I had all the same problems with my Comptech sway bar. I ended up taking the bar off and pulling it apart to lube the inner portion of the bar. There was corrosion and metal shavings from manufacturing still inside the outer bar. I cleaned up these areas with a file and used a ton of grease to quiet the noise.

So far so good going on three months. Now that I think about it I never checked to see if the bar was even (bent).

-Derek

 

I recieved one of the defective bars from comptech. Instead of sending it back, I fixed it myself.

It looked to me when I took it apart, the inner bar was once together and then cut. I heard about this noise before. Although mine does not do it, I heard that putting the pipe tape between the bar and the bushings eliminated this noise. I am not sure you guys are experiencing the same thing, but I am just passing alone what I read a while back.

I run mine full hard all the time, track and street. about 6000 miles and 3 autox later....no problems. I live in New Orleans and the streets are crappy here....so I have put it through the ringer.

Chip

 

I understand that people have put some use on these, but to me it's just a matter of time before the bolts break. The way I see it, the hole will continue to elongate which will damge the bolts. You can replace the bolts, but each time they will last less time because the holes will be more elongated.

The question to me is, do you want the bolt to break during a run at Nationals? Sure stock endlinks can break, or rod-ends - but to me the design of the Comptech bar is an unecessary risk and certainly not worth the price.

The first set of bolts might last 10 months, but then the next might last only 6, and then 4... or worse yet as the holes get elongated there will be a moment of slop before the bar engages.

My advice to everyone running the Comptech bar is replace your bolts early and often.

 

If I remember correctly, the holes are reinforced with a welded "washer." The diagram above does not show this. Granted, there is instant torsion in different directions on the adjustment bolt, it is not enough to shear it. I am going to check mine this weekend, but I do not expect to see any problems.

Being a Mechanical Engineer, I like the way this bar was designed and don't really see any design problems with it. It is kinda pricey, but the demand is supporting it. Anything you drive hard will break. No matter what it is. Heck, I even broke an upper ball joint on a Hummer this past weekend....they are suppose to be unbreakable!

 

Jason S,

Have you done any calcs to back up your idea that the bolts will break? I would think you could make a reasonable guess at the peak loads they might see and the spec on the bolts are known. You were stating your concerns before the "elongated holes" were known, so I'm assuming you weren't taking that into account with your original prediction of failure. Just curious if you'd run any actual numbers or were just guessing.

-Andy

 

To calculate the shearing loads on the screw(s), we first need to establish what the loads in the anti-roll bar (ARB) are. Without a lot of time and expensive instrumentation, I think the easiest method will probably be to calculate the ARB spring rate, and then estimate a maximum body roll angle. From the spring rate, roll angle, and suspension motion ratio for the ARB we'll get to a rough cut at the shear stress in the screw(s). I say screw(s) because I understand that some folks are running two screws in the bar, say one in the #1 hole and one in the #5 hole to make it extra stiff.

First thing - calculate the ARB spring rate. I've got a Mathcad document started with a series of equations to rough out a rate for the bar with one screw and with two screws. However, I need some more accurate dimensions than those already published in the past in this forum. I've revived an old thread https://www.s2ki.com/forums/showthread.php?...?threadid=41567 to ask for the dimensions I need.

One thing I will say though, if the hole in the outer bar is getting elongated, that is probably a bad thing. First of all, it means the material is yielding, so it has been loaded beyond what the steel can handle, and in all likelihood will continue to yield and grow the hole into a slot. Secondly, since the design places the screw in double shear, something else must also be yielding (for you non-engineering types, double shear means the entire loading on the screw is applied at two separate locations, and thus 1/2 the stress at each location - 1st just where the screw passes into the inner bar, and 2nd just where it comes back out of the inner bar). I'd guess the inner bar/tube hole is also getting elongated, or the screw is bending.

For those that have elongated holes, do you notice any sloppiness on center because the bar must move that little bit before the screw contacts the hole and loads up? If you disconnect one end link, can you move the bar's lever arm up and down a noticeable amount because of the elongated hole?

Sorry for the novel, but this is an interesting little engineering problem, and I needed a break from work for an hour (or two).

 

My inspection of the adjustable bar has shown that the inner bar's holes, and welded stiffener have a larger diameter than the bolt. This allows a little rotation of the bar before the inner bar hits the side of the bolt, thus the clunking.

 

I took my bar off last night for inspection and to lube up the bushings again. The teflon tape was almost gone and there wasn't any lube on the bushings, so of course the bar was starting to creak. I consider having to pull the bar and relube normal maintenance for an aftermarket bar on urethane bushings.

On the outer bar the welded on washers looked fine and the welds were good. I didn't see any evidence of the hole in the washer or outer bar elongating.

On the inner bar the tubes that are welded in as stiffeners/guides for the pin had some problems. I didn't see any elongation of the bar or tube (at least visibly), but the welds on the ends of the tube were cracking on some. I don't think this is a problem currently, but could be one down the road if the cracks are really a sign that the material is being overloaded, and not just a weak weld.

I didn't notice that the tubes were a signifcantly larger diameter than the bolts, and thought the fit was tight enough I'd be surprised to hear a clunk from any play there. Also, I have pins at both ends of the bar (jzr "doubly whammy" technique), which leads to less play since I think the fabrication of the bar left enough variance in lining up the holes that getting the second pin to go through was somewhat difficult.

As far as the failure of the bolts, I only did a napkin calc as follows...

Shear strength of bolt = 95,000 psi (per post by rzrsedg)
dia of bolt = 5/16"

shear = strength x cross sect area = 95,000 x .077 = 7286lb

With one pin in the bar, it's bearing the shear in two places so that should be 7286x2 = 14572.

How much load that is at the end of the arm of the bar depends on the ratio between the arm length and the OD of the inner bar. Since I'm at work I'll totally guessing the length of the arm (effective) to be 10". The OD of the inner bar is 1.25", so the moment arm at the interface of the outer and inner bars would be 1.25/2 = .625".

So, the load on the end of the bar arm would be (by this simplistic analysis) .625*14572/10 = 910.75 lbs. Frankly, I don't have the faintest idea what loads are actually being applied, but 910lbs seems pretty far fetched. If you are running two pins in the bar, it would be twice that number.

Of course, as the bar ages and fatigues, welds possibly crack, etc. the numbers will change. Considering the bar may not be stiff enough even with the 2 bolt approach, this may be a moot point.


For reference, I've probably put about 20 days of autoxes on the bar this year, as well as leaving the bolts in for street miles.

-Andy

 

Andy, your observations on the cracking and other wear coincide exactly with mine. My theory on the elongated holes came when I put the same bolt in the #3 and #4 holes and noticed less slop. From that I figured the hole had grown somewhat in the #5 hole, though it's possible that was just a manufacturing variance.

Does your bar clunk Andy?

 

Jason,

The cracking on the weld was definitely more pronounced on the 5th hole (stiffest). I will look again tonight when I put the bar back on to compare the holes as you did. From memory, I don't think the very slight amount of play in the fifth whole was due to the tube deforming, but probably play from the cracked weld. The welds there look to be pretty small, especially after being ground down so as to not interfere with the outer bar.

I didn't have any noise from my bar until about a month ago when creaking became more noticeable (hard to hear it over the annoying Spoon exhaust). Like I mentioned, I would attribute all the creaking to just needing to relube the bushings. No clunks.

-Andy