thnkxs i was looking at the lines hooked up to it there was a lil bit of oil in it but i took the vac line off the modulator and no oil in it, its a freshly rebult c6 with less then 3k on it i wanted to know if i should replace it. ive noticed lately its not shifting as hard as it was but when it got rebuilt. i can still feel it when it shifts.
Here it is;
Vacuum Modulator, Diagnosis & Replacement in an 89; "...The different color bands indicate the diameter of the rubber diaphragm inside the modulator. The two COMMON colors from auto parts suppliers are PURPLE and GREEN. These are for CARS. TRUCKS like OURS REQUIRE the BLACK banded modulator, likely from a transmission shop or dealer. This is reguarding the mid/late 80's models, maybe more... Id venture to say any C6 with a slip in modulator. Again, PURPLE and GREEN are NOT the correct units to use, BLACK is the intended modulator as was designed for TRUCKS..."
Source: by MyFullSize (Andrew) at http://fullsizebronco.com/forum/showthread.php?t=17161