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I removed my master cylinder, cleaned it, painted it, a d will be installing a rebuild kit. Most of what I've read says to bench bleed the master cylinder before installing it in the car.
I don't have a vice... So, what is wrong with installing it in the car and bleeding it there? Assuming I don't connect the brake lines to it? Just thinking that gives me a convenient way to securely hold it and use the brake pedal to "pump" the piston. I purchased a little kit with the fittings and hoses from autozone. Am I missing something?
Just be careful with splashing brake fluid and your paint.
The benefit of “bench” bleeding is you get to tilt the master cylinder forward and backward to help eliminate trapped air bubbles. Bleeding on the car could lead to a bubble trapped
true, but if you jack up the back of the car to get the master perfectly level, you should be able to get the air out. still think bench bleeding would be easier. you don't need a vice. you can hold it with your hand.
OK - perhaps a more stupid question....my master cylinder has additional holes near the top of the cylinder. It does not just have the two connections for the brake lines.
First question - do I put bleeder screws in these, or plugs? I happen to have two plugs laying in the area that look like they came from there?
Second - what are they used for? Are they used for bleeding the master cylinder? If so, can someone point me to a procedure of how to bleed the master cylinder using these? All of the procedures I have seen just use the two brake line connections.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Originally Posted by Mpls Funk
OK - perhaps a more stupid question....my master cylinder has additional holes near the top of the cylinder. It does not just have the two connections for the brake lines.
First question - do I put bleeder screws in these, or plugs? I happen to have two plugs laying in the area that look like they came from there?
Second - what are they used for? Are they used for bleeding the master cylinder? If so, can someone point me to a procedure of how to bleed the master cylinder using these? All of the procedures I have seen just use the two brake line connections.
I don't understand your question.
Do you have a picture?
looking at the tapper on the end of those plugs. sure does look like a bleeder screw type tip. I can't see inside the master. but it does appear you could put bleeder screws in there and with 2 short sections of hose could use them to bleed the master and then tighten up the bleeders. those plugs look like blanks in the photo. you might have to run down to the auto parts store and match up some bleeders to do it.
Last edited by 4-vettes; May 18, 2021 at 11:35 PM.
looking at the tapper on the end of those plugs. sure does look like a bleeder screw type tip. I can't see inside the master. but it does appear you could put bleeder screws in there and with 2 short sections of hose could use them to bleed the master and then tighten up the bleeders. those plugs look like blanks in the photo. you might have to run down to the auto parts store and match up some bleeders to do it.
So, if I put bleeders in those holes and connect hoses and run back into the reservoir, what do I do with the ports for the brake lines when I'm bleeding them? Plug those somehow?
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi again.
Now I got it, 4 holes.
Interesting that your M/C has the top row holes but no bleeders in those holes.
Are those holes blind?
If you fill the M/C does fluid come out from the top row?
The bottom row has the fittings installed so that looks good.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
I would put the plugs back in.
After you bleed the M/C and have it installed it in your car remove the tubes and quickly install the hard lines.
Now have a helper press lightly on the brake pedal while you with a rag under a fitting, crack it open to let the air bubble out. then do the other line.
I removed my master cylinder, cleaned it, painted it, a d will be installing a rebuild kit. Most of what I've read says to bench bleed the master cylinder before installing it in the car.
I don't have a vice... So, what is wrong with installing it in the car and bleeding it there? Assuming I don't connect the brake lines to it? Just thinking that gives me a convenient way to securely hold it and use the brake pedal to "pump" the piston. I purchased a little kit with the fittings and hoses from autozone. Am I missing something?
And then once it is installed in the car and connected to the brake lines, I do this to get the last bit of air that bench bleeding still leaves in the MC .
So, if I put bleeders in those holes and connect hoses and run back into the reservoir, what do I do with the ports for the brake lines when I'm bleeding them? Plug those somehow?
I can tell you to never plug the ports with bolts. There is a machined flare inside made of cast. A bolt will destroy the flare, rendering the entire MC worthless.
Put the bleeders screws in the proper ports.
Certain year models came with the bleeders on the MC. In theory they were used on the production lines to bleed the system. Perhaps DOT3 was introduced "Into" those bleeders to flush all the way to the right rear caliper while moving down the line. Who knows?
If you don't have a vise you will need another way to secure the MC on the bench. Check out my profile > photo albums > bench bleeding for some tips.
So, if I put bleeders in those holes and connect hoses and run back into the reservoir, what do I do with the ports for the brake lines when I'm bleeding them? Plug those somehow?
Those bleeder screws were used by the factory but they have no use in service.
I would advise you to just put bleeder screws in the holes and forget about them. Bench bleed with 2 short hoses or 2 made up hard lines looped back into the fluid resevoirs.
Bleeding master cylinder question
