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My 51 is supposta have the tall differentials. Now that I can drive the truck, I will be paying some more attention to roading conditions.
What have you done to correct speedometer indications? Are there different cable drive adapters available?
Dana

Your diffs should be 5.83:1, it may have had 4.9:1's fitted at some stage in it's life though.....
I can't help you with the correction query but if you search the forum you should find it is in there and has been discussed previously, you can also fit a GPS based speedo to get accurate readings.

MM

The mechanical ratio adapters used to be very common. They can still be had if you know where to look, although they are expensive as compared to what they used to go for.

I got my truck out on the road with my daughter following me, so I could verify my new speedometer. My truck is running at just about 5 mph faster than the speedometer says. I have std NDT tires on it.

DCook wrote:I got my truck out on the road with my daughter following me, so I could verify my new speedometer. My truck is running at just about 5 mph faster than the speedometer says. I have std NDT tires on it.

The speed difference should be very close to 10 MPH; if yours shows only 5 MPH, there is something else going on; most likely in the speedo head. A new speedo head is not that expensive, you may want to replace it, then a 1.200 ratio adapter should get you a correct speedo reading again.

the speed difference will depend on how fast you are going. If the speedo is showing 5mph, you should be doing closer to 6. If the speedo is showing 20, you should be moving at more like 23.8mph. If you can get the truck up to 40 on the speedo your actual speed should be around 47.6. based on 4.89 vs 5.83 diff

The local police have a radar gun/display trailer at the city limits. My truck seems to be spot on at that speed. There is some fluctuation of the needle though. Tires are 9.00x16 power king premium traction tires.

Edit. Stock gearing on my truck. post may not be relevant