Big Brakes

[pormgb]

Originally Posted by DanEC

That would be a tough question to answer - it will depend on the car. You would need to total the area of all the caliper piston bores, assume an amount of piston travel to bring the pads against the rotors and compute a volume of fluid from that. Then convert that volume in to piston travel based on the area of the 1 inch piston in the MC.


For instance - the combined piston area of your front brakes is 11.65 sq inches each or 23.3 in sq for both fronts. I don't know what your rear brakes are but for example use a 2-piston caliper with 2 inch pistons. They would be 6.14 in sq per caliper or 12.28 in sq for both. All brakes would total 35.58 in sq piston area.

Assume the pistons travel 1/32 inch on each side to bring the pads into contact with the rotor - that's 1.112 cu inches of brake fluid.

The 1 inch MC piston is .785 sq inches. 1.112 cu in / .785 in sq = 1.417 inches MC piston travel.

Not sure if that 1/32 inch travel is reasonable or not. The MC definitely should not bottom when applying the brakes.

Hmm, make sense and means I have way too much travel.

I am using GM Metric rear calipers, the type found on Cadallac Eldorado's with built in parking brake. These calipers have 2.380 in pistons.

To state again, when I pump the brakes the pedal gets quite hard, wait a minute and it soft.

[cycleguy55]

Originally Posted by pormgb

Hmm, make sense and means I have way too much travel.

I am using GM Metric rear calipers, the type found on Cadallac Eldorado's with built in parking brake. These calipers have 2.380 in pistons.

To state again, when I pump the brakes the pedal gets quite hard, wait a minute and it soft.

The fact it's going soft says to me there's air in those lines. I went with 'speed bleeders' when I did my brake conversion (Wilwood 4 piston front, GM rear) and I'm convinced they're the way to go. Bleeding is never a 'fun' task, but using them took the real hassle out of doing it so much I'm also planning to install them on our daily drivers.

[pormgb]

Originally Posted by cycleguy55

The fact it's going soft says to me there's air in those lines. I went with 'speed bleeders' when I did my brake conversion (Wilwood 4 piston front, GM rear) and I'm convinced they're the way to go. Bleeding is never a 'fun' task, but using them took the real hassle out of doing it so much I'm also planning to install them on our daily drivers.

Yep, I do have a power bleeder, I will pull it out this weekend and bleed all four corners,

[DanEC]

Originally Posted by pormgb

Yep, I do have a power bleeder, I will pull it out this weekend and bleed all four corners,

He's referring to the auto-valve bleeder screws. They have a one way valve in them to prevent air from getting back in the calipers. To use them you loosen them slightly, hook up a bleed hose to a can and then start pumping the brake pedal. When the pedal is pushed it forces fluid past the relief valve and as soon as the pedal is released the valve shuts - so you can pump all you want as long as fluid is in the reservoir of the MC. You don't need pressure or vacuum bleeder pumps.

They are how I finally got my ERA bleed out. But I thought back in the early part of your thread that you had these on your calipers ???

[cycleguy55]

Originally Posted by DanEC

He's referring to the auto-valve bleeder screws. They have a one way valve in them to prevent air from getting back in the calipers. To use them you loosen them slightly, hook up a bleed hose to a can and then start pumping the brake pedal. When the pedal is pushed it forces fluid past the relief valve and as soon as the pedal is released the valve shuts - so you can pump all you want as long as fluid is in the reservoir of the MC. You don't need pressure or vacuum bleeder pumps.

They are how I finally got my ERA bleed out. But I thought back in the early part of your thread that you had these on your calipers ???

Yes - you can see the Russell ones here: Aftermarket Brake Kit Application Guide - Speed Bleeders - Russell Performance Products

They're widely available in parts stores, speed shops, etc. and come in a variety of sizes to replace bleed screws in OEM and after-market calipers. For Wilwoods you only need a pair for each caliper to replace the upper bleed screws - you can leave the lower bleed screws in place as you'll never use them anyway.

BTW, my rear lines were pretty much completely dry when I bled them, and I was astounded how many pumps it took of the brake pedal before I got anything out. The key message is it may take a lot longer than you think before you get all the air out. Brake fluid is relatively cheap - don't be afraid to waste some, and always start with the wheel furthest from the MC and work closer as you go (RR, LR, RF, LF - for LH drive cars).

[pormgb]

Originally Posted by cycleguy55

Yes - you can see the Russell ones here: Aftermarket Brake Kit Application Guide - Speed Bleeders - Russell Performance Products

They're widely available in parts stores, speed shops, etc. and come in a variety of sizes to replace bleed screws in OEM and after-market calipers. For Wilwoods you only need a pair for each caliper to replace the upper bleed screws - you can leave the lower bleed screws in place as you'll never use them anyway.

BTW, my rear lines were pretty much completely dry when I bled them, and I was astounded how many pumps it took of the brake pedal before I got anything out. The key message is it may take a lot longer than you think before you get all the air out. Brake fluid is relatively cheap - don't be afraid to waste some, and always start with the wheel furthest from the MC and work closer as you go (RR, LR, RF, LF - for LH drive cars).

I just finished using my pressure bleeder, still no luck.

I will revert back to my wife's assistance and see how that goes.

[pormgb]

Originally Posted by DanEC

He's referring to the auto-valve bleeder screws. They have a one way valve in them to prevent air from getting back in the calipers. To use them you loosen them slightly, hook up a bleed hose to a can and then start pumping the brake pedal. When the pedal is pushed it forces fluid past the relief valve and as soon as the pedal is released the valve shuts - so you can pump all you want as long as fluid is in the reservoir of the MC. You don't need pressure or vacuum bleeder pumps.

They are how I finally got my ERA bleed out. But I thought back in the early part of your thread that you had these on your calipers ???

I have them on the rear calipers (GM Metric) and they are clean and work really well. The Sierra's have 1/8" bleeders, I could not find speed bleeders to fit the calipers. I take that back, I just found a 1/4-28 speed bleeder that fits in the 1/8" NPT housing.