[DML] Re: Speedometer is wacky

["dadoc2791" <gekko@xxxxxxxx>]

David,

The most common cause for a speedo to jump (a mechanical speedo, like 
we have in our D's) is a failing speedo cable.  The inner cable is just 
that, a cable, made up of many strands of wire woven together.  Most 
commonly, as they begin to fail, one, two or more strands will break, 
usually on the outer layer or surface of that inner cable.  Those loose 
ends fray outward, contacting the inner surface of the cable sheeth, 
causing the cable to stop or slow for just an instant, until the 
turning of the wheels (and the cable) breaks it free again and it  
catches up with the rotation rpms of the drive.  It sort of rubber-
bands quickly up to speed until it hangs up again on the inner jacket 
again and starts the process all over.

Sometimes these tiny frays can last for thousands of miles, causing 
this same behavior in the speedo.

My best suggestion would be to pull your upper speedo cable from the 
sensor gearbox under the dash and clamp the chuck of a hand drill on 
it.  Spin up the drill slowly until you reach 60 mph or so (about 1000 
rpms) and see if the speedo acts smoothly or if it jumps.  This 
technique will isolate whether the problem is in the upper or lower 
cable section.  If it runs smoothly there, you can bet your lower cable 
is going.  (the most likely candidate)

Replace the bad cable section (and check on and greese the heck out of 
the angle drive) and reconnect everything.  Be sure to use or replace 
(if you don't have it) the cable support by the wheel.  It saves a kink 
that commonly occurs in these cables.

Hope this helps.

Best of luck.

Craig Werner
07181

--- In dmcnews@xxxxxxxxxxxxxxx, "daviddelorean" <daviddelorean@...> 
wrote:
>
> I had my speedo worked on to make it more accurate. It is better, but 
> not 100% up to par. What causes a speedo to jump around? 
> 
> From 0-15 it fluxuates all over, from 15-45 it is steady. From 45-55 
it 
> fluxuates. From 55-65 it is accurate. From 65-85 it fluxuates wildly.
>




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