12 bolt truck help... gov lock

ok fellas,
im thinkin of swapping my 3.73 gear for a 3.08.. also thinkin of throwing in a gov lock... yes ive read all the bad shit about them.. here's my combo.

65 c-10
mild 4bolt 350.. +/- 300 hp
close ratio saginaw 4speed. not sure of the gears but has a real low 1st.
12 bolt truck rear

questions.
-is the gov lock a bad idea?
-how can i tell between a 3 series and 4 series gov lock?
-does anyone know for sure the gear cut off between 3 and 4 series carriers... ive read that 3.73 can be either 3 or 4 series????

thanks in advance

 

anybody?

 

Hold off on the gov loc, I have found the superior 12b truck clutch type posi units under some 4x4 trucks and blazers.

When that gov loc engages it is very violent- imagine one side of the rotating assembly of the axle moving 200rpm faster than the other (20lbs tire + 20lbs rim + 20 lbs of axle shaft and brake drum) vs the inertia of the same assembly at a complete stop. The shock load will either granade the gov loc or snap the crappy c clip axle shaft. I have seen the aftermath and it usually includes a new gearset and carrier as well as body work for when the axle falls out.

I would just search for a complete axle or a mated gear and carrier as most of them were 2.73s or 3.08s already.

 

We got a complete rear posi 3.73 truck 12 bolt that was in good shape from a salvage yard here for $250 all we had to do was call then drive to pick it up. That might be a solution.
later
mike

 

i have two 12 bolts.. one with a 3 series one with a 4. im gonna rebuild one either way, because i want to be able to count on it 100%. ill probably look for a better posi. what i really need to know is the gear cut off between 3 and 4 series carriers???

 

I have the "granny" 4-speed (1st gear is 6.08:1) in my '63 C10 with the 3.73 rear ratio. Instead of changing the rear end, I located a NPG A833 3-speed w/ OD transmission that was used on Chevy trucks (1972-1978, as I recall). First gear is around 3.09:1 and OD is around 0.7:1. I haven't had a chance to install the transmission due to recovering from a long term illness, but I hope to get it in this summer.

There were two versions of that transmission used by Chevy: One had the MOPAR bolt pattern and the other had the SBC pattern. If you find the MOPAR one, make sure you get the bell housing with it.