Odometer works-Speedo does not

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Nov 17, 2006 | 07:03 PM

royharper

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Odometer works-Speedo does not

Hello all. I'm not a first time poster, but I'm a noob for sure. I will appreciate any advice on this problem. My Ford is a 79 f-250 4x4,351m, with a 4 speed. Today as I merged onto the highway I noticed my speedo reading 80 mph(estimated speed was about 50 mph). It was steady and I soon learned it was frozen at that position. It made no noise at all like I would expect from a bad or loose cable, and the odometer was working normally.The cable is, in fact tight to the back of the cluster. Any idea what this may be? Thanks in advance for any insight you can give.

Roy Harper

Last edited by royharper; Nov 17, 2006 at 07:12 PM.

Nov 17, 2006 | 07:20 PM

Torque1st

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Time for a new speedometer head. They are available in trucks thru 79 and vans thru ~88, can't remember exactly, in salvage yards. You can also get them off ebay for twice the price.

Nov 18, 2006 | 06:37 AM

royharper

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Thanks for the reply. I sort of thought the same thing. I should be able to visit about 4 wrecking yards an hour doing 80 mph. Thanks again.

Roy

Nov 18, 2006 | 11:26 AM

Torque1st

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When you get a new cluster watch for crumbling plastic in the housing. Also try to get one with the same functions yours has so you have more spare parts. Check the numbers on your flex circuit. When changing a speedo head keep everything absolutely clean. The speedo drive is a magnetic coupling that will attract any small metal chip. Any dirt or magnetic particles that get into the speedo head will cause it to do just what yours did. The particles are almost impossible to remove once in there.

Remove the flex circuit and clean all the contact points on the circuit with a pencil eraser or a fiber brush. Remove all the dust and coat ALL the contact points with silicone dielectric grease. The instruments work on very small currents and low voltage which is why they often do not read correctly on these old trucks. The silicone grease will exclude moisture and oxygen from the contact points but allow metal to metal contact which prevents corrosion. I even go in and clean wire crimp connections and solder them.

Nov 18, 2006 | 08:29 PM

gbrett

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tourque1st why not just change the speedo instead of the whole cluster also new units are avail aftermarket and mabey even from ford

Nov 19, 2006 | 04:37 AM

Torque1st

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You can change just the speedo head when you get back home. I have never seen any aftermarket units available. New units from Ford would be very expensive. A cluster is about $10-15 in a scrap yard. Always get the whole cluster. The last thing you would want to do is pull a cluster apart in a dirty scrap yard.