240z Brake bleeding issues. Faulty master cylinder?

[Tomzern]

Hi

I am struggling with brake bleeding these days.

I have had the complete brake system off the car, and rebuilt the front calipers with new seals. The rear brake cylinders were completely blocked, so I had them out, inspected and cleaned them good. The master cylinder and brake booster was just taken off to have the engine bay painted, and then mounted back in without inspection.

Now the issue is that I can't seem to get rid of the air in the rear brake system. I bleed and bleed and bleed, but it is just like it pulls in air through the master cylinder:mad:

I follow the procedure, bleeding the master cylinder first, then rear right, rear left, front right, front left.

A friend keeps pressure on the pedal while I open the bleeder. Brake fluid streams out (with tiny air bubbles). Then the pedal drops to the bottom, I close the bleeder, and he releases and press the pedal again.

When bleeding the front brakes, there seems to be no air, but the pedal DOES NOT DROP to the bottom as it does when we bleed the rear brakes...

No matter how many times I pump the brake pedal, it does not get any harder. No pressure buildup what so ever...And oh, the brake lamp in the dash comes on when I push the pedal hard, which means that the pressure between front and rear is uneven, right?

Does this sound like a master cylinder problem?

Thanks,

Tomzern

[Kurbycar32]

could be that the master cylinder is drawing air through a faulty seal. If you havent already, rebuilding a MC is pretty darn simple. Also at least here in the states you can buy a pre-rebuilt MC for around 35 bucks, but i notice you are in Norway so i have no idea whats available in your area.

[EuroDat]

I would change the MC. An old MC is often pitted and corroded in the sections where the piston seals dont reach. When you bleed the brakes the seals will be damaged when they move over this corrosion and fail shortly after.

If Im bleeding the brakes with an old MC, I use a vacuum bleeder. That way I don't have to push the pedal to the floor and damage the piston seals.

The rears wheel cylinders are generally hard to bleed. Sometimes leaving it settle a couple of hours and try again can help. That lets the air accumulatein sections instead of small bubbles through the hole system.

Chas

[black gold man]

Are the adjusters tight enough . When spinning the wheel by hand it should only go half a revolution.

Then the cylinders will have something to push on and not overextend .

[Jeff G 78]

How are you bleeding the MC? It is critical to get the MC bleed right before moving to the corners.

[Tomzern]

Thank you guys for all the answers

Jeff; I bleed the MC like I bleed the corners. Pressure on the pedal, open and close valve, then pump and pressure again. Is this incorrect?

Anyways, I just ordered a new MC on eBay along with a new oil pressure sender as mine is leaking. Hopefully it will make things work better. I will also borrow a vacuum bleeder the next time

[Jeff G 78]

Tomzern, the way that most Z guys and gals find works best is to attach a tight-fitting 6" long hose to the MS's front bleed valve with the free end submerged into the reservoir under the fluid level. Now crack the bleeder and simply pump the pedal slowly up and down until no more bubbles appear. Close the bleeder and repeat for the rear bleeder. Using this method, I've never failed to get an air-free MC. If you open the bleeder too far or can't get the bubbles to stop, remove the bleeders and add a light coat of grease to the threads to seal them with the bleeder is cracked open.

[Darrel]

This is what I use when bleeding brakes. I keep it above the corner I'm working on so the air goes up. When disconnecting it, put it on the ground and close the bleeder.

[Tomzern]

Found out after I did all the other things, that I had switched left and right front calipers so that the bleeders were at the bottom:rolleyes:

Also found out that the rod inside the brake booster was adjusted waaay to far in, so now that I have fixed those things it seems that the brakes are working just fine

Thanks for all your help guys!

[EuroDat]

Thanks for all your help guys!

Your welcome. Only thing is none of us mentioned the two causes that gave you this problemLOL.

They have been suggested before, but not in this thread.

Glad to hear you solved it. Now you can enjoy the summer driving safely.

Chas

Edited May 16, 2014 by EuroDat