RPO axle ratio questions

[loonatic72]

I have 2 79' k5 blazers, one military with the 6.2 diesel. One has a 12 bolt rear-end and the other a 10 bolt. Well the 10 bolt has a RPO code of 7G01 and the other doesn't have a code. Does anyone know what gear ratio that is?? I'm trying to figure out which one has the better axles in it. I tried the spin and count method but when the tire rotates around once on the 12 bolt the pinion spins around only 1 1/2 times and the 10 bolt spun around 1 5/8 times. Can anyone give me some heads up on this?? thanks

 

[Georgia Mike]

If you've got an open diff, spin one tire 2 revolutions and count the driveshaft revolutions to get an estimated ratio. 1.5 revolutions the you did it would equate roughly to 3.08, and the 1 5/8 revolutions is probably 3.30-ish. Also, the military version probably would have a gov-lock in it. To find out if it does, jack both wheels off the ground with the trans in neutral. Spin one tire by hand increasingly faster and see if the diff locks. It usually takes around 100-150 wheel RPM difference to make the diff lock up.

 

[loonatic72]

I went out and spun both axles, both of them after rotating the tire 2 time the pinion went around about 3 1/4 times???? I know the military blazer has a t400 and will only go about 60 mph while the other blazer has a 4 speed in it and it'll go alot faster. See im trying to fix up the non-military blazer cause its in better condition but I just want to know if the axels in the military one is better. The military has the 10 bolt and the other has the 12 bolt. thanks

 

[Georgia Mike]

I would bet that the 10 bolt from the military truck has the gov-lock. If so, I'd use it if the gears are the same. If all else fails, pull the diff covers off and count the teeth on the ring gear and pinion gear. Divide the number of ring gear teeth by the number of pinion gear teeth and you'll have the correct gear ratio. My guess would be either 3.08 (most likely), or 3.32. There isn't that much difference in the 10 and 12 bolt axles from trucks, save for maybe a slightly (and I mean barely) larger ring gear, and possibly thicker axle tubes.

 

[loonatic72]

I was also thinking of switching over the master cylinders too cause the military blazer has the hydro-booster (I think that what it's called im having a brain fart) and the other has a vacuum booster.

 

[rick88blaze]

I looked on my RPO listing and couldn't even find 7G01. As far as the axle ratio's. The military blazer would have 3.08 gears and a gov bomb. As far as the 12 bolt, it's not much stronger if at all than the 10 bolt. If the RPO codes aren't in the glove box you might look on the passenger fender well. They put some of the RPO lists there too.

Rick

 

[loonatic72]

Yeah I looked all over the vehicle and couldn't find a RPO, but on the military one I found it on the drivers side in fender and it said rear axle 7G04 and rear axle ratio 7G01. I looked all over the net and couldn't find anything that matched that?? thanks for the help

 

[dyeager535]

drop the 7

Edit: sorry for brevity, was on a computer with no keyboard. lol

G0x IIRC is a generic "standard axle ratio" RPO, which means essentially nothing. The drivetrain combo is what determined the axle ratio, never seen a listing of what drivetrain got what ratio, although later on it wasn't optional, and is listed in the brochures I believe.

Maybe a typo, but to my knowledge there are no '79 CUCV's, (GM at least, I know nothing of the Dodge stuff) and the 6.2 diesel was certainly not around in '79, so either some misinfo from who you bought them from that might be steering you the wrong way, or just a typo on your part.