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

[njccmd2002]

it looks like the rotor is dead center. can you show a pic of the mounting bracket and the tabs on the hub. sideways to see if any of those two are bent. Does your hub wobble? that is weird..

[Langing]

it looks like the rotor is dead center. can you show a pic of the mounting bracket and the tabs on the hub. sideways to see if any of those two are bent. Does your hub wobble? that is weird..

You wanted pictures that might show the bent ears. This is coming late because I just finished removing the knuckle, and before that most shots were not all that convincing. The amount of linear movement traversed by the bend is not at all large, so the bending is hard to "see" visually. It can be seen, but while looking at it you tend to ask yourself "Is it really bent?"

First, let me show the best of the pics taken before removing the knuckle that might provide acceptable evidence:



In that shot I held the steel ruler flush against the top ear so the ruler was in the plane of the mating surface at that ear. If you look hard, you might be able to tell that the other ear does not fall in the same plane (i.e., there is space between the lower ear and the ruler).

The next was also taken prior to removing the knuckle. It was an attempt to let the steel ruler be held tightly flush against the mating surface of the lower ear, and I believe it shows a rather significant angle of departure from what it should be like if it were truly parallel to the hub. Still, I agree that it leaves some doubt, but i am putting it in here to be complete:




I didn't believe that would satisfy your curiosity, so after I removed the knuckle I took another pair of photos that show the steel ruler laid out squarely above the mating surfaces of the two ears, and tried to let the pic show the point at which the ruler crossed the backside of the hub so anyone might extract the exact measurement and do the math to discover the discrepancy between the two ears.

First I will show the top ear with the 15 cm point of the ruler aligned with the back side plane of the hub:



15 cm mark is directly over the back plane of the hub (you have to trust me on that). But knowing that, you can pretty easily take the measure of the surface of the ear from the back plane of the hub. I read it off as 19.8 cm (198 mm), so 19.8 cm - 15.0 cm = 4.8 cm (48 mm) between the back side plane of the hub and the mating surface plane of the ear. 48 mm = 1.88976 inches. Associate that number with the upper ear.

Next is a shot of the lower ear, with the 15 cm mark of the ruler aligned with the mating surface of the lower ear. Now the back side plane of the hub aligns with the 4 and 1/4 inch point of the ruler.



Here we need to work in inches. As best I can determine, the inch mark directly above the 15 cm point is 6 and 3/32". Since at the ear we have 15 cm = 6 and 3/32", and at the hub we measure 4 and 1/4 " = 4 and 8/32", we can subtract 4 and 8/32" from 6 and 3/32" to get 1 and 27/32" = 1.84375 inches. Associate that number with the lower ear.

Subtracting those numbers, 1.88976 inches minus 1.84375 inches shows a difference in the two ear distances from the back plane of the hub, which is 0.04601".

Now that doesn't seem to be a large difference, however, when I was first measuring the distances from ears to the (then mounted) rotor, I discovered that the perfectly aligned left hand wheel both ears measured 21/32 inches, whereas the two ears on the bad right hand side measured 20/32 inch (upper) and 18/32 inch (lower). That gave me a difference between the two ears of the bad right side of 2/32 inch, and 2/32 inch = 0.0625". My new calculation based on measurements to the back side of the hub gave me a difference between the two ears of 0.04601". Those two measures of the difference in distance from the ears to the rotor and the ears to the hub are only 0.01649" discrepant.

But that isn't the most important thing to understand. What is most important is the comparison with the good left hand measures that I found when measuring from ears to rotor. In the case of the left hand side, the two ears were measured to be perfectly the same, both were 21/32". In the case of the right hand side, the two ears were both measured to be less than the ears on the left, but the top right was just 1/32" less (20/32"), while the lower one was 3/32" less (18/32"), indicating that both right side ears were bent, but the lower ear was bent more than the top ear.

You might as well get the chance to take a look of the knuckle ears with respect to the hub without any ruler interfering with your view. Can you see any bending going on? I believe that I can, but then I still hesitate. What say you? How about this evidence for 'bending of cast iron'? Are you now a believer, or do you still doubt climate change?

Hey, believe me, it's the best I could do!



Now poor Betsy is on life support while I go on junk yard adventures attempting to secure a replacement knuckle for her right foot.

PS: I welcome being informed of any arithmetical errors.