Having a very hard time finding my brake problem

[Forrest]

I've been trying for a week to get my brake pedal to feel "normal" and so far I've been completely unsuccessful. If anyone has any suggestions, please let me hear them.

 

The car has been down for 19 months while me and a friend of mine cut up our suspensions, measured, welded, cleaned, powdercoated, etc. Along the way I've had a lot of distractions, but the point is, now all the new and modified suspension/brakes are on the car. The only problem is, my brake pedal feels very spongy.

 

By spongy, I mean, it goes down too easily, but it's not slack, like when you have air and the pedal is really soft until it's all compressed, and then the pedal is suddenly hard. It's just not very firm and it slowly gets harder after you press down much farther than you ever normally would to stop the car.

 

I have the 4piston AZ-Z brakes on the car, with a brand new 79 280zx master cylinder and stainless lines. I got the front brakes new from AZ-Z and the rears were "slightly" used from Kyle at Z-driver.

 

I bled the brakes with a pressure bleeder 3 times before taking the car off stands, just because it's so easy when it's up in the air without wheels. The 2nd and 3rd time there was basically no air coming out. I couldn't start the car up but the pedal felt very firm without the booster (no real surprise.)

 

So a couple of weeks ago I finally get it fired up and try to drive around the block and low and behold, the pedal is really spongy and feels scary. I drive back in to bleed it and expect to see a lot of air coming out, but almost none comes out, with the exception of a few really really tiny bubbles here and there. After bleeding the pedal feels exactly the same.

 

I've read all the posts about people having problems after swapping masters, so I was really careful about not moving the rod when I swapped my master out. I also measured from the cup to the edge of the flange on the stock and the 79 master and the distance is almost exactly the same, so no adjustment of the rod should be necessary. It doesn't feel like it is either, pressing the pedal just a tiny amount can make the calipers start moving, far before the pedal gets firm.

 

I called Dave to see if it would make any difference if the Wilwood porportioning valve was installed. I have held off on putting this in because he is supposed to be selling a rear linelock kit that is controlled by the stock handbrake handle. I want to put that in at the same time. He told me not to use the pressure bleeder to bleed, and the pedal should still be firm without the extra porp valve.

 

Now, I've used the pressure bleeder to bleed brakes on at least 6 other cars and it's worked very well. I use low pressure and I pump it slowly. It's never been a problem. But at this point I'm actually hoping it is the problem and very willing to try anything to fix it.

 

Before trying to manually bleed, I took the master off and pulled the rod out of the booster. The reaction disc was not glued on the end of the rod any more but it was firmly in place in the indention that it normally sits in at the end of the rod.

 

I reassembled it all, and then I spent 2 hours and bled over 2 quarts of brake fluid through my brakes with a friend of mine. I made sure he knew the correct way to manually bleed (steady pressure on the pedal to the floor, let up slowly.)

 

I notice that under a really bright light you can see really really tiny bubbles coming out of the master. In daylight they would be invisible; they look like tiny flecks of dust. There are not a ton of them but they keep coming out. At the end of the night the pedal is exactly the same as it was when we started.

 

So thinking that the master must be bad, because these really tiny bubbles keep appearing, even after I've bled over a pint through the front reservoir master alone, I swapped another 79 master that I had bought for the other car in, and bled it again (manually.) Maybe the other master was bad, or maybe there was just a lot of tiny air bubbles trapped in the fluid that regrouped. After bleeding the new master I don't see many tiny bubbles. But I do start seeing what looks like really tiny pieces of trash. It's not round so it's not air. I bled the entire car again and I saw it coming out everywhere. This is brand new brake fluid of course, (having gone through about 6 quarts at this point it had to be.)

 

This stuff is so tiny and so hard to see, there is no way anyone would notice it during a routine bleed. I had to put the spotlight directly on the bleed hose. I don't know where it's coming from or if it's even relevant. After bleeding the entire car for another 2.5 hours tonight, the pedal is exactly the same.

 

Before and during the bleeding, I went and rechecked all the connections to see if any of them were leaking. I've looked at them all before and they have all been dry. But this time I put the wrench on them and tried to tighten them. They were all pretty tight and moved very little if at all.

 

The only thing I haven't done is tried to adjust the pedal, but it moves the calipers when you press it very slightly. I'm worried that if I try to adjust it down a little bit, the brakes will be dragging all the time.

 

I talked to a friend of mine that suggested trying to spin all the wheels to see if all the calipers were moving. I did this and all them are grabbing hard enough that there is no way for me to turn the tire by hand with the brake depressed. Maybe one of the calipers could still have a problem?

 

I can't think of anything else except that maybe I got 2 bad master cylinders in a row. The second one was part of a small lot of random new old stock Nissan parts. It -does- look a little aged but it's new. I'm guessing the trash is coming out of there. I ordered a 3rd one just in case. If I can't find anything wrong before it comes in, I'll try swapping that one too.

 

Any suggestions welcome. This is really really getting me down. The car is ready to go tear up some road and this is the only real holdup. Thanks in advance.

[Zmanco]

Two things come to mind:

 

1) Did you bench bleed the MC before installing it? If not, I don't think you are ever going to get all the air out of it, no matter how many times you bleed at the wheels. I just swapped a 15/16" into my '73 and it took a long time on the bench to get rid of all the bubbles. And the hose popped off a few times spraying brake fluid all over. Quite a mess, but the good news is the pedal has been firm since.

 

2) Assuming you did bench bleed, have you bedded the pads in yet? I would NOT recommend you do that until you're sure you have everything bled properly, but brand new pads can feel squishy/soft for a little while until they are bedded in (if that's a term). You can speed this process up by doing a series of 5 or 6 gradual but firm stops from 50 mph. There's nothing magic about that speed, you just don't want to go too fast and overheat the brakes. This helps get some of the new pad material embedded on the surface of the rotors as well as help the pads conform to the surface of the rotors.

 

That's where I'd start.

[Forrest]

Thanks. Maybe I'm not bench bleeding them correctly? I bench bled the first master with a set of brakelines connected to the bottom, recirculating to the top. I didn't have those lines today, so I when I bled the second one, I used the bleed screws on the side. I'm not seeing any more air come out of the lines now like it was with the first one. I guess I'll take it back off tomorrow and try again. I can't think of anything else to do at this point.

[kcelectronics]

You have probably already checked but have you got the calipers on the right side with the bleed nipples to the top?

[Pop N Wood]

I bled the brakes with a pressure bleeder 3 times before taking the car off stands, just because it's so easy when it's up in the air without wheels. The 2nd and 3rd time there was basically no air coming out. I couldn't start the car up but the pedal felt very firm without the booster (no real surprise.)

 

You wrote a lot of words, so let me see if I am reading this correctly. The pedal is firm with the engine off, but gets spongy when running?

 

Reaction disk. Classic symptom.

 

BTW, with stainless brake lines the pedal should move freely until the MC starts to engage, then it should be like stepping on a brick.

[rags]

Forrest,

 

I think I'm having thr same problem as you. A very low pedal. I'm attributing the problem to the rear disks. How did I come about this diagnosis? It's the only thing left and I still don't understand how the adjustment/spinning piston works. Have you checked to see if the slight pedal pressure that you say moves the calipers is having the same clamping force on a rear wheel? If you ever figure it out I'd sure like to know what you did!

 

Joe

[Forrest]

You wrote a lot of words' date=' so let me see if I am reading this correctly. The pedal is firm with the engine off, but gets spongy when running?

 

Reaction disk. Classic symptom.

 

BTW, with stainless brake lines the pedal should move freely until the MC starts to engage, then it should be like stepping on a brick.[/quote']

 

Yes. I was hoping it was the reaction disc. But I pulled the rod out of the booster and the disc was still in place, so unfortunately, no easy fix for me.

[Forrest]

You have probably already checked but have you got the calipers on the right side with the bleed nipples to the top?

 

Yes.

[quicker240]

I put the AZ kits on mine a few years ago and had similar issues.One thing I hav'nt heard you address is how you are bleeding the calipers.Each half of the caliper has a bleeder and you need to bleed each half,not just crack the line coming in.i am pretty sure you have already done it this way,just thought I'd bring it up.The other thing is that after I got the system bled,the pedal feels COMPLETELY Different than it did with stock brakes.Although the pedal is VERY VERY soft(almost like the brakes are not working at all!),when driving the car,they will stop the car VERY quickly with nearly no pedal effort at all.I attribute this to the factory valving of the proportioning valve being set up for disc/drum,and the fact the wilwoods are so much more efficient(about 3 or 4 times the pad area and larger rotor contact area.)

It took quite a bit of getting used to and I still have a bit of trouble adjusting from my average daily driver car to the ultra low pedal effort Z brakes when I jump into it.Hope this helps a little.Steve

[johnc]

You wrote a lot of words, so let me see if I am reading this correctly. The pedal is firm with the engine off, but gets spongy when running?

 

Reaction disk. Classic symptom.

 

Maybe I'm mistaken, but when the reaction disk fell out of the boosters on two of my 240Zs the pedal feel while running made for a horribly grabby brake pedal. Inital bite was very abrupt.

 

Did Dave at AZC recommend the master/caliper combination that you are using?

[JMortensen]

Is the soft then hard feeling with the engine off or on? If it's off, then I don't know. If it's on, then it might be that the reaction disk isn't sealing properly.

 

I have the ZX master that I took out of my car. It's listed in the classifieds, or at least it was. I bought it brand new from Nissan and it has 8 years on it, and it is known to be good. Make me an offer. I think I paid $200 for it...

[Forrest]

I put the AZ kits on mine a few years ago and had similar issues.One thing I hav'nt heard you address is how you are bleeding the calipers.Each half of the caliper has a bleeder and you need to bleed each half' date='not just crack the line coming in.i am pretty sure you have already done it this way,just thought I'd bring it up.The other thing is that after I got the system bled,the pedal feels COMPLETELY Different than it did with stock brakes.Although the pedal is VERY VERY soft(almost like the brakes are not working at all!),when driving the car,they will stop the car VERY quickly with nearly no pedal effort at all.I attribute this to the factory valving of the proportioning valve being set up for disc/drum,and the fact the wilwoods are so much more efficient(about 3 or 4 times the pad area and larger rotor contact area.)

It took quite a bit of getting used to and I still have a bit of trouble adjusting from my average daily driver car to the ultra low pedal effort Z brakes when I jump into it.Hope this helps a little.Steve[/quote']

 

This is something I was worried about - not knowing how the pedal is supposed to feel. If this is how it feels, I'm not happy with this brake setup. I can't drive the car hard with a soft pedal. Can anyone else with the 15/16 master and wilwoods chime in on how your pedal felt close to stock?

 

Maybe I'm mistaken' date=' but when the reaction disk fell out of the boosters on two of my 240Zs the pedal feel while running made for a horribly grabby brake pedal. Inital bite was very abrupt.

 

Did Dave at AZC recommend the master/caliper combination that you are using?[/quote']

 

I agree, this doesn't feel like the reaction disc has a problem, because the grab is not abrupt. The pedal is just soft. Dave did recommend this specific master, that's why I got it.

 

Is the soft then hard feeling with the engine off or on? If it's off' date=' then I don't know. If it's on, then it might be that the reaction disk isn't sealing properly.

 

I have the ZX master that I took out of my car. It's listed in the classifieds, or at least it was. I bought it brand new from Nissan and it has 8 years on it, and it is known to be good. Make me an offer. I think I paid $200 for it...[/quote']

 

The pedal feels pretty firm with the car off. With the car on, it doesn't feel to me like other pedals have when they have air. It's consistent, it's spongy, and it doesn't go from soft to hard very quickly. It's pretty linear, and pumping the pedal doesn't change how it feels at all.

 

I might take you up on the master if it really is the problem...I already have a third one paid for, it will be here Monday or Tuesday. Let me try that one out first. Thanks.

 

If this is the way it's supposed to feel, maybe going to a smaller bore master with larger reservoirs would work?

 

 

Thanks for the replies guys. I'm going to go pull the master off and bleed it again, and try again. I don't think it's going to make any difference but I have nothing else to try right now.

[JMortensen]

Larger master gives a firmer pedal but requires more pedal effort. Smaller master give a longer softer pedal that doesn't require much effort.

[Forrest]

Is the soft then hard feeling with the engine off or on? If it's off, then I don't know. If it's on, then it might be that the reaction disk isn't sealing properly.

 

Jon, I pulled the disc out. The hole it came out of looks greasy - I'm guessing it's supposed to. The disc looks ok to me, still rubbery and there is no dirt on it or behind it. How can I check and see if it's sealing correctly? Anything else I should look for while it's open?

 

Thanks for the help!

[240hoke]

Forrest I have had the same problem since I installed my azcar rear brakes. Pedla is MUCH more spongy then it used to be. Im curious to see what you find out. The car stops fine the pedal is just really mushy up top.

[Forrest]

Austin, did you put in the porportioning valve? Are you running the 79 MC too?

[JMortensen]

The proportioning valve doesn't do anything that would make the pedal mushy. Sounds to me like you guys need a bigger master if Austin has the same problem...

 

I don't know how to check the disk for sealing, I just figured that it might be a problem. If nothing is obviously wrong, then I don't know where to go from there.

[240hoke]

Im running a 15/16th master cylinder, willwood proportioning valve, 2psi residual pressure valve, and a line lock. Im pretty confident that I have bleed hte master and all my brakes throughly.

[quicker240]

I am running the 280zx master cyl.(2 large reservoirs) with the larger 2 + 2 booster.Stock proportioning valve,wilwood adjustable on the rear half(never have adjusted it,but its there) and a B&M line lock on the fronts.The feel of the brakes are soft but linear.Very little pedal effort for even very heavy braking.Also has a bit more pedal travel than I like,however I have found this common on 4 wheel disc brake cars.The light pedal seems to be a common thing among this thread.Has anyone else found a solution to this issue or is it just a "thats how it is" thing? I have been living with it for quite a long time...

[JMortensen]

Bigger master cylinder seems to be the common theme here guys.