Brake problems after rebuild

[derek murray]

My car has been up on jacks for the last two and a half years while I puttered away at a bunch of repairs. During this time I rebuilt all four calipers and installed new pads and rotors. This spring after having the car painted and motor put back in I set out for my first drive in a long long time. Unfortunately I got as far as the end of the drive way as I had no brakes whatsoever.... The pedal went right to the floor with zero stopping power. I then flushed out all the old brake fluid while thoroughly bleeding the the lines. The pedal was firm for one push and then down to the floor it went as soon as I started backing down the driveway. Today I replaced the master cylinder (thinking that was my problem), bled the lines... no change.

If I continually pump the brakes I can get a firm pedal, but no stopping power... and then the pedal drops to the floor again...

There are no leaks and I'm not losing any brake fluid... What could this be?


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[jass]

You may have installed the calipers on the wrong sides resulting in the bleeder screw being on the low side, which makes it si you cannot bleed all the air out of the system and then your situation results (I made that mistake myself).

[derek murray]

Originally Posted by jass

You may have installed the calipers on the wrong sides resulting in the bleeder screw being on the low side, which makes it si you cannot bleed all the air out of the system and then your situation results (I made that mistake myself).

Thanks for the response, but the bleeders are all on the top of the calipers.

I should add that when I did the front calipers the system worked fine as I still had the engine in at that point. So the only work done on the brake system since then was to rebuild the rears.


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[70basket]

How about the lines if they were open for that period of time they could have internal corrosion blocking the flow. Were the flex lines replaced?

[derek murray]

Originally Posted by 70basket

How about the lines if they were open for that period of time they could have internal corrosion blocking the flow. Were the flex lines replaced?

The lines were never open for more than a few days and fluid does pass through them when bleeding.

I'm wondering if I should manually bleed the brakes, as I've been using the Motive power bleeder exclusively.


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[timmy2]

Try manually bleeding as you suggested, just be sure not to push the brake pedal all the way to the floor as you could score the master cylinder. Put a 2x4 block of wood behind it.
(Love your location signature, I grew up there.)

[70basket]

+1 on the manual bleed, a plus is you can see how much fluid is pushed thru.

[doublebuffle]

Originally Posted by 70basket

How about the lines if they were open for that period of time they could have internal corrosion blocking the flow. Were the flex lines replaced?

Since he bled them the flow is not restricted, motive is 15psi, pedal is much higher psi. Motive was much easier for me since it moves enough fluid to watch it come out in sustained stream.

How much fluid have you put through the system?

[derek murray]

Originally Posted by doublebuffle

How much fluid have you put through the system?

About 16oz.


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[jjeffries]

I'd bet you need a new master cylinder. John

[doublebuffle]

Originally Posted by jjeffries

I'd bet you need a new master cylinder. John

I want to say this too. However, I think there is no harm in putting another bottle or two through just to make sure he got a good flush.

[AVDCAV]

With all that work you did why wouldn't you do a new master, its the heart
of the system.

[jjeffries]

Sorry Derek, saw you already did m-c. Did you bench bleed new one? John

[dfhtrhjn]

I've had excellent luck with the same power bleeder you use; I also rebuilt some calipers. You started with the caliper farthest from the master and worked to the closest right? (right rear-> left rear-> right front-> left front)

Did you put a long clear tube on the bleeder nipple? You can see bubbles move through the tube that way. Even one bubble can screw your pedal feel up.

In your shoes, I'd run a couple pints of fluid through the system just for good measure.

[mnez]

^^^ As he says. I've used the motive many times. How you move the fluid is not important.
You have air in the system. Make sure the fluid does get low enough in the reservoir to introduce new air. 16oz is almost certainly not enough to get the air out.
Buy a big jug of cheap clear brake fluid that you can waste. Once you have a good pedal, open the RR bleeder, and let it drain until the reservoir is almost empty. Top it off with a good fluid that has a bit of color and then let each wheel bleed by gravity until you see the new fluid appear. Top off the fluid as needed and work around to finish on the LF.
Good luck.

[derek murray]

I picked up a 4 litre jug of brake fluid this morning.... after work I'll thoroughly re-bleed as you have all suggested. I'll report back!

[derek murray]

I bled, re-bled and bled again.... pushing through almost 2 litres of brake fluid. No change... I am so bummed out. I'm at a complete loss. Other than taking everything apart and starting from scratch, I don't know what to do next.

[DRACO A5OG]

Time to test your booster.

Lightly put your foot on the brake pedal pushing in about 10MM and keep the pressure on the pedal.

Start the car does the pedal drop? If Yes, booster is good, if not booster is shot.

Next thing would be the calipers. Did you clean all the dark residue from the pistons and inner walls of the calipers? How did the pistons and inner wall look, any pitting of any kind, even ever so slight pitting? Did you use assembly lube or brake fluid for assembly?



I ask this is because when I did a recent rebuild. My rears pistons were pitted and I thought nothing of it. I had mushy brakes. replaced rear the piston, VOILA, rock hard brakes.

Jim

[SC-Alfa]

derek,

Some years ago I had an almost identical problem. Since you replaced the master cylinder I assume you are also bleeding the front calipers, since some air undoubtedly got in there? I'm not sure what type of calipers you have installed on your car, but my car has S calipers (PO backdated). If you have S calipers they have two bleed valves on them. One of the valves kind of hides on the upper back side of the caliper and can be easily missed as I did.

Anyways, just a thought. Good luck, I know its very frustrating.

[reddogmotrsprts]

It sounds like a bad master to me. While doing the bleed, do you note identical flow rates of fluid at each corner? I'm guessing you don't.

Also check that when you release the pedal during a bleed, fluid is sucked into the master from the reservoir, as opposed to simply flowing backwards from the caliper. This is another behavior of incorrectly manufactured masters.