Re bleed needed?

[Wally]

13 hours ago, Zed Head said:

Kind of sounds like the MC was damaged when you ran it through a full stroke to bleed the brakes.  Not uncommon, EuroDat has described it in past posts.

Basically, for brakes, if you can pump the pedal and it gets higher and firmer it's air in the system.  More bleeding necessary.  If pumping does not work at all it's an MC seal problem.  The MC pressure seals can leak without the MC having an external leak.

If you installed a new MC it can still be bad out of the box.  Today's aftermarket parts.

p.s. I also just read a post on a different forum where a guy had a wheel cylinder that sucked air but did not leak fluid.  Impossible to bleed.

the pedal definitely gets firmer when its pumped. I bled it pretty good at all the wheels, starting with farthest and working toward the closes to MC. i can do it again but doubtful on results. Just not sure how the Booster might play into this knowing what we know.

[Zed Head]

Two common bleeding problems are having the bleed screws on the bottom on the front calipers, and having one of those disc brake swaps on the rear, with the bleed screw in a new orientation from the factory design.  Air in the system shouldn't be affected by the booster.

I mentioned the guy who sucked air in to the rear cylinder.  Air will get past a seal much easier than liquid will get out.  A description of your bleeding method might have a clue.  Are you using a vacuum bleeder?

[Wally]

5 minutes ago, Zed Head said:

Two common bleeding problems are having the bleed screws on the bottom on the front calipers, and having one of those disc brake swaps on the rear, with the bleed screw in a new orientation from the factory design.  Air in the system shouldn't be affected by the booster.

I mentioned the guy who sucked air in to the rear cylinder.  Air will get past a seal much easier than liquid will get out.  A description of your bleeding method might have a clue.  Are you using a vacuum bleeder?

On front end bleed valves are on top side, on back end (drums) bleed valve is near bottom area. Here is process i used to bleed brakes.

1) I took off tires

2) filled reservoirs and made sure they stayed full in MC

3) Started at farthest tire from MC working to closest.

4) Had wife or son pump brakes about 4-5 times and hold pedal to floor. I then released valve pressure, then tightened valve back. Wife/son then let off

the brake pedal. I repeated this about 3 times for each tire.

[Zed Head]

I'm no expert but I've always done one slow pump with the bleed screw open, close screw before end of pump, release pedal slowly so that the fluid can get in from the reservoir, repeat.  Pumping 4 or 5 times doesn't really accomplish anything, I think.  It might even force the bubbles in to solution in the fluid, from the pressure, or cause them to break up in to many small bubbles.  Ideally, you want one big bubble sitting at the bleed screw opening, waiting to get out.

Or, if I don't have a helper, I open the bleed screw, press the pedal down with a broken shovel handle through the driver's window, prop it against the seat at the bottom of the stroke, walk over and close the screw.  Still a very slow pump.

On the back I installed speed bleeders.  They made a big difference.  Again though, a very slow pump.  Once the air gets out you want the hydraulic lines to refill from the reservoir, not suck back through the bleed screw or the bleed screw threads.  Air has much lower viscosity than brake fluid.  It moves fast.

[Wally]

5 hours ago, Zed Head said:

I'm no expert but I've always done one slow pump with the bleed screw open, close screw before end of pump, release pedal slowly so that the fluid can get in from the reservoir, repeat.  

will give your method a try...it cant hurt

[Wally]

On 12/21/2022 at 10:51 AM, Zed Head said:

I'm no expert but I've always done one slow pump with the bleed screw open, close screw before end of pump, release pedal slowly so that the fluid can get in from the reservoir, repeat.  Pumping 4 or 5 times doesn't really accomplish anything, I think.  It might even force the bubbles in to solution in the fluid, from the pressure, or cause them to break up in to many small bubbles.  Ideally, you want one big bubble sitting at the bleed screw opening, waiting to get out.

Or, if I don't have a helper, I open the bleed screw, press the pedal down with a broken shovel handle through the driver's window, prop it against the seat at the bottom of the stroke, walk over and close the screw.  Still a very slow pump.

On the back I installed speed bleeders.  They made a big difference.  Again though, a very slow pump.  Once the air gets out you want the hydraulic lines to refill from the reservoir, not suck back through the bleed screw or the bleed screw threads.  Air has much lower viscosity than brake fluid.  It moves fast.

it worked. brakes working pretty good now. Thanks a bunch