240hoke Posted February 3, 2009 Share Posted February 3, 2009 Hey Guys, I am been plagued by a spongy brake pedal ever since I built my car. Ive tried just about everything to get rid of it so I hoping some of yall can help. My setup: - 280z Brake Booster - 15/16" 280zx master cylinder - All new brake lines (no leaks) - Wilwood 2psi residual value in the rear circuit - Wilwood proportioning valve in rear circuit - Corvette C4 Single Piston brake calipers up front w/carbotech panther xp pads - AZC Wilwood 4 piston setup out back w/standard pads - SS brake lines all around I have bleed multiple bottles of brake fluid through the lines with my Motive Pressure bleeder and I am 99% confident there is no air in the system. Ive gone along the lines and thumped them with a mallet along with the calipers as well while I was bleeding. I bleed the rear calipers from both inner and outter ports.....no air. I took my master cylinder off and there was a tad bit of brake fluid behind it so I swapped it out for a freshly rebuilt one. I triple checked the pushrod length and Bench bled it before mounting and again bled the entire system...no change. The only thing I am down too is my brake booster, but I wasnt sure how this could mess with it too much. It is a rebuilt unit that I got for my 260z 5 years ago or so. What happens is the pedal goes down about half way to the floor before doing much of anything and never feels firm...I cannot press the pedal to the floor. A spongy brake pedal is the one thing I HATE the most in a car. I dont know what its supposed to feel like stock, since its been 6 years since I drove one with stock brakes, but I know it doesnt feel right to me. I prefer a super firm pedal from the top of the travel. Anyway I fell like Ive kinda exhausted my knowledge on the matter, please help!!! Quote Link to comment Share on other sites More sharing options...
blue72 Posted February 3, 2009 Share Posted February 3, 2009 Have you eliminated the possibility of it being the reaction disk yet? Here's my little writeup on it: http://forums.hybridz.org/showthread.php?t=138712 There are one or two things that usually cause the symptoms you're experiencing, but the reaction disk is the one I'm most familiar with (hence the new subscript under my member name) Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted February 3, 2009 Share Posted February 3, 2009 I'll bet it's the reaction disc. Blue72 posted a sticky here already.http://forums.hybridz.org/showthread.php?t=138712 Quote Link to comment Share on other sites More sharing options...
240hoke Posted February 3, 2009 Author Share Posted February 3, 2009 Wow, Id never heard of that, I even searched for quiet a while....I guess those sticky's have a purpose Its definitly something I need to check but It sounds like there is no brakes and then full brakes. Mine are definitely not like that the first half the the pedal travel you can feel pressure and the car starts to slow down and then it almost kinda ramps up at the end as more pressure is applied. Definitely not a on-off situation... Quote Link to comment Share on other sites More sharing options...
ZZZeee Posted February 3, 2009 Share Posted February 3, 2009 Yeah... those sticky oily residues can really muck things up. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 4, 2009 Share Posted February 4, 2009 Austin, I know how you feel, my WRX has had spongy brakes from day one, brand new, and it's the only thing that deducts from driver confidence in that car. I think it's the norm for Subaru brakes, aside from the STI which is very firm. My Z setup is the 15/16" ZX MC, original 280Z booster, all the factory safety&prop valves, stainless/teflon flex lines, AZC brake kit, and I have an extremely firm pedal that works right off the brake light switch. They bled easily with no hassles. I actually had to ease off on the linkage to get the brake down low enough to do heel and toe comfortably. Something is wrong with yours so don't think it's inherent. I am not familiar with the vette calipers. Check for firewall flex, out-of round rotors that push the pads back, and maybe mess with the safety and proportioning valves if you still have them in the lines. They could be holding air, dirty, or part clogged. I HATE spongy brakes as well. Pet Peeve. One of my recurring nightmares (yes I have dreams about it) is a spongy pedal with little or no brakes...probably from when I boiled the fluids in the stock system at Limerock Park. Quote Link to comment Share on other sites More sharing options...
spotfitz Posted February 4, 2009 Share Posted February 4, 2009 Did you switch the lines on the master cylinder around? They are reversed from the normal 7/8" 280Z master cylinder. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 4, 2009 Share Posted February 4, 2009 Did you switch the lines on the master cylinder around? They are reversed from the normal 7/8" 280Z master cylinder. Shouldn't matter for the pedal feel. You want the larger reservoir to feed the front brakes because they have a larger capacity and they'll drain more fluid out of the reservoir as they wear down, but the master works the same way for the front and rear sections so that wouldn't explain the pedal feel. Quote Link to comment Share on other sites More sharing options...
mcx Posted February 4, 2009 Share Posted February 4, 2009 ..i never had luck with "rebuilt" master cylinders..i had the horror of swapping three..one after the other, and none would hold pressure correctly?...they were affordable compared to the new part but you get what you pay for[cheap seals/scored bores]....i wasted so much brake fluid trying to bleed the system.....anyway,go buy a "new" master,my guess anyways!! Quote Link to comment Share on other sites More sharing options...
blue72 Posted February 4, 2009 Share Posted February 4, 2009 When I had the stock MC my symptoms were 3/4 throw nothing, then grab. I also had a booster which leaked (engine would almost die with foot on brake at a stoplight) After I switched to the larger ZX MC, installed a used booster and later played around with new pads and such it worsened to no significant grab. The brakes were applying, but weakly, and holding the pedal to the floor would only gradually slow it down. That's when I finally searched and found out about the reaction disk. My system was stock though, except for the ZX master cylinder and some fancier pads and shoes. There are some other cases that cause similar symptoms though. For example, from what I've read the guys that install the Toyota 4x4 calipers accidentally upside down and on the wrong sides (can't get all the air out of the lines) usually have some similar pedal problems. Once they switch sides and get the bleeders at the proper altitude they can get rid of the air. Quote Link to comment Share on other sites More sharing options...
240hoke Posted February 4, 2009 Author Share Posted February 4, 2009 cygnusx1 -- Thanks for the info, I hope I can get mine to feel like that. I think Id rather have stock brakes and a stiff pedal then big brakes and a mushy pedal. I have Tilton reservoirs on the MC and I have the lines going to the correct place. I highly doubt its the MC because there is no fluid leakage and no change in height between the two reservoirs. No bleeder problems they are all in the right spot, I laugh everytime I hear about somebody doing that I have a feeling it has something to do with the booster, Ill play with it next time I am home. Quote Link to comment Share on other sites More sharing options...
aziza z Posted February 4, 2009 Share Posted February 4, 2009 Subscribed. Unfortunately i have this same problem and always have since I got the car. Switched out everything as well. Nothing. Quote Link to comment Share on other sites More sharing options...
EMWHYR0HEN Posted February 4, 2009 Share Posted February 4, 2009 Austin, When my reaction disc was off the push rod I didn't have an on/off pedal it was just mushy up top and had a deep throw. I ignored it for quite some time and drove it like that. After spending hours messing with everything else I had already checked I was amazed that the mushiness was caused by a simple little piece of rubber in the booster. Quote Link to comment Share on other sites More sharing options...
stony Posted February 4, 2009 Share Posted February 4, 2009 Did you bleed the master cylinder to make sure there is no air trapped in it. I had a similar problem after swapping mine and was told to do that. After i did had solid brakes. Stony Quote Link to comment Share on other sites More sharing options...
Lazeum Posted February 4, 2009 Share Posted February 4, 2009 I do also have the problem I've got 4x4 toyota non vented disk brakes in the front, stock rebuild drums on the back, 280zx MC, SS brake lines and 280z booster. The feeling is not good but I've got the car like this when I bough it. I've always assumed it was the way an old Z should feel. I fixed the booster valve that was stuck; this improved the feeling a bit but it is still not good. It is mushy but I can lock the wheels if required. I'll start by checking if calipers are not reversed as discussed in this topic (I did not notice anything wrong when I checked them last time - but I was not looking for anything specific) Quote Link to comment Share on other sites More sharing options...
240hoke Posted February 4, 2009 Author Share Posted February 4, 2009 Myron - Good to hear, I really hope it is as simple as that ill be really happy..first thing im gonna check when I get back. Stony, yes, I bench bleed the master and then I was using a pressure bleeder to bleed the system which should take care of the air in the master. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 4, 2009 Share Posted February 4, 2009 Austin, with the car idling, pump the brake pedal a couple of times. Does the pedal get stiffer? If it does, you might have some air bleeding into the master from the rear seal, or your caliper piston seals may be pulling the pads back away from the rotors. Some caliper seals are designed to do this. They require a special master cylinder to eliminate the pad gap quickly when pressing the pedal. I think Corvettes use these types of seals. http://www.ucx.com/documents/squareseal.pdf http://www.babcox.com/editorial/ic/ic30642.htm Quote Link to comment Share on other sites More sharing options...
drmiller100 Posted February 4, 2009 Share Posted February 4, 2009 start the car. pump the brake pedal fairly steadily. Do they pump up, and does the brake pedal get higher? if so, it is either air or the rear brake shoes need tightened up. Pull the emergency brake. Now does the pedal get higher? If so, it is either air or rear shoes need adjusted. Once the pedal is up fairly high, hold the pedal pretty hard. If it slowly sinks, and no fluid on the ground, master cylinder is shot. If pedal will not pump up, it is something in the linkage between pedal and master cylinder. To confirm, open the tops of the brake fluid reservoirs. have a buddy slowly push the pedal down. normally, there will some circulation in the reservoirs as you first start to push the pedal down, then it will quit. Quote Link to comment Share on other sites More sharing options...
blue72 Posted February 4, 2009 Share Posted February 4, 2009 pump the brake pedal fairly steadily. Do they pump up, and does the brake pedal get higher?if so, it is either air or the rear brake shoes need tightened up. Pull the emergency brake. Now does the pedal get higher? If so, it is either air or rear shoes need adjusted. His rear drums and shoes are long gone. He's got nice Wilwood rear disk setup. Quote Link to comment Share on other sites More sharing options...
TimZ Posted February 4, 2009 Share Posted February 4, 2009 Stony, yes, I bench bleed the master and then I was using a pressure bleeder to bleed the system which should take care of the air in the master. But did you bleed the MC once it was installed in the car? This has made a big difference for me, too. It seems like it ought to take care of itself with a system bleed, but it ain't necessarily so. Try bleeding the MC in the car - it's easy to get to and will only take a minute or two. Quote Link to comment Share on other sites More sharing options...
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