Guest 240hybrid Posted September 16, 2003 Share Posted September 16, 2003 I'm stumped on this one. The brakes seem to work fine and I have locked them up to test them to make sure they work, but there is no resistance in the pedal. I can push the pedal all the way to the floor without much force at all. I'm pretty sure the brakes work and theres no air in the lines, but am alittle concerned since there's no resistance. Here's what I've done so far, some was reg. maintanence and some to try and solve the problem I'm having. I have replaced all the shoes and pads. Replaced the rear slave cylinders cause one was seized, one was leaking. I installed SS brake hoses. Swapped out MC's with a spare one-bench bled it and bled it again on car. Replaced Check valve. Checked both calipers and all brake unions for leaks. Replaced proportioning valve. Adjusted rear brakes out so that its difficult to remove the drum. Adjusted the pedal several times. Adjusted the pushrod out to the correct spec. And I have bled the brakes, oh about 7 times at least. The only solution I can think of is that my Brake Booster has gone south or has a flaw in it. I'm gonna call around and see if I can find a brake booster rebuild kit(if they make them), but might be forced to go to ZcarAtlanta and haggle my way out of there with one. Anyone have any ideas as to why I get no resistance, but have good brakes??? I'm stumped here. Thanks Chase Quote Link to comment Share on other sites More sharing options...
Guest rick458 Posted September 16, 2003 Share Posted September 16, 2003 is the little restrictor in the vacuum line to the booster? Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 16, 2003 Share Posted September 16, 2003 You mean the check valve? The little one way valve inbetween the intake manifold and the booster....yeah its there and have tried a few spares from the JY too. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 16, 2003 Share Posted September 16, 2003 Can the pedal go to the floor without actually pushing on the master??? I admit that I am not terribly familiar with the innards of a booster, but I thought it was basically a rod that went straight through and a huge vacuum diaphragm that helped to depress the master and I think there is a spring in there too which helps to return the diaphragm. The point is that I would think that even if the booster is completely wasted there still should be some resistance in the master... Jon Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 16, 2003 Share Posted September 16, 2003 You would think so mortensen and I would be running without power assisted brakes if the booster is bad. As for the pushrod making contact with the MC, I'm pretty sure it is, cause I can lock up the brakes. I might just try bench bleeding the MC again as I believe most brake problems are related to improper/insufficent bench bleeding. Might just be time for a full brake upgrade I think thats what shes trying to tell me. Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted September 16, 2003 Share Posted September 16, 2003 If the brake booster was out wouldn't that make the breaks have even more pedal pressure? Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 16, 2003 Share Posted September 16, 2003 I think I might have found my problem. I checked the rotors to see how thick they are and their just barely above the minimum regrind thickess of 10.5 mm. I haven't check the drums yet but suspect they are near their throw out thickness as the rotors are. Has anyone else ever had rotors/drum that are near the end of their life, if so what are some of the symptoms? Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 17, 2003 Share Posted September 17, 2003 Are the bleed screws pointing up on the calipers and wheel cylinders? Also check to make sure you new wheel cylinders are not leaking. I would bet you still have air in the brake system. Most likely in the rear lines or wheel cylinders. It's happened to me before. Finally had to get a power bleeder to get the air out of the rear lines. Good luck what ever it turns out to be. Mark Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 17, 2003 Share Posted September 17, 2003 Yeah the calipers are on the correct sides and the bleeders are up. I have tried manual pump bleeding and I too finally bought a power bleeding too that pulls/sucks the fluid out. I'm pretty sure the rotors need replacing though, cause I didn't use a micrometer (need to buy one some day) a measure the thickness a 1/2" in on the rotor surface as suggest in my manual. I just used a tape measure and measure the outside edge. If I'm not mistaken the brake pad is set in just a bit so it doesn't ride on the very edge, this would cause the outer edge to be just a bit thicker than the actual contact surface. I guess thats why they say to take the measurements a 1/2" in to the surface area. I measured the outer edge to be just barely above the recommended replacement thickness, so the rest of the rotor is definitly at its discard point. I'm gonna consult a few shops and ask them what the symptoms are of rotors that are too thin before spending any $. Quote Link to comment Share on other sites More sharing options...
denny411 Posted September 17, 2003 Share Posted September 17, 2003 Check to be sure your rear brakes are adjusted properly. This is a very common reason for soft or low brake pedal. Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 17, 2003 Share Posted September 17, 2003 I adjusted the rear wheel cyliders to where its difficult to get the drum off and still have the problem. I'm pretty sure their adjusted properly. Its hard to describe, but its like theres too much power assistance in the brakes. Like the booster is doing such a good job, that theres no resistance in the pedal when applying brakes. I'm going to look into the excessively worn rotor and measure the drums too, and see if they're the same. Quote Link to comment Share on other sites More sharing options...
80LS1T Posted September 17, 2003 Share Posted September 17, 2003 A few thousands on the rotors or drums shouldn't make you pedal easy to push down. The rear brakes are what control pedal height. Are the drums resurfaced? Are you sure it isnt the master cylinder? To check the master... run the car so that the booster is full of air...then shut the engine off and pump the brakes up...does the pedal, A.) get hard after a few pumps and stay hard? B.) continues to stay soft no matter how long you pump it up? If A...now turn the engine back on and while holding the pedal down with a firm but not extremely hard foot...does the pedal go to the floor? If so then your master is ok. If B....your master is junk. Hope that helps, Guy Quote Link to comment Share on other sites More sharing options...
srgunz Posted September 17, 2003 Share Posted September 17, 2003 It sounds like your reaction disc in your booster has fallen out. If so you will see it laying in bottom of cannister. This has happened to me and several others when doing a cylinder or booster change . It is a hard rubber black disc and goes in back behind the booster push rod. Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 17, 2003 Share Posted September 17, 2003 It does A. LT1. Its stiff until I start the car, then the pedal will go all the way down without much force. Like its too much power booster assistance. So that means the MC is good which I figured, cause what are the chances that I have 2 that are bad? I'll check out that reaction disc too and see what the deal is with that. Hopefully thats it, I'll keep ya guys updated. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 17, 2003 Share Posted September 17, 2003 That last bit sounds like air in the lines. Jon Quote Link to comment Share on other sites More sharing options...
srgunz Posted September 17, 2003 Share Posted September 17, 2003 See my post above. The telltale sign I did not mention is if the pedal feels ok then goes to floor when engine is started and vac. is applied to booster. See this caution in the FSM brake section. Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 17, 2003 Share Posted September 17, 2003 Well Steve I opened the booster up(with some difficulty) and the reaction disc(small hockey puck) had fallen out of place like you said. I guess when I pulled the booster from the 280z I let the pushrod come out some and the disc fell out when the push rod was out of place. I put it all back together, but it still feel like there too much vacuum boost, and no resistance in the pedal. Now, on top of that the damn pedal won't come back up now, it stays on the floor and I have to pull it back up with my foot. This is driving me nuts. I think that I damaged some seals during reinstallation of the booster, cause when I was bolting the booster back up, the valve operating rod ( the rod that attaches to the brake pedal) wasn't seated around the pedal like it was supposed to be. It was stuck off to the side of the pedal and I think I damaged the #8 seal in the Hanyes manual. Or I didn't get a good seal on the diaphragm plate during reassembly. I called around and couldn't find a rebuild kit for the darn thing, and a rebuilt/remanufactured brake booster runs about $136. I'm thinkin of buying one, and if it doesn't fix the problem return it. Im almost 100% theres no air in the lines, and I have done everything that everyone mentioned already. I'm starting to lose it. I hope I figure this out soon, then I'll be happy. Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted September 17, 2003 Share Posted September 17, 2003 Well, I have had this problem for the longest time now, and it is no longer a problem anymore . I got sick and tired of screwing around after opening the booster up to put the reaction disc back into place and still have the problem plus another problem added to it after the work. I went and bought a booster/master vac from auto zone and just got done installing it. The pedal now has resistance!! I have to bleed each corner still, but the pedal feels pretty good and I am very please to be done with this. The worn out rotors can wait just a bit longer till I do a total upgrade. Time to go bleed them all out and return my core. Quote Link to comment Share on other sites More sharing options...
Guest cag4 Posted September 29, 2003 Share Posted September 29, 2003 Hey Guys, I just had the same problem: New brake booster installed and the brakes worked fine (they stopped the car), but felt completely overboosted (the pedal went right to the floor, with no pedal feel). I had the work done with a local mechanic who knows my car well (78 280z w/ Ford 302 and Ferari GTO body kit). We ended up ordering three (3) boosters... turns out that the later 280z's started to use the brake booster from the 280zx at some point in the year -- and they are "identical" except that the diaphragm travel is longer in one than the other, hence the overboosting. So, if you have a later 280z model, this might be the issue... once we got the right one, the pedal is firm, with great feel, and the brakes work great. CAG4 Quote Link to comment Share on other sites More sharing options...
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