Blower air volume is excellent once I removed the nearly completely blocked old filter

DISK DRIVE FILTERS AIR TO EXCLUDE PARTICLES IN 125 MICROINCH RANGE

Because the heads fly as low as 125 microinches (3.2 microns) above the platter on a thin film of air, any particles larger than the flying height might drive the head down into the surface of the platter, potentially causing a head crash. IBM employs an almost HEPA-quality filter to ensure clean air enters the cartridge. 

The mice with their nests and urine have almost completely clogged the old filter, resulting in very little air flowing up into the cartridge. Once I removed the filter, the volume of air coming out was superb. The blower operates all the time that the IBM 1130 is powered on, thus it is blowing clean air into any cartridge placed in the drive and exhausting contaminated air out around the heads into the drive compartment. 

I will look for a replacement filter with decent filtering. HEPA filters down below 0.3 microns, ten times finer than the problematic particles for a disk drive. I am not sure I will get a filter as good as the original IBM part but it should do a good enough job filtering air. 

CLEARING DUST OUT OF CARTRIDGES 

The disk cartridges should have all the dust cleared from them before the heads try to load. To accomplish this, the cartridge should first be inserted into a drive but the run switch left off. The blower will be forcing air through the cartridge for all the time it sits in the drive even though the drive motor is off. 

After a suitably long time, the drive should be switched on but turned off before the heads load. Generally this is done with 60 second intervals of run switch activation. I however can block the head loading solenoid from attempting to lower the heads, thus it can spin as long as I want in that state. This will knock off any additional dust and get it out of the cartridge.