Master Cylinder bleed screws
Thread Starter
Racer
Joined: May 2005
Posts: 399
Likes: 4
From: Suffield CT
Master Cylinder bleed screws
Hi, i have 69 with L-46. i think master cylinder is correct one in the car. Anyway i can't find any documentation on the 2 bleed screws in the master cylinder, like how and when to use them ?
I have the 1969 chassis manual and they show the bleed screws in the master cylinder in the pictures but never mention them.
i got the Dorman 13910 bleed kit and am starting to wonder if i need to connect it to the brake lines in the master or just put the tubes on the bleeders and just unscrew them to try and bleed the master cylinder a little.
My goal was to see if i could make sure little to no air is in the master cylinder while it is still on the car.
Thanks.
-ALF
I have the 1969 chassis manual and they show the bleed screws in the master cylinder in the pictures but never mention them.
i got the Dorman 13910 bleed kit and am starting to wonder if i need to connect it to the brake lines in the master or just put the tubes on the bleeders and just unscrew them to try and bleed the master cylinder a little.
My goal was to see if i could make sure little to no air is in the master cylinder while it is still on the car.
Thanks.
-ALF
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From: Madeira Beach, FL
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I have a 68 w/ PB and recently replaced the MC with the same one you described. I bench bled it using the those bleeders and the kit. I then installed and bled again with wife behind the brake pedal same method. Finally bled all 4 all around. Start with the right rear outer/inner bleeders than the left rear same and move to right front then lastly drivers side front.
Rear calipers have two bleeders fronts have only one. Bleed both backs.
Marshal
Rear calipers have two bleeders fronts have only one. Bleed both backs.
Marshal
Thread Starter
Racer
Joined: May 2005
Posts: 399
Likes: 4
From: Suffield CT
Thanks, this always happens, i post and then i find my answer with google...sorry for the noise.
https://www.corvetteforum.com/forums...nder-72-a.html
https://www.corvetteforum.com/forums...er-screws.html
-ALF out...
https://www.corvetteforum.com/forums...nder-72-a.html
https://www.corvetteforum.com/forums...er-screws.html
-ALF out...
Le Mans Master
Joined: Mar 2004
Posts: 7,477
Likes: 1,495
From: Little Rock AR
Thanks, this always happens, i post and then i find my answer with google...sorry for the noise.
https://www.corvetteforum.com/forums...nder-72-a.html
https://www.corvetteforum.com/forums...er-screws.html
-ALF out...
https://www.corvetteforum.com/forums...nder-72-a.html
https://www.corvetteforum.com/forums...er-screws.html
-ALF out...
The bleeder screws were used on the assembly line only. The service manual does not ever address them because they are never used in service.
Le Mans Master
Joined: Mar 2004
Posts: 7,477
Likes: 1,495
From: Little Rock AR
While we are on the subject....It is possible that the bleeder screws on the master cylinder could have been originally applied to power brake systems where the master cylinder is mounted at an angle. The idea is it would be used to get the original trapped air out. The idea sounds like it could be true but if so, you would expect it might be covered by the factory service manual. The manual DOES cover bench bleeding a fresh master cylinder before installation and that would be done with the master cylinder off the car and level. The master cylinder bleeder screws would serve no purpose there so no need to mention it. Not 100% certain here but it seems plausible.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Having worked numerous years in automotive production lines, I can tell you that every task there is designed for speed & efficiency. If one worker / work station screws up, the whole line goes down and that backs-up the preceding lines. And if the line goes down, somebody is going to get an ***-chewin.
Having said that, try to picture these Vettes coming down the line at a fairly good clip, doors closed, hood open and all caliper bleeder screws are open. The master cylinder is empty but the MC lid is on with bales clamped. At this point on the assembly line there could have been a pit under the car. Down there was likely a worker that attached six hoses to the bleeders. Topside a worker grabbed a hose from the ceiling and attached a twin snap-on fitting to the MC bleeders. Pulling a trigger DOT3 filled the MC, all the lines, prop valve, calipers and out the bleeder hose all in about 10 seconds. Worker underneath verifies no bubbles, closes bleeders, detaches hoses. And never touching the brake pedal. Next !
Having said that, try to picture these Vettes coming down the line at a fairly good clip, doors closed, hood open and all caliper bleeder screws are open. The master cylinder is empty but the MC lid is on with bales clamped. At this point on the assembly line there could have been a pit under the car. Down there was likely a worker that attached six hoses to the bleeders. Topside a worker grabbed a hose from the ceiling and attached a twin snap-on fitting to the MC bleeders. Pulling a trigger DOT3 filled the MC, all the lines, prop valve, calipers and out the bleeder hose all in about 10 seconds. Worker underneath verifies no bubbles, closes bleeders, detaches hoses. And never touching the brake pedal. Next !
Last edited by HeadsU.P.; Oct 22, 2020 at 04:01 PM.
