jumpy speedo?

[Classicfordguy]

Started last summer on a trip to indiana pulling a light enclosed trailer. Truck was pretty hot running about 80 down the highway trying to keep up with the caravan, the speedo would get jumpy then actualy quit working for a while all together. Now it happens all the time, not just when the truck is hot, speedo bounces all over the place between zero and my actual speed. In the 94 it's an electronic pickup in rear diff right? Do I need a new pickup or something or could it be dirty?

Thanks,

-Rob

 

[Diesel JD]

Mine does it sometimes too, but its just a mechanical pickup on my 86 I think. I was told the speedo cable probably needed some lube, but it only seems to do it on mine when I stand on the throttle especially with the engine relatively cold.

 

[RLDSL]

Grab a can of electric spray cleaner and get some conductive grease like Noalox ( they carry it at places like Lowes near the circuit breaker boxes ) , pull the connector offat the diff and clean the pins on the sensor and the connector plug with the spray cleaner , then lightly coat the pins with the conductive grease and see if that takes care of the problem.
If not check the wires carefully for any signs of breaks in the insulation where they might be grounding out intermittantly or pulling loose.

If not it may be time for a new sender in the diff.

 

[Diesel JD]

Robert do you know how my mechanical version works and what parts might need attention?

 

[RLDSL]

Robert do you know how my mechanical version works and what parts might need attention?

On a cable type you need to take the cable loose at one end, pull the cable out,inspect it for fraying along it's length. If it's OK, rub it down with light grease, insert it back in the casing and re attach and you should be good to go.

 

[Classicfordguy]

Thanks RLDSL, I'll give it a try. When I changed my diff fluid I saw the large speedo gear wheel thing next to the ring gear. Does the speedo sensor just count the number of teeth or spaces that pass by it or is there some mechanical connection to it?

-Rob

 

[RLDSL]

Thanks RLDSL, I'll give it a try. When I changed my diff fluid I saw the large speedo gear wheel thing next to the ring gear. Does the speedo sensor just count the number of teeth or spaces that pass by it or is there some mechanical connection to it?

-Rob

It's a magnetic trigger, much like the engine speed ( RPM , or cam position) sensors on computer controlled engines. No actual mechanical connection to the teeth on the thing, but sometimes on rare occasions,the gap can get bounced out of whack , where they get spaced too far or too close to the wheel , but then the reading will usually just go dead. when the reading is swinging intermitant, it;s usually a dirty connection ( imagine that ,from a couple hundred thousand miles of road grime being flung up into the connector ) or a loose wire from it being on a weak flex point.

 

[riotwarrior]

On a cable type you need to take the cable loose at one end, pull the cable out,inspect it for fraying along it's length. If it's OK, rub it down with light grease, insert it back in the casing and re attach and you should be good to go.

I have found that along with this suggestion.....take a small amount of lubriplate or similar grease....squeeze it into the empty speedo cable housing and slowly slide the cleaned and greased cable into the housing all the while adding a touch of grease as you go. That has been my personal favorite way of lubing the speedo.

 

[RLDSL]

I have found that along with this suggestion.....take a small amount of lubriplate or similar grease....squeeze it into the empty speedo cable housing and slowly slide the cleaned and greased cable into the housing all the while adding a touch of grease as you go. That has been my personal favorite way of lubing the speedo.

I would have mentioned Lubriplate, but these days, most folks look at me like I just fell off the turnip truck when I mention that stuff
Only place in the state that still carries the stuff is the International dealer.

If you can find it, its great stuff