How to Remove EF 400 2.8L IS USM Tripod Ring

[benjamincortega]

I have a Canon Lens EF 400 1:2.8L IS USM (version1) lens.  The color tensioner knob has come undone, and I would like to reinstall it.  It appears from all of the diagrams I am able to find that the tensioning mechanism has to be installed while the ring is off the lens.  However, I am unable to find a way to remove the ring from the lense itself.  Does anyone know how this would be accomplished?  The product is out of support and warranty, and canon will not service it or provide assistance according to the folks I've spoken with in support and "right to repair".

[March411]

It's been a long time since I had this lens but I believe this is the trick. 

Place front element down with the lens cap on a large flat surface to ensure plenty of room in case the lens  topples over while you are working. Having it on a towel laid flat as a cushion can't hurt.  Unscrew the lock screw and rotate the collar slowly lifting very lightly. Continue to rotate the collar until the collar aligns the ring's locking pins (can't see them) and the corresponding exit slots, pull the collar up off the lens.

[benjamincortega]

It looks like I might also need to remove this part first?

[March411]

I don't remember pulling off the cover but it's been a couple decades. Have you thought about just pulling the foot. I could be wrong, it may have been another lens but personally I wouldn't pull the cover. 

[wq9nsc]

The EF-300 f2.8 IS USM was the only one in that series where the tripod ring slides off once you align it with the pins.  The longer focal length lenses in the series will require further disassembly to remove the tripod ring.

I believe there are one or more websites where you can buy an inexpensive scan of the service manual and that would be something I would purchase before digging into disassembly.

Rodger

[benjamincortega · Accepted solution]

I figured it out!  So sharing here with some photos that will hopefully help someone else in the future.

1. Remove these screws.  There are 6 of them.
   
2. Remove the Drop-In filter as it is in the way for the next step.
   
3. Slide the back cover off (this does not expose any glass or internal components)
   
4. Unscrew these 4 screws and remove the placard
   
5. That will reveal this access port.  Spinning the collar will allow you to access these screws/guides.  Unscrew and remove all of these.  The collar will then slide freely off the back of the lens housing.
   
6. When reassembling and reversing step 5, ensure that the round guide pieces and screws are placed BETWEEN the two guide "wires" (don't know what else to call them).  Failure to do so will result in poor performance and binding.

[March411]

Appreciate the heads up Rodger, I thought it was the 400mm. I just remember it coming off pretty easy with a bit of a spin.