GMT-900 Pickups: More Than Just Towing and Payload

[Ghrankenstein]

Trucks as Trucks.

So far, I’ve talked about the GMT-900 pickups, and their competitors, in terms of how nice, how fast, and how agile. Their respective abilities to serve their owners as trucks, that work, haul, tow, and carry, are what will ultimately determine their success.

So far, I’ve hopefully demonstrated that the GMT-900 pickups offer the best overall packages in terms of accommodations, performance, and handling. In terms of truck duties, which are measured in tow ratings, payload, and GVWR’s, I have yet to make my case. A lot of this is basic truck stuff, with a point I could make to the general public in a sentence or two, so you might want to skip this.

Permission Ratings #1: GVWR and GAWR

GVWR equals Gross Vehicle Weight Rating. That is, at least in GMC terms, the maximum that the entire loaded truck can weigh, making allowance for curb weight, all vehicular fluids (including gas), and a 150 lb. driver. GVWR includes trailer tongue weight, and any cargo or payload. It’s also important to calculate these various weights on the front and rear axles; Chevy and GMC provide the ability to estimate these calculations.

Ford: has the highest half-ton GVWR crew cab, by a margin of 650 lbs. over GMC. The problem is that Ford also has a curb weight that is 602 lb. greater than GMC. That means that the Ford crew cab lugs around an extra 602 lb. in order to carry an extra 48 lb.

Other manufacturers tend to lag behind GMC in GVWR, and even farther in payload, because GMC has the lowest curb weight in its class, unless the current Tundra is counted.

In addition to GVWR, manufacturers provide Gross Axle Weight Ratings, and even the curb weights of their trucks on each axle. GAWR, like GVWR, cannot be safely exceeded, and GM trucks tend to have higher axle ratings than the competitors, a sign that the trucks are typically overbuilt for their specifications.

Permission Ratings #2: GCWR

GCWR equals Gross Combined Weight Rating, the total weight of the truck (with options), trailer, payload, and fluids; GMC includes curb weight (including engine fluids), a full tank of gasoline, and a 150 lb. driver. As before, axle weight ratings cannot be exceeded. The ability to safely handle, and stop, this extreme level of mass is the maximum allowed by the manufacturer.

The operative term here is safety. And with safety in mind, GM vehicles tend to be rated more conservatively. Owners need to take their payload, fluids in trailer tanks, and additional passengers into account to make sure that these ratings are not exceeded before purchasing a possibly useless or unsafe truck. Knowledgeable GM salespeople have the ability to calculate much of this, with weight factors for fresh water, black water, gasoline, and diesel.

Permission Ratings #3: Maximum Tow Rating

Maximum Tow Rating equals GCWR minus curb weight (with options), which, with GMC, includes the previously included allowances. This rating is, again, largely limited to what the manufacturer publishes as the safest maximum GCWR. The caveat here is that manufacturers give maximum bumper hitch, dead hitch, weight-distributing hitch, fifth-wheel, and gooseneck hitch ratings. Look hard enough, and you’ll even find a GMC or Chevy salesperson who knows how to access these ratings; keep in mind that a knowledgeable salesperson will probably recommend a 2500 or 3500 if you’re concerned with fifth-wheel or gooseneck applications. Savvy Ford and Dodge salespeople can be similarly helpful; Nissan salespeople usually aren’t. Can Toyota salespeople be?

The point I’m emphasizing is that GM is very conservative when it comes to corporate permission, especially when it comes to GCWR and maximum towing. GM’s stance has been, and largely remains, that if you to do the work of a ¾ ton truck, you need to get a ¾ ton truck.

The Silver Bullet (“The Humiliator”)


I’ve included a section on this feature in every truck review I’ve ever written, and I’ll continue to write it as long as the competition continues to offer nothing that compares. I’ll also promote it as long as people fail to understand it, or its benefits. Combined with Stabilitrak stability control, which now includes an active anti-rollover algorithm and is standard on all crew cabs (optional on extended cabs), GM has the most comprehensive all-weather performance package available in a pickup, bar none.

That feature is the American-made (North Carolina) Eaton G80 locking rear differential, and in terms of safety and capability, it is beyond reproach in a rear-wheel drive truck application. General Motors offers the G80 as a superior alternative to the limited-slip rear differentials offered by Ford and Dodge, and to the restricted-use electronic “E-locker” of the Nissan Titan.

The main principle behind the G-80 is that, in a normal open rear differential, torque (“engine power”) takes the path of least resistance. In the most basic description available, a limited-slip differential (in truck applications) uses centrifugal force-actuated friction pads to transfer torque away from a spinning wheel. This is the engineering route opted by Ford and Dodge. The result, in these competitors, is usually around 25% to 30% of the total available torque transferred from path of least resistance, and excessive continuous wheel spin, even in 4x4 LOW mode. One of Ford’s own commercials even shows this.

This is how good the G80 is. And I’ll continue to repeat it in future reviews.

The test we GM salespeople have seen, often multiple times by now, involves a competitive vehicle attempting to climb a slope with zero traction to the right side of the vehicle. In 4x4 Low mode, the competitor (it’s usually one in particular, but it doesn’t really matter if it doesn’t have a G-80) spins both of its low-traction wheels wildly, and fails to ascend the slope. The Chevy/GMC 2X4, in comparison, spins its high-torque rear wheel once. The G80 then locks both half-shafts together, and the opposite wheel pulls the truck up the slope. I’ve gone out of my way to find locations to demonstrate this to customers, even if it has been a simple curb at a diagonal. When the customer predicts when/where the wheel will spin, and then it doesn’t (more than one revolution), it’s a done-deal.

The Eaton G-80 uses a centrifugal locking/unlocking mechanism that activates on one rear wheel spinning at only 100+ rpm than the other, but limited to 20 mph. It’s completely mechanical, and foolproof, to the point that Lexus could advertise it as the next invention of the wheel. We need to advertise this test, and the G80 at the same level, and we need to advertise that we’ve made it standard on Z-71’s since practically the beginning of time.

Since the G80 uses a physical/mechanical locking of the rear axle shafts, owners will not encounter the wear symptoms associated with friction-based limited-slips.

The Nissan E-Locker Locking Differential: Of our direct competitors, Nissan is the only to offer any kind of locking differential, which comes with its off-road suspension package. We don’t know how they’re tested, and we don’t know what Nissan tells the press about testing it, but we do know what Nissan says about using it:

For all intensive purposes, you can’t use it. According to the 2006 Titan owner’s manual, the E-locker may/must only be engaged:

• In 4x4 LOW mode.
• To free a stuck vehicle.
• On a non-slippery surface

The Eaton G80, however, is automatic, based on traction needs under 20 mph, is available for the same price as a Ford limited-slip ($325), and does not require an expensive 4x4 “off-road” trick package. Chevy and GMC offer the Z-71 off-road suspension at a price that is much less than “trick” levels, largely because the G80 is so affordable to begin with.

More advice forthcoming.

Ghrank

[tama z71]

I've got the G80 in my 04 Canyon, and everything you said about it is gospel. Those things are unbeatable in bad weather.

[Ghrankenstein]

Tama,

Normally, especially lately since I've been so darn grumpy (wish me some good meds in the future), I don't so closely monitor my article-threads.

All I wanted to say is that you have an awesome truck, the 2004
Canyon. While my Cavalier was in the body shop (there goes my resale value, assuming I had any in the first place), I drove a Colorado (Z-71 Crew Cab 4x4 LS 3.5L) for two weeks, and it was an absolute joy. I'm working on a Canyon review, but we haven't gotten a full complement of 3.7L, 2.9L, and suspension setups.

I'll say that, pound-for-pound, dollar-for-dollar, the ZQ8 (e.g. "X-treme") Colorado and Canyon are currently the best driving enthusiast-oriented vehicles that GM offers. They're better than the X-Runner, the G5 GT and Cobalt SS, and even better (by a slim margin) than the G6 with the 3.5L Sport package. I wish more enthusiasts would check them out.

Needless to say, noone who comes on my lot will have any problems with taking a quick joy-ride in a ZQ-8 Canyon. They're too good that it isn't fair, and yet they sell so poorly it's a shame. Anyway, expect a writeup at some point.

Ghrank

[kool_zx3]

I'd never touch a g-80, heard of way to man horror stories with these rear end's grenading and blowing up....

[Ghrankenstein]

They don't grind metal on metal like a cellulose (i.e. paper) lined Ford limited-slip after four cumulative minutes of low-traction.

[Bvonscott]

Originally Posted by kool_zx3

I'd never touch a g-80, heard of way to man horror stories with these rear end's grenading and blowing up....

The chance of grenading a G80 is so small it's almost near impossible. As GRANK said the limited slip's are WAY more likely to have problems. I work at a truck dealer I KNOW. I don't hear of this EVER. Stop LYING to us. We know you haven't been hearing all these "horror stories".

[chris442]

Yeah, people definitely have grenaded the g80 gov-lock in the past. Generally, these problems involve racing slicks and increased amounts of power. The fact of the matter is that it was not engineered for that application. That is why cars like, the Corvette, Camaro, GTO, etc. come with regular limited slip diffs. These cars need diffs that work above 20 mph, too. The point is, if you want a race truck, the g80 probably should go, but for regular truck stuff for 99.9% of truck owners it works great.

[Dano702]

My 04 GMC short box regular cab 2 wheel drive has the G-80 and the 5300 with 300hp , 300 ft lbs . I have over 80,000 miles of daily abuse in 120 + degree Vegas weather . Zero problems , besides the inability to spin the stock goodyear wrangler hp's more than a chirp. I abuse the day lights out of that poor thing , constantly locking . I will buy them in all my new trucks.

[MyRental]

Originally Posted by Dano702

My 04 GMC short box regular cab 2 wheel drive has the G-80 and the 5300 with 300hp , 300 ft lbs . I have over 80,000 miles of daily abuse in 120 + degree Vegas weather . Zero problems , besides the inability to spin the stock goodyear wrangler hp's more than a chirp. I abuse the day lights out of that poor thing , constantly locking . I will buy them in all my new trucks.

5.3L - 295hp - 335 ft-lbs

[hdmax]

Originally Posted by kool_zx3

I'd never touch a g-80, heard of way to man horror stories with these rear end's grenading and blowing up....

I have put way over 1,200,000 miles on them, with not a single problem. And the truck I have now (2002 Chevy, 2500HD, 4X4, crew cab, Duramax/Allison!) has almost 100,000 miles at over 400 rwhp, and well over 800 rwtq. With no problems.

It always seems to be the guys that have never owned something, that knows about all its problems.

[Chevy Ryan]

I work in the forest industry and our office has 23 3/4-ton pickups to choose from, including GM, Ford and Dodge. All of them have either the limited slip or locking diff. There is no comparison. They all have the same tires, and the limited slip rear ends are nearly useless. I've lost traction in many situations where the other rear tire wouldn't even budge on a limited slip. The G80 makes a clunk noise as the axles lock, and then away you go. I read a comparison a few years ago where they measured the effectiveness of limited slips and the G80. Under the same poor traction conditions, a Ford and Dodge would go up a 9% grade before spinning out. The GM went up a 27% grade before stopping. I hope GM never drops the G80!!!!

[Corr69]

Hello? Haha, Did anyone miss me? Guess not, but seriously, holy moly, alot of news since I was gone! Is it true the new Tundra will have 381hp?

[TimR]

Originally Posted by Bvonscott

The chance of grenading a G80 is so small it's almost near impossible. As GRANK said the limited slip's are WAY more likely to have problems. I work at a truck dealer I KNOW. I don't hear of this EVER. Stop LYING to us. We know you haven't been hearing all these "horror stories".

Where people get into trouble with these is when one wheel has traction and the other does not, and they get on the throttle hard (like most people do cause they can't drive) the one wheel is accelerating up fast, the mechanical engagement takes place but the loads are huge since you now have one wheel that is accelerating rapidly and the other barely moving, its all over. The engagement mechanism comes apart. I know a couple guys that have done that.

That said, lots of truck make it 100's of thousands of miles with no issues.

[DeliveryDave]

I'm a little confused, sorry. Does the G-80 come in the 4x4 or only 4x2? I have an 04 Silverado w/t 1500 with be bare bones limited slip I think, and I try to run it without 4 wheel drive in the snow and it's terrible. I don't need the 4x4 many times in PA but the few times I do it's worth it. Maybe with the G-80 wouldn't need 4x4. Also are do they put them in the vans?

[ermatthe]

DeliveryDave I'm a little confused, sorry. Does the G-80 come in the 4x4 or only 4x2? I have an 04 Silverado w/t 1500 with be bare bones limited slip I think, and I try to run it without 4 wheel drive in the snow and it's terrible. I don't need the 4x4 many times in PA but the few times I do it's worth it. Maybe with the G-80 wouldn't need 4x4. Also are do they put them in the vans?

The G80 is an option for both 2wds and 4wd trucks. You can get it on any truck you could think of regardless of trim or suspension.
And yes, you can get it in the the Savana\Express cargo and passenger vans as well.


Ghrankenstein, great articles. I also sell GMC's in Virginia. I had to miss the Ride and Drive in Greensboro, NC. because me and my wife had some plans. Thanks for the detailed coverage. I really hope we start getting our first Sierra's in real soon.

Thanks Again