Civi 2WD axle in the back of my M1009, I need to match up my ratios

[RedneckMilenko]

Alright, here's my problem. I bought this M1009 a little over a year ago and after driving it for about a month my trans went out and I had roller bearings pouring out of my transfer case. Luckily the man I bought it from was nice enough to give me a TC out of another 09 and I found the trans out of a wrecked 09 in a junk yard locally and replaced them both. After that she seemed to run perfectly fine. I took her wheeling in the bottoms and got some lock wire wrapped around my rear drive shaft and pinion so I had to replace my pinoin seal. Thats when I saw that on the back side of the gear housing it was stamped "2WD". After thinking about it I figured when put in 4wheel the axles were fighting eachother and thats what caused the trans and transfer failure. Pretty much what I'm asking is what should I do to fix this issue? I'd like to match the front with the now different rear so I can have a stronger gear for bigger tires. I assume it's around a 373 in the rear instead of the 308. I've never replced a ring and pinion before and would like to put a spool up front since it has manual lockers so I wont have to worry about any issues on the road. Any advice?

P.S. - I just picked up the front and rear axle out of a 79 K5 blazer so if it'd be easier to just rebuild those then replace them then I'd probably do that as well.

 

[Recovry4x4]

Don't assume. Remove the cover and determine what the rear gear ratio is. Report back and we can give you a plan of attack.

 

[RedneckMilenko]

How would I go about figuring out what the current ratio is in the rear? As I said before, I've never tackled a ring and pinion job.

 

[DieselBob]

The only 100% foolproof way is to pull the cover and count the teeth on the pinion and the ring gear.

 

[RedneckMilenko]

Alright, now this may seem like a dumb question but how would you count the teeth on the pinion? When I serviced the rear axle I didn't notice being able to see it. It has a posi unit in the chunk.

 

[DieselBob]

I have had good luck using a small inspection mirror to look around the differential to see the pinion when the differential fills most of the housing. The tough part can be keeping a reference point to start counting from. I find in smaller areas like this the rectangular shape mirror works better than round ones.

 

[RedneckMilenko]

Ok, sounds good to me. Thank you. I'm a little under the weather right now but I should have the results of that on here soon enough.

 

[doghead]

If they are different ratios, it would be pretty easy to notice if you simply mark the drivesafts and the tires and roll ahead one full tire revolution, then compare the driveshaft mark positions.

It's pretty easy to identify your actual ratio like this as well. You only need chalk or a crayon and a helper.

 

[RedneckMilenko]

How would you calculate your ratio that way?

 

[southdave]

Or if donor truck is still around the RPO number in the glove will the code for what the number is.. on a chevy in the glove box most in the late 80s where 3.42

 

[wdbtchr]

The way I count the teeth is to mark the pinion gear on one tooth and count them as you rotate the drive shaft and count. Ther is just enough room to the the teeth on the pinion. Ring gears and pinions are also stamped from the factory with the # of teeth.

 

[RedneckMilenko]

Well see, the previous owner of this truck bought the rear axle that's in it now as a supposed CUCV axle. He drove to KY from here in TN to get it. So theres no telling where the donor truck is. Also, I'm not sure of the ability to get to the pinion. But I will definatly try that, if worst comes to worst then I'll just remove them and re-install. a bit of cleaning up couldn't hurt ether.

 

[doghead]

How would you calculate your ratio that way?

Lay down and watch the driveshaft while it rolls ahead. for one rotation of the tire, you will see 3.08 rotations of the driveshaft(3.08:1).


It should be easy to see 3.08 or 3.73 rotations to determine if it is 3.08 or 3.73 ratio.

If you see a very large difference between the front and rear, you will know if you have miss-matched axles.

 

[86m1028]

Or if donor truck is still around the RPO number in the glove will the code for what the number is.. on a chevy in the glove box most in the late 80s where 3.42

Thats not completely true A LOT of the civi blazers were 3:73's

 

[RedneckMilenko]

That's why I was guessing 373, a few of my friends have civi blazers and they all have 373 gears.

 

[DieselBob]

My 85 K5 had 3.08's from the factory and a 305 sbc. My 89 GMC v1500 jimmy had 3.42's from the factory with a 350TBI sbc.

 

[martindc1]

Just put the rear on jack stands, mark one of the tires and count how many times you have to turn the driveshaft to make the tires turn 1 revolution. If its a tad above 3 turns of the driveshaft you have a 3.08, nearly 3 and half turns you have a 3.42 and almost 3 and 3/4 turns you have a 3.73.

 

[BikerBi11]

If this rear end does not have a locker in it, jack up ONE rear tire, rotate it TWO revolutions and count your drive shaft revolutions. 3.08= just over 3 revolutions, 3.42= 3 and 1/2 revolutions, 3.73= 3 and 3/4 revolutions. this will also work on the front if it doesnt have a locker. (tranny must be in neutral)

 

[Cletus09]

Just putting it out there, but according to LMC Truck, the 78-91 k5 (civy) Blazer, with a 10 bolt rear-end, came with the following ratios:

2.73, 3.08, 3.42, 3.73, and 4.11

However, I have also learned that when building the CUCV, GM mixed and matched parts from previous years. For example I don't think the Dana 44 was an option after 1980.

Obviously some of those ratios were more popular than others. I would say the safest way is to just tear it apart, count the pinion teeth and do the math. (divide the ring teeth by the pinion teeth) However this is coming from someone who has zero experience with differentials.