Guys,
I posted this on "The Diesel Place". While the info applies specifically to '01 and later Chevy/GM 2500 HDs, the general prinicpals apply to IFS trucks in general.
Blaine
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NOTE: I have updated this post with current info as of 14 Apr 04, based on my recent 4" Rancho Kit install.
I have done a bunch of research on lift kits lately. Here are the high points of what I have found. I will provide more details if desired. I am not a suspension expert, just a customer who is looking for the absolute best solution.
As much as I love the smooth ride of our trucks independent front suspension (IFS), they have a lot of limitations. Now I do like how I usually can drive faster over rough roads than my brethren with straight axles, though they would beat me in really rough stuff. However, I did not get the truck for heavy off roading. I got it for smooth travel and hauling over rough roads, like when going hunting.
I am looking at the lift because our HDs are low slung and have tiny wheel wells. With 2"of torsion lift and 285s on 16x8 rims with 4.5" of backspacing, my clearance decreases to about 3/4" when turning the steering wheel 3/4 tavel. This is not enough to run chains, and I do get rubbing sometimes on a moderately heavy bounce when turning.
The general consensus seems to be 35x 12.5s are the max tire size that our IFS can handle without premature wearing of components, and if you off road hard with 35s you may get the early wear anyway. Realize most of the IFS experience is with the 88-98 trucks, and our HDs do have a sturdier suspension--or so I'm told. Folks that don't off road "hard" have had long life from 35s and even a bit bigger.
There are five ways to get lift with the HDs.
Cranking the Torsion bars
There are even aftermarket keyways (Hill 4WD) that will allow up to 3" of lift in the front. At 2" of lift and below, the ride is very good and the CV axles are not at too bad of an angle. Many guys have run 60-100,000 miles with their HDs lifted this way.
However, as you go over 3" with the torsion bars, the ride gets choppy. This is not because we are loading the torsion bars more. Raising them simply resets their "zero" point. Their spring rate does not change. What is happening is we are getting the shock absorber too far from the center of its travel and it doesn't dampen as well when we do that.
I currently have 2" of torsion bar lift and my ride is excellent. Part of this is because I have Bilsteins, but another reason is that I have a 1" spacer under the top shock mount which puts the shock closer to its center of travel.
While I did think of trying a 2" spacer and maybe getting 3" of torsion lift, I decided against that because I did not want to limit the travel of the shock anymore than I already have. Bottoming/topping out a shock is a bad thing.
Yes, if we could use a shock 3" longer than stock, we might be able to get 3" of torsion lift with a good ride. We probably wouldn't even hurt our CV axles, as this amount of change is well within their operating limits. However, no one makes such a shock. I also imagine that at 3" of torsion lift we'd want to flip our tie rods.
I rally don't like having my torsion bars cranked. While it doesn't hurt the CV axle itself, it does cause the folds of the CV boots to constantly rub against each other, which has to incease wear a bit. When the CV boot gets a hole in it, the dirt can get into the CV joints and then they will wear. The good news is CV axles are not that expensive. I was told $60-$70 each.
Body Lifts
Nobody yet makes a body lift for the diesel. However, some guys have installed them and made some simple mods. You will need to get some extended fender liners to cover the front wheel wells. Our trucks already show a lot of frame, and a body kift adds to that. If you run an aftermarket bumper like I do, there may be some additional brackets that need to be fabricated. The consensus of those I talked too on body lifts was they are not good for a work truck. Towing would be fine but it might be hard to get someone to install a 5th wheel hitch. You could do it yourself and fabricate spacers for the hitch to make sure it connects to the truck frame, but no one really knows how such a set up would hold up.
Fender Flares
Bushwackwer makles some 3.5" wide fender flares that require trimming 1.25" off the aft portion of the fender. They claim that with these flares the truck will clear 35 inch tires. If the T-bars were cranked a couple inches, I agree. Without cranking the T-bars I think a 33" tire would be about right. I say that without having seen these flares on a HD, so keep that in mind. However, a 4" kit with these flares will easily clear 35s, and you get the advnatage of the lower and more stable lift with the bigger tires and plenty of clearance.
Suspension Lifts in General
There are two basic kinds--he kind that drops everything and the kind that has longer steering knuckles or spindles. There are two 4" lifts--Rancho and Trailmaster, several 6" kits (Tuff Country, Pro Comp, Fab Tech, Trailmaster, CST, RCD, Skyjacker, Superlift), and a couple 8" lifts (Fab Tech and CST). This is always changing, and I may have missed one or two. Most kits require cutting off the stock mounting ears of the front differential, so it would be hard to put the truck back stock with these kits. But not too hard. using a recopricating saw, we were able to get a very clean cut on the aluminum diff mounting ear and it could easily be welded back on. We also got a very clean cut on the frame mount, tough it may require a bit of fabrication to re-attach, it would also be doable.
Non-Spinde Drop Suspension Lifts
These kits lower the entire drive train except for the transmission. They make brackets that drop everything--front differential, steering components, etc, the proper amount. The truck can be aligned to stock specs. The two I have come across are Pro Comp and Superlift. The Pro Comp sells additional components to fix the problem of front drive train vibration when in 4WD at higher speeds. I think Superlift had solved that problem as well. These kits keep the same front track width as our trucks have when stock. Both of them have two piece sub frames. While a one-piece sub frame is sturdier, you probably don't need it unless you are doing some heavy off roading.
Spindle Drop Suspension Lifts
This seems to be the newer technology. The steering knuckles or spindles are longer than stock. These systems keep steering components--like the center link, tie rods, and pittman arm, in the same location relative to the frame of the truck as when stock. This method seems to reduce wear on these components, and these components have been weak points in the IFS in the past. These kits also allow alignment to stock specs.
I am told all the spindles are made by one or two companies. Also, they say all the spindles have the same amount of drop, whether they are for the Trailmaster 4" kit, the Rancho 4" (or 5" kit depending on which catalog you read), or the Tuff Country 6" lift. In fact, Trailmaster's 4" and 6" kit use the exact same spindles. The difference in lift comes from the difference in how much the subframe lowers the lower A-arms and front diff.
I personally don't like a lowered front diff. The reason I got my torsion bar keys and lifted the nose of my truck in the first place was because when hunting on a rough, rutted road, I filled the skid plates with mud and grass because the front diff in the stock location is kind of low to the ground. When I raised it, that problem went away. The spindle kits lower the diff. The diff is angled forward to kep the front driveline at the proper angle, so the rear portion is higher than the front portion.
Last year, the Rancho kit was advertised as a 4" lift, this year it's a 5" lift but nothing has changed. Rancho uses a 2.5" rear lift block. I have the Rancho kit, and when you set it up per the instructions, you raise the front end 4". There is another 1-2" of lift available if you crank the T-bars. This wouldn't be as bad as cranking the T-bars on a stock truck, since the Rancho kit also flips the tie rods to the top side of the steering knuckle so the angle isn't so bad.
One thing to keep in mind is all the spindle drops increase our front track width. Stock, out trucks are already about 2.5" wider in the front track than the rear. With the Rancho, Trailmaster, and Fab Tech kits, the front track is increased another 1.5" per side, not even accounting for wider tires and wheels. My 285's on 16x8s already stick out past the front fenders 1.5" per side. If I installed one of the three kits I just mentioned, they'd stick out 2.5" per side. Wider tires would be worse. Now the guys with these kits tell me they look fine--and they do. However, they say it is hard to keep mud, water, and debris from hitting the sides of the truck. After having my Rancho 4" lift for a month and driving though much rain, it really isn't a huge problem. The looks are not exactly what I like, but that 3" increase in front track makes the truck very stable. I'd say it handles better now than when it was stock. To improve the look, I'll eventually add 2' spacers to each rear wheel and then add Bushwacker cut out flares--painted to match the truck--to cover the tires.
The Tuff Country, RCD, and Skyjacker kits only increase front track width about 1/2" each side. Tuff Country offers a one-piece sub frame. Skyjacker does not require cutting the mounting ears off the front diff, so it is easily reversible. RCD comes with Bilstein shocks.
While I did get the Rancho, becasue I need to be able to have a stout truck capable of doint it all, the Tuff Country was my second choice. I think the CST may be the sturdiest 6" lift, based on the pictures they have on their website.
All these suspension kits have a big flaw, and that is they drop the torsion bars and torsion bar crossmember (TBCM) down as much as the truck is lifted. This means you may well have less ground clearance under the frame with your lifted truck than when it was stock. Many say that's not a big deal, because the real clearance is from the tires. I disagree. Many guys routinely scrape their frame and skidplates on uneven terrain. Imagine driving over a log or a rock shelf. The front and rear diff and axles will clear since the travel with the tires, but when the obstruction is between the axles it can often hit the frame. If you whack your torsion bars or TBCM, you can damage your suspension.
Fortunately, there is a good solution. A compay call "Realift" makes torsion bar relocators that work well. I have a set on my truck. With them, my torsion bars and TBCM are back up in the frame, out of the way. The ride is not affected. I checked the ride of my truck with the Rancho kit installed per Rancho's instructions, which included the standard dropped torsion bars. Then I installed the relocators and check the ride again--there was no difference.
http://realiftsusp.com/ I have left a lot of stuff out, but I hope I can point folks in the right direction. All the company reps were very helpful, and I think any one of these kits would be a good choice, depending on what you prefer.
Blaine
