The Stovebolt Site Forums The Shop Area Engine Shop Gear ratios question

Hello,

Got a 63 GMC 4x4 1/2 ton and I just got it on the road. When I drove it, it was EXTREMELY low and sluggish like the gears are not at all high enough. I believe I have 2.54 gear ratio in the front and rear end and I was wondering if anyone knew..
1. What that years transmission ratios are?
2. Should I just change the ratios in the front and rear end and problem solved, or will I have to do the transmission as well?
3. If so, what ratios should I go with?

Any help is profoundly appreciated! I have been working on this truck for 2 1/2 months solid and it was kinda of a dissappointment to run into this when I thought I was finally finished. LOL, Just hoping I don't have to do the tranny.

Shane Hamilton
Warrensburg MO

Welcome Wayne. I'm not sure what the original gearing was on a 63' 1/2 ton 4x4 but it certainly is not 2:54. That would be very, very high. It is most likely 4:56. Jack up the rear with the the trsnsfer case in N and one wheel on the ground and turn the rear wheel over twice and counting the # of turns on the driveshaft. Transmission is N also naturally. Divide x 2 and that will give you the ratio. Do a search on gear ratios and there will be a lot of info.

3.90 was the fastest ratio they offered for that year.

Actually, it won't be necessary to divide by 2. With one wheel on the ground, counting the number of revolutions of the drive shaft while making two revolutions on the raised wheel will give you the drive ratio.

Well yes...no need to divide. Hard to have your mind in twelve places at one.

Thanks guys!
I have an extra front and rearend in my shed. A fella around here, told me that if I count the teeth on the big gear and divide it by the # of teeth on the small gear that it will give the gear ratio. I counted 41 teeth on the big gear and depending on what little gear (one had 10 teeth and the other had 16) so.. the one with ten teeth (perpendicular to big gear) figures out to be 4.1 and the 16 (parralell with big gear) teeth figures out to be 2.56...

Anyway, it is raining crazy right now so I can't check what is currently on my truck. Any insight as to what I have in my shed? (came with the truck BTW, that's why I don't know)

ONe last ??? What would you all suggest I put in there? and lastly, is there something that is on the transfer case that will put it in neutral?

Sorry for being so unknowledgable..

Thanks
Shane Hamilton
Warrensburg MO

The ring and pinion are the two biggest (in size gears) in the whole assembly. The smaller 16 tooth gear is part of the differential and has nothing to do with the gear ratio. 41 to 10 is a 4.10 gear ratio.

Joe

Thanyou all very much for your help!
Shane Hamilton
Warrensburg MO

take the cover off, and with the ring gear to your right, adjacent to the mounting ring, wipe the sludge? off of the 3/8"ish edge while rotating the gears, and you'll find numbers like 3797341-10-39. and dividing 39 by 10 you get 3.9, or 3.90s. like joe h said, just divide the larger number by the smaller number. it also gives you an opportunity to eyeball the teeth's wear pattern etc

With one wheel on the ground, the spider gears double the gear ratio of the ring & pinion. 1/2 turn of the rear wheel will yield the proper number of turns of the pinion gear (driveshaft), or make one full turn with the rear wheel, and divide the driveshaft turns by 2. Try it sometime! That's why we had to watch the speedometer very closely when doing an on-the-car spin balance with one rear wheel on the ground- - - - -30 MPH on the speedometer had the raised wheel doing 60 MPH!
Jerry

FWIW, to the newer guy's and gals:

High Gears, or the expression "Hey I could use higher gears in my truck". This means lower numerically, as for example you are going from a 3.90 to a 3.08.

Low Gears, or the expression "Hey I could use lower gears on my rock crawlin' 4x4". This means higher numerically as if one is going from 3.90 to 4.56.