Hello drsmonkey, I saw that "I've got Cognito UCAs for 1500 Silverado on my 08 awd van. "
I'm getting ready to order parts:
Cognito control arms and limiting straps; do you have part numbers and perhaps a pic?
I'm looking at doing Maxxcam torsion keys
Suburban 3/4 ton leaf springs
Bilstien shocks
Z71 Bump Stops
Any other recommendations for a successful lift?
What size tires were you able to mount?
Thanks
Short answer. (but you should read the long answer)
UCA part number is UCAK100009. Straps are LSAK13. Our vans use the same UCAs' as 1999-2006 1500 pickups so any aftermarket UCAs' for that application will fit. For pics see the late December post from NWExpress in this thread. I am running 265/75/16's (about 31.6"), but I know others run 285's(32.8") with a little trimming. Even though you can fit 33"s, for me they compromise gas mileage, braking performance, and wear intervals of suspension more than I would like since my van is a daily driver. You may have to adjust your wheel offset to fit 33"s as well.
Long answer.
I likely understand suspension less than some, but definitely better than I can explain it. I took the time to write the long answer below for anyone looking to lift one of our vans safely (a lot of it applies to any gm front torsion, rear leaf spring suspension), not to say that anyone else is doing it wrong. I am not an engineer, just someone who has been building, breaking and wheeling lifted vehicles on and off for 30+ years. This is my first GM, so do your own research before taking my advice. If you don't, it is on you. If there are mistakes, missing info, etc. please feel free to let me know and I will gladly edit, but you may have to convince me first.
Below are some things to consider before lifting your van that may save you and hopefully others some money and increase safety. A lot of people buying these vans don't have a lot of experience with lifts and offroading, so there is a lot of misinformation floating around in this thread regarding lifts. Unlike most other trucks, there is not a lot of aftermarket support for our vans, and no turn-key solution available (except one that is over-priced and poorly designed) so it is important to understand the basics of suspension when doing your own lift. Two things to keep in mind when lifting a vehicle without going into extensive suspension mods...Everything in suspension is a compromise, and the engineers designed the suspension to balance those compromises to work optimally with some safety margins built-in. Moving the center of gravity of a vehicle up is inherently less stable, but it can still be safe if you know that and keep your lift within the limits of the suspension design.
Torsion keys = Before buying new ones crank the oem keys and see if you get the lift you are looking for without bottoming out...their seems to be a belief that what keys you use effects the spring rate, but it doesn't. A different key allows you to index the torsion bar differently and that is all. It is NOT equivalent to increasing pre-load on a coil spring. The spring rate of a torsion bar is static at a given load no matter where the load is applied in the travel of the suspension, and torsion bars have a relatively flat spring rate within their travel. Each one of our vans rolled off the assembly line with slight variations, so sometimes new keys are needed, but usually only when going for max lift (which comes with a lot of other problems.) Look at your halfshaft angles before you lift, it should be sloped slightly upward toward the hub. Post-lift your halfshafts should be sloping downward at no more than about the same angle. Much more and you will experience much faster wear of CV boots, tie rods, and ball joints. At extreme lift heights you severely limit down travel which can harm offroad performance and is dangerous on the road. Aftermarket keys allow you to adjust to the extremes, usually the OEM keys will allow enough lift while staying within a safe part of the suspension travel. Cranking torsion keys does not change the total suspension travel or where the top and bottom of the travel are relative to the frame, just the static point at which the suspension sits within the travel. By lifting the van you increase up-travel and reduce down travel available relative to ride height.
Front Bumpstops = You may or may not need them...the bumpstops on our vans are designed to act on more of the suspension travel range then "traditional" bumpstops. They act upon the suspension system through most of the uptravel cycle in order to give a more progressive spring rate. than a torsion bar alone. Because there is little to no uptravel before the bumpstop makes contact it also helps to control body roll reducing the amount of work the sway bar and shocks need to do. Look closely at where the bumpstops are located relative to the pivot points of the lever (lower a-arm) and the contact pad. You can see how much of the suspension up-cycle they affect. When you crank your keys you are moving the static point of your lower control arm away from the bumpstop which diminishes initial control of body roll. Z71 bumpstops moves the point of contact closer to the pad providing a progressive spring rate sooner. The compromise is that they will physically bottom out sooner and get rapidly progressive near the top of the travel, slightly limiting the total amount of travel. I have a hightop, travel in and live in really windy places with lots of wildlife, so I like the Z71 bumpstops for crosswinds or sudden maneuvers at high speeds.
Rear bumpstops = With the OEM leaf springs installed the bumpstops act much the same as the front ones, but because of the geometry they act on less of the suspension cycle than the front.. The stock leaf springs also have a relatively flat spring rate, but when you swap to suburban springs you have a stiffer spring with a much more progressive spring rate. The bumpstops move away from the pads, but because the spring rate is higher they are not as needed to control body roll but will still work on the very top of the suspension range as a bumpstop. I left mine stock to maximize wheel travel, but also added a rear sway bar for the same reasons I use Z71 stops up front.
Front Shocks =
DO NOT USE SHOCK EXTENDERS, EVER! Cranking or changing the torsion keys to lift a vehicle does not change the total amount of suspension travel or where the bottom or top of that travel is relative to the shock. Those extensions only limit the amount of shock up-travel available to the shock. This likely will cause the shock to bottom out before the bumpstop, causing broken stuff. This is why the extensions almost always break when used offroad. The OEM shocks will work exactly the same post-lift as they did before. Neither the Bilsteins or the OEM shocks are position sensitive, so lifting does not effect their performance. As long as the shock has the correct OEM spec extended and collapsed lengths they will work. If your shocks are still functional there is no need to change them. When they die, or if you want a stiffer ride then it is worth getting the Bilsteins. The 4600 and 5100 series of Bilsteins only differ in finish and valving. The 5100 are valved more aggressively and will give you a more stiff ride feel.
Rear springs/lift blocks = Swapping your rear springs to 3/4t suburban works to increase ride height, spring rate, and travel. It also changes the front to rear balance of the suspension and makes the van ride more like an empty truck. It does unbalances the ride a bit. A custom leaf spring built by a good shop for your load and use is the best, and most expensive option. Lift blocks are an OK way to go if you want to keep the same ride quality, but only when the blocks are minimal and designed for the proper pinyon angle.
Rear Shocks = When you swap springs you have effectively changed the spring rate and the total amount of suspension travel significantly. You will need new shocks sized appropriately in order to not limit down travel. The Bilstein suggested in previous posts work. Lift blocks change the distance of the lower shock mount on the axle relative to the upper shock mount on the frame. Longer shocks may be needed to not limit droop, but I have not measured this to be sure that the OEM shocks wouldn't work.
UCA's = I would adjust your ride height (lift) first then get an alignment and see if you get sufficient caster (3+ degrees) without compromising camber. Every van is slightly different and you might get lucky and not need the Cognitos. The higher you go the more likely you will need a way to correct caster. The ball joints in the Cognito UCA's wear out about twice as fast as OEM for me, but they are also much easier to replace. The other reason to get aftermarket tubular UCA's is for tire clearance at steering lock. My 265's did not contact the OEM UCA's, but it could be a problem as tires get bigger. Downside is you will have to pay for a second alignment if you end up installing aftermarket UCA's.
Limit Straps =
Mandatory with aftermarket tubular UCA's. The down travel on our stock suspension is limited by the UCA contacting a metal pad attached to the frame. If a tubular UCA is allowed to limit down travel in the same way it will bend and/or break. This could lead to sudden, catastrophic re-alignment of your front wheels at high speeds, which is no fun for anyone. The way I mounted my limit straps (drilling through the shock tower like Cognito suggests for pickups) is not ideal for shock life, see NWExpresses pics for a much better solution.
