Just had to replace the brake master cylinder in the 66, and decide to go with a duel manual disk/drum master cylinder for safety reasons. I have read several post and or help sites that say to bleed the brakes you do it with the lid on and some say to do it with the lid off. So I guess what I'm asking is which one is it? On or off?

 

Go lid off but be careful when you pump the brakes. It can splash out and brake fluid will eat through paint quick. Not sure what bleed procedure you're using. Hope you have a brake pumping person to help you. New master cylinder, bleed at the two lines from the master first. Crack the line and have someone slowly depress the pedal. Hold it down until you tighten the line back up.

 

I just finished this same job on my 66, I leave the lid off so I can tell how much fluid is in the master, as mentioned you just don't want to pump the peddle too fast or it will go everywhere. If you get it on any paint get it off ASAP, this is one of the reasons when I did mine I changed the master, hoses, and wheel cylinders and went with DOT 5 brake fluid instead of DOT 3. As far as bleeding, pump the brakes several times and hold, then go to the left rear, open your bleeder, let the air out, close your bleeder, release the brake peddle, then follow the same on the right front. Repeat until you have a solid peddle.

 

Lid. On.

The burping is very not-easy to control. Best to put the lid on, do two or possibly three bleeds, and then top off. Brake fluid is very corrosive on paint, and do you really want to take the chance you'll catch it fast enough?

I won't. Ever. Lid on 'cause I'm a klutz.

 

If you do get it on paint rinse with a lot of water. DON'T WIPE IT OFF FIRST!