Help! Broken front sway stud.....

[mwiener2]

So what you are saying is the D-Blocks don't see a significant amount of force that wants to rip them off their mounts.

 

Ok, that's what I thought

[Norm Peterson]

So what you are saying is the D-Blocks don't see a significant amount of force that wants to rip them off their mounts.

No. And yes.

 

From the torsion effect, there is zero force applied to the D-blocks, their brackets, or the bolts/studs. A tiny torsional moment due to friction as the bar rotates inside the D-blocks exists, but this is small enough such that it can be ignored.

 

From the arm bending and shear effects, there can easily be several hundred lbs force.

 

 

 

The adjustable front bar that I just swapped onto the Mustang ranges between 700-ish and over 1000 lb/in and could actually see ±1" deflection in service (about 2° roll). Multiply that by an "E" distance of 41.5" and divide by a "B" distance of 26" for that particular bar and the blocks could see anywhere from 1100 and 1600 lbs, or 550 – 800 lbs/bolt when it's tensile. Bushing compliances (based on polyurethane D-blocks and rod-ended endlinks) only drop those numbers by perhaps 5%. For comparison, the car's OE bar is a little softer at 670-ish lb/in and rides in slightly softer D-blocks.

 

 

 

Have an idea – grab an old bar and hold it at points A and B as shown below. Or bend up a piece of heavy-gauge coat hanger wire into a U shape. Get a friend to hold it at points C and D – you'll need four hands (or at least four sets of fingers). Now try to push bar end A down to put torsion in the center section while you hold point B steady, and your buddy does likewise at point C (and is pulling up at bar end D). Prove one way or the other whether there are significant forces at B and C.

 

 

. B . . . . . . . . . . . . . . . C

._▼_______________________________▼_

| . . . . . . . . . . . . . . . . . |

| . . . . . . . . . . . . . . . . . |

| . . . . . . . . . . . . . . . . . |

A . . . . . . . . . . . . . . . . . D

 

 

 

Norm

[esleepy]

Can't just let this die yet :-) Ok, I see where you say that there are forces on the D links. My first understanding was that All forces are applied to the D links. It's clear that that is not the case. Now one more question/statement...

I would think that basically most of the of the "pressure" on the D links are pushing into the frame and not pulling away from it.

Example, car enters into a corner. Force is applied to the outside front corner and pushing UP on that A-arm. The force is pressed against the lever (D link) on that same corner - pressing it into the frame.

One the other side (inside A-arm), the anti-roll bar is applying torque pushing down on that A-arm. This A-arm also has a lever, the D link on that side. I don't believe that this inside D link is receiving anywhere near the pressure pulling on the frame because of the very fact that most of the CG of the car is pressing into the outside A-arm.

 

 

. B . . . . . . . . . . . . . . . C

._▼_______________________________▼_

| . . . . . . . . . . . . . . . . . |

| . . . . . . . . . . . . . . . . . |

| . . . . . . . . . . . . . . . . . |

A . . . . . . . . . . . . . . . . . D

 

Using your diagram, we enter a left hand corner. D is forces up while C is being forced down for CG rotation. Now if D is being forced up, then A MUST be forced up as well. But I don't think that the same amount of force pressing into C (both up from chassis CG and down from right A-arm).

In summary, I would think that most of the push-pull on the D links is push into the frame on the outside corner.

 

Does this make sense?

[Norm Peterson]

Near as I can tell, you're getting a couple of things confused.

 

When you're following a load path and its effects, you need to stick to looking at either actions or reactions. Mixing and matching is guaranteed to cause confusion. Here, you either look at how the chassis roll moves into the bar, out to the endlinks, and into the suspension – or look at how the assumed change in suspension loading and displacement works its way back to the chassis. Not some of each.

 

An anti-roll bar only resists roll. A spring resists both vertical forces such as weight and in conjunction with the spring on the other side, roll. I think this is what you're getting at with your "most of the CG of the car is pressing into the outside A-arm" remark. A sta-bar starts out with no force in it to give anything up from, so it can only have load added to it (and only when opposite direction displacements exist at the two ends).

 

 

BTW, the CG does not "press down on" the outside suspensions or anything else. It isn't even a real "thing", so it can't in and of itself "do" anything. What a CG is – is an analytical convenience.

 

And it's "endlinks" that attach to the bar at the ends of the arms, and "D-blocks" grab the bar on its torsional section, at least for most front suspensions. Perhaps we should agree to use the term "chassis bracket" instead of "D-block" just to eliminate this confusion.

 

I probably could have labeled the sketches a bit better, but it's a little late now.

 

 

Norm

[mustangendsley]

way to much for a broken bolt HaHaHa.

[OhBe1]

Short answer.

To produce an anti-roll couple, forces are applied to the ends of the bar through the endlinks - one side up, one down.

If those forces were not balanced by other forces, then the bar would start rotating about the car's roll axis, relative to the car. Since it does not, there must be other forces involved, and there are. Those countering forces are applied through the bracket bushings.

 

Thus the need to reinforce the rear sway bar bracket mounts, where vertical forces torque the wimpy mounts. There, the vertical forces are fed through fore-aft bolts, torquing the mounting fingers, which sometimes break. Mine were only slightly bent by the time I added the AVO reinforcements; other have not been so fortunate.

 

Happily, the front geometry is different, with the bracket mounting face in a approximately horizontal plane, and so the bracket bolts/studs are in tension rather than shear. And the mounting structure is beefier than the rear. Usually not a problem unless you over-torque them in an installation.

 

The threads are, BTW, M8x1.25. Most bolts you buy will be 13mm head, unless specifically labeled for Asian vehicles, in which case they'll be 12mm. Stainless, or at least zinc plated, would be a good idea if you're in the salt belt.

 

As for bushing wear - they do.

[mwiener2]

[quote=OhBe1;2991551

 

Thus the need to reinforce the rear sway bar bracket mounts

 

I track my car and off-road it. The stock rear mounts havn't moved an inch. I don't think the need for re-enforcement back there is as great as the aftermarket parts guys want you to think it is.

[TSiWRX]

I track my car and off-road it. The stock rear mounts havn't moved an inch. I don't think the need for re-enforcement back there is as great as the aftermarket parts guys want you to think it is.

 

^ Tell that to those of us (myself included) who've managed to bend/break the rear mount in simple, non-aggressive daily-driving, on factory suspension components, with no trauma recorded that area of the vehicle otherwise.....

 

Given how simple it is to install the popular AVO reinforcement brackets and their minimal expense, I'd honestly say that it is worth the 30 minutes of labor to DIY it. The trouble that it saves, in terms of having to address that area after-the-fact (my damaged side - granted, that damage took damn near 5 years to happen...but it did - took me 1 and 1/2 hours to address, the non-defective side? I was done in 10 minutes), is worth the cost and labor time, IMveryHO.

 

Are there BL/BPs which have seen rather severe duty without this part having manifest any problems?

 

Certainly.

 

But are there more than quite a few that have seen problems here? That's just as undeniable.

 

This isn't an expensive or difficult or even time-consuming modification. People spend more time (and money) putting in a catch-can.

 

 

----

 

 

Back on-topic..... RE: the front mounting points -

 

So, the question, from someone who took "Physics for Poets" during his undergrad years and is now a biologist who basically plugs-and-chugs statistics into nice "this is your result, stupid!" computer programs.

 

I'm one of those guys who now has a torque wrench for every application, because I've learned from hard-won experience that I will over-torque damn about everything. I didn't have a problem with the bolts for the front sway's mounting brackets. They came out cleanly with just a dash of P'Blaster, and went back in nicely, too.

 

But when someone upgrades the front sway, what -if any- implication does this have in terms of both the factory bolts as well as the factory brackets? Are they strong enough?

 

And if not, then what?

 

What grade of hardware would be suggested (it's not too hard to source stuff here, but I do find a problem with Adamantium....)?

 

And if the bracket is potentially problematic, what are the professional's views on modification (cutting) of the heavy-duty brackets that come from Energy Suspension, to fit in that area, in this manner:

 

http://legacygt.com/forums/showthread.php/energy-suspension-bushings-review-install-cusco-97981.html?t=97981

 

- is that safe?

 

Thanks to the engineering whizzes out there. If you guys ever need microsurgery on your rats or mice, I'm your man.

[korpsepatrol]

So I decided to start my summer project for this year a little late.

 

I would like to know if anyone has had the issue where the front stud/bolt on the sway bar mount has sheared off? Also what did you do to fix it?

 

I am planning to drill right through where the stud use to be and use a bolt and nut. Its just odd to me that this has happened since i have done 2 sway bar installs(2005/2006) and never had this happen.

 

I will post pictures of what i am talking about once I get under my car again hopefully this weekend.

[wpmarky]

I've heard people do the same, just drill through it and replace with bolt/nut.

[TSiWRX]

http://legacygt.com/forums/showthread.php/help-broken-front-sway-stud-138528.html?t=138528&highlight=poets

 

My last set of questions there were never answered.

[korpsepatrol]

Dude thanks for finding that, i put in the same title as a search and it wasn't coming up.

 

The funny part was i was using a torque wrench and using the cobb directions of 40 ftlbs and snap... off comes the bolt. Thanks for the responses! I will be combining both threads.

 

Merged both threads.

[nemo]

The funny part was i was using a torque wrench and using the cobb directions of 40 ftlbs and snap... off comes the bolt. Thanks for the responses! I will be combining both threads.

 

Same thing happened to me. I couldn't drill out the bolt so I had a shop do it. Replaced it with a bolt and nut and it's been fine ever since.

[TSiWRX]

Dude thanks for finding that, i put in the same title as a search and it wasn't coming up.

 

No thanks needed - I just happened to remember the rather fascinating conversation: one I barely understood/followed , and also had an unresolved question pending.

[korpsepatrol]

Fyi, about those energy suspension brackets, i bent them to fit on my 05/06 and attempted to bend them to fit as best as i could this time around without the appropriate tools. I didn't cut them though.

[TSiWRX]

^ In retrospect, I think that's what I should've done.

 

I'll order another set - they're nicely priced. Thanks!