I recently purchased a set of new bleeder screws for the rear drum brake wheel cylinders and the front disc brake calipers on my '69 Z28. The kit (from Heartbeat City) included a pair of blue plastic dust caps for the front calipers. I checked the fit of the blue dust caps on the new caliper bleeders and found that the cap's opening was quite small and I feared the cap would split if I forced them on. I contact Heartbeat City and they sent me a replacement kit of bleeders and caps but they were identical to the first batch. Now that I had 4 blue caps, I went ahead and pushed one onto the new bleeder screw and it did split as I expected. One of three things could cause this: 1.) the dust cap material currently being used by the maker is not as compliant (or stretchy) as the original material, 2.) the hole in the dust cap is smaller than the original, or 3.) the tip of the bleeder screw is larger than the original.
To fix this, I drilled a 3/8" hole through a small flat piece of 1/2" thick aluminum, to fit the body of the the new dust caps. I inserted a dust cap into the aluminum and clamped it down to the drill press table, so that the hole faced up and the flange on the dust cap lip was clamped tight to the table and would then prevent the cap from turning when drilling. Using a 9/32" drill bit, I then carefully drilled out the hole in the cap, being sure not to run the bit too far down to poke out through the top of the cap. The resultant fit of the cap onto the bleeder screw felt right - lightly snug. Perhaps the next size smaller drill bit (17/64") would also work and give a slightly tighter fit to the bleeder screw, but I went with the 9/32" bit.
