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Dreaded speedo gear questions

4x4blaze

4x4blaze

That's not going to work
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Hey guys, finally got my K5 done! Lifted it 3", Threw on some 33's, and swapped out the gears from 3.08s to 4.56s.. Really helped wake it up, but now my speedo is way off obviously.. This truck has a 700r4 paired with an np208 as well.. Was wondering if any of you guys have this same combination and knew what gear worked, or if any of you had some super easy formula to help figure it out!

Thanks guys!
 
4x4blaze said:
Hey guys, finally got my K5 done! Lifted it 3", Threw on some 33's, and swapped out the gears from 3.08s to 4.56s.. Really helped wake it up, but now my speedo is way off obviously.. This truck has a 700r4 paired with an np208 as well.. Was wondering if any of you guys have this same combination and knew what gear worked, or if any of you had some super easy formula to help figure it out!

Thanks guys!
Click to expand...
I went from 31's and 3.08's to
33's and 3.73's.
All I did was remove the stock speedo box from the t-case.
My speedo cable hooks right to my t-case.
It is very close, within 5mph.

Cost nothing.
A lot depends on what gear you have in the tail housing of your 208.
If i were you, i'd remove the speedo gear box and hook the cable right to the t-case.
Drive it and calculate the error by checking against gps or time between mile markers.
You want the percentage fast or slow.
Then buy a speedo range box to correct.
They are $88 on ebay custom made.
 
Figure out exactly how far off your speedo is (GPS, phone app, etc). Then pull your driven gear (one bolt) and check which combination you have. Multiply the ratios and you'll know what your new gear should be.

For example, if your speedo reads 60MPH when you're going 65MPH, and you have a 39-tooth driven gear, your new gear should be (65/60) * 39 = 42 teeth. With a change from 3.08 to 4.56, you will need a change of drive gear (unless perhaps you have a ratio adapter box like @K5wrench mentioned).

Post up what you find and we'll walk you through the math. No need to dread this.
 
You guys are the biggest bunch of babes:haha::haha::haha: I really dont know what I would do without this site! Thanks for all the really quick replies! Lots of killer info..

And I actually tracked 160 miles in this old girl today, so I had plenty of time to play with it.. with the needle right on 85, the truck is actually doing 67 via gps
 
4x4blaze said:
You guys are the biggest bunch of babes:haha::haha::haha: I really dont know what I would do without this site! Thanks for all the really quick replies! Lots of killer info..

And I actually tracked 160 miles in this old girl today, so I had plenty of time to play with it.. with the needle right on 85, the truck is actually doing 67 via gps
Click to expand...

Ok, so you need it to read 67 instead of 85. 67/85 = 0.788.

Multiply that by the number of teeth on your driven gear and you'l be good to go. Though probably that gear won't exist, and you'll need to change drive gear or use an adapter box to achieve the new ratio.

But now you know what your correction factor will be. :thumb:
 
When I had one made years ago, I had to disconnect my speedometer cable at the dash and plug in his meter. That meter would do 1000 revolutions per mile. He had a route measured out at i mile. I ran the course twice, wrote down the readings each way. From that he made the correction device.
 
4x4blaze said:
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/132306820963

Started looking into reducers and was wondering if something like this would work? Guess I'll just have to figure out the most appropriate percentage for reducing and getting my numbers somewhat in the ballpark
Click to expand...

Yes. You can adjust the ratio inside the case or outside the case. The gear sets are cheaper than that gear box, but any combination that yields the appropriate correction factor will be fine. And putting a box on is easier than changing the drive gear. You can change out the driven gear from outside the case fairly easily to get it finely tuned.

If you can get a clean view of the housing where you plug in your speedo cable to the NP208, you'll be able to see the color of the driven gear, and that will tell you how many teeth it has (without taking anything apart). Very convenient.
 
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