tarett swaybar stuff broke ..., anyone else had problems? Options

[eeyore]

I figure the lower heim joint broke off while it was pointing inward, at full compression.

This is hard for me to explain, but I think the problem is the 90 re-orientation of the u-tabs and I think the axis of the heim joint on the a-arm needs to be parallel to the axis of the a-arm itself.

If you put a big plate (green lines) into the rotated u-tab, you'd see that the plane of the plate (especially the top) move inward and outward through the a-arm travel. However, the top of the droplink in fixed in its left-right orientation, and at some point the droplink tries to bend.

The forces on the utab (yellow) push down, but since the u-tab is at an angle, 'down' is also 'inward'.

(The left side of the picture is at ride height, the right side is my interpretation of a-arm, u-tab orientation at full compression.)

[airsix]

QUOTE (john rogers @ Aug 4 2005, 11:28 AM)

Got me thinking that when I went to put the mounts on the A-arms for my race car someone (forget who) told me to align the bolt holes fore-aft and not crossways as Andy has his. Wonder if that makes any difference?(snip)

It IMHO makes all the difference in the world. Andy, this isn't meant as a jab, but I'll stake (what little there is of) my reputation on this statement - This failure has everything to do with the U-tabs being rotated 90 degrees from the original design. You eliminated one form of binding and unintentionally exchanged it for a worse one. In the stock orientation the control arm can move through it's entire arc without changing the angle of the heim joint pieces - The outer joint piece rotates around the axis of the through bolt. With the tabs rotated 90 degrees the angle of the outer joint piece to the axis of the ball changes dramatically as the control-arm moves. It wouldn't take very much control-arm angle change to bind and snap off the heim joints.
Since you changed the U-tabs to give more adjustment I think the root of this is recognizing that we're trying to get too much range of adjustment out of this swaybar. I think the solution is putting the U-tabs back in the stock orientation and living with less adjustment.

-Ben M.

[airsix]

QUOTE (Cloudbuster @ Aug 4 2005, 12:00 PM)

This is hard for me to explain, but I think the problem is the 90 re-orientation of the u-tabs and I think the axis of the heim joint on the a-arm needs to be parallel to the axis of the a-arm itself.

Thank you Mark. You said that MUCH better than I did. (Good illustrations too)
-Ben M.

[SirAndy]

QUOTE (Cloudbuster @ Aug 4 2005, 01:00 PM)

I figure the lower heim joint broke off while it was pointing inward, at full compression. ...

yes, you are correct with all of the above.

the problem with the stock rotation was that i could not run the bar on full soft (or close to it, or full tight or close to it) as the heim joint would bind on the top of the u-tab as well (on normal load!) ...

effectively depriving me of the use of ~ 1/3 rd of the bar ...

again, my question would be, how important is it to have the "arm" parallel to the ground?
if i could make the droplinks much longer, i'd be able to get around the problem, but then the arm would be up in an 45 degree angle with the car on the ground ...

(IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) Andy

[SirAndy]

QUOTE (SirAndy @ Aug 4 2005, 01:16 PM)

again, my question would be, how important is it to have the "arm" parallel to the ground? if i could make the droplinks much longer, i'd be able to get around the problem, but then the arm would be up in an 45 degree angle with the car on the ground ...

ok, i'm just going to answer my own question here ... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

making the droplinks longer would help getting rid of the binding problem, but in effect all i'd do is exactly the same as not using both end of the sway bar arm in the current setup.
thus limiting myself to only ~2/3rd (if i'm lucky) of the possible adjustment ...

there has to be a better solution for this ...

can i grind down the top of the u-tabs? if so, how much would still be safe?
how about a lower mount that goes around the small round support rod on the a-arm with a top that can move freely and won't hit anything?
how about a hole through the a-arm with some sort of joint on the top that can move freely?

(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) Andy

[Mueller]

how about having 2 sets of U-tabs?

[Dave_Darling]

It's tough to tell from the pics (mostly due to the rust or whatever is there), but I don't see the "broach marks" that signal a progressive failure. Then again, my main examples are from Carroll Smith's books, and those may have been spiffed up for photographing. Anyway, it looks like a one-time catastrophic failure to me.

Would it make sense to trim town the tops of the "U" to get back your full range of adjustment, once the tabs are the correct way around? Or perhaps to make them wider, and use thicker spacers? I'm just trying to toss ideas around.

--DD

[john rogers]

Has anyoner snapped a bolt off? Remember what heppened? There was a large amount of kickback and I would almost bet that is what happened here. The threaded part broke at the other extreme and the shock/force of the snapping action caused the heim joint to wedge the other way. In looking at the picture above with the A-arm compressed, that is a huge amount and I would think the inserts would have bottomed well before hat could have happened? From the picts of the car if I remember it is already sitting low and I would bet the compression is not that great, but from the looks of the suspension travel I bet there is a large amount of extension when lifting that inside front wheel. If it were me, I'd pull a strut insert to see what kind of rebound and compression the insert has?

[airsix]

I don't think heim joints are compatible with this bar's full range of adjustment. Mueller has the right idea - two or more sets of U-tabs (assuming there is room on the control-arm).

-Ben M.

ps - I think it's a good product (the bar) and I wish there was one on my car. I think we're just trying to get too much adjustment range out of this design and taking the geometry to the extreme.

[eeyore]

Even if the droplink is shortened, the mounting point need to go forward, so...

I'd take a block of steel and drill / tap it for the droplink crossbolt. Weld the block onto the top of the a-arm with the bolt hanging off in front of the a-arm body. Orient the bolt fore-aft. This gives all the articulation space necessary to get the swaybar to full soft, and solves the issue of too-long droplinks.

Problems are:
1) the bolt in in single shear instead of double. A real shoulder bolt that fits inside the mounting block would help
2) there's even more binding on the heim joint trying to set the bar to full stiff. This should not really be a practical concern, unless you are running a prototype rear swaybar (2x stiffer than stock) and 200 lbs springs.

[mightyohm]

Maybe the solution is a different diameter bar???

Avoid this whole mess...

[SirAndy]

i like the idea of U-Tabs that are simply wider plus using wider spacers.

that would give me all the room i need to use the full adjustment of the bar (with the u-tab back in the stock rotation) ...


stock: |_||_|

wider: |___||___|


that should solve the problem, right?
(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) Andy

[SirAndy]

QUOTE (jkeyzer @ Aug 4 2005, 03:04 PM)

Maybe the solution is a different diameter bar??? Avoid this whole mess...

nope, i need to step up on my rear springs some more anyways, a smaller bar would be counter-productive ...

(IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) Andy

[Demick]

QUOTE (SirAndy @ Aug 4 2005, 03:07 PM)

stock: |_||_| wider: |___||___|

Maybe - maybe not. It depends on if the hiem joint hits it's own limit before or after it hits the bracket. In this picture that Ira posted, it looks like the heim joint will hit it's limit before it will hit the bracket. So making the U-tab wider won't help.

However, the limit is partially based on the diameter of the spacers. Some spacers that taper to the min diameter necessary as it approaches the heim joint will increase the range of the joint.

Demick

[Demick]

Another consideration is that the lower heim joint range is not the issue - it could be the upper heim joint. I'm going just by pictures here, but the way that the upper joint is mounted it looks like the big washer severely restricts the amount of side to side motion of the drop link. If the top one binds (under decompression when the A-arm is extended which pulls the lower mounting point inboard), it will try to bend the drop link, and that could cause the bottom joint to fail.

Demick

[SirAndy]

here's another observation ....

the way the top hime joint is mounted, without spacers and large washers on each side, it's *very* limited in how much it can move ...

maybe adding 2 spacers like on the bottom would help getting more movement out of the top joint ...

(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) Andy

[SirAndy]

QUOTE (Demick @ Aug 4 2005, 03:20 PM)

it could be the upper heim joint.

damm, you beat me to it ...

(IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) Andy

[Demick]

QUOTE (SirAndy @ Aug 4 2005, 03:24 PM)

damm, you beat me to it ... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) Andy

Hey Andy - as long as I'm 1 second faster than you - I'm happy. Especially on the Autox course. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Demick

[SirAndy]

QUOTE (Demick @ Aug 4 2005, 03:31 PM)

Hey Andy - as long as I'm 1 second faster than you - I'm happy. Especially on the Autox course. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

don't get too used to it ... i'm still learning ...

(IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) Andy

[jonwatts]

Is our application different than a 911? I'm confused as to whether or how this is a 914 only problem.

Interesting discussion.