Touring - Anyone ever break their rear rack?

I'm wondering at what point a rear rack will/has failed. If it has been just a matter of weight, or un-even or unbalenced loads. I imagine the lower mounting bolts would be the weakest link on a good quality rack.
Thanks

Yes, I've broken both front and rear racks - though on fairly rough roads.

I haven't broken the mounting bolts in the rear, though early on I learned to keep checking bolts for tightness since I had one occasion where a bolt slowly worked loose and then fell out. If you are going for extended time, it also helps to have an extra bolt of key components.

I had a rear blackburn rack and a front surly rack when I cycled across Russia. There was ~1700km of gravel road that was more obnoxious than gravel roads I've traveled in North America. I was carrying a reasonably heavy load in my panniers. What failed on the rear rack was the metal strap that connected the rear rack to seat stay. Only one of two straps failed and I was able to duct tape it to keep it going.

What failed more than once on the front rack was the metal bracket in fashion similar to what happened to Herman Veldhuizen on his ride: http://www.hermanveldhuizen.com/wp/?cat=28

In these failures I believe it was a combination of weight and extended touring over rough roads. Even some of the paved/concrete roads further west in Russia were occasionally quite rough. I had some touring miles ridden before then including two trips across the US, one across Canada and one lap around Australia without problems.

How much weight to you think you had at the breaking point on the rear rack?

Here's one possible way of making it something you don't need to worry about.

For mounting bolts you might spread RTV silicone on the threads. They won't vibrate loose and I suppose it'll help fight rust.

I carry comparatively light loads, and mostly manage to avoid rough roads. But over time, the second law of thermodynamics prevails: the universe is becoming increasingly chaotic and disorganized! In my case, a weld on the rear rack snapped.

My temporary repair involved dental floss and crazy glue. Everything held together long enough to finish the trip.

Nothing lasts forever, especially thin tubes and strips of metal held together with bolts and welds that are subjected to thousands of hours of vibration and movement.

How much weight to you think you had at the breaking point on the rear rack?

My guess ~15-20kg, but I think it was weight in combination with large amounts of vibration from riding gravel.

I haven't broken the mounting bolts in the rear, though early on I learned to keep checking bolts for tightness since I had one occasion where a bolt slowly worked loose and then fell out. If you are going for extended time, it also helps to have an extra bolt of key components.

http://images.westmarine.com/full/loctiteblue.gif

My friend's cheapo rear rack cracked after a few days of riding with a full load in Europe. We had to carry her stuff until we found a bike store. I don't remember specifically what part of the rack broke.

my experience is the rack stays break during rough road touring. happened in the middle of nowhere for me back in the 80's which i fixed with some bailing wire.

better off with a tubus and the tubular aluminum stays.

My 70's Blackburn rear rack is installed on its fourth bike. Used daily for commuting over most of its life, but has also done some fully loaded touring. It will probably be in my will.....