Heavy 1/2 ton GVW option experts?

[Coley]

I've had a few of these trucks (almost all 1/2 ton) and I haven't been able to figure out rhyme or reason on how GM dictated the heavier GVW option (5400lbs vs. 5000lbs) on these trucks.
I've had 1/2 tons with the heavy rear spring option and overloads still showing a 5000lb GVW on the rating plate...and then my current truck with no heavy spring option listed on the build plate with a 5400lb GVW plate.
Has anyone ever figured this out fully? Then I've seen trucks with 6000lbs stamped on the lower front portion of the box by.....the dealer? owner? or? I'm not sure if this 'added' rating matches the plate rating in the door or not.
GM strikes me as not being the best on organizing their truck line as compared to the cars, engine numbers, etc.
Any info or insight on this?
All Good
Coley

[special-K]

Do the two trucks you gave for an example both have coil or leaf? Do they both have 12-bolt rears or does one have a Dana? How about tire options,what are they?

[Coley]

Originally Posted by special-K

Do the two trucks you gave for an example both have coil or leaf? Do they both have 12-bolt rears or does one have a Dana? How about tire options,what are they?

Both the 1/2ton trucks in question had/have the coil rear (trailing arm) suspension with the 12Bolt rear diff. Both were running the 235-15" tires (pretty standard on these I think).
I had a '72 Cheyenne Super that had the 'leaf spring' option combined with the HD rear spring option which had the 5400lb GVW (heavy 1/2) option...which makes sense.
I'm trying to find the background on why my current C10 ('72) which doesn't show anything on the build plate has the 5400gvw rating as well.
I've included a quick pic of my build plate here...which doesn't indicate much if anything regarding suspension.
I was wondering how random the 'plating' of these trucks was?
All Good
Coley

[WorkinLonghorn]

Regular brakes vs Hydro boost?

[Coley]

Originally Posted by WorkinLonghorn

Regular brakes vs Hydro boost?

I don't think that option plays into it being a heavy 1/2 ton vs. a standard 1/2 ton. ie: 5400lb vs. 5000lb.

I'm wondering if maybe with a/c, V-8, ps, pb and a few options they just 'bump' the H.Duty factor up...which shows up on the GVW plate?

Maybe a California thing?

Coley

[DANTIP]

In order to get the highest GVW rating on a 1/2 ton, you need heavy Front and Heavy Rear Springs along with an L-78-15 Tire.

In '72, all US made big-block 1/2 ton trucks, were required to have both heavy Front and Rear Springs with either an H-78-15 tire or an L-78-15 tire. These combinations always gave the highest GVW rating with the L-78-15 having the maximum Rear Axle Weight.

Dan

[special-K]

On your SPID the Hydro Brake Booster is just what they called Power Brakes...the vacuum type. I see no tire or spring options,but I do see shocks. I don't know if HD shocks cod raise the GVW alone,but it does appear it had HD shocks ordered. This is an interesting thread.

[DANTIP]

This is pretty well researched because it is used to help identify "fake"/clones/tributes, etc. 1/2-ton '72 big-block trucks (BB trucks without the correct GVW ratings are not authentic).

[special-K]

What about this truck with a small block,5400 GVW,and no optional tires or springs listed? That's what is baffling.

[DANTIP]

Originally Posted by special-K

What about this truck with a small block,5400 GVW,and no optional tires or springs listed? That's what is baffling.

I agree, but I'd like to see a photo of the Gross Weight Data/VIN plate for the truck with the SPID show above before jumping to any conclusions.

Dan

[Ozark Tim]

All my 1/2 ton trucks with 350 V8, Auto, a/c (higher optioned trucks) were 5400
In fact I currently have a 72 GMC 1500 that is leaf rear, 350, a/c, auto (Sierra) and it is rated 5400. No HD front spring option.
All my 6 sticks or even small V8 sticks with no significant options have been 5000.
Also I have a 71 with coils, HD frt & rear springs and it is a 307 3-spd. It is 5000.
Probably only made this more complicated...

[DANTIP]

Originally Posted by Ozark Tim

All my 1/2 ton trucks with 350 V8, Auto, a/c (higher optioned trucks) were 5400
In fact I currently have a 72 GMC 1500 that is leaf rear, 350, a/c, auto (Sierra) and it is rated 5400. No HD front spring option.
All my 6 sticks or even small V8 sticks with no significant options have been 5000.
Also I have a 71 with coils, HD frt & rear springs and it is a 307 3-spd. It is 5000.
Probably only made this more complicated...

Tim,

When possible, would please post an example (SPID and VIN Tag) where there is no HD springs mentioned but the GVW is 5400?

Thanks!

[Ozark Tim]

Sure thing!
Give me a little bit and I will post em.

[Coley]

Originally Posted by Ozark Tim

All my 1/2 ton trucks with 350 V8, Auto, a/c (higher optioned trucks) were 5400
In fact I currently have a 72 GMC 1500 that is leaf rear, 350, a/c, auto (Sierra) and it is rated 5400. No HD front spring option.
All my 6 sticks or even small V8 sticks with no significant options have been 5000.
Also I have a 71 with coils, HD frt & rear springs and it is a 307 3-spd. It is 5000.
Probably only made this more complicated...

Very interesting.....it would be interesting to see if other members with this option combo have the 5400lb plate?
(Interestingly as soon as tire technology improved over the next few years after this they immediately raised this threshold to 6000lbs for the 1/2 tons.)
In the past I actually found the coil spring part no/id tag on the spring(s) themselves on the truck which I was able to reference back to the GM parts catalogues.
They are kind of hard to find because they are covered in grease and nearly invisible but they are typically wrapped onto the coil somewhere.
Coley

[Ozark Tim]

OK
Here are two samples for you.
Med. olive 72 1/2 ton Chev (notice it has HD front, rear springs, Shocks, and look at the wheel and tire options. Really rare for a 1/2 ton). This one I understand getting the 5400 rating on this one though it is coils.
Dark olive/white 72 Sierra 1500. It gets the same rating. I wonder if 350, auto, a/c trucks got HD fronts regardless of labeling on spid???
Both trucks are LWB.

[Ozark Tim]

I did not realize until after the last post that the tires werent notated on the spid on the 72 Chev.
I have the build sheet on this truck and it had 16" 5-lug wheels with 16" tires on this one. I would have to say it was a real heavy 1/2 ton.
BTW, funny when you really look at the GVW plates on axle ratings and mfg. rating plus max rating.

[Keith Seymore]

A short discussion on GVW:

We consult a MMEC (Minimum Mandatory Equipment Chart) that lists the attributes / systems that would lead to GVW. Basic list includes: tire rating (note pressure can influence), wheel rating ,suspension rating, shocks, and brake system rating for the front & rear. From these ratings you determine the vehicle capacity and payload is calculated in a range of min curb to GVW. In some special cases powertrain cooling system may limit GVW but you want to avoid it if possible.

Note there is also a FGAW (Front Gross Axle Weight) & RGAW (Rear Gross Axle Weight) rating; trucks need it for trailer ratings that can lead to GCWR (gross combined weight rating) for trailering.

Lastly the location of this weight affects the center of gravity location, and loading can be limited in order to prevent the CG from moving to an undesireable spot. If you look in the body builder's book it will show a target range of where the CG is permitted to fall.

Hardly "random", but complicated in order to try to comprehend all of the variables in loading mass and location seen out in the field.

Cars don't even come close to this level of complexity, since their primary "cargo" is in the form of passengers (constrained in terms of both overall weight and placement within the vehicle); option content (ie, 1/2, 3/4 or one ton, 2wd vs 4wd, 7 different powertrain choices, multiple wheelbases and cab lengths) and they don't see anywhere near the swing in mass from base curb to GVW.

K

[Coley]

Tim....I would think that the 16" tires would easily allow the truck to be stamped with the 5400lb rating. That said, your truck(s) doesn't show it as an option....yet it came with the 16" wheels...correct? That sounds like exactly the 'important missing info' issue that I'm talking about where there seems to be some randomness in the end results coming off the assembly line? Makes me wonder what part the dealer did or could play in all of this?
eg: Who stamped/marked those '6000lb' GVW marks on the sides of boxes back then? (dealer?)
Keith, I'm not sure they were as specific about MMEC then as they are now. My guess is that most capacity ratings from that era probably defaulted to the safe side when they weren't really specifically ordered.
My 66' has a 5000lb rating...and it doesn't even have a front stabilizer bar (yet) which you would think would be required on just about any truck from that era.....go figure.
All Good
Coley

[PanelDeland]

Just to throw another variable in the mix.How hungover was the guy stamping plates that day?Was it a Monday or Friday? I'm just pointing out the "human" factor may cause some differences as could the plant location.Maybe one plant did it one way and the others different.And one more,What about country of Manufacture.The translation to metric may have a bit to do with it.Just mnore variables to cause confusion.

[DANTIP]

The Owners Manual has a table that shows what equipment is necessary for the GVW ratings. According to the table, in order to get the 5,400 lb rating in a 1/2 ton truck (34 series), you need HD springs Front & Rear, H-78-15 tires and Power brakes. The SPID's shown do not meet the criteria for the 5,400 lb rating.

[DANTIP]

Here are a few 5,400 lb SPID's.