Speedometer needle bounce?

[Popeye2347]

On my early 1994 F250, 7.3NA, auto, the speedometer needle is steady up to 65MPH, but at or above 70MPH it will bounce. This is only an irritation except that it also causes the cruise to 'hunt', and no doubt hurt the fuel mileage.

I picked up some white lithum to lube the speedo cable, but to my surprise there is no cable to lube!! So, where is the electronic sender/pickup unit, and
is there anyway of telling beforehand if the problem is the sender or the speedometer head without blindly replacing parts and see what fixes it?

On a side note, I had the instrument cover off this last weekend to repair [hot glue] the tank selector switch that 'fell' into the dash. On the speedometer part is a bright orange label cautioning anyone not to turn the speedometer module 'upside down', and to call Ford at 1-800-***-xxxx. What is this all about? I cannot fathom anything that would be harmed, but then this 'modern' stuff is full of surprises!

 

[k_williams1982]

I may be wrong, but I believe the VVS for the elecetronic speedometer is in the same location as the mechanical (cable driven). Look at the tail of the transmission (2wd) or on the backside of the transfer case (4wd).

 

[Popeye2347]

On my early 1994 F250, 7.3NA, auto, the speedometer needle is steady up to 65MPH, but at or above 70MPH it will bounce. This is only an irritation except that it also causes the cruise to 'hunt', and no doubt hurt the fuel mileage.

I picked up some white lithum to lube the speedo cable, but to my surprise there is no cable to lube!! So, where is the electronic sender/pickup unit, and
is there anyway of telling beforehand if the problem is the sender or the speedometer head without blindly replacing parts and see what fixes it?

On a side note, I had the instrument cover off this last weekend to repair [hot glue] the tank selector switch that 'fell' into the dash. On the speedometer part is a bright orange label cautioning anyone not to turn the speedometer module 'upside down', and to call Ford at 1-800-***-xxxx. What is this all about? I cannot fathom anything that would be harmed, but then this 'modern' stuff is full of surprises!

OOPS---all that and forgot-it is a 4x4. I did not see a sending unit on the transfer case but will look again.

 

[EMD_DRIVER]

It'll be in the rear diff on your truck.. Same as mine.

 

[snicklas]

I have a question about this. Since the speedometer is electronic and is run off of an electrical pickup. Why would it only bounce above a certain speed? We had an 83 that the speedometer bounced on, all across the spectrum, at higher speeds it bounced less, we replaced the speedometer cable and it helped the problem. There was an mechanical bind in the first cable. On an electric speedometer, there wouldn't be a cable to bind, and the rear sensor is a tone ring, so there is no physical connection or mechanical parts. On the other end, is an electronic stepper motor that is controlled by some type of electronic motor driver. I would think there is some issue with the speedometer stepper motor in the dash, or the driving circuit associated with it. I may be completely off on how this thing works, but that is my take on it.

 

[towcat]

just for *****-n-giggles pull the sensor and see if the magnet is full of metal shavings. If you have some miles on the rear, it will have shavings and that will throw the readings. if nothing else, it's a cheap attempt before spending on a sensor. Ford speedo heads don't go bad too often, so I would check out the sensor first.

 

[Popeye2347]

just for *****-n-giggles pull the sensor and see if the magnet is full of metal shavings. If you have some miles on the rear, it will have shavings and that will throw the readings. if nothing else, it's a cheap attempt before spending on a sensor. Ford speedo heads don't go bad too often, so I would check out the sensor first.

Well...good try but no banana. I found only one or two 'hairs' on the pickup, cleaned them and took it for a test drive. Same bounce over ~67 MPH.
FWIW I don;t need to go that fast often, but I do like to drive the posted limit and sometimes that is 70. Any more ideas?..replace the pickup/sensor? I need to go to a yard anyway so I may just as well get what I need while I am there.
Thanks....

 

[Popeye2347]

Towcat, you mentioned the speedo head, I noticed on mine there is a warning sticker not to lay the head 'face down' IIRC. It even gave a 1-800 number at Ford tech to call---like a dummy I failed to copy the number down, but I cannot imagine why that would damage the speedometer head. Can you [or anyone else for that matter] tell me why that would matter? I cannot envision UPS or USPS keeping a package upright for the entire journey from sender to receipient. Inquisitive mind wants to know. TIA

 

[towcat]

i've never heard of "do not lay face down" before either.
especially how i've seen parts get treated at a wrecking yard let alone the UPS monkeys.
i have a speedo head off a '93 that I can take a look at for the 1800 number later on today.
there is another rebuilder in the east coast I use for speedo heads I can get you a number for too.

 

[Agnem]

I've seen that sticker too. Don't know why it is sensitive, but I would try to honor the request.

 

[Popeye2347]

Note to all-I'm still 'bouncing along' without a solution. I thought I may look at the cables going to the IP and see if there is any wear/rust on them. The previous owner may have only driven it at 65 MPH come h@ )) or high water and created a wear spot or something......

Meanwhile, any further thoughts on the warning label?

Cheers.........