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Discussion Starter #1
After about 1/2 an hour on the road, the speedometer gets tired....

It gradually shows a lower and lower speed, until 60 MPH looks like 25...

Cable or meter itself, is the question!
 

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Mine (77 spider) does the something. reads accurately until the needle starts to drop all the way to zero. If I stop any reason she will start reading properly again for an indeterminable amount of time then repeat the drop to zero.
 

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I just replaced broken cable and needle was steady for a week while and move jumps around at low speed. Why


Sent from my iPhone using Tapatalk
 

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My vote is speedo. Analog speedos are a combination of jeweled bearings and magnets that are surprising that they work at all. Palo Alto speedometer will solve your problem...expensive. If you're lucky you can find a good used or OEM replacement for less. I just went through this on my 1974 spider and if I had to do it again I would use a gps speedo available from a number of sources.
 

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Discussion Starter #5
My vote is speedo. Analog speedos are a combination of jeweled bearings and magnets that are surprising that they work at all. Palo Alto speedometer will solve your problem...expensive. If you're lucky you can find a good used or OEM replacement for less. I just went through this on my 1974 spider and if I had to do it again I would use a gps speedo available from a number of sources.
My backup right now is my trusty old Garmin. It has a mode that shows MPH in nice big easy to read characters.

I'd considered a GPS speedometer - my tach is already non-OEM (Speedhut custom).

It seems like nowadays you could just optically watch the road with a little camera and calculate speed!!
 

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My needle used to start off smooth although reading slower, and eventually would start to bounce a bit. While checking things out I found the speedo cable to be really dry, so I sprayed it with some grease. That helped quite a bit.
 

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Pull your speedo cable out of the housing and lube it up with wheel bearing grease.

Also check that your front heat shield is there as the cable passes between the heat shield and the underside of the car. Missing heat shields or heat shields missing there heat material on the back side will heat up the outer cable housing which cause the inner cable to bind in the housing.

Last check the squared end of the inner cable that goes into the drive on the transmission. The corners will get rounded in one spot. You can add several small washers on the other end of the cable to shim it forward.
 

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I agree that the speedometers and tachs need to be serviced after many years of use. I would send the unit to Palo Alto or maybe Parts Correct and have it repaired.
 

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Discussion Starter #9
Pull your speedo cable out of the housing and lube it up with wheel bearing grease.

Also check that your front heat shield is there as the cable passes between the heat shield and the underside of the car. Missing heat shields or heat shields missing there heat material on the back side will heat up the outer cable housing which cause the inner cable to bind in the housing.

Last check the squared end of the inner cable that goes into the drive on the transmission. The corners will get rounded in one spot. You can add several small washers on the other end of the cable to shim it forward.
Heat shield! :sweatdrop:
That seems to be the heart of the issue - the total lack of any heat shield.... Timing sounds right too - about 1/2 hour of intense exhaust heat probably cooked the cable good.

I pulled, cleaned & re-lubed the actual speedometer...
Then I fabricated a heat shield for the exhaust header and got it mounted. GPS shows that the speedometer is now reading just a bit low of actual speed, but not drooping.
 

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Discussion Starter #11
I have the same problem. the speedo is intermittent at best.
1989 Graduate?

Does that year still use a cable all the way up to the speedometer?? Or is there a short cable to a sending unit under the car??
 

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I have two great speedo clusters out of working cars, no idea their value.

I'm not out to rip anybody off, but, I am trying to restore a 74 and centerline needs my money.

Message me.
 

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1989 Graduate?

Does that year still use a cable all the way up to the speedometer?? Or is there a short cable to a sending unit under the car??
Yes. All the way to the side of the brake booster.

It defiantly change to down lower on the S4's. Not sure if it change on the 1990's when they went to motronic.
 

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Pull your speedo cable out of the housing and lube it up with wheel bearing grease.

Also check that your front heat shield is there as the cable passes between the heat shield and the underside of the car. Missing heat shields or heat shields missing there heat material on the back side will heat up the outer cable housing which cause the inner cable to bind in the housing.

Last check the squared end of the inner cable that goes into the drive on the transmission. The corners will get rounded in one spot. You can add several small washers on the other end of the cable to shim it forward.
Where do you pull it out of the housing? Do you have to take off the cluster?
 
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