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Old Dodge speedometer problem
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terryschimm
Novice
Dec 6, 2008, 7:51 PM
Post #1 of 5
(2700 views)
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Old Dodge speedometer problem
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I just bought a 1979 Dodge Adventurer pickup. For some reason, the speedometer is 10 mph off. When it reads 55, is actually going 45, etc. Can anyone help?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 6, 2008, 8:09 PM
Post #2 of 5
(2696 views)
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Re: Old Dodge speedometer problem
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First - are the tires way too small for the vehicle?
It's possible that a trans or differential was changed and ratio for speedo doesn't match. If that's it - find a good old timer trans person and ask where to get the right gears for this drivetrain for speedo. I only recall some GM trucks had a thing right at trans that adapted speedo cable speed to match drivetrain but not for MoPars....dunno what they did,
T
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terryschimm
Novice
Dec 6, 2008, 8:17 PM
Post #3 of 5
(2692 views)
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Re: Old Dodge speedometer problem
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Yes, the tires do appear to be too small, but it's been so long since I had one like this, I wasn't sure. As for trans/differential replacement, I tend to believe they are original, due to the overall excellent condition of the truck & only 68K miles.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 6, 2008, 8:35 PM
Post #4 of 5
(2689 views)
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Re: Old Dodge speedometer problem
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Sounds like a neat truck. Tires alone could easily do that much difference. Basically you are seeing 20% or about - right?
Quite litterally if you measured how far one rotation went in distance from a large and a small tire you'd be shocked.
Even back then they used to put a decal of suggested tires on door jams or perhaps inside glovebox with tire pressure suggestions.
I'll take a wild guess if this is a 1/2 ton rated truck that something close to 235-75R-15 was the common tire for it. If you see 215-70R -15 or so that would account for most of the speed difference.
Smaller will read faster and larger slower that OE at dash,
T
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terryschimm
Novice
Dec 6, 2008, 8:51 PM
Post #5 of 5
(2686 views)
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Re: Old Dodge speedometer problem
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That makes perfect sense to me. As I recall, the Dodge I used to have seemed like it had huge tires & I know those were factory. I'm betting this problem is solved. Thank you very much! By the way, yes, it is a neat truck. I thought the guy was crazy to sell it for $800. Good running 318, no rust...couldn't pass it up.
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