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A new one for me...


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The Set Up:

 

For the last year or so I have had a slight clunk in the front right of the '47 Desoto. Usually I only hear it when I am just starting backing out of the garage. I have inspected the suspension and could not come up with a thing. Now, I did not take any of the suspension apart.

 

The second odd thing is that I have been getting a fairly good outer Camber wear on the that same front right side. A lot of camber wear.

 

Today:

 

I pulled off the right front tire today to swap on a better used tire. I am looking into having wire wheels made for the car. Read my wheel hell thread about why.

 

So, since I have the wheel off I decided to pull the caliper slider-mounting bolts and have a good look at the rotor and the pads. I stick in the allen wrench and give it a light tap with a hammer. I use a lot of anti-size compound to make sure those bolts come out nice.  As I turn the wrench I notice that the end of the bolt is not moving.

 

Oh Crap!

 

Turns out that the bolt sheared on the last thread. Wow, I have never seen that.  No other marks. Nothing looks bent on the threaded plate. It just failed. Standard GM D52 single piston caliper with HP slider bolts with the built in bushing.

 

Wondering:

 

I am now wondering if that top bolt (at about 11 O'Clock) failed, could the caliper cause the brake disk and hub assembly to move enough to cause a camber change when braking and that is what is causing the outboard saving of the tire?

 

I have not wanted to do a alignment check until i get new wheels and tires...

 

This is a new on one me I can tell you. I am going to have to have a drink or two and see if I can get this into my head in 3-D and "see" the load path.  If it has done so, I also wonder if it moved the spindle over time (bent it) and that is causing the camber shaving.

 

See something new every day when working on the old cars.

 

James

Edited by James_Douglas
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That break location is typically indicative of the metal yielding due to overtorqueing.   Not necessarily over spec, but a bolt that is under spec and failed at its weakest point.  That is especially true of bolts with cut threads vs rolled threads.    lots of incidences of 'off shore' bolts not meeting strength specifications for the marked grade.  grade 5s that are not even good grade 2.   

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It has been some years, but I think these were high performance picked up from Jegs or Summit. The stock type uses a sleeve on the HP units the sleeve is machines into the bolt-pin.

 

The type that broke looked like : https://www.wilwood.com/Hardware/BoltKitProd?itemno=230-0619

 

The stock ones use a sleeve like: https://www.jegs.com/i/Wilwood/950/230-11529/10002/-1

 

Very odd....

 

James

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It's unlikely that a loose caliper would cause a wheel misalignment. But it could be the source of your 'clunk'. Since the hub is exposed, have you checked for excessive movement in the wheel bearings? Loose wheel bearings could cause an alignment issue as well as strange noises. 

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I can't see your caliper bracket from here, but most, if not all have the caliper fitted into a big 'slot' in the bracket.  So, all the braking torque is transferred from the caliper directly to the bracket.  The bolts are just guides.  Only if there is too much clearance in that 'slot' to caliper fit would be bolts be loaded during braking.

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It would be worthwhile looking for pins made of stainless or hardened steel. The alloy designation sorta makes me wonder if the supplier sourced these parts from the big red garbage dragon in the other hemisphere. I insist on USA made fasteners even if I have to buy them separately. 

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8 hours ago, kencombs said:

I can't see your caliper bracket from here, but most, if not all have the caliper fitted into a big 'slot' in the bracket.  So, all the braking torque is transferred from the caliper directly to the bracket.  The bolts are just guides.  Only if there is too much clearance in that 'slot' to caliper fit would be bolts be loaded during braking.

 

As was mentioned by another poster in me Rusty Hope swap thread, that bracket is supposed to carry the load, not the pins.  If the pins carry the load they break.  I had a heck of a time finding the specs on caliper to bracket clearance. 

 

 

caliper clearance.jpg

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Cannot say what brand your caliper pins were originally but the the example you show is Wilwood Brake brand which makes many aftermarket disc brake kits from mild to Wild with many for racing purposes.

 

Those pins say they are for racing use without use of the sleeves that were factory added ? to ease movement of the calipers and increase the alignment float of  the calipers and pads, etc.??

 

But even under that race use the pins are still a hardened grade 5 steel, I am sure not of Chinese origin (I assume as these are all made in So. Cal. USA).

 

I have heard that their tech line is readily available to call and is quite friendly.  I tried once myself recently and found it so.

 

 

DJ

Maybe a call??

 

 

Contact Wilwood Disc Brakes – Wilwood Store.htm

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I would have to dig to figure out where I purchased them. It was either Wilwood or Jegs or Summit.

 

Keep in mind that I do not put them in to tight as I do not want to take a change that the threaded holes in the mounting plate get messed up. I also use a lot of anti-sieze on them all the time.

 

The pins do wear from the sliding on them. They can pick up a groove.

 

I have been using this setup since about 2006 or so. I replaced the factory style with the sleeve with the "hardened" version to help with the sliding wear. 

 

A close look at the pin shows a narrow band of rust about a 1/16 of an inch below the bolt outer circumference. Like drawing a line from 10 o'clock to 2 'o'clock.  That rust band is about 3/32 wide.  What that tells me is that the thing cracked at the thread line but not all the way. Then it rusted for some long period of time, then it fractured and failed completely.

 

It could be just a bad bolt. I replaced it a cheap auto parts unit. I am going to replace the other side just for grins. I will keep and eye on it. I will also carry a spare just in case there is something wrong.

 

James

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On 7/13/2022 at 5:05 AM, Sniper said:

 

As was mentioned by another poster in me Rusty Hope swap thread, that bracket is supposed to carry the load, not the pins.  If the pins carry the load they break.  I had a heck of a time finding the specs on caliper to bracket clearance. 

 

 

caliper clearance.jpg

This is something I want to look into. In my case with a steel plate, there is no stop further out on the caliper. In this photo it shows the stop as being at the center of the caliper.  Now, is it possible that if the stop is just near the inboard side (steel plate) AND the clearance is too much that the caliper will cock slightly at the top?

 

If that is the case then the upper pin will get loaded and the rotor will see a side load pushing out at the top which would induce more camber which would account for the tire shaving. With a cracked pin, that would induce even more camber...even 1 degree would cause my tire shaving....

 

Hummm.....

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2 minutes ago, James_Douglas said:

Now, is it possible that if the stop is just near the inboard side (steel plate) AND the clearance is too much that the caliper will cock slightly at the top?

 

Exactly right.  One of the members here was/is a GM tech and that's what he said would happen if there was too much clearance.  The bolt would eventually break as it is not designed to handle any braking loads.

 

As for the effects on camber, I dunno.  Possible I imagine but I never really looked into that.  This is my first ever car with this brake setup (GM)

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Posted (edited)

So, here is an interesting little bit...

 

I noticed on the Master Power brake website that they are selling what they call an improved conversion kit for GM A, F and X bodies.  What I noted was in the video.  Their new bracket only has a caliper rotational stop on the steel plate at the inboard edge like most of our conversion kits. If you look at the factory stamped bracket they they show next to their new one one can note that the stop sits almost to the center-line of the caliper. 

 

You may be on to something Sniper, in fact on to something that a lot of people including myself, may have never given much thought to. Is it just the actual clearance distance and/or is it the clearance distance AND the Moment Arm of where the caliper push's on the stop?

 

https://techtalk.mpbrakes.com/new-products/new-caliper-mounting-bracket-design

 

James

 

*************
The more I think about this, the more I see it in my head. The video showing the stock versus retrofit bracket has helped me to see it in 3D.  When the stop is at the inner side of the mount AND it has too much clearance the caliper will cock a little under the braking load. If the outboard end cocks a little it will try to bend the sliding pin. Since my pin cracked right at the last thread on the caliper side of the bracket...that is the exact spot where the flex would take place. A repeated bend and return - bend and return - bend and return would cause the the type of failure I have seen.

 

Ummmmm...

Edited by James_Douglas
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