Speedometer Anomaly

[67step100]

My speedometer reads accurately (using a GPS to compare) below about 35mph. Once I start climbing above that the speedometer almost seems to double the speed so that when I get to around 55mph the speedo is reading 70mph. What would cause this? The speedo seems to jump around a bit as well.

I don't know if this is a new thing since the truck is relatively new to me and all my driving to date has been has been limited to about 35=40mph. Today I took it out for a spirited drive and noticed this anomaly.

[PwrWgnDrvr]

Dirt and dust built up in the head, between the magnet and rotating can. They also have to be lubed thru the tiny hole in the top of the casting just in front of where the cable connects. That hole is usually solidly plugged with dirt and requires a sewing needle, or similar, to clean out.

[67step100]

Dirt and dust built up in the head, between the magnet and rotating can. They also have to be lubed thru the tiny hole in the top of the casting just in front of where the cable connects. That hole is usually solidly plugged with dirt and requires a sewing needle, or similar, to clean out.

Thanks. Not being familiar with these (I assume mechanical?) is the head at the gauge end or where it screws into the transmission? Is it worth removing the entire cable, unscrewing at both ends (I assume this isn't arduous?) and cleaning/lubing the entire cable? Or am I talking a pipe dream? I notice cables are reasonably cheap. Appreciate the assist.

[PwrWgnDrvr]

By head I am referring to the needle and mechanism that moves it in the dash cluster. Pretty simple to pull the entire gauge assy and disconnect the cable from it. Then disconnect from tranny and clean/lube as you mentioned. Then remove the speedo from the cluster to work on it. Its a delicate mechanism so be gentle and careful with it.

[67step100]

By head I am referring to the needle and mechanism that moves it in the dash cluster. Pretty simple to pull the entire gauge assy and disconnect the cable from it. Then disconnect from tranny and clean/lube as you mentioned. Then remove the speedo from the cluster to work on it. Its a delicate mechanism so be gentle and careful with it.

OK I get it now, thanks. I was fixated on the cable and you were talking about the gauge. I will try to clean and lube the gauge and see if that sorts it out.

[67step100]

Dirt and dust built up in the head, between the magnet and rotating can. They also have to be lubed thru the tiny hole in the top of the casting just in front of where the cable connects. That hole is usually solidly plugged with dirt and requires a sewing needle, or similar, to clean out.

Worked perfectly. thanks again. Just pulled the dash cluster, unscrewed the speedo cable and sure enough the hole on top was full of crud. Cleaned it out, a couple drops of oil and now the speedo no longer jumps around and pegs exactly the speed showing on my GPS, even at 60mph.

[PwrWgnDrvr]

right on!