99 Suburban c1500 gearing

[bravocharlie]

Unsure where to post this thread, my concern may be within the rear axle configuration. And so, I am asking for as much input on those who have had similar experience in correcting this. All input is appreciated.

A little about my jewel, I recently acquired a 1999 C1500 Suburban with a 5.7, 4l60e, 10 bolt fear end. 1 owner, 114k approximately. Owner claims to never had major repairs, only mods where a reusable drop in air filter, larger wheels/tires. Previous owner had installed 265/70r17, factory set up 235/75r15.

I'd like to install a less popular tire size, for cost reasons but with many benefits as well. A cooper discover s/t maxx, 255/80r17 (33"), skinner but taller tire with a 10ply-stiffer sidewall and higher load rating. Current tires are rotted.
So id be going from a factory 29" to a 33" tire.

I have not calculated mpg, haven't burned through a tank of fuel yet, she puts down about 42 gallons...
Burb feels underpowered, specifically getting up to highway speeds.

I did some math, and determined the most effective gear ratio I should be running is at about 3.91/1.
Ill share my math, (New Tire/original tire)original ratio=Required ratio. (840mm/734mm)x3.42=3.91.

Question is, what axle/final drive would you recommend? Posi/LSD would be preferred, but I understand they are limited. The rear suspension can use some additional support. On dirt roads, I can hear the leafs compress as the burb sways side to side. And I am not a fan of the rear sag, nor the inverted rear axle when compared to the front end. Ill post pictures shortly.

 

[bravocharlie]

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[bravocharlie]

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[bravocharlie]

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[RocketRed]

very clean suburban *

 

[95burban]

Don’t be afraid of gear. 4.10 would be my choice, I’ve ran it with a 4l60e and it was great.

 

[OutlawDrifter]

I would agree with the 4.10 ratio and a 33" tire.

Front looks lifted on your 2wd 'burb.

 

[Schurkey]

10 bolt fear end.

Good name for it.

Scrap that weak ten-bolt, step up to a 14-bolt semi-float axle from a light-duty (6-lug) C2500.

3.73 will be very common, 4.10 somewhat less-so; but probably still "find-able" if you're willing to drive a ways to get one from a friendly Treasure Yard. You'll need the u-bolt mounting plates from the 14-bolt axle donor vehicle, a conversion U-joint, new U-bolts 'n' nuts, and whatever repairs the brake need. Pop the cover off, inspect the guts, re-fill with fresh axle lube. New axle seals recommended.

The only real issue is that you'd need 5-lug axle shafts to fit the 14-bolt SF. Available in the aftermarket, probably discontinued through GM.

That, or replace the wheels with 6-lug units, and front hubs to match.

 

[bravocharlie]

I would agree with the 4.10 ratio and a 33" tire.

Front looks lifted on your 2wd 'burb.

right. well, my driveway is on a slope. But that would have transferred more weight forward. I suppose it’s possible the previous owner may have adjusted the torsion bar. Front end is all OE. Bushings will have to be addressed soon.

 

[bravocharlie]

Good name for it.

Scrap that weak ten-bolt, step up to a 14-bolt semi-float axle from a light-duty (6-lug) C2500.

3.73 will be very common, 4.10 somewhat less-so; but probably still "find-able" if you're willing to drive a ways to get one from a friendly Treasure Yard. You'll need the u-bolt mounting plates from the 14-bolt axle donor vehicle, a conversion U-joint, new U-bolts 'n' nuts, and whatever repairs the brake need. Pop the cover off, inspect the guts, re-fill with fresh axle lube. New axle seals recommended.

The only real issue is that you'd need 5-lug axle shafts to fit the 14-bolt SF. Available in the aftermarket, probably discontinued through GM.

That, or replace the wheels with 6-lug units, and front hubs to match.

Going to have to look for those axle part numbers. That conversion would make it more ideal.