No ground on rear axle?

[trouble]

Got a good one for you. Early 99 Superduty. Installed a differential temp gauge in truck awhile back and it would only work now and then when the truck was driven in the rain. Got under it to check it out and I had no ground on the rear end! Now with all those parts tying it to the frame I couldn't believe that it wasn't given a ground. I can see shocks and leaf springs with the rubber bushings and all not giving it a ground, but thought for sure it would get one through the drive shaft and tranny. Learn something new everyday.

 

[DaveBen]

My truck has a speed sensor on top of the rear end gear housing. It has a couple of wires, and I believe one is ground to the sensor, but not the axle. I never thought of this.

Dave

 

[KRISTOLSON]

pretty crazy... brakes, driveshaft, springs, shocks and everything and no good ground.

 

[DaveBen]

You can add Parking Brake cables to your list Kristolson. I am not understanding why the rear axle is not grounded electrically. And I mean from Ford.

Dave

 

[trouble]

Yep, no ground whatsoever on my rear axle. Stuck that test light all over it. Ran one up from axle to frame. All is good now. Never would have thought though.

 

[KRISTOLSON]

I guess thats why my grain trucks with electric 2 speed rears all have big ground straps from the axle to the frame. Ford probably crunched the numbers between a dedicated sensor ground wire all the way back up front and a grounding strap and saved a nickel or two.

Can you imagine the damage you could do by welding on the rear axle with a ground clamp on the frame, or vice versa? All the current trying to run through the sensor wire and the drivetrain module (for speed sensor) or whatever your temp sensor runs to? Or further? yikes. Guess thats why they teach you to put the ground on the same piece of metal if possible

on edit- assuming the sensor would have a chassis ground as well as a ground wire

 

[trackspeeder]

You can add Parking Brake cables to your list Kristolson. I am not understanding why the rear axle is not grounded electrically. And I mean from Ford.

Dave

The only electrical part on the diff is a VSS. It has its own wiring. Nothing else need electricity, so a ground is not required.

 

[JLDickmon]

The only electrical part on the diff is a VSS. It has its own wiring. Nothing else need electricity, so a ground is not required.

a VSS is an AC pulse generator anyway.. both wires are hot AND ground

Think about it.. the rear axle is suspended in rubber bushings on the shackles and the shock absorbers. It's insulated.

I'd just take a braided strap like a chassis ground and go from a diff cover bolt to the frame.. probably right where the vent tube or drop hose for the brakes is..

 

[FORDY2]

Good to know for future reference, I would have made the mistake and asssummed, But then again my electrical skills are about the same as a 6 year old lol. No I'm not kidding.

 

[Dogman]

You would think you would have a ground with the drivetrain. Everything in the trans. is steel.