Important Heads Up!

[57imposter]

I have been running a Wurth-It power rack and pinion for about 10 years with no issues. Friday morning I went to exit the Freeway and the car did not turn properly to hit an exit.. Scared the crap out of me! A road side check revealed nothing but a called a Roll Back and hauled it home. I found that both of the bolts that hold the Tie Rod bracket to the rack were backed off. These were installed to the proper torque and safety wired! I cut the safety wire and one of the bolts fell out. It had sheared off right at the top of the threads in the rack and the only thing preventing it from falling out on the road was the safety wire.
  I am posting this to alert anyone running this or a similar system to carefully check those bolts and depending on the miles driven to maybe even replace them. I know both of mine are new! If this bolt had been able to fall out going down the road, there would be no saving the car or, quite possibly, myself.

[Wirenut]

Wow, pretty scary. I?m running that same set up, I have mine with thread lock on the threads and wired but never thought about them sheering off inside, especially that far in. Glad you?re safe, thanks for the heads up.

[Ford Blue blood]

I had the nearly same thing happen to the same type rack install on a 51 Chevy.  Good friend wondered why his car felt "funny" when going straight on the interstate.  Did some checking for him and found those same bolts loose.  Pulled both, red lock tight, torqued to spec and he was happy.   About two years later he complained again and asked if I could check it out.  Sure enough, both bolts had backed out and were loose.  Did the same again but this time I hit both heads with a spot weld.  Never heard back that the spot welds "fixed" the problem, car has been sold and is out of state now.

[57imposter]

When you look at the bore for those bolts, they are a bit oversized down to where the threads start. The bolt pictured, sheared off right at the top  of the threads in the rack. The amount of the bolt left is not supported by a snug bore any pressure on the bolt will have all that length of leverage to shear the bolt. I kinda patched mine together with one new bolt to get to an event Saturday night. It's going to get two new hex head bolts today and I am going to tack a piece of flat stock between the heads. That should get me thru the summer and I am taking this whole system out in favor of a new Borgeson power box set up.   Man, It's always something!

[RICH MUISE]

Wow......what coulda been!! Glad you found out the easy way.
Thanks for the head's up. I was surprised to see your bolts were socket head cap screws..........are they even available in grade 8?
When I removed and replaced my rack recently, the old bolts were still tight. I'll recheck them soon though, I just put 730 miles on the car yesterday/today.
Sheared rather than loose is even scarier, wonder what caused that. You obviously were able to get the remaining stub removed.
How were they wired? is the bolt in the pic just turned so we can't see a drilled hole?

Wow, something weird just happened.........I just went back to relook at the bolt and when it opened, I was looking at a sheared bolt for about a second, then it changed to a full unsheared bolt. WTH? May be too many hours on the road yesterday.

[gasman826]

I was told allen head cap screws are grade 8.

[57imposter]

The allen  heads came in the kit. we used regular stainless safety wire. I will say that my kit was an early one. I bought two 12X 1.25X 70 mm with an 8.8 rating. I was told by the smartest mechanical I've ever known that if you are looking for shear resistance that something closer to a grade 5 is preferable since a grade 8 is more brittle. I'm sure there are many opinions on this but I took his word for it. I also took some 18ga. sheet metal and made a double lock plate.  I made the tabs long enough to go up the flat on the head and to wrap over onto the head so if I have a repeat of the problem the broken bolt won't be able to fall out. 

[RICH MUISE]

OK, for sure I'm not a metalurgist, but drawing on my 20 years in areospace machining.....
Gotta disagree with Gary on the shcs's being grade 8 across the board. That is a style of screw, not a grading. They come in many different materials, even plastics, and I'm sure the ones I've seen at Harbor freight and hardware stores made in China are no where near the quality of a grade 8. With that said, a "standard" shcs is tougher than a grade 8 screw, but those are industrial quality screws made to military specs. "Standard" has a specific meaning here. check out www.mcmastercarr.com for info.
Also gotta disagree with Doug's friend. I think he is confusing heat treating for hardness and the heat treating they go thru to arrive at other specific needs. I am going to assume here that a grade 8 bolt uses a higher grade steel that is heat treated for toughness, not harness and is tougher than a grade 5 bolt. Big difference. I understand his line of thinking, but I do believe a grade 8 bolt is treated to be tougher, not harder, and toughness is measured by shear strength.

The racks used in our kits as far as I know are pretty much the same rack, with minor variances,regardless if made by Wurthit or John Sparks. I have no clue what Unisteer uses. I just cut the boot on the old rack I just replaced to see what was under there. I knew something was moving around, but couldn't tell what.
The main shaft of the rack is round, has the two threaded holes we're discussing. Those two holes are counterbored about 1/8" deep. The clearance "holes" the bolts pass thru are not connected to the shaft. They are two bushings encassed in a plastic block that snaps into place. They can easily be unsnapped and slid back and forth. The two bushings, when the block is in place, locate onto the counterbores. So, the bolt didn't really shear off "way down in the counterbore", It sheared at the top of the threaded hole in the shaft. It's still mindboggling how one bolt could shear without the other shearing as well.
It is posible for that block to be out of place allowing one bolt to be tightened, but the other bolt actualy being guided pass the end of the large diameter of the shaft.

[djfordmanjack]

those sheared off bolts are horrible! Great move giving other guys a heads up.
concerning toughness and hardness, Rich. both is the case.
the tougher the bolt gets, the harder it also gets.
Going back to metric specs the grades would be 4.6 , 5.6, 8.8, 10.9 and 12.9
the first number is the ductile strength of where the material tears/ breaks/shears. it means 400, 500, 800, 1000 an 1200 Newton per square millimeter. the second number gives the percentage at which the steel stops being flexible and starts a permanent deformation without breaking yet.
it means that lower grades  start permanent deformation at 60% of ductile strength ( =.6)  mid grade at 80% (=.8 ) and high grade at 90 % (=.9).
That means a high grade bolt will not only have extremly high ductile strength before breaking or shearing, and have a nearly as high value for starting deformation (90%). that means only 10% are left for the deformation, which nearly equals to snapping of a hardened part. on a low grade bolt you have 40% left of slow elongation or bending, which equals to a soft, non hardened steel.
Of course this is just a very short and non scientific summary IMHO.

In any case, I believe a steering rack installation like this setup either calls for silent bushings, shear bushings or so much bolt torque that surface friction will keep it in place. shearing off such a bolt , IMHO, must be caused by loose mounting ( not necessarily by intention or accident, but by design) or overtorquing.

[RICH MUISE]

great info, Guenter, thanks for the input.

[djfordmanjack]

You're welcome. I thought it was of interest to you American guys because I was educated in the metric sizes and strengths which some of you might not be aware of so much.

[RICH MUISE]

Is the grading universally similar so that a grade 8 bolt here would be equivalent to an 8.8 on the other side of the pond?
On a side note.........a new member has joined with a message to me that he has some info on a rack for our systems that has more rack movement for decreased turning radius.

[djfordmanjack]

Is the grading universally similar so that a grade 8 bolt here would be equivalent to an 8.8 on the other side of the pond?

Rich , no. the US 5 grade (3 lines on bolt head) equals the 8.8 , as far as I know. this is a medium strength bolt.

check out this table at bolt depot. has lots of info. BTW they are a terrific source for hard to find hardware in MA. I have bought from them several times, very satisified.

https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

[lalessi1]

those sheared off bolts are horrible! Great move giving other guys a heads up.
concerning toughness and hardness, Rich. both is the case.
the tougher the bolt gets, the harder it also gets.
Going back to metric specs the grades would be 4.6 , 5.6, 8.8, 10.9 and 12.9
the first number is the ductile strength of where the material tears/ breaks/shears. it means 400, 500, 800, 1000 an 1200 Newton per square millimeter. the second number gives the percentage at which the steel stops being flexible and starts a permanent deformation without breaking yet.
it means that lower grades  start permanent deformation at 60% of ductile strength ( =.6)  mid grade at 80% (=.8 ) and high grade at 90 % (=.9).
That means a high grade bolt will not only have extremly high ductile strength before breaking or shearing, and have a nearly as high value for starting deformation (90%). that means only 10% are left for the deformation, which nearly equals to snapping of a hardened part. on a low grade bolt you have 40% left of slow elongation or bending, which equals to a soft, non hardened steel.
Of course this is just a very short and non scientific summary IMHO.

In any case, I believe a steering rack installation like this setup either calls for silent bushings, shear bushings or so much bolt torque that surface friction will keep it in place. shearing off such a bolt , IMHO, must be caused by loose mounting ( not necessarily by intention or accident, but by design) or overtorquing.

I agree with Guenter. The bolts provide force to clamp things together so that friction becomes the force that acts to function. The bolts failed because they loosened over time perhaps they were not properly sized and did not provide enough "clamping". They could have been over torqued or under torqued by specification as well. The bolts can loosen over time even if they do not unscrew they can still stretch by repetitive cyclical loading.

[john2747]

   I am a new guy making my first post on this site.
   Richard; ok some information on steering racks that have more travel than the cavalier rack.During the mid 1990's GM apparently owned SAAB,their cars used two different rear steer,center take off rack's from 1994-98.The SAAB rack that I mounted
on a 57 t-bird was the aluminum bodied rack that ZF corp.manufactured for SAAB.The other rack is steel bodied and is called the
'saginaw',likely produced by GM.Both rack's have 6 1/4" of travel.I've never measured the travel of a cavalier rack,but others say
it's about 5 1/2".I would not be surprised to find that GM modified the cavalier,to get more travel,and it's possible they both use the same mounts.If their mounts are the same they could be swapped by just altering where the inner ty-rods are mounted.I put
a small article in y-block mag. issue #116 about SAAB steering racks.Both racks are on e-bay.Some investigating would be
necessary to determine if they can be interchanged.I did view a steel bodied rack at a local auto recycler it was bolted to the firewall of a SAAB 900 sedan.3 turns lock to lock.The work you have in your car sure paid off ...john2747@telus.net