Bleeding Master Cylinder

[LJS30]

I have bled my brakes before the standard way at the wheels. However what's the procedure for bleeding them at the master cylinder?

 

[69signetv8]

Bleeding or priming a Master is usually the first thing done prior to brake bleeding. Traped air left in the master "could" have you running in circles. Also doing it on a bench is EZer to contol then in the car. You will need a extra person of course.
I made up 2 extra fittings with 4" steel tubing for the outlets and then added 14" clear tubing to the steel tubing. These two outlet ends will go into a jar with about 1" of brake fluid.
Ensure the master is full and have someone "GENTLY" push the brake about 1-inch and hold it steady without pumping. This first opens of the valve to let fluid fill the rod cylinder and some air excape. You will notice (looking into the master) air bubbles coming to the surface. This could take some time. Repeat this a few times to ensure the rod cylinder has no air. Add more fluid if required. Next will be the pumping, however do it slowly or fluid will fly all over the place. Watch the clear tubes at the outlets to jar. When the fluid comes out clear and without any air your set. It's important to keep the master full and don't allow any air back into the rod clyinder or you will have to start all over again. The outlet have valves, so you shouldn't loose much fluid returning doing up the "real connections".
The remainder of the system brake bleeding is "the regular" method. KEEP the master full at all times and start bleeding the furthest rear brke first working to the closest. Use again a clear tube around the fitting and watch for air.
IMPORTANT...
Ensure your helper pumps up the system until it's firm and holds it. Crack the fitting and watch for air. As the peddle go's to the floor ensure your helper doesn't let up on the brake peddle until your fitting is closed or air will be sucked back into your system. Repeat until your satisfied no air is in the system.
PS New clear fluid showing at the fitting with no air is the plan..
Cheers.

 

[LJS30]

Thanks for the quick response and exellent instructions. I will go right ahead.

 

[redfastback]

you can also just use brake line and fittings and plumb them up and back into the master cylinder bowls. keep the fluid level up, leaving about 1/4" from the lip. press in with a #3 phillips screwdriver in the pushrod hole. it will go in pretty far, but will eventually get to the point of being hard to push in. at that point it will only go in about 1/8-1/4" and you will see only a stream come out of the bowls and no more air bubbles.

 

[LJS30]

Okay guys, I actually went ahead and ordered both the master cylinder and booster together. They came as one package already bolted together. One guy says I don't have to bench bleed while another says I do. What is it?

 

[340mopar]

you can also just use brake line and fittings and plumb them up and back into the master cylinder bowls. keep the fluid level up, leaving about 1/4" from the lip. press in with a #3 phillips screwdriver in the pushrod hole. it will go in pretty far, but will eventually get to the point of being hard to push in. at that point it will only go in about 1/8-1/4" and you will see only a stream come out of the bowls and no more air bubbles.

This is exactly how I bleed a master cylinder. I cut off the first 6" of brake line off of a parts car and this is what I use.

Chuck

 

[69signetv8]

This is exactly how I bleed a master cylinder. I cut off the first 6" of brake line off of a parts car and this is what I use.

Chuck

Your right if talking about bleeding a "new" master with new fluid...The idea of the jar methed is not to return the older crap fluid back to your system which makes sence in my mind. :read2: (each to their own) on this one I guess

 

[340mopar]

Your right you don't what to recycle the old fluid back thru the system. I was speaking of a new master and I am stuck bleeding by myself that is another reason why I use the "tubes". By the way your method of the jar and clear tube works good for bleeding at the wheels by yourself. As long as the tube is below the level of the fluid in the jar you can just pump away without getting air back into your system. This is what I use.


Chuck

 

[69signetv8]

Your right you don't what to recycle the old fluid back thru the system. I was speaking of a new master and I am stuck bleeding by myself that is another reason why I use the "tubes". By the way your method of the jar and clear tube works good for bleeding at the wheels by yourself. As long as the tube is below the level of the fluid in the jar you can just pump away without getting air back into your system. This is what I use.


Chuck

If I could find a long enough hose to WA..I would get you to help me Chuck:toothy10:

 

[LJS30]

Okay, everything looks good, brakes nice and easy with little effort. One problem though, I slightly overfilled the front reservoir so a little fluid was seaping out of the top. This happened when I really slammed the breaks for testing purposes. Will this level go down or have I screwed up the rubber gasket?

 

[redfastback]

no, just always leave about 1/4" for expansion. also check to see that the cap is on center and not just off to one side.