Bench bleeding a Master Cylinder
Thread Starter
Advanced
Joined: Apr 2009
Posts: 96
Likes: 0
From: Columbus GA
Bench bleeding a Master Cylinder
I am in the process of finishing a conversion from Manual to Power Brakes. I have modified the fire wall and the break pedal to accept the new power booster. I have heard the term "Bench Bleed" in reference to the master cylinder. Can anyone explain what this is and the process to get fluid in the system and bleed correctly?
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
Bench bleeding a MC refers to the process used to fill the piston well with fluid before installation. It's not absolutely necessary, but if you don't bench bleed, you'll send a lot more air down the lines that you'll have to bleed out of the calipers anyway.
There are bench bleeding kits you can get cheap. It's just 2 plastic fittings that go into the hardline ports with short lengths of tubing that you route back into the reservoirs. Fill the reservoirs up, hook up the bench bleed kit, pump the piston slowly in and out with a screwdriver until you don't see bubbles going through the tubes, and keep the reservoir topped off.
There are bench bleeding kits you can get cheap. It's just 2 plastic fittings that go into the hardline ports with short lengths of tubing that you route back into the reservoirs. Fill the reservoirs up, hook up the bench bleed kit, pump the piston slowly in and out with a screwdriver until you don't see bubbles going through the tubes, and keep the reservoir topped off.
Pro
Joined: Feb 2006
Posts: 718
Likes: 7
From: Jacksonville , NC
I am in the process of finishing a conversion from Manual to Power Brakes. I have modified the fire wall and the break pedal to accept the new power booster. I have heard the term "Bench Bleed" in reference to the master cylinder. Can anyone explain what this is and the process to get fluid in the system and bleed correctly?
Hope this makes sense. Im sure others will chime in.
Thread Starter
Advanced
Joined: Apr 2009
Posts: 96
Likes: 0
From: Columbus GA
Heres my understanding and first hand experience. When you are installing a new master cylinder there is a great chance of having air trapped in the master cylinder. There is a bench bleeding kit (I got mine at NAPA for around $15. It consists of some plastic fittings that screw into the master cylinder ports that you would normally attach the brake lines to. Use a small section of rubber hose , attach it to the fittings and return the hose back into the master cylinder resovior. Pump the MC rod until no bubbles appear, remove the fittings, attache your lines and bleed the brake system as normal. It is important to have the MC level when you do this so many, but not all recommend doing it prior to installing on the car.
Hope this makes sense. Im sure others will chime in.
Hope this makes sense. Im sure others will chime in.
Le Mans Master
Joined: Mar 2001
Posts: 6,639
Likes: 287
From: Ann Arbor Michigan
I was able to pick up this kit from NAPA. It has variuos plastic fittings but came with only one length of rubber hose. Do you blead both fittings at the same time or do them one at a time. When finished, if you unscrew the plastic fittings, will the MC leak fluid out of these fitting holes?
Gary
Thread Starter
Advanced
Joined: Apr 2009
Posts: 96
Likes: 0
From: Columbus GA
Do them both at the same time otherwise you will eventually build up pressure in one side and won’t be able to bleed the other. You basically want to just pump the fluid back into the reservoir until all the air is gone. This pic shows using a couple pieces of copper tube.
Gary
Gary
