heck of a time bleeding brakes.

G

gas man

Member
I have a 39 mercury with a new original style master cylinder, I also replaced all the brake lines, wheel cylinders, and brake shoes. so now I'm on to bleeding the brakes. what I'm having a hard time understanding is do I fill the master from the little 3/8 plug ? or can I pull that bigger looking plug with about a 1 1/8 socket? Also how do you know when your getting low on fluid in the resevior since you cant see it? I'm paranoid and adding a tiny bit of fluid after every time I loosen the bleed screw. I dont want to suck air back in.
 
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I have the small plug out in the picture. sure seems like it would be a lot easier if I took the bigger one out . dont want to break anything .
 
well I figured it out . half inch ratchet , 6 inch extension, 1 1/8 socket , and some busted knuckles when it broke loose.
 
Glad you got it apart. I will have to say that I've never seen a master cylinder with a filler cap like that.

Also, Welcome to the Barn! There are a lot of knowledgeable people here.
 
I think that filler cap is tapped for a pipe thread so you can plumb in a remote filler mounted up on the firewall or other convenient place.
 
brian is correct when you put the filler cap on just make it hand tight. most caps are made of alm. or die cast two different metals fuese together. i cant count how maney caps i had to bust to get off. whitch ruiens the cylinder for some reason people tighten them it is not nessary i know i cant spell
 
The cylinder I bought from Rockauto has a cap like that. I used a 1" square drive socket "backwards" to remove and replace it. I think Brian has stated the purpose of the smaller plug, which could be pretty handy.
 
I agree with Brian's post above . I've done it a few times , mounted the remote on the exterior firewall .
 
When I do a brake fluid bleed I go two full, slow strokes and check, refill master. ( many will disagree or cite some 'better' way ). I work alone, with a full master, begin by opening the bleeder at the farthest wheel. Open the valve, ( with the car positioned low enough to work the pedal a full stroke slooowly by hand, while watching beneath the car for squirt from the bleeder. When the flow becomes steady, I cinch the bleeder valve closed.

While this may take more than two slooow strokes of the pedal, I'll have to add fluid on the way.

All I can say is I've used this process over fifty years commercial and private without any problems ( Taught to me by a Packard mechanic ) Before learning this I was using the 2 person method with mixed results.

As far as air sucking in,,, the pistons can't move thanks to the shoe return springs holding them. The pressure in the line exits through the open bleeder valve. Therefore as the pedal moves up fluid is supplied via the reservoir. If you can't picture that, tell me you never, braked while slowing down, hit the pedal a second time and felt a higher pedal.

Apologies for stretching the topic to personal values.
 
My master cyl. had a cap like that . I replaced it with a plastic/nylon one I had laying around , that only requires to be hand tight .
 
When I bleed brakes by myself I loosen the bleeder and attach a hose to it and run the other end of the hose into a container with brake fluid in it. Make sure the end of the hose is submerged. Pump the pedal a few times watching the fluid level. Do that with each wheel starting with the wheel far wheel and moving to the closer one.
 
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