At 08:48 AM 9/10/98 -0400, Kirby T. Kenyon wrote:
>I've got a weird one on my '80 Spit.
>
>I drive the NYS Thruway to work. When I drive my Spit, early in the
>drive the Speedometer reads the correct speed (70MPH @ 3400 RPM with OD,
>verified by time over mile marker method) but approximately 30 miles
>later, it reads low (63MPH @ 3400 RPM).
>
>I verified that I was still going about the same speed at the end of the
>trip that I was in the beginning so I know there is no slip in the drive
>train.
>
>Could this be a symptom of a slightly binding speedo cable? It does
>bounce some at lower speeds but smooths out about 30MPH.
>
>Has anyone else encountered this?
Kirby,
To answer this one it is neccessary to understand the principals of
speedometer operation.
Inside the Instrument is a small yet nimble mammal (similar to a Marmot,
but not really, and on a much smaller scale.) The one in my car is named
Eric.
As the car goes faster or slower, a raisin is held closer or farther from
Eric's nose, causing him to run correspondingly fast or slow. This moves
the needle you see from the cockpit.
After several miles, Eric is tired from all that running (and on a toll
road no less!) so it is understandable that he runs a bit slower when the
car is going the same speed.
This is not always a real problem. Do not be concerned, unless Eric
starts leaping and jumping, in which case he is on his "Last Legs". In
that case you may have to rely on the Tach to gauge your speed.
Sometimes the raisin falls out of the speedometer. In this case, the
indicated speed will be zero.
Please try to be more understanding of the forces at work inside the
machines we use every day. I hope this helps you.
Your Public Servant,
Atwell Haines
'79 Spitfire FM96062 UO
(53 HP)
Succasunna, NJ USA
The One Immutable Rule of Automotive Satisfaction:
"It is more fun to drive a slow car fast than to drive a fast car slow"
- Cory Farley in Autoweek, 8/17/98
|