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Hi everyone,

 

HybridZ is really where I come when I'm at a complete loss and everything I've tried hasn't worked. I'm going to be as detailed as possible so bear with me, I'll try to keep it concise.

 

A few weeks back, I replaced the passenger side rear suspension assembly- everything from the control arm to the shock insulator. The driver side had already been replaced as it was previously damaged in a crash around the spindle area. At this point both sides of the suspension are from a later 280z.

 

When I was adjusting the drums, the flathead I was using slipped and bumped the rubber boot of the wheel cylinder and a little fluid oozed out. Guess that explains my inconsistent brake pedal. I wasn't drastically losing fluid or anything, but it must have been a small leak that would occasionally rear its head and my pedal would be just a bit softer than usual. I grabbed an extra wheel cylinder I had that looked like it was in good shape and replaced it. That's when the trouble really started.

 

I stripped the brake line bolt and the wheel cylinder threads. Bit the bullet and ordered a brand new wheel cylinder... cheap and not a bad thing to replace while I'm in there. I also got pre-flared brake line to replace the OEM one I messed up. I made sure it was Japanese style brake line- double flare and 10mm bolts. I "rented" a tube bender and shaped it as close to the OEM one as I could. I ended up with a 30" line as it was either 20" or 30" and I figured it was better to be a bit long than a bit short. Replaced the wheel cylinder, bolted the line up, made sure it didn't leak and didn't hit anything with the car lowered, and bled the rear brakes. Here's where I may have gone wrong- my understanding is the front and rear circuits are separate so leaving the fronts alone I only bled the rears at first. Finished the rest of my work and finally was ready to drive my car after not doing so for several weeks.

 

I could tell immediately something was off. The pedal practically went to the floor right away but I could pump it and build up pressure. Ok, air in the lines or drum is adjusted way too loose. Checked both drums and they're tight but rotate as much as I want them to. Must be air in the lines still. Bleed the rears again and retry but it feels exactly the same. 

 

I think I bled my rear brakes about 4 times, then bled the front and rears, then bled the master cylinder, rebled the rears, and the pedal never felt different. On a recent endeavor to bleed the rears for god only knows-th time, the passenger bleed screw snaps in half inside the wheel cylinder. Fair enough, now I can have two new wheel cylinders. Again, cheap insurance. Replaced it, bled the rears again, and the pedal still feels the same. I get very light braking on the first push, but if I pump it quickly I get normal feeling brakes.

 

Today I attempted to bleed the rears yet again. I bought a simple vacuum bleeder to do it myself. I'm a bit stumped because the driver side wheel cylinder just doesn't seem to want to bleed. I recruited someone to hop in and push the pedal so I could get a better view of what's going on. I crack it wide open and it seems like fluid is barely moving through it. On top of that, the pedal feels normal with the bleeder open and seems to build pressure better than with it closed! Is my cylinder bad? Am I going insane?

 

To quote Zoolander... "I feel like I'm taking crazy pills!"

 

I have a turbo motor waiting and this is really the one thing standing in the way. SOS!

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I just had a bitch of a time bleeding an entirely new system, and using a syringe and pushing the fluid through the bleeder to the master finally gave me a good pedal. I think you can buy syringes for this purpose, I happened to have one left over from my older kid who was tube fed for a while as a baby. Good luck.

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Yes, I think the fluid drained almost completely.

 

If you allowed all of the fluid to drain out of the  rear section then you will have air in the master cylinder which will require bench bleeding.  Sometimes you can get the air out by bleeding the MC on the car by running a plastic hose from the bleed screw back into the tank. Even though the plastic tube is immersed in fluid in  the tank air can still enter around the threads of the bleed screws.  Have a helper open and close the bleed screw while you push the brake pedal. Just like bleeding the wheel cylinders. You can also install speed bleeders on the MC so you don't need a helper.

 

If bleeding the MC in the car still does not result in a firm pedal, then you will have to remove the MC and bench bleed it.  The procedure is documented in the brake forum. Don't allow the fluid to run out of the MC when reinstalling it in the car. Plug the output ports. To make mounting the MC easier,  start the hard line fittings back into the MC before bolting it to the booster.

 

In the future do not allow the tanks to empty out while working on the brake system. Fill the tanks and use a large rubber stopper or other means to plug the tank to create a vacuum so the fluid can not flow out.  Secure the plug/stopper so it can not back out and leak air.  You can also plug the ends of the brake lines to stop the flow of fluid.

 

http://www.speedbleeder.com/

 

http://www.summitracing.com/parts/ear-280022erl?seid=srese1&gclid=CN2v8PrfksQCFYVqfgodGFYAcw

 

Edited by Miles
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I think i might have the same situation. After a long winter snooze i took the Z out and immediately noticed i had almost no brakes. Sure enough the front reservoir was completely empty. I still have no idea where the fluid went. After refilling i have taken the car on 5 or 6 separate short drives over about 3 months and haven't noticed any more fluid loss but the brakes are still more spongy than id like. Mine is also similar in that a quick pump or two firms them right up but quickly dissipates after releasing the brake.

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Jon, thanks for the quick response I just want to clarify as I’m not too familiar with brakes, are you saying you think I need a new Master cylinder and to drain the brake booster? again I appreciate it if you can dumb it down or point me in the right direction I’d like to tackle it myself it all possible but again the personal knowledge on my part is lacking.

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Yes. Masters can leak out the back, so if you lost a lot of fluid and it didn't end up on the ground, there's a good chance that it leaked straight into the booster. I think the front reservoir goes to the rear brakes, so you could have a leaky wheel cylinder and the fluid is inside the drum too. Probably check the rears first and if there is no leak there, then pull the master and look inside the booster.

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To check for fluid in the booster, you don't have to completely remove the master cylinder. There is enough flex in the hard lines connected at  the bottom of the master cylinder that you can unbolt the master cylinder, pull it forward and then push it aside to look inside the booster for fluid. If there is no fluid then the leak is somewhere else in the brake system. If you remove the master cylinder completely you will have to bench bleed it before reinstalling it.

 

Check the wheel cylinders and calipers for leaks first.

 

Probably best  after finding the leaks to take the car to a brake shop for any repairs.

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To check for fluid in the booster, you don't have to completely remove the master cylinder. There is enough flex in the hard lines connected at  the bottom of the master cylinder that you can unbolt the master cylinder, pull it forward and then push it aside to look inside the booster for fluid.

Even easier, the back of the master cylinder will be wet if it's leaking.  Pull it forward and stick your finger in there.  Sometimes the fluid will leak down the front of the booster also, from the mounting surface.

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Even easier, the back of the master cylinder will be wet if it's leaking.  Pull it forward and stick your finger in there.  Sometimes the fluid will leak down the front of the booster also, from the mounting surface.

 

The old finger trick.

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Maybe I'm just getting hung up on the wrong information. I'm concerned that my driver side wheel cylinder is faulty. The passenger side bleeds like you would expect- a steady flow that fills up the whole tube, whereas the driver side does not. Is this even relevant? Something to be concerned about? I disconnected the hard line to the cylinder just to make sure it wasn't some sort of blockage in the line but that drips once it is taken off so it seems fine.

 

I'm going to try bleeding the master cylinder in the car tomorrow. Should I put the car on an incline of any sort?

Edited by Pac_Man

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 I disconnected the hard line to the cylinder just to make sure it wasn't some sort of blockage in the line but that drips once it is taken off so it seems fine.

 

I'm going to try bleeding the master cylinder in the car tomorrow. Should I put the car on an incline of any sort?

Seems like you're getting distracted and not really finishing the individual tasks.  Confirm that master cylinder is not leaking in to the booster, confirm that wheel cylinder is not clogged, confirm that line to wheel cylinder will flow freely, etc.  You still don't know where that fluid went, and you've shown that the hard line will drip, just like the bleed valve.  Not really any new knowledge.

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No,  you don't need the car on an incline.

 

There is most likely air in the rear section of the master cylinder.  You will not be able to bleed the system with air in the MC.

 

If you haven't done so, research how to bench bleed a master cylinder. If you do it off the car be sure all of the hoses and fittings you attach to the MC are air tight.

 

After researching, make a logical check list of what you need to do starting with the MC.

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