Suburban rear axle into C1500?

[Jerryred94silvy]

Alrighty, if this has already been written up I apologize. I couldn’t find a thread with the info I was after anywhere else.

I want to put 3.73 gears and an Eaton true trac posi into my ‘94 C1500 RCLB.
I have read that a Suburban rear end will swap right over with the sway bar and better rear brakes. This would be good for me since this is a street truck and would help handling and braking all in one shot.

I have also read that the 10 bolt in my truck is weak and useless and should be thrown away immediately and replaced with a 9.5 inch (12 bolt IIRC) diff.

SO

Is it worth it to

1.find a junkyard 2wd ‘Burban with the gears I want and swap a posi into it and run it?

2.Look for a 4x4 ‘Burban with the better rear axle and desired gears to swap a posi and 5 lug shafts into? If that’s even possible.


This truck is not tow pig or abused, so I don’t see blowing up the 10 bolt anytime soon (if at all). I do plan on towing a camper in the future though, along with doing other miscellaneous truck things. The camper will be one that I know the truck can handle without overloading it. Idk if that makes a bigger axle worth it or not.

What do y’all think?

 

[Jerryred94silvy]

Also how do I adjust the speedometer to compensate for the gear change?

 

[spitanddirt]

The speedo is calibrated by changing jumpers in the DRAC, Digital Ratio Analog Converter.

https://harristuning.com/Tbi/vssb-drac-calibration/

Sent from my SM-N975U using Tapatalk

 

[stutaeng]

9.5" 14 bolt.

I helped my brother swap the rear axle from a C2500 6 lug. Those came with a 9.5" 14 bolt 6 lug and his had 3.73/G80 He also got the front spindles with brake calipers from the donor truck to match. It was an easy swap. His is a C1500 RCSB '90 that had 3.08.

Stick with a 2wd, and the above is your best bet. 4x4s have different axle widths, and other 14 bolt is going to be 8 lug. The only 14 bolt with 5 lug were those ultra rare 454 SS...



I don't know about the rear suburban brakes, but those also got the same 10 bolt you have, except for the rear sway bar. I think you are right about the better gearing though....but if you are going aftermarket posi, just regear yours while you're at it.

 

[Jerryred94silvy]

9.5" 14 bolt.

I helped my brother swap the rear axle from a C2500 6 lug. Those came with a 9.5" 14 bolt 6 lug and his had 3.73/G80 He also got the front spindles with brake calipers from the donor truck to match. It was an easy swap. His is a C1500 RCSB '90 that had 3.08.

Stick with a 2wd, and the above is your best bet. 4x4s have different axle widths, and other 14 bolt is going to be 8 lug. The only 14 bolt with 5 lug were those ultra rare 454 SS...



I don't know about the rear suburban brakes, but those also got the same 10 bolt you have, except for the rear sway bar. I think you are right about the better gearing though....but if you are going aftermarket posi, just regear yours while you're at it.

Would I have to adjust pinion depth and all that fun stuff no matter which axle I put a posi into? Cause if I can throw a two wheeler peeler unit into an axle with the 3.73s already in it without having to do too much math or or measuring that would be preferable lol. And I wouldn’t have to spend extra money on new ring and pinion gears. Not wanting to put your idea down at all, I’m just thinking out loud.

 

[stutaeng]

Would I have to adjust pinion depth and all that fun stuff no matter which axle I put a posi into? Cause if I can throw a two wheeler peeler unit into an axle with the 3.73s already in it without having to do too much math or or measuring that would be preferable lol. And I wouldn’t have to spend extra money on new ring and pinion gears. Not wanting to put your idea down at all, I’m just thinking out loud.

Yes, unless you do a "lunchbox" locker. Those just drop into an open carrier. No pinion depth check on those.

And obviously, none of that is required if you swap axles...

 

[someotherguy]

A 4X4 doesn't just automatically come with a "better" axle. Most K1500's will come with the same weak 8.5" 10 bolt you already have. Only a few were optioned with the 9.5" 14 bolt.

Definitely no stock application 5 lug shafts that will drop into that 4X4 axle anyway, since it's wider than a 2WD axle. You could have some made...at considerable expense...and then you still have an axle that is wider than your original, and then what you gonna do for brake drums? Pay a machine shop to carefully re-drill the pattern on some 6 luggers.

The 8.5" 10 bolt in a 1500 Suburban is the same 8.5" 10 bolt in your 1500 pickup, other than the Suburbans did indeed get larger brakes standard (and has the attachments for the rear sway bar you mentioned.) They've also been hauling around a whole lot more weight every single mile they have traveled, and often are displaying noticeable wear at only 100K miles. Many a Suburban out there that still looks and runs great but rear end is moaning down the highway letting you know it's not happy.

If your goals are: stronger rear axle, locker, 3.73's, better brakes, and better handling.. get a 9.5" 14 bolt from a 2WD truck with RPO codes GT4 and NO G80 code. Stronger axle, 3.73 gears (very common in 9.5" 2WD trucks), big brakes, and an open carrier so you have options on aftermarket lockers and not have to automatically replace the entire carrier as you would if it had the G80 Eaton Gov-Loc. Then just add your choice of aftermarket rear sway bars. Done.

And as someone else mentioned it's super easy to re-calibrate the speedo since you're a '94, mod the DRAC module.

You'll have a 6 lug rear, you could pay for some 5 lug axles, re-drill the drums.. or just swap your front rotors for 6 lug and change to 6 lug wheels all the way around.

Richard

 

[Jerryred94silvy]

Thanks for the info! A 6 lug conversion seemed like it was inevitable when I got the truck, all the wheels nowadays are 6 lug and run a 16 inch tire. I’ve been trying to avoid it so I don’t have to buy new rims....but maybe that’s an excuse to get 16” or 18” torq thrust wheels I’ve been eyeing

Maybe this is a dumb question...but what is it about the 10 bolt that is so bad for it to have garnered such hatred from this fine group of enthusiasts?

 

[stutaeng]

Thanks for the info! A 6 lug conversion seemed like it was inevitable when I got the truck, all the wheels nowadays are 6 lug and run a 16 inch tire. I’ve been trying to avoid it so I don’t have to buy new rims....but maybe that’s an excuse to get 16” or 18” torq thrust wheels I’ve been eyeing

Maybe this is a dumb question...but what is it about the 10 bolt that is so bad for it to have garnered such hatred from this fine group of enthusiasts?

I think it's the small-ish ring gear mostly. I think axles tend to break also.

I think it's mostly if you are running big tires and/or wheeling and/or beating on your rig... donuts and driving like an idiot, lol. Big power on the track (or street for that matter) also seems to be torturous on the 10 bolt, especially with abundance of engine power these days, lol!

For stock tires on pavement driving normally you are okay. My 99 10 bolt/G80/3.42 made it to like 265k miles. The few times I was off-road I just didn't beat on it. Ran stock tires and LT265/75/R16 for like the last 50k. My buddy has almost 400k on his.

You can build them up too. My nephew has a 91 C1500 with nitrous 6.0LS/TH400. I think he said 1000hp +/-. He was going to do a 9" Ford, but shop guys convinced him to build his 10 bolt. 4.10 gears, Detroit locker and aftermarket axles...spent a good chunk of change though. I think he's made a few passes with it at the track with some slicks...

But I think for off-roading, no built 10 bolt can handle the abuse of a stock 14 bolt, specially the full float 10.5"... seriously. Especially with them being so inexpensive at the wrecking yards. It's a pretty common axle for those Jeep guys running 44" tires and such to swap the "one ton axle" 14BFF on the rear. It's like the "LS" of axles: Strong, cheap and abundant!

If you read the "14 bolt bible" article and then compare it to just about any other common axle you can clearly see the inherent strength of the 14BFF.

 

[Schurkey]

The 8.5 axle was designed as a passenger-car unit, originally used on intermediate and compact cars. It has no business going under a full-size pickup/Suburban.

The axle shafts (and side gears) got upgraded to 30 (?) splines from 28 splines (?) which made them stronger, about 1989. I suppose they'd have increased the outer bearing diameter as well.

Even so, the guts are on the frail size for the load it's expected to haul around. Buddy of mine exploded the ring gear and carrier on an '89 extended-cab long-box. I gave him the 8.5" axle I took out of my truck when the 9.5" axle went in.

The 9.5", 14-bolt axle assembly is twice the axle the 8.5" is. In full-size truck use, an 8.5" axle is totaled when it needs the fluid changed. They're just not worth putting money into.