Need HELP !!! 1970 GMC 3/4 .

[firedawg99]

I am new to all this so please be gentle with me.

I just bought a 1970 3/4 ton GMC truck and am triing to get all the information I can about it.

So could someone please direct me to a webpage that I can get information about the truck and especially a Dana 60 differential. I know I have a small block 350 and a Turbo 350 Transmission but I don't know about the rear end. I am interested in see what gearing is in it. PLeas someone Help !!!!!!

[krue]

Welcome to the board from South Mississippi! You're at the only place you'll need for info. The best way to find the ratio is to pull the rear cover and look. Probably needs an oil change in the rear end anyways.

[Aarons72s]

Welcome to the board from oklahoma. You are in the right place for the questions. Pull the cover to get the gear ratio. Since you just bought it it is a good time for preventavie maintance. So you might as well change the gear oil and you can find the ratio at the same time. Count the ring gear teeth and divide it by the pinion gear teeth count and you get your ratio. Then put a new gasket on the cover, reinstall and add fresh gear oil. Get 2 things done quickly. Hope this helps.

[WorkinLonghorn]

I agree completely with the above 2 replies (And welcome from so. calif.) but I wanted to add that on my '69 GMC with Dana 60 there is a small metal tag on one of the lower bolts with the # of teeth and resultant gear ratio.
Or you can just jack up one side and turn the wheel one rev.exactly with the tranny in Neutral and count the drive-shaft revolutions exactly and multiply by 2.(unless of course you have traction control,then jack both wheels and don't multiply).

[KAILUAZ]

Welcome, nice to see another 70 GMC 3/4. My tag was broken but there was once one there.
Here is my glove box options list, to give you an idea of what the 70's came with;

Post some pics!!

[FarmTruk]

Hello firedawg99...A big HOWDY from Wallburg, NC.

I agree with all the others above, this is THE place to get the info you need. Just ask away.

[rage'nrat638]

welcome from chigaco

[special-K]

For a quick check on the ratio:mark the tire and the driveshaft yoke with reference marks as mentioned.Spin the tire one full turn while counting the revolutions of the driveshaft.If it`s a 4.10,it`ll turn a bit past the mark after 4 spins.If it spins about 3 3/4 turns,it`s a 3.73.Around 4 1/2,it`s a 4.56,etc.
I don`t know why you`d want to multiply by 2.I`ve never heard that and can`t see a reason.There are only so many ratios and they basically run shy of a 1/2 turn apart with the spread increasing as the numbers go higher:3.73,4.10,4.56.So,that`s as accurate as you need.

[WorkinLonghorn]

I don`t know why you`d want to multiply by 2.I`ve never heard that and can`t see a reason

No disrespect here,but go out and try it.If you have an open diff. you have to multiply.

[firedawg99]

Thanks to all that responded. I am just getting started on it and all this is very new.

Have you ever heard of a aftermarket factory a/c under the dash.
I might need a replacement unit later on.

Thanks again for the warm welcome

[hvychve]

welcome to sight, yes drop cover count teeth on both gears and dived the two, fill with fresh new clean fluid, silicone works too inplace of gasket.

[WorkinLonghorn]

Let's see some more pics too. With the 4spd CR and G70 springs I'll bet it saw camper duty or maybe trailering.

[KAILUAZ]

Originally Posted by WorkinLonghorn

Let's see some more pics too. With the 4spd CR and G70 springs I'll bet it saw camper duty or maybe trailering.

That was my option list, I posted it so Firedawg could see what options were out there. I don't know much about my trucks life either. Heres a pic for fun (not hijacking );
[IMG][/IMG]

[Mt Man Chad]

Welcome to the board from Oregon........ Nice start for a truck!

[Aarons72s]

Do you mean you already have an aftermarket a/c in it or are you asking about putting a vintage air or old air type retrofit unit? I have seen the under dash aftermarket a/c. Took one off of a 68 chevy a few years back. Does it stick out below the stock heater? If so then it is probably a old knee knocker a/c system. Pics would help.

[1969k10stepside]

No need to count the teeth.Look for the numbers in the last column.Match them to some numbers you will find on the ring gear,and then you can find out what gear ratio it is this way.
Ratio 2.56:1 - Tooth Combination 41,16
Ratio 2.73:1 - Tooth Combination 41,15
Ratio 3.07:1 - Tooth Combination 43,14
Ratio 3.08:1 - Tooth Combination 40,13
Ratio 3.08:1 - Tooth Combination 37,12
Ratio 3.31:1 - Tooth Combination 43,13
Ratio 3.36:1 - Tooth Combination 37,11
Ratio 3.42:1 - Tooth Combination 41,12
Ratio 3.55:1 - Tooth Combination 39,11
Ratio 3.73:1 - Tooth Combination 41,11
Ratio 4.10:1 - Tooth Combination 41,10
Ratio 4.11:1 - Tooth Combination 37,9

[WorkinLonghorn]

Quote:
Originally Posted by WorkinLonghorn
Let's see some more pics too. With the 4spd CR and G70 springs I'll bet it saw camper duty or maybe trailering.


That was my option list, I posted it so Firedawg could see what options were out there.

OOPS! Duh.

[70gmcjimmy]

Hey Firedawg and all, cool to see the 3/4 GMC's guys. Nice trucks!! My 72 is a 4:10 according to the diff. tag. Never bothered to actually count the teeth when the cover has been off.
A bigger pic would be cool too!

Later---DAC

[KAILUAZ]

I like that green, military looking!