Looking into lifting my 2002 blazer 4wd, my buddy said all I need to lift it is a new set of torsion bar keys and shackles for the back, my only concern is will it be safe? Is there anything else I should do to make it better or more stable??

 

You'll get an inch or so, and your front end will wear more.

do a quick search on here, theres a couple of build threads that will give you a good stepping stone.

not saying it's not safe, but just saying theres "cheaper" ways for a longer lasting lift. It all depends on how high and how much you got...

 

Your buddy is correct but there are other options.

With the lift you described it can be hard to get the alignment right and with the stock upper control arms the upper ball joints will wear out faster.

My solution was to install the upper control arms ftom the Rough Country 2.5" lift-kit.

The RC kit of course is another option.

A big question is what tires to choose. The 31s will have some interference issues. Also the larger the tire, the higher the effective gearing will be.

You can see what I did in my build thread.

 

I've been running with about an inch of torsion bar lift for a a few years now just to clear 31"s on my non ZR2 4x4.

Couple things I'd like to mention.

The ride quality WILL suffer, as when you tighten them up you're stiffening the preload, thus taking away from the suspension's ability to absorb movement and generally just making the ride more bumpy. In the case with my Blazer, this effect was alleviated a little when I installed my winch plate and winch on the front, since it added more weight to fight against the higher spring rate, but it's still noticeably stiffer than stock.

You WILL ware out ball joints faster. I've changed mine twice since adjusting the t-bars, however I will say that the first set I installed were cheap and just weren't up to the task for a stock suspension... I've had Moog joints on the truck now for over 4 years with no issues. I haven't had any trouble with CV axle shafts yet, but I can definitely tell that they're at a pretty good angle, however the boots are still in good shape and I do keep my eye on them.

Alignment afterwards can be tricky. The tires tend to want to camber out \---/ and there's only so much adjustment in the control arms to account for this.



Most people run into the most issues when they just max out the adjusters. That's when you'll really push the suspension and driveline components way past their normal operating angles and have parts ware out very quickly, and it's also when you'll have the most alignment issues. But if you're easy with it and keep your expectations reasonable, cranking in only 3/4" - 1" of lift, you can usually get away with it without too many issues, at least that's been my experience with my Blazer and an old Toyota Pickup I use to have.

Is it the "right" way to achieve lift, technically speaking, no. The adjusters main purpose are to counteract suspension sag and to keep the front suspension at a correct height to keep the steering geometry in line. Alignment shops are SUPPOSE to include adjusting these in their alignment procedure, however I highly doubt that most ever do... most are just going to align the steering components at whatever height adjustment the vehicle is at when it rolls onto the rack.

 

I have changed out the upper and lower control arms with new ball joints as well as the inner and outer tie rods and the sway bar end links, if I go from those to an aftermarket parts, let's just say RC, should I replace just the control arms or go ahead and change everything else? I know if I get the full kit it will be expensive but I know if you go cheap, you get what you for, as for the tire size, I am not sure what size I would go with, I wanna get something big, but not too big to where it rubs the inside when I turn or hit a bump

 

If I get aftermarket shocks/struts would it improve the suspension with the lift?? If not necessarily what could I do with a lift to help improve suspension to where it's not so bumpy or rough??

 

Your suspension is what in engineering or physics is called a "just under critically damped harmonic oscillator." An oscillator is a spring. Damping is what reduces the amplitude of oscillations by turning kinetic energy (the motion of the mass, here the wheel etc.) into heat by moving fluid around inside the shock absorber. A critically damped oscillator is one where if given an instantaneous displacement from neutral (you go over a pot hole) the wheel comes back as quickly as it can with a smooth decay. I.e. The energy dissipated by the shock is just sufficient to keep the wheel from overshooting the neutral position. (see picture below)

In practice it is really hard to predict what the exact value should be for the damping so what is done is to slightly under-damp the spring relative to being critically damped. This results in about one oscillation before the amplitude comes to zero.

To soften a ride, i.e. slow down the response of the system, you will need a lower-rate spring (softer spring) and then the appropriate damping for that spring. What you feel as bumpiness, is the acceleration of the system and with F = ma (force = mass times acceleration), and the acceleration proportional to the spring rate, the stiffer the spring, the more abrupt the shocks will be. This can be what you want to keep the tires against the road in a race car but can become uncomfortable. Reducing the spring-rate was what they did for the "land-yachts" of the late 60s and early 70s.

With the advent of progressive rate springs (which torsion bars cannot do) and shocks for which the density of the fluid could be adjusted electrically, the suspension system could be made active; i.e. active feedback to fine tune the suspension for any sort of displacement of the wheels to keep the ride soft but give you control.

So in short, you are stuck with the springs/torsion bars of your truck and what will find are shocks that have been matched to the spring rates of the springs you have and the mass of the vehicle to give you an almost critically damped oscillator so that you don't keep bouncing long after you hit a bump.

But, there are reasons to get new shocks after a lift:

The first one is that you want the shocks to not reach their end of travel. If the original shocks are kept, then when the vehicle is at its new normal height, the shocks will already be extended beyond the middle of their range. Also, with a suspension lift there is the possibility of a greater range of travel.

The second reason is that if you are putting a lift on a truck, you are more likely to be hitting larger and more extreme bumps. You will want a shock that can withstand the greater forces (even if it still has the same damping ability).

For this picture, don't worry about the equation or the numbers. Just consider the shape of the curves of the displacement as a function of time.


Damped Harmonic Oscillator

 

It all depends on what you want to be able to do with your truck. I added my suspension lift more for peace of mind rather to enable me to take on harder roads/trails. I use my truck for hunting and fishing in the woods and mountains of north Idaho. I don't go fast but I wanted a bit more clearance. Also for me, I did not want to do any mods I could not undo. The RC 2.5" kit is nice but to make it work, you have to lower the front diff assembly by cutting off one of the mounting tabs and bolting on their extended one. Since I was not interested in the largest lift possible and liked the idea of having the front diff raised a bit (and not lowered back down with the new bracket), I went with my options of the new upper control arms, longer front shocks and shock mount extenders in the back because of the stock self-leveling shocks there.

Now, if you are want to get even more height and want to push the type of trails you run, then the full RC kit could be the way to go. Note that to use the 31" tires (as were used on the ZR2 models), you will have some interference issues. These are not horrible but can be an issue depending on your priorities. On my truck, with the 31s, the side wall would hit the frame rails when the steering wheel was turned all the way. Also there are reported issues with rubbing the inside of the fenders but these can be addressed. On mine with the 30s, I lose 1/2" of clearance but I was willing to live with that. I also have running board that crowd the wheel wells.

BTW, the ZR2 suspension has a wider track width with longer control arms so that they don't have the issues with hitting the inner rails. I don't know how they overcome the issue with the fenders though.

 

So, I thought I'd make a comment to clear up some concepts and language about springs and torsion bars in particular.

So, the spring rate for a coil spring will be the ratio of the change in force divided by the change in compression; (change F)/(change in x) = k. (technically there is a negative sign too but that just gives us a direction, i.e. F = -kx) For those who have had calculus, the expression is dF/dx = -k.

For an ideal spring (Hooke's law spring) the spring rate is constant for all amounts of compression.

Modern suspensions now have variable rate springs or springs that have a different spring rate depending on the amount of compression. I.e. at larger amounts of compression of the suspension, the spring might get harder (a larger spring rate).

Now, for our torsion bars, these are constant rate springs. This means things are bit simpler but also that there is less to work with to tune the suspension. And as you know torsion springs work by twisting. For these, the amount of change in rotational force (torque) divided by the change in angle of rotation is a constant. For a vehicle that is stationary, the amount of twisting will be just enough to offset the force of gravity the weight) of the front of the vehicle. So how does this come in to our "torsion bar cranks?"

Well, since the amount of twist is fixed for a fixed weight, what we can do is rotate the end of the torsion bar that is attached to the frame. By rotating it, the front end that is attached to the lower control arm also rotates the same direction. The amount of twist is the same before and after we crank the torsion bars but we have rotated both the same amount. The equivalent of this for a coil spring would be to put a spacer between the end of the spring and where it attaches to the frame; the amount of compression of the spring due to the weight of the car would be the same, but the lower control arm would be lower.

So why then use the torsion bar keys? One reason is so that we can rotate the anchored end of the torsion bar more so that we can rotate the end attached to the lower control arms more to get more lift. The other reason is that in practice we can come up against some limits to the travel (the amount of twisting) of the torsion bar.

In the video, you can see the wheel going up and down. The white arrows show the amount of twist in the torsion bar due to the weight of the car. When at its resting position where the weight of the car is balanced by the force from the twisting of the torsion bar; the lower control arm is wanting to rotate its end of the torsion bar counter-clockwise (upward) where the amount of twist in the torsion bar is shown by the different angles of the white arrows. Now if we were to rotate the torsion bar key at the other end of the torsion bar clockwise, the lower control arm would rotate clockwise too to keep the amount of twist the same. What does change is the height of the suspension because the lower control arm is now at a new angle to the ground. (BTW there is a small effect of of the amount of twist not quite being constant due to the geometry of the angle the lower control arm makes with the ground but this is a small effect.)

I hope this helps.



https://i.makeagif.com/media/3-04-2015/wrMxio.mp4

 

One more thing to think about changing: The CV joint boots for the front drive axles. I had the inner ends of the inner boots slip off due to the new larger angles for CV joints. The original boots are pretty stiff but I found that the new neoprene boots are much more flexible. (The ones from NAPA worked great.) If your CV axles are still fine, it is not too hard to put on the new boots. When doing all this front end work, you'll likely have them out anyway so you might as well do it. You don't want to find that the have slipped off and ruined your CV joints necessitating getting new axles. The new boots are much cheaper than new axles!