Installing a 6 lug rear axle in 1989 GMC 1500

[MJMullinII]

Hello and Hello!

My project is a little different than the Duramax Conversion, *however* the engine I'm going to be using is pretty similar in power (Ramjet 502) so I think this can be a valuable resource.

First, I'm very much a n00b when it comes to trucks, but I do have a high degree of interest in upping the specs on my GMC.

It was mentioned on the Conversion page that the rear axle was a little light to handle the 600+ft. torque produced by the Duramax, so I'm concerned mine won't be able to handle the 560+ft. torque produced by the Ramjet.

My question is what I should be looking for as a replacement axle? If I need to go to 6 lugs in the rear, how difficult would it be to also replace the front with 6 lugs so as too only have to carry one spare-tire?

If possible, I'd like to stay with the 15 inch tires I have now.

Thanks in advance!

[trbankii]

I thought the 1500s had six lugs...

Do you mean going to eight lugs?

A full-float 14 bolt rear would certainly be beefy enough. But you're talking eight lugs and 16" rims to clear the brakes.

[MJMullinII]

I thought the 1500s had six lugs...

Do you mean going to eight lugs?

A full-float 14 bolt rear would certainly be beefy enough. But you're talking eight lugs and 16" rims to clear the brakes.

No, only 5. Now, this one DOES NOT have a towing package, so maybe if it did it might have had 6, but at the moment it's 5 all the way around.

[More Power]

I installed a 6-lug GM 9-1/2" semi-float rear axle in Lil Red. This replaced the original 10-bolt rear axle. At the same time, I fabricated disc brake mounts so I could install 2000-2003 model year 1500-series rear disc brake components.

There may be 5-lug 9-1/2" axles out there, but I'm not sure.

If it's in the budget, a custom Dana 60 could be built for your app, but a complete custom axle is close to 3K$. That's about what my 9-1/2 cost, when adding the cost of the salvage axle to the new Eaton posi, new 3.42 gears, new bearings/seals and the disc brake components. I also upgraded the driveshaft's rear u-joint from a 330 to a 350.

By the way, the 9-1/2" has held up well with more than 600-hp and 1200 lb-ft (short term and a light truck).

Jim

[MJMullinII]

I installed a 6-lug GM 9-1/2" semi-float rear axle in Lil Red. This replaced the original 10-bolt rear axle. At the same time, I fabricated disc brake mounts so I could install 2000-2003 model year 1500-series rear disc brake components.

There may be 5-lug 9-1/2" axles out there, but I'm not sure.

If it's in the budget, a custom Dana 60 could be built for your app, but a complete custom axle is close to 3K$. That's about what my 9-1/2 cost, when adding the cost of the salvage axle to the new Eaton posi, new 3.42 gears, new bearings/seals and the disc brake components. I also upgraded the driveshaft's rear u-joint from a 330 to a 350.

By the way, the 9-1/2" has held up well with more than 600-hp and 1200 lb-ft (short term and a light truck).

Jim

AH! The person I was wanting to talk too!

That has got to be the coolest 1989 I've ever seen (Diesel, gas, whatever)!

What did you do about the front? Meaning, are the front independent suspension wheels still 5 lugs, or did you convert those to 6 as well. Again, the reason I'm asking is because I would like to not have to carry two spares .

[tanman_2006]

Hello and Hello!

My project is a little different than the Duramax Conversion, *however* the engine I'm going to be using is pretty similar in power (Ramjet 502) so I think this can be a valuable resource.

First, I'm very much a n00b when it comes to trucks, but I do have a high degree of interest in upping the specs on my GMC.

It was mentioned on the Conversion page that the rear axle was a little light to handle the 600+ft. torque produced by the Duramax, so I'm concerned mine won't be able to handle the 560+ft. torque produced by the Ramjet.

My question is what I should be looking for as a replacement axle? If I need to go to 6 lugs in the rear, how difficult would it be to also replace the front with 6 lugs so as too only have to carry one spare-tire?

If possible, I'd like to stay with the 15 inch tires I have now.

Thanks in advance!

Ok, just taking a shot but your truck must be 2wd 1/2 ton. Chevy 4x4 1/2 tons and 4x4 1500HD comes with 6 lugs. The 1500HD will have the 9 1/2in 14 bolt you're looking for. you might be able to either find a 5 lug rear end or convert a 6 lug hub to a 5 lug hub

[More Power]

AH! The person I was wanting to talk too!

That has got to be the coolest 1989 I've ever seen (Diesel, gas, whatever)!

What did you do about the front? Meaning, are the front independent suspension wheels still 5 lugs, or did you convert those to 6 as well. Again, the reason I'm asking is because I would like to not have to carry two spares .

Thanks for your comments!

Lil Red was originally a 4x4, so it had 6-lug wheels at all four corners from the factory. The 2WD trucks used 5-lug wheels.

Whichever way you go, I suggest making all four wheel hubs the same (either 5 or 6 lugs). Incidentally, the 6-lug 4x4 front hubs must have at least the outer splined portion of the CV shaft installed. The splined outer shaft & nut hold the hub assembly together.

Jim

[trbankii]

Ok, just taking a shot but your truck must be 2wd 1/2 ton. Chevy 4x4 1/2 tons and 4x4 1500HD comes with 6 lugs.

The 2WD trucks used 5-lug wheels.

Learn something new every day. Everyone I've personally known has had a 4x4 so I never took notice that the 2WD versions were different.

[MJMullinII]

I've just about decided to just do a full frame swap from my 1/2 ton to a (if I can find the exact year, that is) 1989 1 ton SWD. I figure for all the work, I might as well gain a good cargo capacity (with a 1 ton I'd get a full-floater, etc.) *without* having to piece it together as I go about.

Then, with a 1 ton frame, I could ponder whether to stick to my original plan of putting a 502 gasser in it, or look at the diesel conversions I've seen (such as the one here). Both make a lot more sense economically when your talking about being able to use them to pull real weight (such as a good sized 5th wheel, etc.)

People keep moaning "oh just buy a new one..." I DON'T WANT A NEW ONE! I want *MY* truck

[More Power]

Learn something new every day. Everyone I've personally known has had a 4x4 so I never took notice that the 2WD versions were different.

Here's a pic showing what 5 & 6-lug wheels were available for the 1996 model year C/K trucks. A 2006 GM truck brochure I have shows only 6-lug wheels for the half-ton. So, it appears GM made them all the same at some point, but the 80's & 90's 1/2-ton trucks had either 5 or 6, depending on whether they were 2WD or 4.