I recently bought an Epiphone Wildkat and found issues with the vibrato and tuning stability. Using the vibrato the strings would sometimes stick and then snap free creating a "hammer on" or "pull off" kind of effect instead of a smooth bend. Also, using the vibrato would often leave the guitar way out of tune. This happens when the strings continue to stick after the bridge is returned to neutral. There will be extra slack or tension either behind the nut or in front of the saddles causing the section between the nut and saddles to be looser or tighter than they are supposed to be.
My first suspect was the nut. I took the strings off and inspected the slots and everything looked good. Next I held the strings over the nut one at time (each in their corresponding slot) and flossed them back and forth putting leftward, rightward, and downward pressure on the slot. I expected the strings to stick but they all moved perfectly through their slots. (Don't apply any more tension than the head stock would. Some guitars put sideways pressure on their nuts by creating an angle in the string going from the nut to the tuning machine. The strings only need to pass through their slots with the same pressure that they will be under when the guitar is strung. Applying more pressure may damage the nut.)
The next suspects were the bridge saddles. I didn't bother doing any tests here; I just bought a roller bridge. Actually I bought two; make sure to check the post spacing, post/stud size, and saddle radius before buying a replacement bridge for a TOM equipped guitar. After installing the bridge I still had issues, the only thing left in the string path was the tensioner bar on the tailpiece. I
The tensioner is the bar directly behind the bridge that the strings go under. The tensioner is supposed to roll with the strings but mine was so tight that I could barely roll it by hand. I had to grip it on both sides to make it turn it at all. At this point Google told me that this was a common problem on my guitar, and I suspect it's common on all B70s.
The mechanism is pretty simple so I figured I could probably tweak it to make it spin freely as intended. Overall I've very unimpressed with the B70. It wasn't hard to make it work but given the retail price I felt like it should work right out of the box and maybe make me breakfast on the weekends too. Anyway, here's how I did it.
Step 1: Get the Tailpiece Off of the Guitar
The B70 has a hinge-like mechanism where a small piece is screwed into the side of the guitar where the strap pin is, then the body of the tailpiece lays on the top of the guitar. The hinge allows the angle between the two pieces to fit a range of guitars.
I don't like taking screws out of end grain (they occasionally go back in feeling sloppy) so I decided to tap the hinge pin out instead. Unfortunately the hinge pin appears to be made of soft plastic and covered with chrome paint. I used an allen wrench and a tack hammer to try to push the pin out but instead the allen wrench sunk into the end of the pin and made it mushroom out and get stuck. The head of the pin moved out slightly so I tried pulling it out with pliers. After a while I got worried that I was putting too much pressure on the screws holding the bridge on so I reluctantly removed the strap pin and the other 2 end grain screws, then removing the screws from the front of the guitar.
I was annoyed about the pin so I continued trying to get it out but in the end the head ripped off and I tapped it out backwards.
Step 2: Disassemble the Tailpiece
The tailpiece is essentially just a frame that holds the roller that is attached to the vibrato arm, and the roller for the tensioner. The pins are held in by snap rings. I only removed the tensioner because there was nothing wrong with the other roller. Ideally you would use snap ring pliers but I don't have any. I settled for using 2 awls and ~10 minutes later the snap ring was off. I only removed one.
Step 3: Figure Out Why It Wont Roll
I looked for places where friction might impede the rolling action.
First I checked whether the inner pin could roll freely inside its bushings (the hollow plugs that side in the outside of the tailpiece's frame. This rolled fairly freely, though I'm not sure this really matters.
Next I made sure the outer roller could roll on the pin when it wasn't installed in the frame, this also rolled smoothly.
The last thing I checked was how tight the outer roller was between the sides of the frame. In the last picture where I'm holding the pin you can actually see the roller wedged between the frame and holding its self up. This was my culprit.
Step 4: Make It Roll
The roller had a second set of plastic bushings that were about 1mm proud of each side. I sanded most of one of them off then reassembled the tailpiece. This left enough of a gap that the tensioner could spin freely.
Step 5: Play With Cats
A critical part of any guitar repair or modification.
Step 6: Less Is More, Cut Things Off
The B70 frame has a little nub that stops the vibrato arm from swinging up over the strings. I like to be able to hold the arm while I pick and strum so I removed the nub with a hackside blade (used it like a flush trim saw) then sanded the cutoff with 320, 1000, and 2000 grit to remove any unpleasant textures.
I didn't take any pictures of it, but the arm is attached with a machine screw that isn't threaded all the way to the head. The nut that goes on leaves a little space and the vibrato arm is actually kind of loose on the frame. I put a washer on and now it's just tight enough that it doesn't rattle but still loose enough that the arm swings down out of the way when I let go. I could tighten it so it would stay where I put it, but I actually prefer it to move its self away.
Step 7: Put It All Back Together
Reinstallation is a pretty straight forward reversal of the removal process, but I was missing a hinge pin. I looked for a framing nail that was the right thickness, thinking I could cut it to length and grind the end round, but I didn't find one. I salvaged the broken off piece by wrapping a thin piece of electrical tape around the mushroomed bit and taping it back into place. The piece was just long enough to get 2-3mm into both outside pieces.
Eventually I will replace the pin with something better, but it's low on the list of priorities at this point.
If you're going to buy a Bigsby I would urge you to buy the american series (B7, etc.) over the Korean or Chinese (B70, B700, etc.). The price difference is actually quite small and while I can't guarantee you're getting quality from the B7; I can guarantee that making the B70 playable takes more effort than the savings is worth.