550EX fires but doesn't sync to 40D

During a recent vaction I noticed my 550EX was not exposing shoots. It fires OK but the exposure is as if there was not flash. However, the exposure is corrent when I use the popup flash on my 40D. It also doen't sync with other cameras so I know my 40D is not the problem. During the vacation I shoot many days from the back of an open safri truck with conditions of high temps and humidity and constant vibration and bumps on gravel roads. The flash was also almost always mounted on top an extention bracket. Anyone else had their 550 go out of sync for no apparent reason?

Is this repairable or would I be better off to just replace it with a new 580 flash.

Thanks

Try mounting the flash straight to the cameras hotshoe. If it works fine then the problem is the hotshoe connection on your off camera cord. It sounds like it might be loose from the constant vibrations. It happens a lot to stuff I use at work. It is an easy fix. The hardest part it to get the protective spring cover off then there are 4 small screws under that. If those are loose it will not allow good contact to allow the flash to fire properly. If you need some pictures to show you what I mean let me know I will see if I could help.

Check the remote at the back of the flash foot. Make sure that the switch is not in the "Master" postion. If it is, switch it back to "Off". If it's not the switch, try cleaning the contacts on both the flash foot and the hotshoe.

Ben,
I'm not sure where the spring cover is that you are referring to. Perhaps a picture would help.

Thanks

Here are the pics and info you need, these are for the 20D but I think all the Canon hotshoes are very alike.

I would suggest that you do NOT LocTite the threads as suggested in this nice "how to".

http://www.conraderb.c​om/flashrepair/

Enjoy! Lon

Lon that is a perfect link to explain what I was trying to say. That is the same thing to do for the the off shoe cable mount also.