Caliper Mounting Bolts Keep Backing Out

[1987 GMC Jimmy]

So this has happened to me twice this year. It’s the same side (driver), and the big T60 Torx bolts back out after about 4-5K miles. Car’s a ‘90 Cutlass Supreme sedan.   

The first time it happened, I had to tow dolly it back to the house from an hour away, but one bolt was still loosely in place, and the other one fell on the deck of the dolly when I backed the car off. I applied Loctite to the bolts and let it rest the requisite cure time before driving again.   

The second time was the day before yesterday, and I limped it back to the house, but one bolt was gone, and I had to rent a car for work yesterday and drive to the Autozone warehouse to get the bolt, Dorman 13889. I’m back together again, but I know this is gonna happen within that 4-5K mile timeframe.

What’s the problem? Could the caliper itself be twisting or vibrating more than normal when brakes are applied? You can rock the caliper back and forth a little bit perpendicular to the rotor axis, but the bolts are torqued as snugly as I can do by hand. Besides the metal bolt spacers, are there shims or spacers that should be there, and I might be missing them? The other calipers aren’t doing this, and it’s such a random issue, especially considering all the pads and rotors have about 8K miles on them, and the brakes work excellently: totally quiet and no vibration either in general or transmitted through the steering wheel. 

[ron350]

Dorman 13899 are front caliper bracket bolts and are supposed to be torked to 148 foot pounds.

The front caliper slide bolts Delco #18K114 are supposed to be torked to 80 foot pounds.

I had the driver side bracket bolts come loose the first time I replaced my front pads because I only torked them to 100 foot pounds.

 

Edited June 24, 2020 by ron350

[digitaloutsider]

I agree, this sounds like a torque issue to me. 

[mfewtrail]

11 hours ago, ron350 said:

Dorman 13899 are front caliper bracket bolts and are supposed to be torked to 148 foot pounds.

 

 

Yep. Get a torque wrench and tighten those to spec. Even a cheap $10(with coupon) Harbor Freight torque wrench will be more than adequate for this task and the length of it will easily allow you to hit 148 ft-lbs.  While it's apart, I would clean the caliper bracket threads if needed and apply a drop of blue loctite to the bolt.

[55trucker]

Also get yourself a good quality impact T-60, they will twist/break at high torque loads.

[ron350]

After shattering a Lisle T-60 I was told I needed a Snap-on STX60. The STX60 is a snug fit for the job at three and one half inches long but I don’t have to worry about it breaking.

This is a picture of a STX60 beside a Lisle T-60 socket.

Edited June 25, 2020 by ron350

[White93z34]

I would replace both bolts and ensure they are properly torqued. Bolts backing out for no obvious reason can be a sign of stretching before breaking. 

[1987 GMC Jimmy]

Yeah, it’s high time I got a torque wrench. I usually just use the torque-by-feel approach, and if I’m doing something that would be stupid to do without a torque wrench like assembling an engine, I’ll rent one. I’ll check my work with those torque specs, and replacing the other old bolt might not be such a bad idea either. 

[vipmiller803]

On 6/24/2020 at 7:06 PM, ron350 said:

Dorman 13899 are front caliper bracket bolts and are supposed to be torked to 148 foot pounds.

I'd stay away from dorman. I had those very bolts shear around 100 lf-lbs a few times in a row. They still sell ac delco ones.

https://www.ebay.com/itm/Caliper-Bolt-BUICK-REGAL-CHEVROLET-LUMINA-MONTE-CARLO-CUTLASS-SUPREME-GRANDPRIX/232137076234?hash=item360c72ae0a%3Ag%3A5mgAAOSwo4pYIQ6T&fits=Year%3A1994|Model%3ARegal|Make%3ABuick

[Schurkey]

If these are the same caliper bolts I'm used to dealing with, there's a bigass bell-shaped steel spacer that's part of the bolt, it's installed on the bolt before the threads are rolled.  The spacer isn't removable, but IT HAS TO SPIN FREELY when installed.

https://www.amazon.com/Dorman-Help-13899-Caliper-Bolt/dp/B000COCQ88/ref=sr_1_33?dchild=1&keywords=Lumina+caliper+bolt&qid=1593551474&sr=8-33

 

The spacer is always seized into position when I remove the bolts for brake service.  Gotta heat it in a bench vise to get it "unstuck".  There isn't really room to paint anti-seize on the bolt, so the next time I take it apart, it's seized again.  This is also why you need a quality T60 to remove them--with the spacer seized to the bolt, you have to drag the spacer across the iron of the caliper mount to get it unthreaded.

If that spacer doesn't spin freely when you install the bolts, you will have a difficult time getting the bolt tight enough.  Of course they'll back out.  If the specified torque is 148 ft/lbs with the spacer free on the bolt, 148 won't be even close to tight enough if the spacer is seized.

 

I had one bolt back-out on a road trip to the Big City; about 750 miles round-trip.  The lower right-front bolt fell out.  All was well until I tried backing up at the gas station, 300+ miles from home.  The caliper drag on the rotor caused the caliper to pivot on the upper bolt, it would pull "up" into the inside of the wheel, which made the wheel stop turning.  Lots of banging and thumping as the car was in reverse.  All good forward.  Installed a new bolt when I got home.

Edited June 30, 2020 by Schurkey