Bleeding master cylinder

[wipeout]

Hi,

I just lost all of my rear blake fluid in the master cylinder from a rusted line. Replaced all of the brake lines and bled them but now rear brakes dont work good.

Should I bench bleed the master cylinder Im thinking maybe air got in there. Or any other ideas on what I should look for also.

Thanks.

 

[The Car Whisperer]

I had a 69 Corvette many years ago and if I remember there is more than one bleeder screw on each caliper. Also think you may have to rotate the caliper to get the bleeder screw in an upright position to get all of the air out. I'm sure you will get a more definite answer in this forum shortly.

 

[wipeout]

Im looking more for info on the master cylinder. It was completely dry when I took the cover off. The front has lots of pressure but the rear does not. Would it most likely be the master cylinder.

When I open up the rear bleeder screws there is barely any fluid/pressure coming out. There does not seem to be any leaks in the brake lines either.

 

[wishuwerehere82]

Wipeout,

It's not unusual to cut an O-ring in the master cylinder when losing line pressure. The piston overtravels the cylinder and nicks the O-ring at the end of the cylinder.
I think that would explain the loss of pressure in the rear calipers.
Although the front calipers have a larger braking surface, the pressure in the system should be the same, as in there shouldn't be a huge difference in the pressures from front to back.
Also, when you bleed the calipers, you should feel a pedal resistance until you crack the bleeders open. If you don't feel the change and the pedal doesn't immediately start to move, then you probably need a new M/C.

You can bleed the cylinder without removing it from the firewall, but you will need plastic fittings to hook up the pressure lines to return to the reservoir. You can get them at auto parts stores, or they come with a new M/C.
You can see how much fluid is being pumped by the pistons on both of the two circuits out of the cylinder.
Of course, you will need to bleed the lines again after you finish bleeding and reconnect the lines.

 

[wipeout]

Ok i tried to bleed the master cylinder while it is still attached to the car. The front compartment has lots of pressure but still not getting anything out of the rear. Gonna try bench bleeding which most likely wont work.

Then its a new master cylinder I guess.

 

[Vettehead Mikey]

To answer your original question- yes, you should bleed the master cylinder. Without doing so almost guarantees not being able to bleed the brakes properly.

Mike

 

[The Car Whisperer]

If the cylinder was comnpletely dry you may have pushed some air into the calipers, if not properly bleed there you will trap air in the calipers as well as in the master cylinder. You should bleed the master cylinder first then the calipers. Some master cylinders from that era have bleeder screws located on them as well. Once you have introduced air in the system you have to bleed it out no matter were it is or you will never have a hard brake pedal. ALso as stated before in an earlier reply you may have cut the seal on the master cylinder by pushing the pedel down farther than it has normaly been. If that is the case you will most likely need to replace or rebuild the master cylinder. Keep in mind though that you need to follow the bleeding procedure correctly for this vehicle or you will have problems.

 

[crause]

If the old line was so rusted that it broke, there could be some rust that became lodged in the line or in a block. starting at the master cyl. go back to each point that you can open the line and try and bleed from there to see if there is any blockage. Good luck.

Andy

 

[wipeout]

Thanks for all the help guys.

I tried bench bleeding it and there does not seem to be any pressure in the rear chamber. The brake fluid almost shoots out in the front chamber but nothing in the rear so im guessing the seals are busted.


I just ordered a new one should be in tomorrow.

 

[wipeout]

so i bled the new one and now I have amazing brakes. Very solid and responsive. Yippppeeeee

Thank

 

[wishuwerehere82]

ALLLLLLLRIGHTY THEN!
I love it when good solid information is used in a constructive manner.
Good work, Happy trails!