Odd thread problem with caliper

[buickman50401]

I did a front brake job on my Buick yesterday - new rotors and pads - (the rear drums are getting done this weekend). All went fine until I tried to reinstall the drivers side caliper. The top caliper slide bolt wouldn't screw back into the caliper. It would make about 3 turns and then stop dead.

After some brake cleaner and rags, I got the threads cleaned up enough to discover there were no threads. The first 3 or 4 threads were fine and the rest were trashed save for the last two. Rather then go through finding a tap to fit it and screw with chasing out the threads in the hopes it would work, I just bought a remaned caliper ($35), which was fine since when I retracted the piston with a c-clamp the boot didn't accordion in smoothly on itself leaving part of it exposed above the rim of the piston and likely to get damaged by the back of the pad.

What in the heck would cause this. I mean I've seen my share of stripped threads but usually all of the threads are trashed not just the last few. The threads on the caliper slide bolt were fine and I reused it since it was much better quality then the replacement bolt that came with the new caliper. The bolt came out fine and took just as much effort as the others to get out. So what gives?

The brakes were serviced once before at 30,000 mi (car has 100k on it) so I assume my old mechanic possibly screwed it up, unless cast iron threads can somehow just trash themselves for no reason.

 

[demarpaint]

Odds are the mechanic that did the job before didn't do a good job cleaning up parts, tossed it togther messed it up and passed the problem to "the next guy". It happens all the time and is a reason why I try and do all my own work.

 

[willix]

If the threads are messed up there will be damage on the bolt/pin threads. If thats the case the caliper & fasteners need replacement.

 

[mechtech2]

It's hard to believe the pins bolts are perfect with that much damage on the receiving end.
But it could be from the factory, or faulty subsequent service.
You found it and fixed it - that's good.

 

[Gary Allan]

I've had to drill and heli-coil the mounting bracket. The bolt didn't appear to be damaged. Not a biggie

It happens often enough that AA (and I assume everyone else) has specific kits with tap/coil/new bolt all in one.

 

[buickman50401]

Regarding the lack of damage to slide bolt, I was confounded as well as to how it escaped unscathed, but it did. I cleaned it up with brake parts cleaner to get a good look at the threads before reusing it. They were "perfect". There wasn't any sign of damage to them in the slightest.

I wish I had taken a pic of the inside of the bolt hole. The middle section of threads was almost completely smooth. You could see just the faintest indentations of where the threads used to be.

I also forgot to mention that when I was cleaning up the bolt initially with a cloth, among the grease and debris I think there were some remnants of the middle threads stuck in amongst the grease.

Alas it was an easy and relatively cheap fix. Even with the "premium" semi-metallic pads up front (and standard grade rear shoes) the total for the brake job only comes out to $140 including the remanned caliper. It might even end up being less, since I haven't pulled the rear drums yet, and if there is at lest half the friction material left, I'm just going to clean them up with parts cleaner, adjust them and reassemble so that'll save me another $25.

The front brakes really weren't that bad. There was still probably just slightly less then 1/3 of the friction material left on the pads. It was evident that the left caliper had been hanging a bit though as inside pad on that side was worn down significantly more then the outside pad. I redid the brakes anyway though because the OEM rotors warped and I was also getting a horrible constant high pitched howl while driving that only went away when the brakes were applied. The howl is now gone and after bedding in the new pads (which I gooped up with that rubberized stop squeal on the back) it stops on a dime.

I'm not sure how much a pain the rears are going to be as I have never seen a drum configuration (based on the repalcement hardware and repair manual pics) like it before. Instead of multiple springs and retaining screws there are just two springs and two large U-shaped tension bars to deal with. No special brake tools are apparently required acording to the Haynes manual, just a large flat blade screwdriver and pair of needle nose vice-grips.

Another interesting thing was that the manual stated a Torx head wrench was required to remove the caliper mounting bolts but they were just regular 15mm heads at least on my particular car.