Bleeding Brakes

[1moretoy]

Hey guys quick question on the brakes. All components are brand new. Calipers, manual master cylinder and lines. Calipers are C6 Zo6 corvette and a Willwood master. I asked A friend of mine who is a mechanic about bench bleeding the master before installing it. I didn't want to mess with fluid getting everywhere when hooking up the lines. He said to just use his vacuum system to bleed the system and not to worry about bench bleeding the master. What are your thoughts on this?

[Rickysnickers]

Well, I would say that you should bench bleed your new master. I have a Wilwood unit as well. With the parts and bits they include with their master, it makes it very easy and it really isn't that messy.

[RichardJ]

As you suspected, bench bleeding is a bunch of hooey on a horizontally mounted master cylinder. Bench bleeding became important in the 70's when they started mounting the MC at crazy angles. As you can see in this image, there is air trapped in front of both pistons. The fluid is level with the vent holes preventing the air from escaping into the reservoir. Mounted level the air will escape on its own. Sometimes a couple of taps with a wrench will encourage any persistent air bubbles to pop out.

You can go to great lengths trying to keep air from entering when you remove the plugs or bleeder lines, but guess what. It's still going to happen. Unfortunately, with a high angle mounted MC, you usually do need to bench bleed.

[1moretoy]

My master Is pretty level. You can see it in the picture.

[davepl]

That's kind of funny because I had a talk with a respected tech who was installing a new master without bleeding it. I was kind of disappointed, like he was skipping a step, something I didn't expect he'd do.

At the time, however, he had the back of the car 5 feet in the air to make the master level to the ground. Which accomplishes, I guess, the exact same thing! Shouldn't have doubted him :-)

[1moretoy]

Originally Posted by RichardJ

As you suspected, bench bleeding is a bunch of hooey on a horizontally mounted master cylinder. Bench bleeding became important in the 70's when they started mounting the MC at crazy angles. As you can see in this image, there is air trapped in front of both pistons. The fluid is level with the vent holes preventing the air from escaping into the reservoir. Mounted level the air will escape on its own. Sometimes a couple of taps with a wrench will encourage any persistent air bubbles to pop out.

You can go to great lengths trying to keep air from entering when you remove the plugs or bleeder lines, but guess what. It's still going to happen. Unfortunately, with a high angle mounted MC, you usually do need to bench bleed.

So do you think I'm ok not bench bleeding?

[1moretoy]

Anyone else have any input. I would like to finish this up this week.

[tdangle]

I was always under the impression that you bench bled the m/c was so you wouldn't have as much work to do bleeding the entire system at each wheel. What is the difference between pushing the air out at the connection to the m/c or wheel cylinder?

[LPoole]

Just recently added power brakes to my 68 fleet. Mounted the new m/c booster combo then bled it on the truck using the plastic hoses they provided and had no problems.

[70SBC10BOB]

Been a certified tech for 40 plus years and vp of a brake company.

Always bench bleed the m/c. When you try to bleed them on the vehicle, you may not make the piston travel the full stroke of the m/c, that leaves a bubble at the end of the m/c bore. Bench bleeding takes any doubt out of the equation.

With all the work we put into making these trucks nice, why risk a no brake situation if the bubble travels into the system?

Nice drawings RichardJ

That's my 10 cents worth (it used to be 2 cents but we had inflation.)