Not exactly a towing question,

[BloodMoneyOBS]

But I figured you folks would be the best to ask. The Offroad guys want 4.11s in everything...

I plan on putting an LSD in the back of my 1992 C1500 RCSB 350/700R4. This may not be in any way necessary right now, but I have LS powered plans for the truck.

All that being said, I'm pretty set on a gear ration of 3.91, because I run a 29" tire, and my math says that's a good balance of economy and fun.

The brands I see the most are Motive and Yukon. Do you have any experience with these brands? Is there a brand you or the forum seems to prefer that I haven't found?

Thanks

 

[df2x4]

I haven't used either, but I have read some horror stories from users here involving Yukon products. IIRC someone posted a negative experience with Motive gears years ago as well but I can't remember the details.

I would recommend looking into Eaton carriers, specifically either a TrueTrac or a Detroit Locker depending on how you want the truck to behave. 2WD with LS swap plans leads me to believe you'd probably prefer the TrueTrac. For gears and install kits I've had good luck with Richmond.

 

[smdk2500]

I know your question pertained to gears but I had Yukon axle shafts in a 78 f150 years ago. Truck was on 40 inch boggers and when I drove it I was not easy on it. Never had any issues. Truck still had the 9 inch rear.

 

[Schurkey]

I plan on putting an LSD in the back of my 1992 C1500 RCSB 350/700R4.

WHAT AXLE?

Putting money into an 8.5" is a waste. They were engineered for compact and intermediate passenger cars. GM has NO BUSINESS putting them under full-size pickups. And they've got ****** brakes.

You should have--or install--at least a 9.5" semi-float from a light-duty 2500. Not only do you get an axle that's twice as strong, you get real rear brakes, too.

You'll want to deal with the 6-lug axle shafts--either convert the front to 6-lug, or convert the rear to 5-lug. Given that you're planning on more power, 6-lug up front to match the 6-lug rear is the better solution.

Then get a Truetrac and gears to suit.


Truetrac going in my K2500 later this summer--I've bought it but need to actually install the thing.

 

[sntrym]

I run AAM (American Axle & Manufacturing) gears and a Tracrite LSD (just like a Truetrac) in my 2wd Yukon. No problems, but I don't beat on it save for occasional towing 6000lb boat and trailer and some fast accels here and there. I run 3.42 gears and 29" tires and I think you would be fine with 3.73 or 3.91.

I disagree with Schurkey on the strength of the 8.5. I've had them in all my trucks and they are fine for light towing, DD, and a little fun. If you're going to beat on it, go 12 bolt and beef up the tranny. I do agree that the brakes leave a lot to be desired but I prefer the drums in the rear for the parking brake strength for launching and retrieving a boat.

It all depends on what you plan to do with it. AAM has worked well for me.

 

[stutaeng]

Isn't the problem that on those numerically higher gear ratio the pinion gear is TINY? The 10 bolt is already a marginal axle, and I think the miniscule pinion makes it even weaker. Do a search on pinion size on those and you'd be shocked how small it looks in comparison to like a 3.42.

I don't know about the 12 bolt, but I think those are much more rare, and about the same in strength as a 10 bolt? Aren't they from the 70s? They haven't been made in decades, so very unlikely you will find them in a junkyard by now.

The 14 bolt has been installed in square bodys, GMT400/800/900 and on the 2KXX trucks. They made them in 9.5" SF, 10.5" FF, and now even a 9.76" SF! There's even a 11.5". Drums on the earlier ones and discs on the later ones. So lot's to choose from if you figure out the brakes. And the better brakes are just icing on the cake.

For a light, capable truck, the 9.5" seems like an ideal axle. That's probably why GM finally decided to ditch the 10 bolt in lieu of the 9.5"/9.76" (also seem folks are starting to call this a "12 bolt" because they have 12 bolts on the differential cover!) on the 2014+ truck since they came out with the more powerful LT-1 based engines and to increase towing numbers. But I'd agree that for a 100% STOCK GMT400 just doing runs to grocery store, light hauling & towing, etc. and staying on the pavement, the 10 bolt is just fine.

It's much more difficult to swap a 9.5" to a 5 lug anyway.

 

[kennythewelder]

I rebuilt my rear end about 1500 miles ago. 10 bolt 8.5, 30 spline. The OE C1500 axel with the OE 342 gears. I went with an Eaton truetrac and a set of summit 373 gears. My truck is a street truck with 275/60/15 tires, 5 lug. I dont pull anything with my truck. It never goes off road. And almost never has anything in the bed. I have 2 inch drop in the rear and I welded 200 lbs of steel bar around the receiver hitch for traction. This was done a few years ago. I am very happy with my rear end build. The truck jumps to attention when you nail the gas. It cost me about $1100 total. Money well spent. Here is a link to my post one the build.
https://www.gmt400.com/threads/rear-end-hum-again.51882/

 

[kennythewelder]

Oh, and with the street tires I am running, 410 or 411 would have been to low. If you drive on the Hwy at all and dont have big tires, 410/411 will make the RPMs scream at 70+ MPH. I want to say at 70, Im turning 2500 RPMs with the 373s I think. At 85 MPH 3500 I think. I dont spend a lot of time on the HWY any more.

 

[sewlow]

I don't know about the 12 bolt, but I think those are much more rare, and about the same in strength as a 10 bolt? Aren't they from the 70s? They haven't been made in decades, so very unlikely you will find them in a junkyard by now.

A 12 bolt is w-a-a-a-y stronger than a 10 bolt.
Like...6750rpm no-lift power shifts behind a 475hp/540ft.lb's o'torgue BBC at least once a day eight months of the year for the better part of a decade strong.
Plus the weekly Wednesday & Friday night street race grudge matches.
I broke engine mounts, snapped arms off of clutch bell cranks, (!) blew up clutches, driveshafts, (Ever see a driveshaft spiral split from one end to the other?) exploded u-joints, snapped leaf springs in 1/2 & turned leaf spring center bolts into dust.
...and yet, the only time the cover was off the diff was for a gear swap & fluid changes. That rear end took a **** ton of abuse, never let me down & came back for more.
There's a reason why GM put them behind their high horsepower big torque muscle cars.
Yes. They are rare in the wreckers. Most have been picked up by hoarders, collectors & re-sellers, resulting in a greater demand & prices that reflect such.
But...they are still out there.
Only prob would be finding one of the proper width for these trucks & more than likely, it'd probably need the proper leaf spring perches to be welded on in the right spot at the right pinion angle.

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[PlayingWithTBI]

Isn't the problem that on those numerically higher gear ratio the pinion gear is TINY? The 10 bolt is already a marginal axle, and I think the miniscule pinion makes it even weaker.

I think it has more to do with the actual housing and bearing size/strength.