spied 2010 GMc Sieera shows off new perforated grille

[nailhead425]

Originally Posted by member12

I'm glad they are keeping this truck updated...but why does it sit so high off the frame?

At least the wheels and tires aren't so small anymore. Hopefully, they've solved the stupid government diesel mandates and figured out how to get better mileage out of it.

Too bad there isn't a way to make a soot trap that could be cleaned out with a shop vac at service time or in the driveway. There are many more dangerous items put into landfills.

[C/K Man]

Originally Posted by nailhead425

That is a pretty broad statement to say that a well designed IFS is better in every respect.

Let's consider the linear spring rate of the torsion bar IFS. Not only is the capacity less than the competition, the suspension travel is limited and a fraction of the SFA crowd. By limiting the suspension travel the Engineers were able to minimize fatigue in the torsion bars, at the sacrifice of load capacity. Because the spring rate is not progressive, the compression travel is virtually zero and most GM torsion bar IFS trucks sit on (or very near) the bump stops. The deflection of the bump stop is the additional spring rate before bottoming out. I have 5" of compression travel on my coil-spring SFA truck.

Let's consider ball joints, wheel bearings, and half-shafts. IFS runs best a neutral CV joint angle. With about a 23* max operating angle, the combined max angle would be about 46*. While on paper that is outstanding, the amount of expansion in the joint limits the strength and durability of the joint and shaft assembly. So as the total amount of suspension travel increases, the life of the joints and shafts decreases. Also, in order to compensate for the increased moments about the joints, the corresponding increase in mass of the components to provide additional durability further reduces the effective operating range. Another concept that is often discounted is the tendency for a half-shaft to deflect under torque. The moment about the shaft, especially given a heavy static load at the drive wheel, results in deflection of the shaft. The greater the torque input, combined with a greater static load, the greater the amount of deflection. This is the Achilles’ heel of half-shafts. Ball joints have been and will continue to be a supplier issue, not a flaw in the design concept. While Ford uses a different supplier, GM and Dodge HD trucks use the same supplier for the front-suspension drive system. The comparisons should be done Dodge to GM, SFA to IFS. Unitized wheel bearings will always be an issue, but anecdotal evidence has yet to become scientific fact that one supplier is better than the other.

Let's talk about component strength: GM, 22 years after the debut of their full-size IFS, still hasn't sorted out the component strength issue. Tires larger than 285/75-16 or 285/70-17 aren't supported. Where the competition is using larger, heavier tires on their SFA and IFS rigs, why not GM? Let us investigate the H2 tie rod issues with the stock 315/70-17s to gain a greater understanding.

Let's talk about the "death wobble". GM IFS trucks with wider than stock wheels, especially those with a large amount of offset, generate a substantial amount of wobble. In fact, the independent nature of the GM IFS generates an increasing level of bump-steer, especially as the operating angle of the suspension increases. Larger than stock tires exaggerate this condition, beyond deflection of the stock components. While not to minimize the wobble in SFA trucks, it isn't a SFA only condition. But bumper steer is more pronounced with IFS.

Let's talk about "thermal creep". The GM IFS diff housing is made from aluminum, where the Dodge is cast iron with steel tubes pressed into the center section. Both are made by AAM, both have the same torque rating. Aluminum, under repeated thermal loads, exhibits a condition called thermal creep. With cast iron the tolerances vary much less. It should be noted that due to this condition the H3 Alpha was fitted with a cast iron center section for the IFS. Certainly there are many exotic materials that don't exhibit creep to the same degree as aluminum, but they are cost prohibitive. There is a trade-off with each material. Strength or weight. Take your pick.

I'm not saying that every IFS is evil, there is plenty of room to improve. However, it goes without saying that the GM HD system is long overdue for an update.

Those are good comments. Let me address them.

First off, you will get no agruement from me over the limitations of torsion bar suspension. GM does indeed use a progressive urethane bump-stop to partially compensate for the design not being progressive itself. However, it is not a requirement that a 4X4 IFS system use torsion bars. The coil string front suspension used on Oshkosh military trucks is a good example.

With regards to ball joints and wheel bearings, the better reliablity of GM 4X4's could be due at least in part to the Duramax being lighter than competing diesel engines. The fact that GM ball joints are able to be lubricated is probably a factor as well.

Tie rod wear can be an issue with current GM 4X4's. The components seem to be adequate for stock size wheel/tire combo's, nothing more. There seemed to be a lot less issues with steering linkage on GMT 400 trucks.

As you pointed out, 'death wobble' can be caused by improper wheel size or offset, or poor quality wheels, but that is true for any vehicle. I have not experienced the condition in any stock GM 4X4 pickup with IFS. I have seen it many times in both stock and modified Dodge and Ford 4X4 pickups. It is often the result of worn track bar bushings, worn leading arm bushings or poorly engineered lift kits. I saw a Ford Super Duty that had a very bad case of the wobble. The problem was a 4" lift kit that did not relocate the radius arm attaching points. The result was 6 degrees negative caster. That truck wanted to go anywhere but straight ahead! the Dodge is a bit better than the Ford in respect to caster change during front suspension oscillation, as it is a 5 link leading arm design vs. Ford's radius arm design.

'Bump Steer' is something else entirely. I define bump steer as unintended steering imputs caused by suspension deflection. A classic case of a steering geometry induced bump steer condition was the 1973-1987 GM 4X4 light trucks. These trucks used a SFA on leaf springs, frame mounted steering box ahead of the front axle, with a short drag link running parallel to the frame connected to the left knuckle. As the front suspension oscillates, the distance between the pitman arm and the left knucle changes, and this results in an unintended steering input, manifesting as a slight pull to the right as the suspension compresses, to the left as the suspension extends. Ford and Dodge try to compensate for this condition by using a long drag link running perpendicular to the chassis, steering from the right knuckle. The longer drang link moves at a less acute angle with suspension oscillation. However, it does still move and it still results in an unintended steering input. The only SFA design that I ever saw that had no bump-steer was designed by Mack trucks, and used on the Superliner and Cruisliner. Mack mounted the steering box right on the axle. There is no bump-steer in an IFS system as long as the distance between the lower control arm bushing and the lower ball joint is close to the distance between the inner and out tie rod joints, and the tie rod angle is close to the lower control arm angle. Most IFS systems are engineered to give a slight toe-in under suspension compression, which improves stability.

I don't know how much a factor the aluminum front diff. case is on late model GM 4X4's. I suspect that a front diff. doesn't generate much heat on it's own, considering it is usually only engaged intermittantly and uses synthetic lube. I suspect it probably picks up more heat radiated off the engine exhaust than anything else. In any event, the front diff. housing does not run nearly as hot as an automatic transmission, and aluminum is used universally in that application, isn't it? No question aluminum is not as strong as cast iron, but the diff. housing in an IFS 4X4 is under less stress than an SFA axle is anyway.

One factor no one as brought up yet in unsprung weight. IFS wins that contest hands down.

Looking forward to your comments!

[05ChevySilveradoSS]

Originally Posted by C/K Man

Those are good comments. Let me address them.

First off, you will get no agruement from me over the limitations of torsion bar suspension. GM does indeed use a progressive urethane bump-stop to partially compensate for the design not being progressive itself. However, it is not a requirement that a 4X4 IFS system use torsion bars. The coil string front suspension used on Oshkosh military trucks is a good example.

With regards to ball joints and wheel bearings, the better reliablity of GM 4X4's could be due at least in part to the Duramax being lighter than competing diesel engines. The fact that GM ball joints are able to be lubricated is probably a factor as well.

Tie rod wear can be an issue with current GM 4X4's. The components seem to be adequate for stock size wheel/tire combo's, nothing more. There seemed to be a lot less issues with steering linkage on GMT 400 trucks.

As you pointed out, 'death wobble' can be caused by improper wheel size or offset, or poor quality wheels, but that is true for any vehicle. I have not experienced the condition in any stock GM 4X4 pickup with IFS. I have seen it many times in both stock and modified Dodge and Ford 4X4 pickups. It is often the result of worn track bar bushings, worn leading arm bushings or poorly engineered lift kits. I saw a Ford Super Duty that had a very bad case of the wobble. The problem was a 4" lift kit that did not relocate the radius arm attaching points. The result was 6 degrees negative caster. That truck wanted to go anywhere but straight ahead! the Dodge is a bit better than the Ford in respect to caster change during front suspension oscillation, as it is a 5 link leading arm design vs. Ford's radius arm design.

'Bump Steer' is something else entirely. I define bump steer as unintended steering imputs caused by suspension deflection. A classic case of a steering geometry induced bump steer condition was the 1973-1987 GM 4X4 light trucks. These trucks used a SFA on leaf springs, frame mounted steering box ahead of the front axle, with a short drag link running parallel to the frame connected to the left knuckle. As the front suspension oscillates, the distance between the pitman arm and the left knucle changes, and this results in an unintended steering input, manifesting as a slight pull to the right as the suspension compresses, to the left as the suspension extends. Ford and Dodge try to compensate for this condition by using a long drag link running perpendicular to the chassis, steering from the right knuckle. The longer drang link moves at a less acute angle with suspension oscillation. However, it does still move and it still results in an unintended steering input. The only SFA design that I ever saw that had no bump-steer was designed by Mack trucks, and used on the Superliner and Cruisliner. Mack mounted the steering box right on the axle. There is no bump-steer in an IFS system as long as the distance between the lower control arm bushing and the lower ball joint is close to the distance between the inner and out tie rod joints, and the tie rod angle is close to the lower control arm angle. Most IFS systems are engineered to give a slight toe-in under suspension compression, which improves stability.

I don't know how much a factor the aluminum front diff. case is on late model GM 4X4's. I suspect that a front diff. doesn't generate much heat on it's own, considering it is usually only engaged intermittantly and uses synthetic lube. I suspect it probably picks up more heat radiated off the engine exhaust than anything else. In any event, the front diff. housing does not run nearly as hot as an automatic transmission, and aluminum is used universally in that application, isn't it? No question aluminum is not as strong as cast iron, but the diff. housing in an IFS 4X4 is under less stress than an SFA axle is anyway.

One factor no one as brought up yet in unsprung weight. IFS wins that contest hands down.

Looking forward to your comments!

And you forgot the idler arm, it also was an input to these problems (especially) on the GMT400's.

[Michael_S]

I'm only following about 20% of the discussion here. Can anyone point me to an "Idiot's Guide to Suspensions" or something similar, web-based or in a book?

As it is, I'm taking things like "camber angle", "deflection", "half shafts", "coil-over" and "torsion bar" and doing individual web searches on them to see what they mean.

I really appreciate the discussion though, thanks.

I'm in the category of people who really like big pickup trucks. I have no need for one, I have no use for one, I sure don't have the money for one, and I don't like the idea of sending even more American dollars to Saudi Arabia by paying for fuel for one.... but I would love to get one anyway.

[hiluxxulih]

When are we going to get to see the official 2011 GM hd trucks pics and specs this is getting silly and I wish GM would update there site with 2010 truck info at least .

[C/K Man]

Originally Posted by hiluxxulih

When are we going to get to see the official 2011 GM hd trucks pics and specs this is getting silly and I wish GM would update there site with 2010 truck info at least .

I think there will be very few differences between 2009 and 2010, and the 2011's won't be out until next April at the earliest. Might be some time. Keep an eye on www.pickuptrucks.com they seem to have solid information before anyone else, at least as far as trucks are concerned.

[nailhead425]

Originally Posted by C/K Man

First off, you will get no agruement from me over the limitations of torsion bar suspension. GM does indeed use a progressive urethane bump-stop to partially compensate for the design not being progressive itself. However, it is not a requirement that a 4X4 IFS system use torsion bars. The coil string front suspension used on Oshkosh military trucks is a good example.

Tie rod wear can be an issue with current GM 4X4's. The components seem to be adequate for stock size wheel/tire combo's, nothing more.

As you pointed out, 'death wobble' ... I have not experienced the condition in any stock GM 4X4 pickup with IFS.

'Bump Steer' is something else entirely.

I don't know how much a factor the aluminum front diff.

In any event, the front diff. housing does not run nearly as hot as an automatic transmission, and aluminum is used universally in that application, isn't it?

No question aluminum is not as strong as cast iron, but the diff. housing in an IFS 4X4 is under less stress than an SFA axle is anyway.

Sorry, I had to cut it down to save space.

You're correct in your point about Extreme-HD trucks using coils and IFS. They limit the travel and have very rigid frames. That would be more ideal, IMO, but since general 1/2-1 ton truck frames flex some, they limit the true IFS advantages. Ultimately the ideal IFS set would have a slight gear reduction at the spindle and keep the half shafts up high. A tall spindle with the steering high on the spindle along with the input. The gear reduction further reduces the shock on the shaft. But all of these designs posses a disadvantage...weight.

Tire size and components. Last go-around I had the max size that GM would warranty was LT265/75-16. Evidently there was a large number of failures with 285s. It shouldn't have taken this long to get decent sized tires on the HD trucks. The death-wobble is pretty common, even on non-lifted GM trucks, and it comes with cranked torsion bars or keys.

Bump Steer. The issue here, and will all SLA front suspensions is that with the camber change comes the trade off of steering rod length. Run it in the centerline of the axle axis and run it neutral to reduce the instances of bump steer. However, and this is common with the GM IFS, when suspension moves the differing length of the lower arm, upper arm, and steering rod all results in bump steer. Which is exactly as you described. The difference between IFS and SFA bump steer is that the IFS fights itself where as the SFA moves in unison. Thus with IFS there is a resulting range of the ackerman angle based on the position of the suspension as well as the steering input.

The Aluminum diff housing is enough of an issue to be cast iron on the H3 alpha. Thermal creep is important with diffs housings as Ford has learned with the 8.8 and 9.75 and Dana learned with the Dana 44. Diffs get plenty hot, especially in HD use. When not in use they generate very little heat. The creep problem is the gradual relaxation of tollerances when placed under repeated thermal loads. Why it isn't an issue with automatics is that the cases are placed under axial loads, not side loads, and the cases themselves have the passages cast into the case which provides a remarkable amount of support. Thermally, I'd say in normal use the automatic runs a titch cooler than the diff. Remember, diffs use heavy gear oil and are passive radiators, where as automatics are thermally regulated through coolers and use a thinner oil. But the IFS does actually take an impact. Generally through a side load when the suspension is cycled and either the shaft binds or bottoms out. The side loading is one of the common causes of case cracks.

All of this is really moot because of a couple factors:
1) all indications to this point don't even hint that GM is going to return to a SFA front suspension on their HD trucks.
2) the costs involved, unless a near copy of the Dodge system is implemented, would be substantial for a dwindling market.
3) there are alternatives in the market place for those that want a SFA 4x4.

As bad as it sounds, I'm quite certain that the powers at GM aren't going to go back to SFA with the hopes of picking a few sales away from Ford or Dodge. It would seem that each is carving out their own niche.

GM: IFS/Diesel/automatics
Ford: SFA/looks
Dodge: Cummins/stick

So, if IFS is going to stay it needs to be competitive.

[nailhead425]

Originally Posted by Michael_S

I'm in the category of people who really like big pickup trucks. I have no need for one, I have no use for one, I sure don't have the money for one, and I don't like the idea of sending even more American dollars to Saudi Arabia by paying for fuel for one.... but I would love to get one anyway.

The thing about a HD truck is once you need one and have one they are great and the mileage offset is pretty minor. The downside is if you need one and don't have one, finding one can be a chore. Finding one you can tow with, an even bigger chore.

I for one am opposed to the 10,000 lbs tow capacity half-tons. Too much light duty stuff should the trailer brakes fail or the load shift, etc. But the entire truck craze can be traced directly to the implementation of CAFE. Once CAFE hit and cars started shrinking truck sales began to increase. Prior to '77 the truck market was pretty static.

As they say, the road to hell is paved with good intentions.

[05ChevySilveradoSS]

^^^Give it up (an applause) to this man right here guys! He knows his suspensions! Wow, im amazed and i used work on these things lol!

Though i have seen a many of 2007+ Silverado 1500s with the HD trailering pkg handle 10,000LB quite well, from a few of my customers in and out of the dealership. Though i do understand your point whereas to the brakes failing

[ChevyHDGert]

Originally Posted by hiluxxulih

When are we going to get to see the official 2011 GM hd trucks pics and specs this is getting silly and I wish GM would update there site with 2010 truck info at least .

I've been wondering the same thing. We're only 6 months away from when the 2011's are supposed to be hitting the streets.

I think they are worried that the 2010 models wouldn't sell if people knew something new was coming out in 6 months or so. But apparently Ford isn't worried about that as they made a big splash at the Texas State Fair with their new 2011 HD. But then again, Ford has a lot more money than GM.

BTW, are the 2011 1500's getting some sort of front end refresh too?

[Michael_S]

Originally Posted by nailhead425

The thing about a HD truck is once you need one and have one they are great and the mileage offset is pretty minor. The downside is if you need one and don't have one, finding one can be a chore. Finding one you can tow with, an even bigger chore.

I for one am opposed to the 10,000 lbs tow capacity half-tons. Too much light duty stuff should the trailer brakes fail or the load shift, etc. But the entire truck craze can be traced directly to the implementation of CAFE. Once CAFE hit and cars started shrinking truck sales began to increase. Prior to '77 the truck market was pretty static.

As they say, the road to hell is paved with good intentions.

I'm generally pro-smart-regulation, but I absolutely agree that dumb regulation (like the implementation of CAFE) is worse than none at all.

[Michael_S]

Thank goodness for wikipedia. Now I have some vague ideas about torsion bars, camber angles, CV joints, and so forth.

A search for "Death Wobble" turns up a lot of really bad complaints about Dodge HD trucks. There are some complaints about Ford and GM trucks, but the pages I saw seemed to view Dodge as the worst.

[C/K Man]

I am hearing GM will have a gas engine to compete with the Ford 'Boss' 6.2L and the upcoming Dodge 6.4L Hemi. It is not a 6.2L either. Keep your eyes open.

[FanOfDurant]

What are you hearing? New motor? DO TELL!..

[05ChevySilveradoSS]

Originally Posted by FanOfDurant

What are you hearing? New motor? DO TELL!..

IF any itll be atleast a year or two before Gm responds, and honestly i believe it (if anything) will continue to be the 6.2.