Disk brake failure

[RiverPatrol]

I will begin by stating that I have always had misgivings about the disk brake conversions. The Patrols were not designed for disk brakes, the conversions are not being designed by engineers, but I am not knowledgeable enough in the field to put together a reasonable argument so I always just kept my opinion to myself. I know plateaucal would concur if he were still around.

A Patrol owner from San Diego came to visit today. He drove his Patrol because he wanted to show it to me. It's about an hours drive, about 50 miles. About a year ago he had done the disk brake conversion using the kit that Cory made available. He has driven the Patrol a bit with the disk brakes, no off-road just around town, this was probably the longest trip he'd made. He made it all the way here, missed my street and made a U-turn at the next intersection. He had just completed the U-turn and was stopping when the right disk brake caliper fell off. He and his son walked the rest of the way to my house. We chatted, he looked at Patrols, then asked if he could borrow a jack so he could remove the wheel to secure the brake caliper so it wasn't dangling when it was towed. I went with them to see the damage. Apparently the two bolts securing the caliper bracket to the hub sheered completely off. He is fortunate that it happened here and not on the highway. I can venture to guess that it was a stress failure for various reasons.

I guess I can't decide which would be worse: this or a master cylinder failure. With the original drum brakes a single reservoir master cylinder failure is about the only failure equivalent to this.

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Update: He got home okay. He sent this and said that these are the 2 bolts that broke off.

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[zed]

RP,
Is there any marking on any bolt heads to determine which grade (2, 5, 8) they are?
Thanks,
Keith

[faux40]

Ouch! Glad nobody was hurt!

Excellent warning for those of us dumb enough to try disks!

John

[RiverPatrol]

RP,
Is there any marking on any bolt heads to determine which grade (2, 5, 8) they are?
Thanks,
Keith

I don't have that level of detail.

[RiverPatrol]

Ouch! Glad nobody was hurt!

Excellent warning for those of us dumb enough to try disks!

John

I'm not implying that anyone is dumb for doing disk brakes. I am saying nothing is engineered and there are stresses unaccounted for.

[Esteban]

I don't think you need to engineer some things that had been designed previously by many manufacturers. A simple form of copy what's out there. I would have done exactly the same.

Maybe the bolts where not torqued properly or as Zed asked, the grade of the bolts could have played a part.

My suggestions for the ones using these conversions, dismantle after a little bit of time, and check the condition of the bolts.

Tinkerers have always come first. Engineers follow. Comes to mind Ford vs Ferrari. The Ford engineers at some point didn't pay attention to Carroll Shelby that they needed to use stronger head bolts, like Shelby did. The bolts enlarged during the race and the engines failed. The Shelby team cars won that time.

[jwgreen]

The conversion done on this Patrol used a bracket that was only held on by those 2 bolts therefore not spreading out the load very much. The bracket I have put forward in my design has a plate that bolts to all 6 studs to spread out the load of the braking on these studs. Just food for thought.

[RiverPatrol]

The conversion done on this Patrol used a bracket that was only held on by those 2 bolts therefore not spreading out the load very much. The bracket I have put forward in my design has a plate that bolts to all 6 studs to spread out the load of the braking on these studs. Just food for thought.

He's figured out that is likely the issue. He is brainstorming having something made like what the FJ40 conversion kit uses, which sounds like what you had made. Was it Suhail that made the brackets for you? This guy knows Suhail.

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[rjiggy]

Justin nailed it. The original drum brake backing plate utilized all six studs to bear the full braking load presented at each wheel. Disc or drum, the load is essentially the same. Applying it to 33% of the studs is the root cause of the failure.

[Esteban]

Justin nailed it. The original drum brake backing plate utilized all six studs to bear the full braking load presented at each wheel. Disc or drum, the load is essentially the same. Applying it to 33% of the studs is the root cause of the failure.

Excellent explanation! Thanks!