Tightening SL-M570 Thumb Lever

[cc1060]

I have a Shimano Deore SL-M570 shifter (circa '00) that has a lot of up and down play in the thumb lever for the front derailer. Unless I press the thumb lever upward toward the body of the shifter, the loose condition causes it to miss the pawl to shift from the second to the third chain ring. If I open up the bottom cover on the shifter, it would appear that it can be tightened by the hex bolt that is visible, but there is a small metal plate underneath it, with two tabs that stick up on two sides of the bolt, apparently preventing it from turning (see picture here). Is this, indeed, how to tighten the thumb lever, and if so, how can I tighten it with those metal tabs in place?

Thanks.

[DaveM]

I presume the tabs are there to prevent the bolt turning from the rotation of the shifter. You may be able to bend the tabs down, tighten, and then bend back up.

[Painkiller]

It sounds to me that the shifter is worn out, They are not meant to be taken part further than removing plastic covers. however the way I see it as it is broke already so go for it and see what happens. I have had older models torn down to a pile of parts and springs before and assembled back to functioning shifters again.