Quote:
Originally Posted by slacker
well .. in my opinion ..
springs should have been replace a long time ago .. we all know of the dredded rear spring sag of the 4runners ..
as for the blocks .. wether sitting on the OE pirch or a block .. there is almost identical spring "foot print" on the mounting surface , actually better on a block , so that point is irrelevent .
other the spring "wrap" , which your runner is not equipt to exert.. there is no identifying cause to blame this spring failier on the block ..
explain your reason for blaming it on the blocks please ?
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Agreed, springs should've been replaced a while ago, however I've only had the runner a little over a year so.... Anyhow, the springs already had the add-a-leaf on it and weren't wrapped at all. Then a lift kit came up for sale from a guy doing and SAS / chevy spring conversion. Bought the complete lift for 400. I was hesitant about the blocks because I already knew that they could cause the springs to wrap up and the springs were already fatigued / sagging almost 1" in the back even with the add-a-leafs. The plan has always been to replace the springs and blocks so fingers were crossed that they wouldn't break and they didn't.
Fast forward 1 year- my other projects, an '89 Celica GT and a '72 Firebird are on hold so I order the springs and take pictures showing how 1 year of driving on weakened springs and 4" blocks could affect things. All other things being equal, the only thing changed on the rear was the addition of the blocks and the wheels/tires.
Now for the 'newtonian physics' part of the story. With the axle bolted directly to the spring pack, the torque seen by the springs was managable, obviously, since the springs were not bent/wrapped. Being that you've worked on trucks before, you know that there is torque from acceleration and deceleration. It's something every vehicle that moves does- that's what moves and stops a vehicle: torque is applied for acceleration and absorbed for deceleration. That torque can induce that thing called 'axle wrap'- the primary reason many people install ladder bars or traction bars- to keep the spring from wrapping up and binding the u-joints or to stabilize wheel-hop. If you've ever used a breaking bar, or clipped the boxed end of a combination wrench over the open end to extend the leverage, you know the advantages of longer levers acting through a fulcrum.
When you consider the spring as the fulcrum, the spring perch is approximately 1/2" thick. Now, you add a 4" lever on the axle and guess what? The torque applied to the spring mounting surface increases proportionately to the tune of approximately 8 times more than the perch alone due to the fact that the block is 8 times 'longer' than the perch. You've increased the mechanical advantage the axle has over the spring.
Now, add in the add-a-leafs which extend approximately 6" to the front and 8" to the rear. You are then distributing the torque through the comparatively stiff add-a-leaf to the points at ends of the add-a-leaf where it contacts the spring. So now it's not simply a matter of the axle wrapping the spring, it's the axle torquing the lift block and transfering that force through the the add-a-leaf to a well-worn spring. Imagine what would happen without that distribution of torque away from the axle mounting point.
So my point in starting this thread was to show the possible outcome of using lift blocks to compensate for the 'sagging' rear end most stock 1st gen 4runners, and many pickups with shells or toolboxes- well any vehicle with leaf springs for that matter, can develop.
Feel free to look at the pics at the start of the thread. They display exactly what I'm describing- the main leafs abnormally tweaked by the AAL's due to the torque imposed by the lift blocks. The springs were worn, but had a correct, albeit shallow downward arch before installing the blocks.