Rear Drop Link - Sheared bolt go case hardened or not

Something didn't feel right. Inspection of rear suspension found this: Sheared top bolt, we used what was supplied with new Tarret drop links. It is supposed to look like this: Tarret sent new bolt and taped spacer right away. The rest of the bolt is still inside the welded not on the Bilsten B8, waiting on right angle drill to removed with ez-out, I hope!! My question is should all of these bolts be hardened or not? Why did these happen? This car is daily driver, Autocross, DE and once a year drag strip. Still it should've held up.

Same thing happened to me recently only with OEM drop links. Taretts now on & surprised to see this. How much use did you get out of them before the failure?

That spacer setup really cantilevers the bolt doesn't it? Does Tarret provide a torque spec for this bolt? And did you follow it? Seems like if that bolt loosened a bit it would break soon after.

Just for interest sake are there any markings on the head of the bolt?

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8000 miles on street 3 Autocross events 5 Track days 2 Drag times

Post a pic of the bolt head, they have markings which show what grade steel they are made from

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Wow, I am glad you asked about the bolts. I got them out to take pics, and looked at the length, and it appears that my bolt also loosened and then snapped. I read on another unrelated thread, that this bolt loosened and fell out. So what does this mean, should a certain type of loctite be used? Really uncertain on repairing method.

Grade 10.9 is a heat treated, high strength bolt. Judging by the beach marks on the fracture surface, it looks like cyclic fatigue. I'm guessing the joint wasn't torqued properly or lost preload for some reason.

Agree with Coopduc. On installing I would torque to spec for a 10.9 ( 12mm ?) bolt adding a few drops of 271 red Loctite to clean threads.

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I had a local shop with a fella who is very experienced in suspension do the original install. I will find out if in fact he used the proper torque for install. I am not clear of what your seeing in the sheared surface, as the lenght of the bolt clearly shows it had backed out almost 2/3 of the threads that are supposed to be in the strut. That is judging now, but will be more conclusive when the broken portion is removed from strut. Are you thinking the torque damage was done at install, and then when bolt backed out, it snapped at the stressed point?

In simple terms, it looks like the bolt backed out, subjecting the bolt to high bending loads, and over time caused a fatigue failure, similar to what happens to a paper clip when you repeatedly bend it back and forth. Why did the bolt back out? Possibly because it wasn't adequately torqued, or more accurately, the joint wasn't adequately preloaded. Realize that the goal when torquing a bolt is actually to stretch it. It's the amount of stretch than creates the clamp load that keeps the joint tight. That's why critical joints specify a "torque + angle". The torque ensures the mating parts are in contact with each other and the angle is what creates the stretch, via the geometry of the helical threads. Another possibility is that some other component in the joint yielded (crushed) causing the loss in clamp load, with the same result. Hope this helps.

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Everything you said makes sense, except the geometry part. This bolt takes all of the torque from the sway bar doing it's job, isn't it, or am I not understanding where the force from a sway bar goes? BTW, thanks for your input David

The force from the sway bar is transferred through the bolt into the strut. The clamp load of the bolted connection is what prevents the bolt from bending. When that clamp load is lost then the bolt sees bending, like the paper clip example, leading to the failure.

Red threadlock and decent torque might have prevented this

That’s a high strength bolt. It’s not common for them to break. Install at OEM torque. Make sure the large diameter of the spacer is against the bracket on the shock. Also make sure the bolt is tightened all the way, and not hitting the shock. It shouldn’t break again. Blue Loctite if you’re worried about it coming loose. Make sure the swaybar is not contacting the toe link, it looks close in your pictures. Ira

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The bolt is strongest in tension, being pulled along its length, if the bolt backs out a little and there is a side load on it, especially cyclical it is much weaker. The threads also create a great place to start a stress crack across. You could replace with 12.9 bolts but if there are cyclical side loads on they might still crack the same.

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Ira, First, thanks for getting the bolt and spacer shipped to me quickly, I appreciate it. Second, this is a picture of the left side, is what your referring to the larger diameter side of the spacer goes against the bracket on the strut? Third, darn it, I just went to parts store to get some titanium drill bits and picked up Red 271 Loctite , should I get something different? Forth, are you thinking, maybe lengthening both side drop links for more clearance? David

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Chris Is the 12.9 , is that what track cars usally use instead of 10.9? I am not sure what the sway bar is doing when the car is launched from a standing stop, ie. at a drag strip. The new Porsches have launch control, my car has a Evoms Stage IV tune with a 5k launch. The car only squats for a very brief time, then accelerates smoothly with no wheel hope, previously, before Techart Springs, Sway bars and Bilsten B8s, there was a good amount of wheel hop.

During straight line acceleration, no force is generated by the sway bar, no matter how fast or hard, or amount of squat. The only time a sway bar generates any force is when the car leans in a corner.

Yes, it looks correct in the picture. Red Loctite will work, but it will be difficult to remove it. Just use a very small amount. Lengthen the link if needed to insure the bar doesn't touch the toe link. It looks close in the picture. Contact there can generate a lot of force. I have longer links if needed. Ira

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Thanks I will update after the repair

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The saga continues Had the car on a lift today, over an hour with right angle drill. The titanium drill bits worked ok, but the EZ out would not grab the broken section of bolt left in the strut. Considered drilling larger and retap but the bit keep sliding and would of started to obround the hole. Made the decision to pull the strut out and attack it out of the car.

Find a small brazing tip and heat the bolt remains and only the remains, let it cool. Once it has cooled off it should come out. If not repeat the process. Can be done in place if you are careful.

Interesting that today my mechanic and I put new rear drop links on my, new to me, 2001 C4. Trying to get rid of a clunking noise. Well....the bolt to the strut was sheared and the link just clunking in the hole. TRW links. Don't know how old they were. Oh and yes the clunk is gone and rear is now solid. Love this car....

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Yikes, this problem seems more common than I ever thought. Was the broken piece stuck inside the strut?

Yes the broken bolt was stuck in the nut that is welded into the strut bottom with no room to drive it through. My mechanic used an air hammer to break the nut and bolt remnant off the strut. Easily done as the strut nut is just spot welded on. Then we just used another nut to attach the link. This was the drivers side. Passenger side was fine but we replaced both.

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So he must have gone up through the hole in the bottom of the strut bracket, in order to punch off the nut? We considered that same move, from what can be seen with small mirror, is that there is two spot welds on the nut. How difficult was it to break off? Thanks David

Exactly! Mirror and light then punch it off via the bottom. Popped of surprisingly easily with the air hammer.

If it were my car, I'd try less destructive stuff first and progress to taking that captive nut off with a chisel. Once the strut is out of the car and you can put it in a drill press, you have more precision options. I'd try heating and cooling - especially if the original install involved red loctite (it needs a lot of heat to break), and even if it didn't have loctite, heating and cooling can cause corrosion to let loose. If that didn't work, I'd try to let some good penetrating oil soak for a couple of days, then go at it with a properly centered LEFT HAND twist drill. You get multiple benefits - if it catches, sometimes is spins the fastener remnants out. Make sure you use a good sharp drill with cooling lubricant at slow speeds appropriate for metal - the last thing you want is the metal to work harden. Even if it doesn't spin out with the drill, you can still continue to drill until you are at the threads, and then chase them out with a properly sized tap. 9 times out of 10 you are done there. Worst comes to worst you can knock the captive nut off and start fresh, with either a loose nut, or a nut tacked to the inside of the housing. Oh, and for my last two cents - throw those easy outs in the trash. They cause more hassle than help. In my experience, they're hardened and brittle and prone to snap. If you've ever had one break one off in a snapped bolt and had to drill it out you know what a nightmare they can be.

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Our last attempt was with a left hand drill bit, it must have been a little dull, it started to walk and did not want to oblong the hole. Appointment for Tuesday is scheduled to pull strut, I really don't want to go through the expense of removing/installing and then another alignment. Yes, I have had the pleasure of breaking an ez-out, you can really come up with some creative cruse words when that happens.