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Hi All
My speedo on my 1988 3.5EFI has started jumping and you can here a "clonky noise" from behind the speedo as it jumps,it only appears at low speed as the car is not on the road yet,this has been my winter project and when i move it in and out the garage or on the drive it does it,any ideas?.I have popped the cover off the back and it is a cable driven speedo with a silver L shaped gear type thing going onto the speedo head.
Any info would be of great use.
Thanks valveboy

1988 3.5EFI
1993 4.2 LSE
1996 Discovery ES
 

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Similar problem on my '88. Eventually the speedo stopped working altogether. A close inspection revealed that the little "l" shaped gear had actually fallen apart. the little end cap that is swedged in place had come off. All of the pieces were still there and I was able to clean, lube, and reassemble. It works better now than it ever did. With the end cap off the gears are able to slide in and out and make intermittent contact. That causes a jumpy needle. So even it looks ok it may not be. If it did fall apart, hopefully you can find the little cap. Once I put it back together I supported the gear on my work bench and using a punch peened over a couple spots to hold the end cap in.

Dave
 

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A jumpy speedo can also be caused by a speedo cable that has had all the lubricant baked out of it. The cable is starting to catch at the instrument end, and it is storing torsional energy like a torsion spring, then it releases. When it stores the energy for part of a rotation, your speedo's input slows, but when that torsional energy is released, the cable is whipped faster than it should be, so the speedo needle appears to show a lower speed than you are traveling, then a faster speed. Eventually your speedo cable will snap if it isn't lubed.

There used to be a grease fitting that you could screw into one end of the speedo cable with a Zerk fitting on it, so you could grease the cable. I haven't seen one for sale for 20 years at auto parts stores. You can always remove the cable from the car, pull the cable out of its sheath (carefully) and then smear white lithium grease on its entire length as you slide the cable back into the sheath. Ford used to sell a special speed cable grease that MG Club guys loved. I don't know if it is still available.

The replacement cables aren't too expensive. I spent about $45 on the one I replaced about two years ago, just after we bought our Range Rover. As repairs go, it's pretty easy.

Scott
 
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