figuring out a gear ratio in a gmc 35 ( 1979)

[RootBreaker]

ok i looked at a truck that i am gonna buy for $500

i am buying it for parts...

front d60 with some weird hubs... you turn the whole damn thing.. it says dura(something) i dont remember.

headers

dual tanks - wiring - guage cluster

guage cluster has factory tach !!!!!

rollbar with 5 kc lights... rusted but can sand down....

front bumper is a rusted chrome... kinda neat tube look...


now my delema... how do you tell what gears are in if you dont want to take the cover off?
I had him lift the front of the truck ( he had a loader there )... i turned the front tire 1 time and got 2 turns from the driveshaft.. now i thought that for every turn of the tire count the times the shaft turns and that is your ratio... so that would be like 2.something.....

well to test that theory.. since my truck is in the garage with the rear tires off the ground and tires off... i rotated my drum and got 1.5 turns ( a little lesss... wtf!?!?!?!?! I know i have 4.56's.... so a lower crawl ratio means the shaft turns more per one tire revolution.... does this mean it may have 4.88's or 5.13's????

can someone with 4.10's and 4.88's lift their front or rear and do the tire rotation???? seriously.....

thanks...

 

[Confedneck]

d60 means one ton, and did you ask if it was ex military? if so its possible it has 4.56s, which i dont doubt at all and i think thats as low as they got factory... maybe 4.10s

 

[RootBreaker]

it doesnt look military to me at all... it even has air conditioning......

it has 38's under it so i dont think the gears are stock.....

if it was 4.56's then the front shaft should have turned the same as mine.... 1.5 times around.. not 2....

so my big question is the lower the gear ratio you have the more times a driveshaft will turn per 1 tire rotation... right? im bankin on it having possibly 4.88's.....
im gonna get the truck and just figure it out.....
im also going in with someone else on this site with the truck......so i gotta get hold of him....
the deal is if it is 4.56's then that is perfect.... cuz i am running 4.56's... if it is 4.10 then i have to get a ring and pinion.... if it is 4.88's i will take front and rear axle and swap both......

 

[Rolled]

[/I may be wrong]
If it is an open rear end you have to leave one tire on the ground to get an accurate rotation count.
[/I may be wrong]

You said your truck had both tires off, is yours an open rear end?

Just a thought.

 

[RootBreaker]

well you are right.. my truck has an open rear... and yes both are off the ground....

i will test that later... i will use a pipe and lock the drum....


but the truck i am gonna get had 1 tire on the ground... and i got 2 turns of the shaft per 1 rotation of the tire...!!! that is the biggie to me.....

 

[tacoma972]

when the tires are off the ground, turn both wheels at the same time and that should give you the 4 and whatever turns that the gears will be.

 

[u2slow]

[ QUOTE ]
when the tires are off the ground, turn both wheels at the same time and that should give you the 4 and whatever turns that the gears will be.

[/ QUOTE ]

Yeah, what he said /forums/images/graemlins/thumb.gif

[ QUOTE ]
it says dura(something)

[/ QUOTE ]

Dualmatic perhaps?