You can use a syrofoam packing pellet. Just unscrew the sender, remove it from the outer casing, and place the styro between the top of the casing and the unit. replace the unit, plug it back in, screw down the outer casing, and you're done. The reason that this works, is because there is a circuit board in the top of the sender with the soldered side pointed up. When you put packing in there, you both cushion it, and put pressure on whatever solder points have wiggled loose over time.
Sometimes, the pins that plug into the base come loose, and those will also need to be reglued
I really wish the originator of this technique had thought of something other than "butts", so we could call it something else...
BTW, before I had read about that "quick fix", I took mine apart, and resoldered the circuit board...
In fact, for too much detail on that subject, and a good laugh as TXBill (before he was a moderator) and I (when I was a new member) get into a little disagreement, and then make up, you can read this (somewhat embarrassing) thread in the archives:
New Info On The 300SD Tachometer / TDC Sender Problem
[Edited by longston on 04-22-2001 at 05:09 PM]