CDC 5 1/4 floppy 77711501 / 77711800 specs

[g-wright at att.net]

Hi
I have a machine with a 77711501 floppy drive and it's bad.. I have 
tried  3 different 360k drives. I tried  to find specs on it but so far have not. 
What is the difference between that drive and a 77711800 used in a PC
The computer just says there is a drive error. I'm using the same jumper
settings on both. I have also tried a Teac fd-55bv.  

Is it a 320k drive ??

- jerry