Quad encoder problems

[mister_e]

The encoders output a positive voltage between ~1.85 and 5 and I have 4.7K resistors pulled to ground on each channel.

So it's never 0V? @1.85 you're probably sometimes in-between Low and High logic Level. You may need to 'filter' it a little bit to avoid oddity.

1.Use the internal voltage comparator, set the threshold and use their interrupt to increment the counter.
OR
2.try something like...
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1067&stc=1&d=115794620 6">
maybe one diode could be enough... maybe not
HTH