GMT900 Inside Info

[Rex Raider]

From an un-named but reliable source:

Last night I had a chance to check out two GMT-900 frames for the up-comming light duty GM Ext/Crew Cab pick-ups. One (a 2WD frame) was built up to an engine, drive train, suspension and exhaust and the other was a 4WD or AWD (the front differential had the letters "AWD" markered on it). The frame rails on these 900 proto-types had the inside face closed, the 800's now have an open face on the inside frame rails. With the 900's being closed on the inside I imagine it makes it more beefier, the width of the rails did seem more larger than the 800's. Both frames had a strut type of suspension on the front, leafs on the back. Rear drums were 11.67" and front rotors looked 14" but the fronts were just an observation measurement. The exhaust on the 2WD came out right behind the rear tire. The exhaust on the 4WD (AWD?) came out straight below the back bumper and that exhaust had 3 units (resonator,muffler and a smaller one near the back. The downpipe and Cat wasn't on that system yet. Gone were the torsion bar set-up and replaced with a large rack-and-pinion unit on the 4WD. The upper control arms on the 4WD were large, tubular and made of aluminum. That made them alot beefier and lighter than the ones on the 800's. The tranny on the 2WD unit may have been a 6 speed auto but there was nothing but the words DEX-6 written on it so don't quote me on that, does GM have a 6-speed auto for trucks available now?

[tosil]

Good news indeed... this sounds like a very robust setup... and we also know rear drums are back. And just to clear something up, did you mean to say the front torsion bars has been replaces by coil springs, and recircular ball has been replaced by rack- and-pinion steering? If so... this almost sound too good to be true.
And having AWD, that would be similar to the SS setup?

[XCR440SP]

The DEX-6 means Dexron 6 ATF fluid.

And just for confirmation, did you say that it had rear DRUM brakes?

[RamJet502]

I'm a little scared by this. Sounds like GM is sacrificing rear disc brakes and the proven selectable 4WD. I doubt they would only offer fulltime AWD on a fullsize truck.

[Ghrankenstein]

The drum brakes are an old issue, and they're no big deal. If they were, 18-wheelers wouldn't use them.

[jfnz24]

Originally Posted by RamJet502

I'm a little scared by this. Sounds like GM is sacrificing rear disc brakes and the proven selectable 4WD. I doubt they would only offer fulltime AWD on a fullsize truck.

Could be an SS model, that wouldn't have the need for 4WD.

[91z4me]

Originally Posted by RamJet502

I'm a little scared by this. Sounds like GM is sacrificing rear disc brakes and the proven selectable 4WD. I doubt they would only offer fulltime AWD on a fullsize truck.

It could have been testing an AWD system for the GMC Sierra Denali, though that is normally the same as the SUVs AWD system.

[member12]

DEX-6 means Dextron transmission fluid.

I heard the six speed take up the same space as the 4 speeds, so maybe you did see a six speed and didn't recognize it.

How high off the ground was the frame? Was it as low as the 800s? Did you see the engine?

I hope the full time selectable 4wd is still there. A full time automatic system will drive cost up considerably....at least we know it has fully boxed frame rails. I am glad they used drum brakes. The Disc brakes on the 99-02 sucked- they kept screwing up..probably why GM changed back in 2005. They still suck on the 800 Tahoes and Suburbans.

The aluminum control arms are to help in the offset crash. They bend so the front tire doesn't intrude on the passeger compartment. compare the F150 crash test to the Trailblazer (steel control arms). Both compartments held up well, but the F150's wheel tucked in when the Trailblazers wasn't, and it came in a little on the passenger footwell.

[Supernoma]

Originally Posted by Ghrankenstein

The drum brakes are an old issue, and they're no big deal. If they were, 18-wheelers wouldn't use them.

It's more of a perceived quality/cost cutting issue- drum bakes are not cutting edge technology, so why would a company use them on a vehicle that will make or brake them?

I should hope these don't make it to the new Caddy EXT/Avalanche

[Steel4ring]

I would rather have rear drums. They wear less and I feel like the stop is more firm.

[psece]

Biggest problem with drums is that they don't dissipate heat as fast as discs. That is why Big Rigs have things like Jake Brakes so they don't have to rely on their brakes when going down hills. The positives are they are cheaper to produce for a given amount of stopping power and produce more friction for a given size wheel. They are also harder to moderate the pressure on during a panic stop but with ABS, that is probably not as much of a negative.

[88Fiero]

The Denali pickup is AWD. That is more than likely what you saw. Our Half tons have had rear drums since 05. The 3/4's get the rear disc. The front suspension sounds like the one on the new Yukons. They have a coil over on the 4X4's. The exhaust system you saw may be for the January '07 diesel which gets the particulate filter.

[kenman923]

Rear drum brakes? Now they are really going retro.

[88montess]

Originally Posted by Ghrankenstein

The drum brakes are an old issue, and they're no big deal. If they were, 18-wheelers wouldn't use them.

Besides if you've driven an 05-06 with drum brakes they feel much better and stop better then then 99-04. also how many have had to work on there e-brake with the drum in hat set up. not fun.

[Highlander]

Originally Posted by 88Fiero

T...Our Half tons have had rear drums since 05. The 3/4's get the rear disc. ....

Really?! I didn't know they had reverted to drums on the 1/2 tons back in 05. Thanks for the info. I'm hoping at least the HD's stick with discs on all corners. I've never even owned a vehicle with drums as even my old 89 GP is discs all the way around.

The heat generated stopping a loaded truck can be rather extreme... I was hoping for the opposite approach and have vented discs on all corners for the 900's (at least on the HD's)... Although I'll admit that that's probably overkill!
I'm really hoping pedal feel is better regardless of the setup... My only gripe about my 2500HD is the spongy brake pedal feel. Although I'm sure it'll be better once I redo the brakes. It seems very bad compared to my Comp G and even my 89 GP (although those pads and rotors only have a few thousand miles on them)