3/4 ton 6 lug axle

teamjnz · October 27, 2004

Hi Friends..

I have heard of something called a half heavy axle. I have seen several late 80's 3/4 ton trucks with 6 lugs instead of 8 lugs. I even asked a guy at a gas station if I could look at his axle. (he probably thought I was weird when I got on my knees and looked under his truck) I did see a 14 bolt pumpkin!! Then I looked again to count wheel lugs. YEP 6. I wanted to ask about looking in his door jam to see what the RAWR was but didn't want to bother the guy. Said thanks and finished pumping my gas. Since then I have been noticing those trucks.

I would like to know what the axle's weight rating is. Anyone know???

I have a 99' 1/2 ton Sub with a 10 bolt pumpkin. The rear axle is rated for 4000lbs. I had my truck weighed with the family and 42 gallons of petro, no cargo. Front axle weight 3040lbs, Rear axle weight 3360lbs (6400lbs total). The trucks GVWR is 7300lbs. Safely I can put put 640lbs over the rear axle. Thats really not much. Maybe you can see where I am going with this.

Here is a thought I have been playing with. Getting one of those half heavy 6 lug 14 bolt axles under my Suburban. It comes with more braking and weight capacity for towing.

Would the axle fit??

I would probably have to get the drive shaft shortened. I don't know if the brake master cylinder would have to changed out. Anything else that I would have to do to make the change complete.

Please comment...

teamjnz

bigdogs · October 27, 2004

I thought a "heavy half" was a 6 lug 1/2 ton axle vs the 5 lug one. My 80 Blazer had a 12bolt 1/2 ton 6 lug axle before I replaced it (and the front) with 1 ton units.

Shawn T · October 27, 2004

I know way back in 89 when by dad ordered his new Sierra he ordered the "light 3/4 ton option". It included a larger(14 bolt) rear end, heavier rear springs and larger rear brakes. Everything else is the same as a half ton(including the 6 lug wheels). I don't know any other technical data on the light 2500 but there they may be more. I also think it was available starting in 88 and discontinued in 95.

FryZ71 · October 27, 2004

Some pre-99 Z71s came with the 9.5" 14 bolts...at work we have 2 Z71s ('94 & '96) with 14 bolts. It seems like they're pretty rare, I've seen them go for some $$ used. I don't know if the newer 1/2 tons ever had the 14 bolt option or not...I've never seen one.

rascal · October 28, 2004

I had a 89 k2500, the ring gear isn't as large as the 14 bolt full floater. guy i bought the truck off raised cattle and the truck had 185k on. the 350 needed rings, the 5speed had been replaced. it had been stuck with goodyear mt buried, with a large cattle trailer behind. he was a big fan of large john deer's btw. any way the truck worked. no axle troubles. I'd have faith in one.

oh btw the truck burned, I gave truck to dad, the bed and axle are waiting to be a farm wagon.

Larry · October 28, 2004

What you are talking about Teamjnz is the increased GVWR option for half-ton trucks in the old GMT 400 body style (1988- early 1999)

The increased GVWR option included a 9.5 semi-floating rear axle (pretty much a terd axle but slightly better than a 10 bolt), increased rear leaf spring capacity, auxiliary trans cooler and I believe Z82 trailer package was also part of the package. This option brought the GVWR up to 6600 lbs vs. the standard 6200 lbs. As previously mentioned this axle did have 6 lugs and larger drums. The option code was C5S….If I remember correctly and was only available on 4x4 extended cab short bed half-tons and standard cab long bed half-tons.. The extended cab long beds half-ton 4x4’s had the 9.5 as standard equipment….even still on today’s trucks.

A 6.5L diesel engine was the only way to get the 9.5 axle in a half-ton suburban. This was the same axle in all early 90 and 91’s SS 454 trucks and all half-tons with a 6.5L diesel.

Providing your 99 Sub is the old GMT 400 body style, yes, the pre-1999 9.5 axle will pretty much be a direct bolt in deal with possibly some drive shaft shortening and a b-astard U-joint to make it work. You would need the proper U-bolts and cradles to fit around the larger tubes of the 9.5. Brake lines and emergency brake cables will be a direct fit. Better by two axle seals and set of brake shoes because every 9.5 I have ever dealt with had blown axle seals with saturated brake shoes. Tons of pinion backlash as well making for a very noisy ride.

I personally would not go through the trouble of swapping in this axle. For the time and money to do the swap you would not be gaining much. Now a 14 bolt full-floater…..now we are talking but then you have a lug nut quantity issue to deal with.

MS3DALE · October 28, 2004

Option code C5S denotes 6600 lb GVWR which is required for the "heavy duty chassis pkg" which gives you the 9.5" 14 bolt rear,the option code for it is "F44"

"Z82" trailering pkg. and "KNP" aux.trans cooler is not part of the "F44" heavy-duty chassis pkg. but bigger brakes and another addtional leaf spring were.

I had two C/K's a '94 and a '97 both ext.cab short bed Z71's that I special ordered with the "F44" option pkg. I still have the window stickers from them and the option was only $240.00 small price to pay for the added GVWR and the more stout 9.5"rear and bigger brakes.

teamjnz · October 29, 2004

Great information.. This is another reason why this forum is TOPS. I believe is was an 88' 4X2 regular cab, standard bed, 2500 I looked at that had the 6 lug axle. Could be wrong...

The 1/2 axle is rated for 4000lbs. What about the AWR (axle weight rating) for the half heavy axle we have been discussing?

teamjnz

Larry · October 30, 2004

Great information.. This is another reason why this forum is TOPS. I believe is was an 88' 4X2 regular cab, standard bed, 2500 I looked at that had the 6 lug axle. Could be wrong...

The 1/2 axle is rated for 4000lbs. What about the AWR (axle weight rating) for the half heavy axle we have been discussing?

teamjnz

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Teamjnz,

I don’t know exactly what the axle weight rating was on the 1988 through 1994? Light duty 2500s with 6 lugs but the axle was the same (semi float 9.5). Now that I think about it I think the 1500 series trucks got the C5S option after the light duty 6 lug 2500 was discontinued. I also think the half-tons with the C5S option even had the same GVWR as the light duty 2500’s. GM did the same kind of trickery when the renamed the 1500HD Crewcab to a 2500 last year. Same truck new name.

MS3DALE · November 1, 2004

No,the light duty 2500 series "old body style" trucks had a GVWR of 7200 lbs. which was option code C5Z.

The heavy duty 1500 series trucks were 6600 lbs. option code C5S along with option code F44.

As far as the axle rating,I'm not sure,I'll have to do some checking into that.

MS3DALE · November 1, 2004

Found it!! It was in one of our old light-duty truck technical guides here at the dealership,you wouldn't believe the info. in one of these!!

The capacity for 9.5" rear axle in the heavy duty 1500 and light duty 2500 is 4800 lbs.

It is 6000 lbs. in the heavy duty 2500 (8-lug)

And the capacity for the 8.5" axle in the light duty 1500 is 3750 lbs.

Hope this helps out a little teamjnz

teamjnz · November 9, 2004

Found it!! It was in one of our old light-duty truck technical guides here at the dealership,you wouldn't believe the info. in one of these!!
The capacity for 9.5" rear axle in the heavy duty 1500 and light duty 2500 is 4800 lbs.

It is 6000 lbs. in the heavy duty 2500 (8-lug)

And the capacity for the 8.5" axle in the light duty 1500 is 3750 lbs.

Hope this helps out a little teamjnz

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