Bleeding Issues

[CDL1542]

Zed Head,

Pumping the pedal during the bleeding process I did build up pressure, however once the system was fully bled and closed off I did not. Even pumping the pedal at this point did not build up pressure. Oddly enough, no leaks developed which is what I thought the issue might have been. I will go ahead and re-bleed the master cylinder and go through the process again, but I am not sure what could be the cause of this.

 

Chris

 

[Patcon]

If you let the master cylinder run low on fluid near the end of the bleeding process it could cause this but rare...if the master cylinder burps when you bleed it you let the fluid get too low during bleeding

[Mark Maras]

IMO it has to be either air or a bad seal in the MC. If you're SURE the MC didn't run dry at any point during the bleed procedure, I'd remove, disassemble & inspect the MC to make sure the problem isn't internal. You mentioned the MC was new. Was it by any chance new(rebuilt)? There was a recent discussion about foreign matter being found in rebuilt MCs.

 

[gundee]

I will give you my method. This is for when the system is drained empty from doing work such as you did. It took me a very long time to figure this

out on my own. I was doing what you are doing with poor results.

First remember the front and rear are separate systems. You can start wherever you want & on which side you want. The farthest bleeder

is a myth in my opinion.

Using the pedal to bleed an empty system is not only time consuming but is also fruitless in getting a good pedal.

Start by filling the master cylinder which is already completed in your case.

Next pick either the front or the rear and open one of the bleeders and gravity drain keeping an eye on the master cylinder level. Then close bleeder and go to the

other side and repeat. Do not touch the brake pedal yet. This is what ruins the process.

Next go to the opposite end you started (front or rear) and repeat the same

process. On an empty system you will go through about one and a half cans.

Now with all the bleeders closed, try the brake pedal. If you have drained enough fluid through you should now have a rock hard pedal.

Try it out. Cannot hurt a thing.

I have not used a hand vacuum pump instead of gravity but that should work good as well.

[Zed Head]

5 hours ago, CDL1542 said:

Zed Head,

Pumping the pedal during the bleeding process I did build up pressure, however once the system was fully bled and closed off I did not. Even pumping the pedal at this point did not build up pressure.

This sentence isn't super clear.  Maybe you're saying that because fluid squirted during the bleeding process, there must have been pressure?  But then after squirting a bunch of fluid and air bubbles, the bleeders were closed, but no pedal pressure could be built.  So that could be a weak seal in the MC, or there's still air in the system.  You can build low pressure to squirt fluid but then still have an air bubble that will compress when the bleeders are closed.

[CDL1542]

11 minutes ago, Zed Head said:

This sentence isn't super clear.  Maybe you're saying that because fluid squirted during the bleeding process, there must have been pressure?  But then after squirting a bunch of fluid and air bubbles, the bleeders were closed, but no pedal pressure could be built.  So that could be a weak seal in the MC, or there's still air in the system.  You can build low pressure to squirt fluid but then still have an air bubble that will compress when the bleeders are closed.

The pedal built up pressure as I bled the brakes and fluid and air came out. When the bubbles stopped, I closed it off and removed the bleed hose. I'm going to bleed them once more starting with the MC and if that doesn't do it, I think it would be safe to assume that the MC is shot. It was a 15/16 master cylinder from a 280ZX that was rebuilt

[Zed Head]

Not uncommon.  If I was having this problem I would remove the lines from the MC that supply the front and rear systems and block them (using old lines and fittings or sticking a piece of rubber under the fitting).  Then use the MC bleeders to bleed the MC.  That should give the firmest pedal you'll ever get.  IF the MC seals are bad you'll never get a firm pedal.  Then attach the rears and bleed them, then the fronts.  Break the system down in to its three elements and test each.

You have to remove those lines anyway to replace the MC.  Might as well test it on the way out.

[CDL1542]

15 hours ago, Zed Head said:

Not uncommon.  If I was having this problem I would remove the lines from the MC that supply the front and rear systems and block them (using old lines and fittings or sticking a piece of rubber under the fitting).  Then use the MC bleeders to bleed the MC.  That should give the firmest pedal you'll ever get.  IF the MC seals are bad you'll never get a firm pedal.  Then attach the rears and bleed them, then the fronts.  Break the system down in to its three elements and test each.

You have to remove those lines anyway to replace the MC.  Might as well test it on the way out.

Seems like a very logical way to do it. I will try it and post back later this week on how it goes. I appreciate the help.

 

[Ravaicito]

Have you find out was the problem was?

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