what gear?

[LAOffroad]

Ok....this is my first 4x4. It is a 72 K-5. My question is if I have 3.08 gearing in the rear what gearing should I have in the front. I assume the ratio should be the same, but I wasn't sure because of the transfer case. I know this may be a dumb question, but I have no experience with 4x4 gearing. Thanks

 

[Hosalabad]

From the factory it had matching gears front and rear. The transfer case only modifies the ratio feeding each axle.

You could have a mismatched front if something was swapped in. Your best bet is to pull the diff covers and count ring and pinion teeth if you feel that there is some reason that they aren't matched.

 

[LAOffroad]

so if I change the rear to 3.73, I need 3.73 in the front. Correct?

 

[GRINCH]

so if I change the rear to 3.73, I need 3.73 in the front. Correct?

Yes, they have to match. Unless you never plan on putting it in 4WD. What size tires do you plan on running?

The gears are also marked with thier ratio. First number will be close to 40 and higher and the other on 10 and higher. Just divide the bigger by the smaller and that will be your ratio. Like 43 14 is a 3.07 gear ratio

 

[LAOffroad]

Yes, they have to match. Unless you never plan on putting it in 4WD. What size tires do you plan on running?

The gears are also marked with thier ratio. First number will be close to 40 and higher and the other on 10 and higher. Just divide the bigger by the smaller and that will be your ratio. Like 43 14 is a 3.07 gear ratio

I am running 33 12x50 tires. I checked the rear gears and it said 43:14 so I guess I have 3:07 in the rear. So they must have changed the gears at some point?

So now I will need to check the front as well?

 

[bp71k5]

3.07 are pretty common in ca. They came stock.

 

[Big Blzn]

so if I change the rear to 3.73, I need 3.73 in the front. Correct?

Not worth the time and money to change from 3.07 to 3.73. Maybe go to 4.10's or so but unless you have a money tree growing in your yard or you are just looking for something to do then by all means. If you are set on getting lower gearing it would be much cheaper to just get the same axles out of another truck with the gears you want and swap the axles into your current rig. Or jsut upgrade to 3/4 ton.

 

[LAOffroad]

Cool. I will just leave them alone.

 

[myraley]

Big Blzn, why do you say its not worth the time and money to change it? I have 4.10 in both axles and 33 inch tires and was thinking of either changing the gear ratio to 3.73 or increasing the tire size to 35 inch, so my rpm's would be lower on the freeway. No?

 

[Big Blzn]

Big Blzn, why do you say its not worth the time and money to change it? I have 4.10 in both axles and 33 inch tires and was thinking of either changing the gear ratio to 3.73 or increasing the tire size to 35 inch, so my rpm's would be lower on the freeway. No?

If his '72 is like mine then it should have a 350/205 combo. If he is looking to get higher speeds with lower RPM's on the freeway with his 33' tires then he should stick with the stock gears (3.08) His truck may lag a bit and may be a little harder in the trans. Most people on here end up having the snow ball effect and start putting on bigger tires, more lift, etc, etc. My point was that if one is going to spend the time and money changing gears the jump from 3.08 to 3.73 is not that much of a difference concidering what the cost is going to be to have someone else do it. Might be talking close to $1200 or close to $500 if you are able to do it yourself. Even if you do the gear change yourself and you go to 35" tires the 3.73 wouldn't be an ideal choice unless it is purely a street driven truck. Right now I have 3.08's on 35's and I get great freeway milage/speed with lower RPM's. I have a built 400sbc so I don't have all the negative side effects with around town driving but do notice a bit of sluggishness with the bigger tires and notice it more offroad. As I type I am doing my 3/4 ton swap with 4.10's to help out my tranny a bit and still not be too low gearing to kill my highway speeds and rev the tach too much.