New member w/ some ?'s

[MNhunter]

Just picked up an '84 silverado 4x4 longbed w/54,000 orignal miles and have a few questions:

1) It's equipped with the 305(LE9),TH700-R4 auto transmission(MX0), and 3.08 rear axle(GU4). Any idea on what transfer case it may be running?

2) Currently running stock 235/75R15, would like to add a modest lift and larger tires (4" and 33x12.5?) without messing with the driveshaft and hopefully gearing.  This will be a daily driver with limited off road hunting use, Would the 3.08 gearing work with the 33's?

3) Would this be a Dana 44 front and 10 bolt rear axle?

[MNhunter]

Found a front 10 bolt and rear 12 bolt with 3.73 gears out of a '87 chevy truck, asking $150.  Would it be worth the axle swap?

[Captkaos]

anything 1982-up will have (factory for a 1/2 ton) 10bolt in the front and a 10bolt in the rear. 
1981 was the phase out year for 12bolts.  Pre-1977 used a D44 front axle, it is basically identical to a 10bolt in strength.
The only transfercase offered in 1984 was the NP208.
The axle swap would be worth it for the 3.73 gears, but an 87 pickup didn't come with 12bolts factory.

[Fordeatinz71]

you wouldn't want a 12-bolt anyhow.  what you gain in ring gear strength, you lose in pinion bearing strength...if you want to lose your 10-bolt, look around and get ya a 14 bolt full-floater.  although you will have to go to an 8-lug wheel, you most likely will never break that axle.  you can either put 8-lug outers on your front axle or get ya a Dana 60 front axle. 

as for the tires/gear thing, yea, the 3.08's will be ok with 33's.  sure, you'll be sluggish, but it'll be ok.  heck, my GMC has 2.73 gears (aargh) and 31's with the same drivetrain you have...and it does ok...

[Captkaos]

For "daily driver with limited off road hunting use" 12 bolts will be perfectly fine.  And is worth it for the gear change if he is going with 33's.  $150 is the norm for 12 bolts.  The 3.08 gears will be a slug with 33's.  You could drive with it but your mileage will suffer, and it won't have a lot of power.

If he was building a offroad only, limited driver, that would be a different story. 

[Fordeatinz71]

well, i was just saying that 12-bolts aren't really THAT much stronger than a 10-bolt...so "upgrading" to them wasn't really worth the money...yea, they will live...but so will a 10-bolt...

[1976Scottsdale]

Yes, the 3.73's are worth it, regardless of what "axles" they are in.  My 78 had 3.08 front and rear lockers and I ran 33's with a 380 horse grunt motor and still got slapped down by stock trucks.  That is when I learned that you can have all the power in the world and it don't do any good if it don't get to the pavement correctly.  I could not even pull a decent hill and hold speed, which in turn burnt up the trans.  Get the 3.73's.  You can get a new yoke if ya need it for the rear from Riverside Gear for like $129.99, or just go to the parts store and get a special u-joint for like $20.00.

[Captkaos]

well, i was just saying that 12-bolts aren't really THAT much stronger than a 10-bolt...so "upgrading" to them wasn't really worth the money...yea, they will live...but so will a 10-bolt...

Not disagreeing with you, but it is worth the $150 for the gear ratio change.

[Fordeatinz71]

yea, there i agree...it is worth the gear swap...i just was sayin that the 3.08's and 33's WOULD work...just don't plan on winning any races...

[VileZambonie]

Probably one of the worst things about these trucks. Almost all SUV's, 4x4s and trucks come with 3.55:1 and higher. Almost every Ford now has either 3.73 or 4.11's and we're plagued with these 2.73's and 3.08's which are such a waste in pretty much any practical set up. Definitely get those 3.73's

Don't worry about all the BS rumors you hear on the internet about 12 bolts being weaker than 10 bolts.... I hammer my 12 bolts and they've held up awesome behind serious big block power. I can't say the same about all of the bolts that either I have broken or my friends & customers under the stress to where they were nothing more than scrap. You may be able to swap the yoke with a new pinion seal or take the best of 2 u-joints or find the correct U-joint to make the swap. A decent parts store will be able to help you out there. I used to have all of the part #'s to do the swap in my tool box but I couldn't find them.

[1976Scottsdale]

Yea, when we swapped in my dad's truck, the only difference was that the u-jooint on the rear axle was wider for the 10 bolt than for the 12 bolt, but they used the same caps.