Front Lift Blocks: Dont do it!

[greasemonkey]

Yeah, I was reading through some of my old 4x4 magazines and thought about how true this is. I see so many trucks around here running front lift blocks. (I didnt write the article, it came from Petersens 4 wheel and off road.)

What makes them so bad? It all boils down to simple physics. Whether driving off-road at high speeds or cruising down the freeway at a normal pace, your vehicle creates a certain amount of rolling momentum. Whenever the brakes are applied, roughly 70 percent of the vehicle's weight is transferred to the front axle. This pitching action causes the front axle to roll forward, thus applying extreme pressure on the front U-bolts and springs. When you add a block into the equation it elevates the leverage point on the front axle, causing the axle roll to become even more dramatic. Enough force or pressure can be applied to fire the front block out from between the axle and the spring. This will result in loss of steering and frontend control, which may have a tragic result for you and the vehicle.
Some argue that welding the front blocks to the axle can eliminate the block from shooting out, and in their mind it's a safe fix. True or not, when you raise the spring perches higher on the axle you place a greater amount of force on the spring. The springs are now working harder to control the vehicle's vertical and lateral movement and can cause the axle to travel unpredictably, cause spring deformation, and also raise the leverage point on the axle. Sure, you won't shoot the block out, but instead the entire axle will wrap violently under the vehicle. Simply put: Don't run front lift blocks.


Welding front blocks or building tall perches creates a high leverage point that creates more stress for the leaf spring. This diagram illustrates the forces the vehicle encounters during cornering (shown turning left). The lateral force is now intensified as much of the vehicle's leverage is placed high above the axle. Axlewrap during acceleration is also compounded.


This diagram illustrates the forces the vehicle encounters during braking. The front lift block sits in a high-pressure area and as a result could easily be ejected from between the spring and the axle resulting in complete loss of control over the front end. This only intensifies as tire sizes become larger due to greater leverage.
The only thing worse than having one block in the front is having two! Not only has this truck raised the leverage point by creating a taller perch, but having a loose block resting between the spring and the perch is a recipe for disaster. Seventy percent of your vehicle's braking power comes from the front. Although the blocks here are only a few inches tall, they can easily distort the leaf springs and become deadly projectiles. Another note to mention is welding anything cast is terribly difficult and requires a skilled professional welder to lay a solid bead. So don't do it!

[75K30]

That is a very good point and a good article. I might add a little bit to this. They did not mention that along with the axle movement brings steering geometry change. Caster is a very key component to keeping a vehicle straight under severe braking. Changing the caster when the axle rolls foward makes the steering too fast and unpredictable, allowing the vehicle to wander one direction or another, add a little driver compensation and a lifted truck could find itself on its roof.
Can't comment enough how bad the idea of blocks in the front are. Heak I do not even like them out back!

[lonestar1128]

Front lift blocks are illegal in Utah, and probably many other states. Not safe on or off road.

[greasemonkey]

Theres guys that swear against lift blocks, then turn around and stack leaf springs up into a massive pack. If Im not mistaken, the same principle applies here as well. It seems to me that this would cause a leverage point like a lift block.

[75K30]

Originally Posted by greasemonkey

Theres guys that swear against lift blocks, then turn around and stack leaf springs up into a massive pack. If Im not mistaken, the same principle applies here as well. It seems to me that this would cause a leverage point like a lift block.

Not quite the same concept, and it gets rather interesting.
With a block, the axle is further away from the strongest part of the spring (the center) and the axle will have greater leverage and move without support.
larger, longer leafs can add lift and provide adequate support for the axle to keep it in the proper location.
Adding leafs is a very good idea if the leafs are thin enough to keep the proper resistance and flex.
There is a giant mis-conception that more leafs is a bad idea. Understanding the leaf spring will help to understand the mechanics behind it. More leafs allow the exchange/conversion of energy into heat through resistance. This is refered to as the rate of the spring. HAving fewer leafs means that the leaf has to be thick, and a thick leaf has to have a bunch of rate / resistance to do the same job as mulitple leafs with the same amount of combined resistance as the single thick spring.
The spring with more leafs can exchange heat more effectively, and still maintain a fantastic ride.
If you look at the desert racers that are using leafs springs, you will see a considerable amount of arch, and a leaf pack of over a dozen individual leafs. This allows them to run cool over repated cycles, and the length allows for some crazy travel.
As long as the axle is right up against the leaf spring, the spring can do its job of controlling / locating the axle without the ill effects like a flat spring with a block.
There is quite a difference.

[436'd skylark]

Another thing I love about old solid axles is when the fron axle rolls forward under hard breaking, the distance between the steering box and drag link get shorter, which forces the pitman arm forward, which causes the truck to dart in one direction or the other.. another problem intensified with lift blocks.

[75K30]

Ah, Joe;
this is a terrible problem with the old push pull system. The inverted "T" and "Y" systems solve this, but these are used primarilly with coil sprung front suepensions and these have link systems, so they do not apply, but the crossover conversions are the way to go.
Even trucks with leaf springs can really benifit from this. Eliminates the bumpsteer associated with suspension cycles, and the different arch that the short drag link moves at.
Steering box on the driver side moving a long drag link that attaches to the pass side steering knuckle is the only way to go.
Pretty easy conversion too.

[436'd skylark]

where is the grease boot for the pitman arm?



just busting your chops..

Originally Posted by 75K30

Ah, Joe;
this is a terrible problem with the old push pull system. The inverted "T" and "Y" systems solve this, but these are used primarilly with coil sprung front suepensions and these have link systems, so they do not apply, but the crossover conversions are the way to go.
Even trucks with leaf springs can really benifit from this. Eliminates the bumpsteer associated with suspension cycles, and the different arch that the short drag link moves at.
Steering box on the driver side moving a long drag link that attaches to the pass side steering knuckle is the only way to go.
Pretty easy conversion too.

[75K30]

That is not one of mine Joe.
That was simply an example. Good eye though. I use a slightly larger TRE when I use TRE's, I like the Moog ES2026, and 2027 when I do these upgrades, but my preference is spherical rod ends rated at over 38,000 PSI, with 7/8" F911 hardware, and my own custom mis-alignment bushings.
check out these bolts. If you are building something that requires the ultimate strength and clamping force, you need these.
F-911 Specifications

Oh yeah, that example I could be really very crtitical of. Those bushings are a little on the light side, and that tube looks like a generic schedule 40.
None of that light stuff on my rides. I use 1.5" x .188 Chro-mo at a minimum.
Have had steering failures, and they are never fun.

[o3shortbed]

Originally Posted by 75K30

Have had steering failures, and they are never fun.

i drove a buick car less tha mile to my shop with little brakes/no brakes. i found like 15 leaks in the rotted out lines. guy didnt want to fix it so on the way back the stearing failed too. so no breaks and no stearin the car ended up in a ditch. the e-break is the only thing that saved me