GM 10-Bolt axle/locker advice needed

[trukman1]

I have a stock '88 K5 that will see very little if any off-road use.

It currently has 28-spline axles with open front and rear differentials. The open diffs aren't going to work for me even when using as a daily driver so...

My question is would it be worth the extra money to upgrade to 30-spline axles and does the fronts use the same outer shafts even if changing from 28 to 30 spline inner axles?
If so, would that create a weak link that would negate the upgrade to 30-spline axles anyway?

I'd like to make it as reliable as possible without breaking the bank bit I also believe in, " buy once, cry once." I don't mind spending the money if it will make it a much better vehicle I just don't want to waste money either.

I planned on installing Spartan lockers front and rear so if I'm going to switch to beefier axles this is the time to do it.

So what advice can you guys give me. Stay with the 28-spline or go ahead and bite the bullet and go for the 30's?

BTW, I'm running 31 x10.5 x15 Toyo M/T tires with 4.10 gears and stock everything else.

Just trying to give as much information as I can to figure out the best course to take.

Sorry for the long post. Thanks for any and all input.

trukman1

[84 400]

Okay what are you using this for?? Are you doing burn outs on pavement or wheeling rocks? My truck had a 10b/12 bolt combo from stock up to 35x14.5 gateway gumbos. I ran a G80 in the rear and a power trax lock rite up front. I loved the posi rear for its street and the locker was awesome up front in the rocks. My front 10 bolt was 28 spline and i never broke a shaft, stub, or axle joint.

Buy once cry once would be a set of 1 tons or 3/4 ton 14 bolt rear and 3/4 ton hubs and backing plates for your current 10 bolt front. I don’t believe in upgrading axle shafts in a half ton axle. If your at that point your money ahead to swap to 1 tons or atleast a 3/4 ton rear.

If you must stay 6 lug… i would go selectable locker out back and sparten or lock rite up front.

If i had to do it all over i would of gone cucv 1 tons and been done with it. But i went from 10/12b to converted 10b/14ff to D60/14ff. I learned alot through actually usibg the diffrent setups but wasted some cash in the end…

[Dexterb]

Swap for 14 Bolt/D44. Easily available, and more robust than any 10 bolt.
Only downside would be new rims due to 8 bolt pattern.

If it were me, I would go straight to D60 and 14 bolt with cross-over steering.

[Dexterb]

Originally Posted by 84 400

Okay what are you using this for?? Are you doing burn outs on pavement or wheeling rocks? My truck had a 10b/12 bolt combo from stock up to 35x14.5 gateway gumbos. I ran a G80 in the rear and a power trax lock rite up front. I loved the posi rear for its street and the locker was awesome up front in the rocks. My front 10 bolt was 28 spline and i never broke a shaft, stub, or axle joint.

Buy once cry once would be a set of 1 tons or 3/4 ton 14 bolt rear and 3/4 ton hubs and backing plates for your current 10 bolt front. I don’t believe in upgrading axle shafts in a half ton axle. If your at that point your money ahead to swap to 1 tons or atleast a 3/4 ton rear.

If you must stay 6 lug… i would go selectable locker out back and sparten or lock rite up front.

If i had to do it all over i would of gone cucv 1 tons and been done with it. But i went from 10/12b to converted 10b/14ff to D60/14ff. I learned alot through actually usibg the diffrent setups but wasted some cash in the end…

I've done pretty much the same thing as you. I swapped D44/14ff and then eventually found a D60.

[Ziegelsteinfaust]

I would do the 30 splines. There are a decent size bigger, and the carrier or posi is the bigger expense. Axles are what $250 for common sizes.

Only do the big axles if you going to whomp on it or run big tires. As at that point the durability start coming to play with just the tires. Plus you will get bigger brakes.

If your cruising the Blazer, and maybe hit dirt roads. It is a waste unless you just want it.

[Greenlee]

This past Memorial Day weekend I was driving down Interstate 10 at 70 m.p.h and it sounded like something under the truck exploded. Turned out the center pin in the rear axle came loose. Ended up getting a ring and pinion at a pick in pull yard in San Antonio to get the truck back to Houston. To make a long story short, I’m getting both axles rebuilt with 3.73s and Detroit Tru Trac front and rear. I’m running 33x10.50s and the truck doesn’t see much off road use. The differential shop said it should hold up just fine. I asked them about upgrading to 30 spline axles and they thought it was a waste of money. I guess time will tell. The shop is Pyle Bros. in Baytown, Texas. They’ve been in business for over 40 years.

[84 400]

87 ? and up front 10 bolts were 30 spline and d44 if my memory is right…..

Okay it sounds like your staying small tire do you NEED lockers? Or could a limited slip work? I have a Detroit locker No Spin in my rear axle, manual trans in a lifted shortbed and it got old real quick on the street and highway. It can pull on the highway while changing lanes and accelerating, draggs tires in parking lots or when parallel parking, makes the truck buck on slow tight turns as it locks and unlocks. Was better in a auto truck. If i had the cash an ARB or E locker thats what would be in my rear axle. I remember hearing about e lockers from hummer H2’s fitting in 10 bolts?? My point is a locker on the atreet and highway can get old fast dependibg on what you do and how you use the truck. Also if you see snow or ice don’t plan on running 4x4 on plowed pavement.

For a small tire street truck i would go true trac or the like but understand they are more spendy then a lockrite or spartan.

[Greenlee]

For what it’s worth my 87’ has the 28 spline axles. Someone told me 30 spline was in 1988. Would be curious to know what the 88 blazer has. Maybe 30 spline was just the newer body style.

[kwmech]

I believe 30 spline fronts were Suburban only. But upgrading is not an issue and highly recommended. 10 bolt fronts with 30 spline are actually a little stronger than a 44. Pinion head is quite a bit larger--everything else is the same for size. Upgrades to chromo shafts are available. Personally I would stay away from the spartan in the front and go with a tru-trac

[trukman1]

Thanks for the input. I put a D60/14BFF in my .67 so I'm not looking to go big on the
K5 just wanted to be able to have traction if conditions get slippery. I think I'll stay with the 28's and put the extra money into some better lockers. At ;least that's how I'm leaning after reading your posts. Thanks all!

[THI]

Posi works better on "slippery" than lockers, both front and rear. Lockers are better for rock crawling than posi's. In snow country, lockers can spin you around in a hurry, posi's tend to dig in and go.

1988 for square bodies was a cross over year - I had a late production K20 Suburban that came with 30-spline on the front 10-bolt axle and an NP241 t-case. The books all show it should be 28-spline front and NP208 t-case and 1989 as 30 spline and NP241. With 31" tires I don't think you will have an issue with stock 28-spline axles.

[buffydores]

A good 6-lug upgrade is a 14 bolt SF (9.5"). It's just beefier. We're just setting one up for a buddy that's working on his '90 Burb. You can find them in OBS 1500s with a GVWR of 9,500. Hunt them down on Car-parts.com. All of them have tons of miles on them, so you'll spend some coin to rebuild. Instant brake upgrade out back. Run a Truetrac and alloy shafts and you're good to go out back. B&M has a nice cover that helps reduce flex inside. Upfront, I wouldn't stress too much unless rocks are your deal. I like the alloy shafts because breaking shafts and seeing your wheels come off is unnerving on these c-clip axles. The 14bsf is just a more rigid box. Less likely to go boom.

Personally, my 12 bolt in the K5 runs a Truetrac and alloy shafts. I have the fancy cover also. I have the NP203, so my power is split front and rear always.

EDIT: I just re-read your post. I don't think you need anything. But if you must, just rebuild a 6-lug 14 bolt SF and add a Truetrac out back. Nothing else. I don't know why in the world you'd want to mess with the front diff if you're not doing much off-roading. There's no point.

[Mike C]

'89 is officially when GM went 30 spline on the 10 bolt. In the front as well from '89-'91 but seems that they had a lot of 28's to use up so check the front to make sure.

I would not run the Spartan in the rear on the street and probably not in the front either. TruTracs in both ends would be how I would spend my money. I have a CJ-5 with Powertrax NoSlips in both ends and they are significantly more street friendly than the Spartan/LockRight style.

A Yukon/Eaton clutch type LSD in both ends would be a good choice as well. In my kids Jimmy we put a '79 Trans Am clutch posi in the front and running Gov-Lok rear in 8 lug SF 14 bolt.

I also agree that if you are considering buying upgraded axle shafts just convert to a SF 14 bolt and TruTrac or Yukon LSD for the street. I found 9.5" 14 bolt Yukon LSD for $389 on Amazon a year ago. Not sure what selling for now. The 33 spline rear shafts are absolutely massive on the SF 14 compared to the 30 spline 10 bolt axles.