broken steering knuckle bolt

[Pete Sprenger]

At my last lapping day the rear steering knuckle bolt on the driver's side broke after 5 hot laps. I have MSA bump steer spacers and used the bolts they provided (grade 5). I was running on my Kumho V710s, and I have a fully tuned coil-over suspension.

 

I removed all 4 bolts and replaced them with grade 8 bolts, but I am wondering if the bolts broke because of the bump steer spacers. Has anyone else experienced this? Do most racers, autocrossers go without bump steer spacers?

 

Thanks for your input,

Pete Sprenger

1972 240Z

[jt1]

Lots of people run the spacers without issues. The bolt could have been a substandard fastener, it could have got loose, it could have been over tightened, or you could have hit something. Look at the parts closely and see if you can see any signs of movement.

 

Can you post a good closeup picture of the end of the broken bolt?

 

John

[74_5.0L_Z]

I have those spacers (and grade 5 fasteners) on my car. I think I'll replace those fasteners now just to be on the safe side. Thanks for the info.

[Pete Sprenger]

We (my brother-in-law was riding with me) were going about 75 mph through a high g right hand sweeper when we heard the bang, then something bouncing along under the car. We knew immediately that something had broken off the car and suddenly I had very limited steering input. Luckily we were at Bremerton Raceway, which is an old runway and the course is outlined by cones, so I simply cut the course, and then moved way over to the side of the runway. If I went over 30 mph on our way to the track exit, the car shook violently.

 

Neither of us saw anything on the track. I could post a picture of the bolt, but it wouldn't show much since I drilled a hole in it to try and use an easy out in an attempt to fix it at the track. Once we finally gave up and went home I welded a nut to the end of the bolt that stuck out the top of the knuckle and turned it out through the top. I checked the other bolts once we were at home too and I found that the front bolt was snug, but not up to the proper torque setting, so my guess is that the rear bolt had worked loose. I had checked all the rear suspension bolts prior to the event, but didn't check the front since I had checked it fairly recently. Lesson learned, check everything every time!

 

I am thinking of converting to the Arizona Z Car steering knuckles with bump steer spacers built in. It is a one piece unit, which may be stronger and it is aluminum so it should be lighter too. Does anyone have an experience with these pieces?

 

Pete

[jt1]

Sometimes, you can tell how a fastener failed by the appearance of the broken end. It's possible to identify a bending failure, shear failure, and tensile failure, and sometimes an internal flaw. In this case, a tensile failure is probably overtightened, shear is hitting a curb or hole, and bending is a loose bolt.

 

The AZC knuckles are nice pieces. I have a set for my mythological track car, but haven't actully used them yet. Tom (mayolives) and Mark both have them on their track cars, and they are faster than me.

 

John

[johnc]

I've never been happy with the fasteners that come with that kit. They are class (not grade) 8.8 metric and should be class 10.9. I always throw away those fasteners and use known good quality stuff for reasons you just discovered.

 

Here in SoCal we've got two tracks with very fast corners (Willow Springs and Cal Speedway) and both tend to focus the mind on suspension build and parts quality.