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Posted by Keith in Washington [24.41.41.111] on Monday, October 19, 2009 at 12:05:24 :
In Reply to: Speedo posted by bill in pa [75.195.239.1] on Monday, October 19, 2009 at 11:22:42 :
If you mean it is erratic by the needle bouncing up and down as you drive it may not be the speedo. If the speedo cable is binding in any way it will result in a bouncing needle. This is caused by the cable snagging/dragging and slowing down (needle drops) and then winding up. Then the cable will let loose and the needle will bounce up. Remember that the inner cable is basically a long spring.
If the inner cable is not inserted into the gears at either end it will not work correctly and can give the some results that you are seeing.
Check your outer and inner speedo cable for any kinks or sharp bends. Make sure that it is lubricated. If the cable is NOS the original grease has most likely hardened with age. Pull the cable out of the case and clean it very well with a solvent. If the cable grease is thick then I would pull the outer cable out of the truck and clean it's inside with a good solvent. Make sure that both pieces are really clean. Then take a good lubricant. I believe that there is a lubricant designed for speedo cables but I have always used white lithium grease. I lube the inner cable really well and run it into the outer case twisting and turning as I insert it. Do this many times until the inside of the cable housing is well lubricated and the inner cable turns freely.
Also check the small gear where the speedo cable goes into the transfer case. Make sure that it is clean and that the inner cable fits into the end of the gear.
Now reinstall the cable. Install the transfer case end first. I usually insert the inner cable after the housing has been installed. With the outer cable installed and attached to the transfer case, insert the inner cable from the speedo end. When it it fully inserted twist it and push it into the cable housing more. This will make sure that the inner cable inserts itself into the gear at the transfer case. You should be able to twist/spin the inner cable until it inserts into the gear. Once it is in the gear you can twist it a little but it will stop after a turn or two and untwist when you let go. You will not be able to spin the gear at all. Now attach the cable to the speedo making sure that the inner cable is inserted into the slot in the speedo drive gear.
Hopefully this will solve your bouncing needle problem.
You stated that it also does not show the correct speed. This may be caused by the problem above or other issues. You did not state if it read high or low or by how much. If is off just a little then your tire diameter may be different than the original. For example I have seen 9.00 x 16 ranging in diameter from 33 to 36 inches. Which will affect the speedo. If you have changed tire size from 7.00 x 16 to 9.00 x 16 that will cause the speedo to be off. The speedo gear at the transfer case may be the incorrect one. If the gear is from a truck that came from the factory with 7.00 x 16 tires and you are now running 9.00 x 16 the speedo will be off. This gear must be matched to the tire size.
I run 9.00 x 16 Michelin XZL tires on my truck. The are the largest 9.00 x 16 tires that I have seen. They are obviously much bigger than the original non-directional 9.00 x 16 tires that the factory installed. The speedo reads about 10% low as best that I can tell from the road side radar guns that they have all around here.
Sorry if this is more information and detail than you need.
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