Brake Bleeding Issue... Soft Pedal, Basically No Fluid at Rear Calipers, help!

[Challenger]

More problems. Still getting clean air free fluid to the calipers but the pedal is still very soft, better than before but still very soft.

 

My concern is when you apply the brake there is almost a bubbling/gurgle noise from inside the mastercylinder. Just curious if this means I need to bench bleed the MC again or if this could be some other kind of problem.

[Challenger]

Also, the MC has the two bleeder valves on the side for I assume just draining the MC. Is it possibly to connect rubber lines from those back into the top of the reservoirs to get air out of the MC if there is any.

[Xnke]

yes, those are bleeder valves. Just like bleeding the brake calipers, but usually if you have bench bled the master, they aren't needed. Probably a good idea to try bleeding it through those. I'm at the same point here, trying to finish it up tonight.

[Xnke]

I seem to be having a similar problem, in that after bleeding the brakes enough to run through a full quart of fluid, the pedal is still soft, but not spongy, nor does it slowly push to the floor, like a leaky master.

 

Challenger, does your brake pedal ever hit the stop? Mine doesn't, but it's not very far from it.

 

I am using an '82-83 ZX master, with S12-8 calipers up front, and 240SX in the rear. I have the brake master hooked up identically to BRAPP's picture below. Do I need to switch the front and back sections of the brake master? Could this be causing the soft pedal, since the two sections (to my knowledge) do not displace the same amount of fluid? Could this possibly be Challenger's problem as well?

[Challenger]

I went and switched my MC out for an 79-81 15/16 master cylinder. Im thinking the first was defective and that a MC meant for all disks might work better for all disks.

 

Hopefully this will fix the issue. Im eating a burrito and then will go put it on.

 

Xnke, I dont think it hit the floor, was really close though. (may be mistaken) Im running 83 280zx calipers, arent they very similar to the SXs?

[Xnke]

Yes, they are pretty similar. What year is your chassis? 78? Mine's a 72, which is kinda why I was asking. I think I need to swap the front and rear sections of the master to get it to line up with the brake systems...but I don't know for sure.

[BRAAP]

Also, the MC has the two bleeder valves on the side for I assume just draining the MC. Is it possibly to connect rubber lines from those back into the top of the reservoirs to get air out of the MC if there is any.

 

Those bleeders are used for "bench bleeding" or "bleeding the M/C" as mentioned on the first page, post 3 and 4.

Always bleed the M/C at those bleeders first, you'll ant to go back and forth between them a couple times, then continue on to the wheels.

 

Yes, just use tube to have those bleeders recirc the fluid back to the reservoir.

 

Be sure to do this with the new M/C.

[Challenger]

Ok, hold on... The instructions I had for bench bleeding included with the Master from what I understood said to put the plastic fittings in the bottom of the master cylinder where the normal brake lines hook up. Then proceed to bench bleed it till there is no air left.

 

Now you say you need to bench bleed with the bleeders on the side of the master cylinder? Ive always bleed it using the bottom ports but never the sides, can there still be air in it that you miss using the bottoms?

[BRAAP]

Ok, hold on... The instructions I had for bench bleeding included with the Master from what I understood said to put the plastic fittings in the bottom of the master cylinder where the normal brake lines hook up. Then proceed to bench bleed it till there is no air left.

 

Now you say you need to bench bleed with the bleeders on the side of the master cylinder? Ive always bleed it using the bottom ports but never the sides, can there still be air in it that you miss using the bottoms?

.

 

 

Derek,

Sorry if I am confusing the process. Sounds like you are on the right track. I don't have a magic bullet technique to bleeding brakes, for reasons described below, though have experienced enough of the "air in the system crap" over the years of bleeding the brakes by gravity, pump and hold, etc, that I prefer to just use pressure bleeder, (I built my own for my various cars).

 

 

Tangential rant...

The whole concept of bleeding brakes the way we have been doing it is backwards to me any how. Air wants to rise/float in a liquid, yet we are trying to force it down! In general aviation, brake systems are bled, starting out with an empty system, pressure feeding fluid from the caliper "up" to the M/C, (each wheel cylinder has its own M/C/reservoir), allowing the air to rise, float, and when the fluid gets to the M/C all the air is gone! In a car, if there were bleed nipples at the "T"'s, you could achieve similar results, or have a way to capture the excess fluid as you switch from one wheel to the next as it over fills the reservoir.

[Challenger]

Yeah, I have always thought the same thing. I was asking my dad last night, "so we pump the fluid down and some of the bubbles move along, then they just rise back to where they were." Didnt ever sound like a good method.

 

And I took it for a drive and the brakes barely work. Again enough to keep me from moving if I let out the clutch or from rolling down the driveway.

 

But, when I got back I got some hose put them on the side bleeders and "bench bleed" the master. A good amount of air came out and the pedal is ALOT firmer.

 

I imagine I will need to bleed the whole system again but do I need to pull the master and actually bench bleed it off the car, or was what I did sufficient?

 

Oops- Just noticed that the past tense of bleed is actually spelled, "bled" not "bleed". I think I used that word about a million times, the next million times Ill spell it correctly.

[RTz]

I imagine I will need to bleed the whole system again but do I need to pull the master and actually bench bleed it off the car, or was what I did sufficient?

 

I'm no 'Master Bleeder' but I can tell you that I've never *had* to bench bleed a MC. Usually, I just remove the two bleed nipples and let them gravity bleed. I did two last week, both new and BONE dry. One MC started flowing within a minute. The other MC, one nipple took a few minutes, the other after 10 minutes or so. Once I get that far, I reinstall the nipples and bleed the rest of the system. Then finish off with last check at the MC.

 

Not saying thats the 'best' way, but I've had good luck with it.

[Challenger]

Alright, you just put the MC on brand new, let it run fluid out the bleeder and then just bleed the brakes at the calipers. Sounds about where Im at. I guess Ill just go bleed them one more time to see what happens.

 

Thanks for the help, Im starting to think there was always just a little air in the MC, I was bleeding from the wrong spot.

[RTz]

Alright, you just put the MC on brand new, let it run fluid out the bleeder and then just bleed the brakes at the calipers.

 

...And then finish with a normal bleed at the MC, ie cracking the bleeders while a helper has the pedal depressed. You shouldn't need to do that more than a couple times. If, after many attempts, you still get air bubbles, the MC might be bad. We've had a couple of those in the last year.

[Challenger]

Well I was pretty set that the last MC I got was bad, it made a terrible gurgle noise. I "bench bled" (the wrong way) my new 15/16 one and it didnt have that sound once I installed it. Luckily I was able to take it back my original 7/8 one and get my money back. Drove to shucks and picked up a 15/16 and I was back in business.

 

Now off to bleed the brakes hopefully one last time! And then Ill crack the MC bleeders again just for good luck.

[Xnke]

Ok, after swapping the front and back pistons in the MC to match up with the car's lines, and rebleeding the whole system, I have a pedal that has approx half travel. At the halfway point, it really firms up and actually feels like it is supposed to.

 

Is this anything like your problem?

[Challenger]

I actually got it to be reasonablly firm. Itll go about 2 inches and then stop. You can pump it forever and it never gets rock hard like my ZX will.

 

Would this have anything to do with the stainless steel brake lines I have, maybe their the wrong size (to large?) and its not getting the same pressure? The other thing is would I have to modify the brake proportion valve in order to get more pressure to the back? I remember reading it somewhere, disks do require more line pressure than drums correct?

[jt1]

FWIW, like Ron, I never bench bleed a master. I put it on the car, bleed it a couple of times, the bleed the rest of the car, and repeat the process. I've found bench bleeding to be a waste of time, but a lot of people think it's a good thing, so YMMV.

 

The best thing I've done is JB weld a quick coupler into an old master cyl. cap. Then I set the regulator on my compressor to about 10psi, hook it to the master, and bleed away. It works great, forces air out better than pumping, and you can do it by yourself. Somewhere between 15 and 20 psi you will blow the cap off the master and blow brake fluid everywhere, so stick with about 10 psi.

 

You may have a little more pedal travel with the discs than with the old drums. The physics are that you have to move a little more fluid for the bigger pistons, which necessitates more MC travel, which means more pedal travel. This is where the ZX mc helps outs. When I went from 1 3/8 pistons to 1 3/4 pistons on the front of my car, I wound up with more pedal travel, but better brakes. This isn't a bad thing since it makes modulation of the brakes easier.

 

jt

[BRAAP]

My pressure bleeder is similar, I use my bubba-remote-regulator apparatus. I use a thread-in Schrader valve in an old M/A cap, (gotta be careful most have vent hole i the perimeter of the rubber seal that will allow the fluid to pump out). I typically keep it between 7-8 PSI. As jt1 said, any more than 15-20 is a huge paint eating mess looking for an engine bay to take place in.

 

 

 

When I did the Z-32, It was a little more elaborate. Pressurizing a gallon container filled 1/2-3/4 full of brake fluid that fed the Z-32 M/C. Modified an extra M/C cap to connect the gallon reservoir to the M/C reservoir. Set it at 7 PSI, go to each wheel and let it bleed... For the Z-32, the ABS actuator is behind the passenger seat in the cabin, above the rear suspension. The ABS has its own bleeder valves which need to be bled as well. Front brake lines ran from the M/C to behind the a passenger seat to the ABS, then 2 separate lines back up front to each wheel! LOTS of fluid in a Z-32! Pressure bleeding is the only way to fly with a car like that.

[Xnke]

Ok, I guess I'll just keep bleeding it until it doesn't get any better, or it gets to where I like it. If I bleed it out, then wait a few hours, then bleed it again, it gets a little better each time.

 

I think Zmanco is running the same brake setup I am, I'll talk to him about the pedal feel.

[DeleriousZ]

This may sound silly but are you using the correct bleeding procedure? I picked up some 'speed bleeders' (basically a ball and spring in the bleeder screw) that made bleeding super easy for me, as well as a 1 man operation. The car (z31) bled perfectly after sitting with no calipers installed for about a year.