Changing gears????

[MTtruck]

I have a 68 gmc SWB with 3/4 ton running gear, it makes about 2500 rpm at about 65 mph. Thinking bout changing the gears to something a little bit taller to make it more officiant and less thirsty. Any help or input would be great. thanks y'all. Oh and by the way it has 35x12.5x16.5 rubber......sigh

[rwolf9653]

What trans?
Numerically lower gear will help on the highway, but around town it might make you floor it all the time to try to get up to speed, especially if you live in a hilly area.
You might want to explore the possibilities of a trans swap. By the time you do the front and rear gears (you were going to do the front....right??) you will have just as much money into the axles as you would have if you had just put in a better tranny.

[69GMCLonghorn]

Yeah, good luck. If you have an Eaton rear end, 4.10's are all you're going to get. If it's a Dana, apparently you can do a little better. If it's a 4 x 4, just multiply the cost by 2 since you'll have to do the front end too.

A couple things: 1) Be aware of how much low end you'll lose and just be sure you have enough power to get those tires moving.

2) Are you sure you speedo is accurate? With those tires, it will be off by quite a bit unless you've already had it calibrated. I only bring this up because you want to have an accurate starting point before you change gears. Related note: You'll obviously have to calibrate it again after changing the gears, too... unless you want to be the guy with a bunch of P-Touch labels on your speedo that reads "55 MPH = 63 MPH", "65 MPH = 72 MPH" etc...

[D.PASSMORE]

If you are going to run big tires (35's) you will need a least 4:10 gears. And check your trans and motor setup. 4x4's uaually run beter when set up for the maximum amount of tourqe that you can squeeze out of her.

[MTtruck]

Hey guys. I have a a muncie 4spd. not sure which one it is though. I'm guessing i have 4:10 now but maybe lower. Also have 14 bolt rear end if that helps you guys out.

[unclewatts]

It would be really nice to know what your rear end ratio is. There are 4 ways: If you have an SPID on the glove compartment door it will tell you.(As long as it's the original rear end) You can also jack up the rear and mark a spot on the driveshaft and one wheel and count the number of turns the driveshaft makes to one revolution of the rear wheel. You can also pull the rear cover on the diff and count teeth or read it on the ring gear. LMC truck does make gearsets up to 4.56 but that's for 10 and 12 bolt rearends. I would do some web or wrecking yard searches to find what you want.