brake caliper guide pin bolts falling off
 

Hi,

I did my brakes 1 1/2 years ago, only ran the car ~10 times since, and then noticed a metal grinding noise while braking recently. It turns out that bolt caliper pin bolts had fallen out on the right front side, and the only thing holding the caliper in place was the inside of the wheel, the brake hose, and the caliper bracket! When the brakes had been applied, the caliper moved such that the outside of the caliper grinded against the inside of the wheel well.

Of the 8 caliper pin bolts on the vehicle (2 for each caliper), two others were very loose and 1 or 2 were not fully tightened. Also, 1 of the 8 caliper bracket bolts was not quite as tight as it should be (was about 100 ft/lbs, should be 125 ft/lbs).

The specified torque on these caliper guide pin bolts is only 23 ft/lbs, they have some loc-tite or equivalent on them, and one is supposed to throw them away and use new ones every time they are loosened. I did not do that, instead re-using the bolts, did not apply thread-locker, and torqued to 23 ft/lbs in two steps. Clearly, that did not work and led to a near catastrophic failure.

I am posting this for two reasons:

1) Warning to others who may have reused their bolts, not added loc-tite, and torqued to the pathetically loose 23 ft/lbs specified in the manual. I believe most people reuse their bolts. At 23 ft/lbs torque, it's hard to imagine the bolts becoming deformed and not re-usable (ie should not be "torque to yield" type bolts in my novice opinion). Instead, it's more likely they want to ensure loc-tite is applied to the bolts. Somehow, I'm doubtful everyone here is doing that.

2) Does anyone know of another bolt situation with bolts that large being torqued only to 23 ft/lbs and requiring loc-tite? It seems strange. Is there a safe way to re-use the bolts? In my case, I torqued them all to 50 ft/lbs and did not apply loc-tite. Next spring I'll pull the wheels after a few trips to check on the brakes.

It seems as if professional mechanics would not replace these bolts, heck the dealership did not even have them in stock and most writers on this forum do not replace. In addition, these same professional mechanics overtighten my wheel lugnuts every time I take it in for an inspection or work to be done. And yet, the pros don't have brakes falling off cars from their customers!! Several "pros" on you tube tighten caliper bolts without torqueing, and to way more than 23 ft/lbs, and do not seem to strip or shear the bolts. Perhaps I should buy a professional torque wrench (not my "trusty" craftsman), or not torque at all?! Someone commented that any more than 23 ft/lbs would break these caliper pin bolts. I doubt it, and will know for sure next spring...

Confused,
Greg

This happened to a local guy the other day...it happens. Clean the bolts and use loctite is probably safe advice. With a good cleaning, 23 and loctite is probably just fine. He pulled in to talk to us about a noise he was having. I took a look and found the issue right away. He had oversized rotors, and the caliper was floating around between the rotor and the rim. What is the actual spec?

http://www.pfadtracing.com/blog/wp-c...mas-banner.jpg

I've never put any loctite on mine nor have I ever had them back out. But 23 ft/lbs sure does seem insanely low for those. :eek: I wonder if that's a misprint? I'm sure I'm putting over twice that much torque on them with my 16" socket wrench. Call me Bubba, but I've never stripped or snapped one of them. :crazy: I like to think I have a fairly good mechanic's feel.

Use the "feels just tight enough" method and not a torque wrench
 

:iagree::iagree::iagree:

Have done scores of brake jobs on GM, Ford, and Chrysler vehicles and have never had any bolts come loose or snap. Only loctited the large caliper brackets on the Vette and reused the original bolts as there were only 3 bolts in stock in over 20 dealerships in the Washington DC metro area. Use a 3/8" Craftsman socket wrench and a calibrated feel.
Think the 23 ft lbs must be wrong.

I've had those 12 year old bolts out of my calipers to grease the guide pins a dozen times over the years. when I remove them they are tight. Of course I used blue Loctite to make sure that heat and vibration does not back out these bolts with a very low torque spec.
Ive never changed the bolts for new bolts, these are the originals. You also need two wenches to achieve a proper torque. one on the guide pin and one on the bolt. the guide pins should be removed and cleaned and regressed every time you remove those bolts.

Here you go.

It is indeed 23 lb.ft & using any thing larger than a 3/8" rachet can snap these bolts quite easily....especially once they have been reused & stretched.

I find it's best to clean the old loc tite off the bolt threads by running them through a 8 mm X 1.5 Die from a tap & die set.
Apply new blu loc tite.

See torque specs below.

http://forums.corvetteforum.com/1580110878-post4.html