Ground locations...

[dhirocz]

Had an issue recently with my speedometer. The sensor and harness we're pretty old and beaten up, so I replaced it. Thought it was fine...

...until this morning, when I started having issues with it again. It bounces around just enough at idle...intermittently...where it will put me back into drive status if I don't watch it.

I've also had issues recently with an inadequate ground to power the trailer lights, when the headlights are on. I was able to fix some of the issue...trailer wiring related...but not all of it.

Now I was already planning on adding a ground strap to the fifth wheel to help with the trailer lights, but looking at the big picture, it looks as if I'm also having problems with inadequate grounds on the tractor. I already ordered a set of crimpers, I'll be replacing my weathered cables with welding cable, and ensuring there is a good ground to both the block and the frame.

What I'm curious about is if anyone knows where I can find all of the little grounds are at...where I can find a wiring schematic maybe? I'm sure they are also due for some love. Gotta love how paccar hides the wiring schematics!

[Chamberpains]

Did you check out the sensor pickup ring inside the tail shaft housing of the transmission thoroughly? Make sure its not chipped or worn. Sometimes the sensors will wear a groove in them if they're adjusted to close.

[Starlight]

Make sure the tranny output shaft nut is tight. A loose nut will cause an issue like that and also cause your pto or high idle feature to cut out after you set it.

[Brock]

Isn't there a specific way to install those speed sensors? Full in back out half a turn or something of that sort..........

[dhirocz]

The tone ring was not damaged.

The replacement sensor is non adjustable. It pops in with an O-ring. The sensor had deteriorated to the point where it was breaking on it's way out, but I got it out in one piece, nevertheless.

I called and had my Qualcomm reset after I replaced the sensor and pigtail. It still works fine...no issues...but let me sit overnight when it rains, then start it up and let it idle and it'll act up. Just enough bounce to set off the parking brake alarm and eventually put me into driving status. When it's dry, I get nothing...leading me to believe it's a ground that's exposed to the weather.

So far I'm still looking...I'm finding manuals for all sorts of trucks, not mine...figures!

[Chamberpains]

That sounds like the speed sensor is to close to the ring. Maybe a very small shim to give it a little extra clearance?
Also can the pick-up ring (tone ring) become magnetized from the magnetic speed sensor? Maybe causing this issue. If so can they be demagnetized?
This also a question I've had for awhile, because your not the only 1 to have this problem. But we used to ignore it because who cares, it's only at an idle. But these wonderful ELD's are forcing more work upon us so we need to address these who gives a damn issues now. Thanks Uncle Sam, I was having that "I don't have enough to do" feeling!!

[Chamberpains]

(04-09-2018 )dhirocz Wrote:  I've also had issues recently with an inadequate ground to power the trailer lights, when the headlights are on. I was able to fix some of the issue...trailer wiring related...but not all of it.

Now I was already planning on adding a ground strap to the fifth wheel to help with the trailer lights, but looking at the big picture, it looks as if I'm also having problems with inadequate grounds on the tractor. I already ordered a set of crimpers, I'll be replacing my weathered cables with welding cable, and ensuring there is a good ground to both the block and the frame.

What I'm curious about is if anyone knows where I can find all of the little grounds are at..

I don't know if you ever checked but the socket that your trailer pigtail goes in on the truck side could be corroded internally. I had a similar problem with my trailer lights messing up in weird ways. I pulled the pigtail out and looked at the socket. It was corroded green all the way through to the back side inside the cab. There is also a ground cable that attached directly to the backside of the mounting bolt inside the cab that was rusted. I cleaned that up and replace the socket and now my trailer lights are on bright and don't do weird things. It may be worth a check. I also installed mine filled with Dielectric grease then sealed my pigtail into it with a silicone sealant bead. To keep water and dirt out.

[slowpoke]

buddy of mine had the same problem driving while parked, speedo up and down triggering qualcom critical events. turned out to be wire harness in between transmission floor and frame rail, rubbed through and shorting out when raining. that was on a W900.

[dhirocz]

Figured I would post on here an update on this.

I replaced the VSS pigtail and all is well so far now. Old sensor was just in bad shape and cracked... definitely NFG. Replaced the pigtail with a good linesman's knot, solder and adhesive lined heat shrink. Also used some wire twisters and made them a twisted pair. No more issues there. I think it might have been a combination of wiring and the sensor that did it.

New sensor was almost .020" shorter than the old. I don't know if it's because it deformed due to age or because it was some aftermarket junk. Old sensor went into the can.

I haven't had time to investigate the ground through the 7 pin more yet, however I did run a braided stainless ground strap to the front of the fifth wheel as a secondary ground. Guess what? Lights on the trailer now are great, no issues there. I'll still be investigating the 7 pin, Im sure it grounds more than just that, but that strap definitely helps the trailer lighting, especially on those trailers without any LED's.

Connector for trailer lights under the cab was also replaced with some fresh wire stripped to crimp down on.