The problem is also very persistent on the stock coil as well. It's a combination of weak coil ears, wrong sized bushing, wrong bushing material and addition of coil ear protectors than can aggravate the problem.
(1) coil ears are too thin with no lateral reinforcement plus cheap plastic.
(2) Although the provided rubber bushing fits nicely, it's actually too thin and when placed where it is supposed to be actually sits flush with the rim of the bushing depression at the end of the forward shaft. As a result there is only a very light physical contact with the rubber bush and the coil ears resulting in only a very light "grip" . As a result causing the coils to easily move which causes users to tighten the screw bolt even more than it should, causing the coil years to bend slightly inward towards each other but increasing grip between coil ears and shaft.
(3) The bushing material is odd. It's supposed to be rubber but it is very smooth and soft. Because it is so smooth, it provides less friction. Because it is soft, after been in place for some time, the rubber bush gets squeezed thinner in areas it come into contact and thus grip between the bush and coil ears is reduced further. Often causing users to tighten the bolt even more. Addition even more tension to the coil ears.
(4)Coil ear protectors can actually make the problem worse. Assuming you have a the stock Minelab rubber bushing, slightly worn and does not provide enough friction to hold the coil securely. You add a coil protector. That coil protector does NOTHING to add friction. It also adds nothing to provide lateral strength to the coil ears as the tension from the coil bolt is from the direction away from the ear protectors.
What happened to my stock coil with original worn bushing and coil protectors, was my coil protector broke as I had to over tighten my coil bolt to provide any meaningful tension so my coil would not constantly slip. Immediately when the coil protector broke, pressure/tension from the coil bolt was immediately transferred to my coil ears which then broke at the same time. Examining the broken coil protector revealed the inside to be mostly hollow with lots of "air" in the material. And I am not rough with my detectors.
Got a free replacment 11" coil but now have to be extra careful with use.
WHAT CAN YOU DO?
(1) Add material to the inside of the bush/washer housing on the rod end. What my friends did was cut a piece of old bicycle rubber tube, put on the inside of the bush/washer holder then place the original bush on top of it. You just need to protrude the bush/washer out 0.5mm to 1mm beyond the plastic ring that make the outside of the Bush/washer holder for friction to occur to hold the coil securely. Or if you want to spend money, Detect-Ed sells coil saves that do just that that is also made of a stronger material with more friction capabilities. The simplest is to remove the original bush/washers and flip them round. Inside to outside. That alone will provide more fiction. But it is just temporary.
(2) If you want to use a coil saver, look for one that is designed with some sort of built in lateral support that gives it more strength. Most coil savers on eBay DO NOT have such lateral support. Only a few do.
DO NOT use one of these coil savers without lateral support together with a stock bush/washer that already shows signs of wear causing you to over tighten you coil bolt!
