I just replaced the original master cylinder with a new single bore master cylinder. Is bench bleeding it necessary? In the shop manual it just says to fill the master cylinder and pump the brake pedal about 5-7 times and then bleed the brakes. Whatís the best/easiest way if I do need to bench bleed it? The master cylinder didnít come with anything for bleeding it. Thanks
Honestly, I never knew of the term "bench bleed" when I replaced any of the master cylinders I swapped out when I was younger. I simply replaced the master, filled it up, and had someone help me bleed all the brakes. How I ever did it without "bench bleeding" and the brakes worked will always be a mystery to me.
I think the purpose here is to make sure all air bubbles are out of the system. If the master were not level on the car, I suppose you could have a trapped air bubble. To me, bench bleeding it out of the car just ensures the master can be held level and you get a complete compression on the master cyl piston. It is also less messy because you are pumping the fluid from the master cyl well through the chambers to eliminate air and pumping right back into the cyl well - kinda like recyling it. You can see when there is no air in the master. Then you can install and then bleed your brake system like normally done.
I use a long screw driver to compress the piston. If you master cylinder did not come with the adapter fitting/clear plastic tubing, you can purchase these very cheap at most auto stores.
Here is a pretty good Youtube video to watch. It is a dual reservoir master cylinder, but the principals are still the same.
Again, you can probably install it and have a buddy help bleed the brakes, but you will most likely go through a lot more brake fluid making sure you got all the air out.