It seems like at this point I have a choice between poor shifting with an accurate speedo reading, or a poor speedo reading with perfect shifts. I would optimally prefer to have both. What could I do to make that happen?

 

Here is a recent thread that might help you out.

 

Okay, it must be rust on the surface of the axle, then. That makes a lot of sense, and there is definitely rust there. I'll scrape it tomorrow. I guess I'll need to replace the fluid again. It's practically new fluid. Darn...

Thanks, Pete. Somebody rep this man for me, it won't let me do it.

 

Don't replace the fluid. Just be as careful as you can not get junk in the hole. Maybe even stuff a rag in there but I think you will be fine even if you get a few specs in there.

 

Okay. I'll try to keep the junk out there, but if worse comes to worst, I can always replace the fluid again. It's not that big a deal. Also, it would give me a chance to clean out that vent, which I forgot to do last time. Where is the vent located, by the way?

 

The vent hose will come off the axle housing and follow the brake line that feeds the rear brakes up. Follow the hose up to the driver side frame and you'll find that funky vacuum y / t looking plastic thing on the end. I use a 1/4 inch plastic fuel filter as a replacement.

 

So the thing to clean out is the plastic thing on the end? I'll take a look at it tomorrow. I may wind up doing the fuel filter thing, too.

 

......Yep........

 

Well, I didn't know if it was advisable to clean out the entire hose or just the end thing. It wasn't entirely clear to me what you meant. Especially without the hose out in front of me, it was difficult for me to tell. Now I understand what you mean.

Thank you for your help.

 

So, I'm still running into the poor shifting and P0500 every once in a while. I'm going to go ahead and rule out the sensor itself for right now, because I've swapped sensors God knows how many times, and the problem still occurs.

I talked to a guy and he said that I've probably got a wire that's chafed down to bare, and it's causing electrical interference when it hits it the right way. Does that sound like a good place to start troubleshooting? I plan on tracking down the wire from end to end and seeing that it's in good condition. While I'm at it, I'll check all of the connections and everything, too.

The guy also mentioned ohm testing at all of the connections. What does he mean by this, and how can I do it?

You guys will have to forgive me. I'm especially idiotic when it comes to electricity. Thanks in advance for help.

 

I'm an idiot with electricity too, so don't feel bad. Definitely visually check the wiring, starting at the rear working forward. Maybe someone else can help you with testing the connections.

 

ohming out the wires typically involves disconnecting both ends and verifying continuity between the pins at either end of a given wire. very time consuming but usually worth it. A thorough visual inspection (looking for chafes, etc) is also a good thing to do.

Only issue with the ohm test, with a DVM, is that it is a very low current test. Fine for sensors but not for anything that has a significant current draw. I've seen too many boat harnesses where the ohm test shows all is well but a wire/connector has corroded and as soon as the load draws current, the voltage drops and nothing works correctly.

We've got the minor wobble at 50+ on the speedo needle so I've got a vested interest in your situation, too. time to reread those other posts.

good luck.

 

Okay, so I followed the wire into the group of wires that runs along the frame with it. Somewhere along there, it looks like someone cut open the protector that covers the group of wires and pulled them out. One looks like it's been repaired and another has the insulation worn away and blue corroded junk on the inside, which I assume is corroded copper wire. Whether it is the speed sensor wire or not, it needs to be repaired. What is the best way to determine which wire is the speed sensor wire?

 

Clean the wires off as well as you can and determine their colors. Many will have a stripe (tracer) in addition to the main insulation color. Some harnesses will also have wiring with different size conductors. When you know what you are looking at, open the service CD and go into the wiring (electrical) section. Find the schematic(s) for the harness you are working on and then find the wire(s) that match.

based on another post, the VSS wires are likely to be LG/BK (light green w/ black tracer) and R/PK (red w/ pink tracer). Also, on the factory schematics, most circuits have a unique ID number assigned. These are mostly of benefit when you need to trace a signal across multiple schematics.

That give you enough to continue down the debug road?

 

Yes! Thank you very much. That is exactly the kind of information that I was looking for. I'll boot up that factory CD when I get off work. I'm on my meal break right now. Don't get off until 8pm. And if I don't get to it tonight, I'll surely get to it tomorrow, since I have tomorrow off.