Speedo stopped working on my 1968.... - Impala Tech
Troubleshooting Diagnosing problems

 
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post #1 of 6 (permalink) Old 05-22-2015, 12:11 AM Thread Starter
 
 
Join Date: Jun 2014
Location: Annapolis, MD
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Speedo stopped working on my 1968....

Folks, my speedometer stopped working on my 68. How do I begin to trouble shoot? Where to look first? Thanks so much. joe
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post #2 of 6 (permalink) Old 05-22-2015, 08:37 AM
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Did it give you any clue as to a problem before hand? This would include a jerky indicator pointer, or one that made a noise.

Usually it is caused by corrosion inside the flexible steel tube rubbing against the stranded bronze wire wound into a cable that transmits the rotation to the speedometer. If the friction becomes too great inside the outer steel housing it could strip the plastic gears on the transmission's out put shaft. The rubbing can also break the speedometer cable.

There generally isn't an issue with the speedometer or odometer as all it is a set of magnets that follow the spinning magnetic field generated by the speedometer cable spinning inside the speedometer. You can find replacement cables easily enough but the outer housing is realy hard to find as a service part.

The outer housing is basically sold by length since the same ends were used on all GM vehicles up until they went metric. If you find a replacement off another vehicle (shopping by comparing the speedometer cable length inside the housing to fdind an outer housing the same length as yours) be sure the ends inter change by taking yours with you to the salvage yard. After the mid eighties most parts on cars and light trucks went "Metric". As such it may look alike; but they will not have the same threads on the ends.

Big Dave
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post #3 of 6 (permalink) Old 05-22-2015, 05:27 PM Thread Starter
 
 
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The only thing hat happened priority the trip is the car bottomed out on a speed bump. Could that be it?
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post #4 of 6 (permalink) Old 05-23-2015, 09:08 AM
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Very possible if it got caught between the crest of the speed bump and the a strong part of the car (such as the frame) you could have either crushed the exterior flexible steel tube destroyed the speedometer cable, or ripped it off the tranny all together. A quick visual inspection for damage should tell you if it is still in one piece but flattened and scrapped (the shinny part should be easy to find if it was crushed). Or if it is not attached how much damage it did to the transmission (since it screws on, it can be forcibly ripped off).

Big Dave


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post #5 of 6 (permalink) Old 05-24-2015, 07:36 AM
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You can probably go to a chevy dealer and buy a new cable
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post #6 of 6 (permalink) Old 06-12-2015, 10:51 PM Thread Starter
 
 
Join Date: Jun 2014
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What size is a 1968 speedo cable?
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