Schwaben Pressure Brake Bleeder Saga

Having a pressurized brake bleeder has been a revelation; in the past, it was always a chore convincing the wife (now ex-wife), girlfriend, or random neighbor to pump and hold a brake pedal.  While the Schwaben pressure bleeder is very nice, the supplied composite plastic reservoir cap fit my master cylinder filler neck poorly, leading me to believe that the thread pitch was off.  I did manage to get it to work, but I have subsequently heard from other Schwaben pressure bleeder users who have had similar fitment issues; some have even had the cap pop off during use, dousing their cars with brake fluid. 

I purchased the Schwaben tool from ECS Tuning, and while I have generally been pleased with their service, they did not respond to two separate E-Mail queries concerning the cap issue.   However, I did find that the Schwaben "Premium" brake bleeder includes a billet aluminum cap  which can be purchased separately, so I rolled the dice and ordered one in the hope that premium might mean "properly threaded, non-leaking reservoir cap".   Nope.

Schwaben Pressure Brake Bleeder

Schwaben Pressure Brake Bleeder

 I quickly determined that the shiny red anodized billet aluminum cap fit just as badly as the basic black composite plastic version.  The thread pitch appeared to be correct, so it was time to break out the calipers; the inside diameter of the Schwaben cap was 2 millimeters smaller in diameter than the outside diameter of the threaded portion of the master cylinder.  While such an I.D. vs. O.D. measurement doesn't take thread engagement into account, it seemed that the problem and solution were obvious; I need to open up the I.D. of the cap a millimeter or so, effectively whittling down the peaks of the cap threads, while still maintaining good thread engagement.

Schwaben 018337SCH01A Billet Aluminum Cap Inside Diameter

Schwaben 018337SCH01A Billet Aluminum Cap Inside Diameter

2000 M Roadster Master Cylinder Filler Neck Outside Diameter

2000 M Roadster Master Cylinder Filler Neck Outside Diameter

After a few episodes of milling and test fitting, the cap finally threaded smoothly onto the master cylinder filler neck and the cap gasket imprinted with a wet ring of brake fluid around the entire perimeter, indicating that it was sealing properly against the top of the filler neck.  

Billet Cap I.D. Opened Up

Billet Cap I.D. Opened Up

Modified Billet Cap Installed

Modified Billet Cap Installed