This is not a new mod or anything, but wanted to give my feedback. I recently was able to do the "ZUK" mod to fix the sag in the bed of my truck. Also, I am fairly new to four-wheeling and truck terms, so bear with me
Found all of the info on this site and through a couple of PM's to ZUK and was able to significantly alter the ride of the rear suspension of my '87 Pickup.
What this mod addresses:
For those who are relatively low profile to the site like I am, this mod was named after the member ZUK who introduced it. Many of the older trucks, especially 4runners, are cursed with sagging rear leaf springs. I'm assuming 4runners just have more weight to carry as well as a couple of other small chassis factors that make this especially noticeable, and there are a few different fixes. To name a couple, you can add-a-leaf, get a full new leaf spring set (both of which are likely to sag again) or jam a coil spring in where the bump stop goes. These are the somewhat low cost and low mod factor solutions that I found... I'm sure others have come up with more advanced solutions... I just did the research that I needed to go forward with what I wanted.
In research, I found that the ZUK mod does a couple of things to the suspension. It raises the height (how much is determined by the existing sag, and which springs you choose to buy, but is usually somewhere between 2'-5"). It will not likely sag again, as a coil spring does not wear out over time like leaf springs do. It gives a springier rear- so make sure that you have shocks that are in good condition or else you will have a trampoline for a bed. I am not too familiar with four-wheeling terms, but it does not create a fold-over problem as the axle is still attached to the leaf springs. Basically, it won't twist around like straight coil-springs would do. It has been suggested that this mod may reduce "flex" (or the distance the wheels can travel reverse of each other), although some members found otherwise.
How I did it:
Unfortunately, my camera was acting up for the "before" and "during" pics, so I don't have any, but the sag in the rear was noticeable (if you're still reading this, you probably already know this from looking at your truck). I have a 3" body lift and 33's on the truck. Installed by the PO but both quickly growing on me
. There was very little spring in the rear of the truck... to test I just bounced in the back a few times.
In the center of the leaf spring on both sides of the axle is a rubber bump stop that prevents the axle from traveling to far or the wheels to hit the wheel-well. On the frame is a corresponding stop that is mounted on the chassis that meets the stop about 3-4" from the frame. What this mod entails is using these two pieces to secure a coil spring. The fastest/easiest way to do this mod is to cut the metal stop, leaving two sleeves to hold a 2" spring and putting the spring over the bump stop. Takes a sawzall or angle grinder, two springs, a few wrenches and about 2 hours.
From start to finish, first I bought an angle grinder (always wanted one, seemed like as good of a reason as any to get one). I raised the rear of the truck on the rear axle high enough to support the truck on jack stands so that when I let the axle drop the wheels were hanging with no weight on them. People have found many ways to do this... If I remember correctly, one member rested the rear bumper on a concrete trash can to support it. Then measure between the bottom of the frame (not the metal stop) and the base of the rubber stop. For pickups, you'll probably be between 13 and 13.5" if I remember correctly. Mine was at 13.25". I think 4Runners are less. I then ordered 14" 100lb springs from the link that ZUK has on his website (all of the mod info I used is in the lower left section):
Waited for the springs. Then lifted the truck like I did before only this time took the rear wheels off. I cut the metal bump stops off about 1" away from the frame.
To avoid needing any spring compressor, I took off the hinge plates on the rear of the leaf spring on both sides... this was two bolts per and very easy to do. I also unbolted the lower shock mounts. Both of these allow the axle to lower as much as possible (and lower than it ever will when it is attached). With the stops cut, I had a buddy press down on the rear of the leaf spring to lower it even further and was able to finesse the spring into the two sleeves made by the bump stop. I found that I needed to hammer the stops slightly to let the spring fit in easier. Cutting closer to the frame may avoid this, but this worked for me very well. Then I bolted everything back together. Instantly a much higher ride...I estimate about 3"... and much springier from bouncing in the back.
Here is a pick of the right side installed:
And the left:
And a closeup of the metal stop holding the spring:
And the side profile of the truck, slightly weighted (and my bro looking at a map on a trip I was just on):
I somewhat rushed this install as I had a trip that I was going on, and was very pleased with how smooth and flawlessly it went down.
It did raise the rear about 3". This made the rear slightly higher than the front, which some members did not like and then tried to compensate by altering the front suspension. I like it, and also feel comfortable with loading the rear. The bed is much springier now. It does ride nicer, although still rides like a pickup (ie, nice'n'bouncy rear end). Cornering is much better, as a passenger noted. Doesn't roll as much.
The rear does creak when going over rough terrain or bumps. This is from the spring compressing and catching the rear bump stops as it shortens. I was aware that this may happen going into the install and it doesn't bother me a bit, but it is there.
Not sure how much it affects the flex of the truck, as I have almost zero four wheeling experience, and didn't get to try the truck out in any "before" situations. I was able to play with it a bit after the mod and never felt restricted in any way... I would guess that it helped the ride quite a bit as the rear actually had room to absorb bumps now.
As a bonus, the truck looks way cooler now all aggressive and angled forward
Glad I found out about the mod, would definitely recommend it... and hope this isn't all redundant info!