Started May 31, 2005 | Discussions thread
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Tom Caldwell Forum Pro • Posts: 45,466

Just wanting to check if anyone else had suffered the "displaced bearings" problems with the 100-400 IS "tombone action" lens.

Seems about 1 in 10 will get a bit enthusiastic with the tombone action and some of the tiny bearings in the extension brake will pop out and get jammed in various places including under the slide itself.

This manifests itself in the symptoms:

The lens gets "sticky" in it action and you may even see slight marks on the inner barrel that look for all the world like grit marks. It is not grit! It is one or more less than pinhead size bearings dragging between the barrels;

Sometimes apparently the bearings find there way into the auto-focus mechanism or the IS works which then "play-up".

If you have these symptoms and you are still within warranty - get it fixed! Mine was out of warranty and it cost nearly AUD$900 to repair the barrels and supply a new IS unit.

The trouble is that the problems don't stop the lens working, they just make it less pleasant to use. I suppose many will just keep on using it wondering why the zoom now seems to be starting with a small jerk rather than a fluid action. Or occasionally the auto-focus just doesn't seem to be working.

Under the extension-brake are two open ball-races with a "thousand" very tiny bearings about the size of pin heads. They should stay there in theory. Now run your lens from one end to the other - notice the clack every time it gets to the end. I have tried and tried to bring it to the end of the travel without a metallic thud but it is just about impossible. Fair enough it should be built well enough to take a bit of banging - but get out in the field following birds or some sports action and lose your concentration on the zoom action and you might just bang once too hard. Oops - back to the factory!

It needs some sort of flexible internal stop to take the shock out of metal to metal contact.

We need to get together on this otherwaise Canon will just pick everyone off who has this problem as an individual and charge you for the repair.

It is not something that will usually surface within your warranty period.

When I brought this up before the site thread was full of those who had not long had this lens and were full of praise for it. I wonder if any of these owners have subsequently had this problem.

As far as I am concerned it is a brilliant lens and I am very happy with what it does for me. I will always have one. I am just trying to be careful in how I use it. However if my repaired lens, after careful use, has a recurrence of the problem I will literally go into orbit.

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Tom Caldwell

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