Speedometer incorrect

[Brian1973]

Seems lately the speedometer is saying I'm going faster than I know I am. Have double checked with gps. I was just doing some brief looking around on here and noticed someone saying something about ABS in relation to speedometer? My ABS light has been going on and off at times and seems there is a slight leak near the box. So I attributed this to the light. Are these two things related? I did just have a new pinion bearing put in and was starting to think maybe the mechanic did something. Is this a speed sensor issue?

 

[RonD]

1983 to 1994 Rangers used speedometer cables, so no on the 1991 Ranger 3.0l and the relation to ABS light

In 1998 to 2000 Rangers used ABS speed sensor on rear axle for the electronic speedometer

 

[Brian1973]

ahhhh, ok, thanks for the clarification!

Soooo, what would cause this 10 mph variation to seem to suddenly appear? No changes to tires or wheels. Speed sensor going into transmission? Speedometer cable? I'm trying to pay close attention to it because it seems sometimes it happens and other times at hwy speeds, all seems correct.

 

[RonD]

Failing cable/gear usually causes no speed or jumping needle

Wrong speed, but stable, would most likely be speedometer itself

Google: how speedometers work

The cable spins a magnet inside a "cup", the "cup" is attached to the needle, but held back by the "hair spring" so it doesn't jump all over.

So as the cable spins the magnet in the cup, the cup starts to turn as well, raising the needle, the faster the magnet spins the more the cup moves and the more the needle goes up.
The hair spring is part of the calibration, holding cup/needle at the correct speed position for the spin of the cable/magnet.

The odometer is also turned by the speedo cable but not part of speedometer.
You could test if odometer is working correctly using mile markers, that would tell you if it is the cable/gear or the speedometer

Found this picture of the inner workings: https://www.engineersgarage.com/sites/default/files/imagecache/Original/wysiwyg_imageupload/4214/10 copy_up.jpg

You can see the hair spring and its tension lock, crimp, which could be loose, so speed reads stable but off now and again because it is moving a bit

 

[firedawg0069]

1983 to 1994 Rangers used speedometer cables, so no on the 1991 Ranger 3.0l and the relation to ABS light

In 1998 to 2000 Rangers used ABS speed sensor on rear axle for the electronic speedometer

I have a 1994 Ranger XLT and it has a Wheel Speed Sensor in the rear axle housing

 

[RonD]

I have a 1994 Ranger XLT and it has a Wheel Speed Sensor in the rear axle housing

Yes, rear ABS uses that sensor but no relation to speedometer until 1998 Rangers

 

[macarchie]

Thanks for the info... I also have a '91 3.0 RWD XLT. I took the cluster out because the tach was about 50% too high. It is the original tach and I was trying to see if there were any connections loose. When I put the cluster back in and took it for a test drive, I noticed the same issue. The speedo was registering almost 60 mph when I know I wasn't doing more than 50. The tach is still off... I will post a new thread about the tach issue shortly.
Now the speedo, tach and fuel gauge are all malfunctioning or not functioning at all.