A thought just occured to me, if I go to 31" tires the speedometer will be off a bit. How do you correct this? In my 94 i can do it through the gauge computer.. i assume for the 76 its replacing the speedo gears that go into the transmission? i might as well take care of this while i have everything out...

Just a change of the gear on the end of the speedo cable. Easy to do after everything is together. I recommend driving it with GPS to determine the actual error in speed first. You'll need a gear with either 1 or 2 less teeth. Math will help determine the closest match.

got it thanks!

Ought to look something like this:


Actually, I can't confirm that. That's what my Atlas has and I think it was design after a different t-case.

EDIT AGAIN:

according to the BC Broncos site, they are plastic:

http://www.bcbroncos.com/dana20.html

Yup - and just an FYI - Colorado mustangs unlimited off Peoria and 37th has them in stock (same as the ones in my son's C-4 (66 stang). Actually it is fairly impressive how many small parts are shared between our rigs and the classic mustangs.

All D20's use the manual trans version of the speedo gear. It's shorter than the auto trans version.

Guess. That's what I did until I changed the gears in the axles, then I went to bigger tires & now I am guessing again.

It's simple. If the driveshaft is turning 10% slower (tires 10% taller) you need the speedo cable to turn 10% faster. Gear needs 10% fewer teeth to turn the cable 10% faster.

Naw, what I actually have done in the past, and it is pretty close right now even, so it doesn't worry me, is I gauged it off of mile markers, did some quick math in the ole bean and figured out that I was roughly 6-10% over what I am really going. My rig was originally set up with 3.50 gears, and when I had 31s I was over a little. Then I changed the speedo gear when I went to 33s and it corrected it. Then I went with 4.10/4.11 gears and it under corrected and now with 35s it is pretty dern close.