1968 Tire Help

james2488

james2488

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Des Moines, Iowa
Does anyone know size tire makes the speedometer right? Tires on it are 245/60r14, and the speedometer is to fast. Does anyone have an idea on how to make it right? It is about 10% too fast, if that helps.
 
the car originally came with a size equivalent ot 225/70R14 which has an approximate tire diameter of 26.4 inches. Your current tire has a diameter of approximately 25.57 inches. Thats a .83 inch difference which is not a 10% difference. The cheapest correction would be to get the correct driven gear for your transmission. If you need help with that provide the type of transmission and what your rear end ratio is.
 
I forgot to say this, but is that the same on Rally II's? Well it is closer to 8%. It an alowable diference of 6% either way of the actual speed is what the geared speedometeres are. Also I can't tell you what the rear end gear is, and I doubt very many people know what the ration of the 2 speed is, but if you know that trany I would like to know.
 
Rally II's have no effect on your question. You have a Powerglide transmission. The link below sells driven gears but you have to check what is in your transmission currently. You have to know the number of teeth and the size of the speedometer gear.

http://www.transmissioncenter.org/GM_Speedometer_Gears.htm
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It doesn't have a powerglide in it. It has the ST-300 in it, that's Pontiac, Buick, and Olds's vertion of the Powerglide, they are hnothing alike other than it is a 2 speed. It is the right trany for the car, the case is mark "68", and the low band servo cap is marked "68" as well.
 
thanks for clarifying that, so do you intend to correct the speedometer reading?
 
Yeah when thoose tires are shot, or close to it. I think the speedometer is right on once the right sized tires are on it.
 
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