bench bleeding new OEM master Cylinder
Thread Starter
Instructor
Joined: May 2018
Posts: 248
Likes: 11
bench bleeding new OEM master Cylinder
I bought an OEM Master cylinder so according to the instructions :
Remove plastic plugs
Add Brake fluid and when the fluid strarts to drip out of the holes screw in the plastic supplied bolts
Using a blunt nose tool ( large phillip screw driver) and push the plunger 3/4 to 1"
Repeat untill it becomes difficult to move it in up to 1/8 "
Well after I started pushing in the plunger I could only mover it maybe 1/4" at a trme. I could see the front reservoir moving fluid and no bubbles'
The back reservoir showed bubbles everytime, but why was the plunger only moving 1/4" strokes. I have bench bled MC's before so I am wondering if I bought a reject.
Remove plastic plugs
Add Brake fluid and when the fluid strarts to drip out of the holes screw in the plastic supplied bolts
Using a blunt nose tool ( large phillip screw driver) and push the plunger 3/4 to 1"
Repeat untill it becomes difficult to move it in up to 1/8 "
Well after I started pushing in the plunger I could only mover it maybe 1/4" at a trme. I could see the front reservoir moving fluid and no bubbles'
The back reservoir showed bubbles everytime, but why was the plunger only moving 1/4" strokes. I have bench bled MC's before so I am wondering if I bought a reject.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
The beauty of bench bleeding is the ability to tilt the master nose down, nose up and level while in the vise.
The reason for all this tilting is, a guaranteed bubble is still lurking in a chamber hidden inside.
The force you exert with your screwdriver on the piston is nowhere near what the brake pedal will do later. So the best you can do is only limited piston travel.
The piston usually travels farther than what you finished with. I believe you need to put more force into it.
But wait! There's more:
Do Not Force Piston / screwdriver In More Than 1 & 3/8 inches. Doing so will void the MC warranty.
But let's go back to these plastic plugs you mentioned. Do they have a plastic hose included? In other words, is this a "bench bleeding kit"?
The hoses (two) would feed the DOT3 right back into the rez with each stroke. The kits are cheap, but do work well.
Remember, that after bench bleeding, installing MC and removing the plugs, you still have introduced a bubble between the master's ports and your brake lines.
A complete bleed, all six screws, is in order.
Click on my avatar, look for bench bleeding photo albums.
The reason for all this tilting is, a guaranteed bubble is still lurking in a chamber hidden inside.
The force you exert with your screwdriver on the piston is nowhere near what the brake pedal will do later. So the best you can do is only limited piston travel.
The piston usually travels farther than what you finished with. I believe you need to put more force into it.
But wait! There's more:
Do Not Force Piston / screwdriver In More Than 1 & 3/8 inches. Doing so will void the MC warranty.
But let's go back to these plastic plugs you mentioned. Do they have a plastic hose included? In other words, is this a "bench bleeding kit"?
The hoses (two) would feed the DOT3 right back into the rez with each stroke. The kits are cheap, but do work well.
Remember, that after bench bleeding, installing MC and removing the plugs, you still have introduced a bubble between the master's ports and your brake lines.
A complete bleed, all six screws, is in order.
Click on my avatar, look for bench bleeding photo albums.
Safety Car
Joined: May 2001
Posts: 4,759
Likes: 1,647
From: Fairfax Virginia
Thank you HeadsU.P. as your post was very educational. I have bled many master cylinders in my mechanical life but I learned that what I am doing is not the complete job. I have been able to get bubbles less fluid out of the bleeding ports over the years.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
I bought an OEM Master cylinder so according to the instructions :
Remove plastic plugs
Add Brake fluid and when the fluid strarts to drip out of the holes screw in the plastic supplied bolts
Using a blunt nose tool ( large phillip screw driver) and push the plunger 3/4 to 1"
Repeat untill it becomes difficult to move it in up to 1/8 "
Well after I started pushing in the plunger I could only mover it maybe 1/4" at a trme. I could see the front reservoir moving fluid and no bubbles'
The back reservoir showed bubbles everytime, but why was the plunger only moving 1/4" strokes. I have bench bled MC's before so I am wondering if I bought a reject.
Remove plastic plugs
Add Brake fluid and when the fluid strarts to drip out of the holes screw in the plastic supplied bolts
Using a blunt nose tool ( large phillip screw driver) and push the plunger 3/4 to 1"
Repeat untill it becomes difficult to move it in up to 1/8 "
Well after I started pushing in the plunger I could only mover it maybe 1/4" at a trme. I could see the front reservoir moving fluid and no bubbles'
The back reservoir showed bubbles everytime, but why was the plunger only moving 1/4" strokes. I have bench bled MC's before so I am wondering if I bought a reject.
Then do this as the final bleeding of the MC.
Get the last bit of air out from the brake master cylinder. - CorvetteForum - Chevrolet Corvette Forum Discussion
