I have a '89 GMC Sub. , 350ci, 4in. Skyjacker lift, 4.10s front and back. 12 bolt in back and 10 bolt in front. The lift, the gears and the axles have been under the truck for almost 35k miles. Detroit locker in rear. At least it did. It just blew out. The entire axle casing is shot. It blew out thru the cover and the bottom of the housing. Looks like the locker blew apart. It was not under pressure or off-roading. Just got inspected and going for a test drive. BANG. What rear axle will fit and what will be strong. I do a fair amount of off-roading, but not serious. I also plow snow. Since I'm going to replace the whole axle, what should I use?  

While it has had at least one rear axle change already because 89 1/2 ton burbs did not come with 12 bolts in rear. They came with 10 bolts. A 12 bolt is not really a upgrade over a 10 bolt either. Detroits add a lot of strain to rear axle assembly because they cannot properly balance torque and in daily driving a lot of stress can build up in axle because of them and they are poor choices for plowing snow too. Throw in big tires. lift and a heavy burb and is it a recipe for disaster. Also, 4.10 is not really enough gear for a burb with a lift and serious rubber either. BTW, I have owned a 89 burb since it was new and still do and I have put over 180K miles on it so I know them really well. Your options? Since you have to start over I would suggest that you forget about Detroit for street and plowing (it is a poor choice for this) and either use a LSD or a selectable locker. Next, look around for a GM 9.5 14 bolt semi floater rear axle. They can be had with 6 lug hubs and are about the equal of a D60 in strength. While you are swapping your axle, take another look at your axle ratios too. If you have 33's you should be looking at 4.56's and with 35's 4.88's. (if you have 35's it is no surprise that rear axle toasted and I know a guy that blew two rear axle in a 1/2 ton burb in a year with 35's and still never figured it out)  

Hey SnoMan, I really thank you for the input.  I just today talked to a 4 x 4 mechanic, and he was steering me to the 14 bolt.  But he didn't say anything about the Detroit or the gears. I will look for the 14 bolt 9.5 semi floater with a limited slip. The gearing is a surprise, but I understand. I bought the Burb back in 2000 and it already had the 4.10s, lift,and axles. I put the Detroit in, but got the advice from a Jeep builder. Now what bothers me is I recently did the ball joints and u-joint up front. When I got in the 10 bolt upfront, it had a totally geared diff that looked just like the Detroit I put in the rear. The previous owner tried to make it a rock crawller/street runner. What would you suggest for the front? I really like the rig and I also have about 185k on it. Drop me a line.  tsmudrat@comcast.net  

There is a lot of misconceptions of what proper axle ratios are. Some tend to think that the holy grail of axle ratios is 4.10's but since true effective ratio (used to get power to ground) is a product of axle ratio and tire size there is no universal magic ratio that works for everything. Also OD trannies changed the equation because while some might argue to be conservative with ratio with out dated non OD trannies, these new trannies open up a lot of possibilities. In your case you should have a 700R4 which is a good tranny but gets a bad rap from some because with its 30% OD it can slow bake and die with big tires and tall gears as it forces tranny to ride stall a lot. When this happens many blame tranny and it escapes them that the problem is the axle ratio's. I have come up with a simple formula here that comes pretty close to find the correct axle ratio for most configurations with OD trannies. You take tire size and divide it by 7.2 for SB full sized trucks and the result is the recommended axle ratio. Example 35's / 7.2 equals 4.86 so a 4.88 would be in order here. If you live in mountains in thin air you want to bump it up one step to a 5.13. Do not let these numbers scare you though as a 700R4 with 35's and a 4.88 is only going to be turning about 2100 RPM at 65 (and about 2200 with 5.13's) in OD/4th gear and rendure 4th gear far more usable than with a taller axle ratio. 4.10 is not a bad ratio with stock tires and OD but is it a poor choice for big tires and OD tranny. And the real silly part of all this is that 4x4's off road it is all about power and gearing and those that will tell you to scape a 700R4 as junk and run taller gears to limit cruise RPM will ham string performance. (you see a lot of that in forums) Let me explain. If you say take a 4.10 with 35's and use a THM350 you will cruise at about 2600 RPM (much higher than a 700R4 with 5.13's) Then on the effective gear ratio side, a THM350 has a 2.52 first gear so you max startup ratio in first high range is 4.10 x 2.52 or about 10.3 plus converter stall. Now same truck with 5.13's and a 700R4 has 5.13 x 3.06 (700R4 has a much deeper first gear too) and you have a start out ratio in high range of 15.7 to one. So with same engine and tire but deeper gears you now have about 53% more start out power and a lower cruise RPM too!! The need to use low range is greatly reduced for most off roading. Same thing in reverse. 4.10 x 2.08 for THM 350 equals about 8.5 to one. With 700R4 combo you have 5.13 x 2.29 or about 11.7 to one (about 38% more power in reverse) Many spend a fortune on air cleaners and dual exhausts and other tweaks trying to gain a few percent more power to make up for tall gears and big tires when the real solution is right in front of them but they are stuck on old logic and math in gear ratio selection.  

Snoman, have you ever considered teaching auto shop? You should get your teaching certificate and then you could help mold our youth.
A lot of stuff you preach is stuff my Dad tried telling me as a kid, I was just to bullheaded to listen.  

Not really. Who would listen to a old guy anyway. I am thinking if retiring from here though. Thinking of pulling the plug at 5000 posts. I think I have given too much "free" advice here anyway.  

are you serious snoman!! too much "free" advice  don't people say thank you after you give them advice? come on this a fourum for helping out  

Yes I kinda am. This forum is after all part of a for profit operation. I was looking at the totals the other day and about 1 out of every 5 posts has my name on it. I know some of you guys really appreciate my help but I am thinking that maybe I need to spend my time and knowledge in a more fruitful endeavor. My mind is not 100% made up yet but I am seriously considering it.  

i'm New to this, I'm not trying to butt in,but I was reading this,And I have a related ?
I have 90 suburban,I've Had a yr now.350 V8tbi 700r4 stock everything else.3.73axles posi in rear.stock tires
I also have an old 73 3/4ton chevy truck w/14bolt full floating rear axle and dana 44 front axle.both have stock 4.10's. would this be a good swap? or is this axle combo old an anaquaited?
or should I find a new combo? I want to lift it alittle not drastic, put 31,32 or 33's havent decided. I do a little off-roading not much at this time YET!My big thing is I'm tired of the rear end sagging!  

well your rear sagging has nothing to do with axle, your springs are worn so get them replaced or re arched or put another leaf in there, the axles out of the 73 chevy may be old but they are plenty stout espeiscally the rear 14 bolt full floater!! they are way better axles than your present ones and parts are pletyfull since gm used the 14 bolt up to about 2004 and the d44 is still in use to this day but your front axle and the d44 are about the same in strength, your front 10 bolt is just 6 lugs while the d44 is probabley 8 lugs if it came with the rear 14 bolt full floater, also since they have 4:10 gears they would be good for up to about a 33 inc tire, way better than 3:73 with 33s  

I would not say that a 4.10 is good with 33's but it is better than a 3.73. I have a different definition of what a 4x4/truck is supposed to be and I do not believe in bigger tire and less pulling power than with stock tires because you did not regear.  

SnoMan:
Yes I kinda am. This forum is after all part of a for profit operation. I was looking at the totals the other day and about 1 out of every 5 posts has my name on it. I know some of you guys really appreciate my help but I am thinking that maybe I need to spend my time and knowledge in a more fruitful endeavor. My mind is not 100% made up yet but I am seriously considering it.

No matter what you decide, thanks for the help!  

circlemw:
i'm New to this, I'm not trying to butt in,but I was reading this,And I have a related ?
I have 90 suburban,I've Had a yr now.350 V8tbi 700r4 stock everything else.3.73axles posi in rear.stock tires
I also have an old 73 3/4ton chevy truck w/14bolt full floating rear axle and dana 44 front axle.both have stock 4.10's. would this be a good swap? or is this axle combo old an anaquaited?
or should I find a new combo? I want to lift it alittle not drastic, put 31,32 or 33's havent decided. I do a little off-roading not much at this time YET!My big thing is I'm tired of the rear end sagging!

I say do the swap, and regear to 4.88's. As far as sagging goes a set of new springs and shocks would solve that.  

actually i think that chevy still uses the 14 bolt 10.5 rear axle in its current 2500/3500 trucks just the ones with the gas motor not the diesel, i thought they had totally phased out the 14 bolt for the aam 11.5 but ive seen two 08 chevy 2500 srw 3500 trucks with the same familer 14 bolt rear axle and then i noticed that they werent the duramax trucks so there you go i just thought id bring that up  

Geo450racer:
actually i think that chevy still uses the 14 bolt 10.5 rear axle in its current 2500/3500 trucks just the ones with the gas motor not the diesel, i thought they had totally phased out the 14 bolt for the aam 11.5 but ive seen two 08 chevy 2500 srw 3500 trucks with the same familer 14 bolt rear axle and then i noticed that they werent the duramax trucks so there you go i just thought id bring that up

The 11.5 was never meant as a replacement for 10.5 over all and 10.5 is still in use today. It was meant as a rear axle for 8.1 and Dmax. Between Allisons deeper first and reverse gear and the torque of a 8.1 or Dmax it could exceed the design application limits of a 14 bolt 10.5. Axles are rated at yoke input capacity and 14 bolt FF is rated at about 2300 ft lbs input and 11.5 at around 2800. These ratings are approximately 40% of design failure limit and are used as application limits when sizing axle to application. input loads at or below this below this 40% limit can be sustained without premature failure.