Does this brake line bracket serve as a stop to keep knuckle from moving up the strut

[jrodrig5]

Hello, I need some help from someone far more educated than I in determining if a brake line bracket spot welded to a strut serves as a stop mechanism to keep the knuckle from moving upwards the strut.

How this question surfaced is that someone has developed a way to lift the "un-liftable" 2014 + Jeep Cherokee

The lift is accomplished by moving the knuckle 3/4 of an inch further down the strut and also enlarging a second, existing hole (3/4 an inch down) to pass the bolt through. The concern is that since the knuckle no longer sits flush against the brake line bracket it will possibly move when placed under stress.

The knuckle seems to be held in place by clamping force alone bolt is torqued to - 100 LB-FT.

My questions:

1) Does the brake line bracket also function as a mechanism to prevent strut movement or is it just there to help align the knuckle/hold the brake line in place?

2) If the bracket also serves as a stop, will placing a steel ring in between the brake line bracket and the knuckle - post-lift - be enough to restore the function the bracket serves?

3) Any other safety issues to be concerned about?


I've uploaded two pictures of the brake line bracket and 1 of the strut/knuckle showing the smaller hole that needs to be enlarged.

Any advice/input will be greatly appreciated.

 

[BrianPetersen]

This is a typical MacPherson suspension.

Is the knuckle in contact with the brake line bracket in the stock configuration?

Even if it is, at most it is acting like a locating stop during assembly. Once that knuckle is clamped over the strut, it is not going anywhere. Probably you will find that the sheet metal bracket that the knuckle is assembled around (the one with the extra hole to be enlarged) is not even actually clamping onto that sheet metal - it should be clamping on the body of the strut itself. The sheet metal bracket is just to hold things oriented during assembly.

There is no need to brace the knuckle against the brake line bracket once it is assembled. If the clamp bolt comes undone, you are in trouble no matter what.

On another note ... this seems like a lot of trouble for 3/4" extra lift.

It will affect the angle of the lower control arms at nominal ride height which will raise the roll center, and it may have some bump-steer effects depending on how the angle of the tie-rods compares to the lower arms. Obviously the car will need an alignment once this is done. Judging by how visibly bad the steering geometry is on a lot of lifted 4x4 trucks (steeply angled panhard rods and steering rods) maybe it doesn't matter that much.

I've had similar thoughts of lowering the front of my van by about an inch by doing a similar thing, and I've heard of it being done and I've taken a look at it and I can see how it's feasible, I've just been too chicken to actually do it.

 

[GregLocock]

Yup. Mind you I suspect that much of the clamping force is generated at the bottom of the tube where the end disc stiffens it. As you move the clamp up the tube the joint will become softer and the deflections greater. If it is a monotube shock, as is quite likely these days, this may well destroy it quite rapidly.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[jrodrig5]

Thanks for the insights!

Since we're moving the clamp down the shock , not further away from the end disk, this shouldn't be an issue correct?

 

[BrianPetersen]

Only if you move it so far that you start significantly reducing the clamping surface. For the small amount that you are planning to move it, I don't think it will be a problem.

Greg has a point about going in the other direction (lowering).

Bear in mind that every motorcycle front end has clamped fork tubes, and they don't have an issue with moving around in the clamps when they shouldn't. If the clamps are round and the forks are round, the clamping imposes compressive hoop stress on the tube, as opposed to causing out-of-round deformation. Theoretically it will "shrink" the diameter of the tube a little bit where it is clamped. If there is a piston moving inside at that location (normally not the case with motorcycle forks) it could be an issue. The stock setup will be designed to accommodate whatever deformation is caused by clamping at the stock location (probably by making sure the internal piston stays clear of that area). How much wiggle room is inside ... I have no idea.

 

[GregLocock]

Yes that's the difference between twin tube and monotube shocks, with a twin tube the ID of the outer tube is not a critical dimension, as it is just a return path for the fluid.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

So I took another look at mine (which is also a Fiat design, although a different vehicle platform). The parts are different but the idea is the same. That brake line bracket has a piece that sticks down and is in contact with the top of the clamp, which is part of the knuckle. It looks like it is just a locating stop during assembly. There are three spot-welds holding that brake line bracket to the body of the strut. Those aren't enough to contribute any appreciable load-carrying capacity.

I did not feel like messing with those spot-welds, given that they are right on the body of the strut, so at least for the moment, I am leaving well enough alone. Attempting to drill out a spot-weld in that location might cause an oil leak ...