What gear ratio do I have?
 

Can anyone tell me an easy way to determine what gears I have short of popping off the covers and counting teeth.
'69 K20, no tach, but it's definately "screamin" at more that 60mph. Do I have 4.56's? If so, anyone with 3.73's want to trade axles? LOL Speed limit on I-90 here is 75mph and I just about get rear ended by 18 wheelers . . . Is it easier and cheaper to change the ring and pinion gears, or to just swap out the whole axle for ones with taller gears?

P.S. I'd Like to do a disk brake conversion also, would I be wise to convert my current axle, or just look for a set of axles with the taller gears AND disk brakes off of a '71 or later and kill two birds with one stone?

Too bad your in SD. I'd love to trade my 3:73 for a 4:56.

it's either 4.10s are 4.56s. What size tires are you running. I have 4.10s w/33" tires and turn about 2850RPM @ 65mph. What rear axle do you have? You could be limited in what ratios are available. Big round cover = no better than 4.10s stock. dana60s came w/3.54 gears I believe. You could try and find a leaf sprung truck w/ a dana 60 and the higher gears. Don't forget to change the front to match.

As for rear disc conversion option you can check out our site to see if we have a kit for you..
This is just an option, there are other companies out there.
So take a look around and get prices.

We are over in Spokane Wa



Blackbird's Custom Trucks

We also have an axle ID page

best bet would be to find a 73 up 3/4 ton 4x4 and take the axles. you would get disc front brakes from the dana 44, the dana 44 is larger diameter on 73 up trucks also, you get the really strong 14 bolt axle, and i believe you could get factory 3.73 gears, perhaps even higher.

I have a formula you can use. take your (rpm) x (tire diameter) and devide that # by your (MPH) x (336) and you will have your answer

There is an easy way to figure your gear ratio without having to remove the differential cover. Block the front tires, jack the rear end up (both sides) and put the truck in neutral. While rotating the tire one complete turn, count the number of turns on the driveshaft, then just multiply by two. Also, if the tire on the other side turns the opposite direction you have an open differential; if it turns the same way it has a locker of some sort.

A factory 69 K20 with a 4-spd should have a 4.56 and with an auto 4.10.

The whining you are hearing at highway speeds though is probably the transfer case and not the gears. That is normal for this type of transfer case.