Right front steering knuckle caliper mounting bracket tabs bent Options

[Langing]

ADDED NOTE: I am not a trained auto mechanic; I try to DIY whatever I can to keep my 300,000 mile Celica happily running. Thanks to a wise comment below, I now see that making the statement 'my steering knuckle is bent' is oxymoronic on its face. The steering knuckle is made of cast iron and it is well known that cast iron does not bend (though exceptions exist). Cast iron acts more like a brick which cracks when a transverse force is placed between its two ends. Nonetheless, there exists a situation with my right front caliper mounting bracket, in conjunction with the disc, that causes it to seem very much like the mounting tabs on the steering knuckle are bent. I am seeking the true explanation for this (at least apparent) bending of a cast iron part. It would be great if some expert in front suspensions would stop by and explain my observations set out below, and pinpoint my problem. Until then, I dare not change the title of this topic; what cannot be is.

2nd ADDED NOTE: After much on-line research, I have been convinced that bending of the tabs (or ears) on steering knuckles is more common than most people believe, despite the fact that "cast iron doesn't bend." Not sure what that has to say about steering knuckle castings, or what exact metal they are made of, but evidently it does happen. See my posting near the end of this thread.

94 Celica ST Coup 1.8L Manual:

Installed a new rotor (measures 0.986"; manual specifies 0.984" maximum). Rotor run-out minimized; much less than maximum. The caliper mounting bracket bolt tabs/ears on my right front steering knuckle are slightly bent toward the rotor (worst is the lower tab; 3/32 inch; shown in following photo). This causes the caliper mounting bracket to be misaligned so much that it interferes with my new rotor.




It has severely scratched the last ¾ inch of the rotor (to the outer rim), during short test drives (less than 1000 feet). Of course it made a lot of noise, but it was the first time I had ever done a job like this and just wasn't aware of the severity of the problem.



What is the best way to fix this problem?

Should I attempt to bend the steering knuckle tabs? Is the steering knuckle a cast iron part? Should I die grind the proper alignment into the caliper mounting bracket surfaces where they meet the steering knuckle tabs? Should I buy and install a new steering knuckle; they cost around $200 and require a lot of work to install?

This post has been edited by Langing: Jun 1, 2014 - 4:44 PM

[Langing]

Thank you for commenting. What you say is true. . . it is HIGHLY unlikely. . .

I have checked the installation again and again, and there is nothing that stands out to me as being done incorrectly.

At first I also agreed with your comment that it MUST have been overly aggressive cleaning of the caliper mounting bracket. Indeed, I did use a die grinder for cleaning, but not anything that would remove more than a slight amount of surface metal. It was a relatively soft "polishing' material in the spinning wheel and it was used with buffing compound. I was so convinced that this MUST have been the case, that I began to easily grind away at what I considered an angle across that surface that was 'deeper' on the inner side of the bolt hole, looking for an angle that would compensate for the misalignment. I eventually succeeded in getting to an angle where, when I torqued down the bolts, I could spin the rotor and not hear the scraping sound. That was not close to a fix. Let me show you the moment when I finally believed that it was going to work (taken when I still believed this MUST be the problem):

https://www.dropbox.com/s/djc2ap689j1jpoo/IMG_0740.MOV

All that being said, since it was taking a very long time, being patient as possible, just to get to that point. I told myself to re-evaluate, looking at what else might cause this much of a misalignment and that's when I looked up at the steering knuckles and even visually they didn't look right. So, I measured (with a good steel ruler) the distance from the inner face of each tab (dog-ear, ear, whatever they are called, that the bolts go through) of the steering knuckle and found that the top tab was 20/32" from the rotor surface, and the bottom tab was 18/32". Then I went to the left front and took the same measures (top = 21/32" ; bottom = 21/32"). When talking about the impact of a 3/32" difference at the lower tab, if it is bent, then the plane of the mating surface (of the tab) is changed as well as its distance from the surface. A ruler isn't good enough to detect that. What's more, the left caliper sits perfectly symmetrically over its rotor and pad sandwich, leaving what (looks to me) the exact same amount of free space for the rotor at all four points of the caliper mounting bracket. There is no scraping noise at that wheel, only the soft sound of the pads rubbing against the rotor.

Hey. . . I agree with your comments, and I very much appreciate your asking me to re-evaluate the situation, looking for some problem other than a bend in the steering knuckle tabs. After all, it is cast iron (you are the first to verify my belief), and cast iron doesn't bend. I've seen a good thread on another website that triples the votes in this line of reasoning:

http://www.practicalmachinist.com/vb/gener...ibility-138869/

I will take it as my next assignment to re-evaluate the run-out of the rotor, to make sure that it is still perfectly perpendicular to the axis of the spindle. I cannot think of anything but the following as possibilities:

1) messed up mating surface on the caliper mounting bracket (that is HIGHLY unlikely, and almost ruled out, judging from the experiential efforts I have put into working this problem assuming that WERE THE CASE -- In cleaning the metals I simply could not have done that much damage using my particular approach),

2) rotor spinning in a non-perpendicular plane (I'm going to re-check the run-out this afternoon),

3) tabs on the steering knuckle bent (by 20 years of stress applied by a poorly attached caliper? or failure in the casting process? or who knows? .

4) something else improperly installed in the wheel assembly that has caused an apparent bending of the steering knuckle tabs. I will do what I can to check this when I take another look at the run-out of the rotor. Several years ago I did change out all of the struts. Today this car has over 300,000 miles on it.

Again, thanks so much, I do appreciate your comments.