Guest zfan Posted November 7, 2005 Share Posted November 7, 2005 I have a question for you brake guru's as I am stumped. I installed the Toyota 4 runner/300zx install up front and the rear 240sx install with the 280ZX master cylinder on my 240Z. My brake suck! I extended the rod in the booster and bled the brake several times and still have a real soft pedal. My motor doesn't make alot of vacuum probably 10-12" of vacuum. The pedal is firm with the car off but when I start the car I lose the firm pedal. I plan on adding a vacuum pump and currently use a vacuum resevoir. The booster diaphram is in place and the booster is not failing, I also did away with the front and back perportioning valves. Any idea's as I am stumped. Mike Quote Link to comment Share on other sites More sharing options...
zcarnut Posted November 7, 2005 Share Posted November 7, 2005 You didn’t inadvertently swap the left and right side calipers did you? On both the front and rear calipers the bleeder screws must be at the top. Otherwise you will never get all the air out when bleeding. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 7, 2005 Share Posted November 7, 2005 No screw up there, I have them pointed up. Wish it was that simple though! Pedal is very firm when you just get in the car and pump the pedal but once you start the car they go to crap! Wilwoods in my future! Mike Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 7, 2005 Share Posted November 7, 2005 When the car is off the pedal should still be soft(er) for a couple pushes of the brake pedal, because there should still be vacuum in the booster. If there isn't any vacuum in the booster when the car isn't running the most likely problem is that the one way valve in the vacuum hose to the booster is either missing or defective. You should have that check valve in there, otherwise you're relying on whatever the engine vacuum happens to be at any given time. So if you're WOT and you step on the brakes there would be very little vacuum, but if you're idling there would be a whole lot available. ANY car with power brakes is going to have a rock hard pedal without the booster. How soft the pedal gets when the booster is working depends on the condition of the brake hoses, quality of the bleed, the quality of the fluid, and the size of the caliper pistons in relation to the master cylinder pistons. I don't think putting more vacuum to the booster is going to make you happy, so I think putting a vacuum pump on there is a waste of time/money. Wilwoods aren't going to change anything for the better either, unless you get Wilwoods with smaller pistons than your current brakes have. Do you have SS brake lines yet? That helps a soft pedal, especially when the old rubber lines are cracked and bulging. If everything is in good shape and the fluid is new and the brakes are bled properly, your only real option is to switch to a larger master cylinder. I can say in my own experience with the ZX master with 4x4 calipers and ZX rear disk I had a very firm pedal. I did have the smaller early Z booster though. Quote Link to comment Share on other sites More sharing options...
skipzoomie Posted November 7, 2005 Share Posted November 7, 2005 I think you'll find that the reaction disk has fallen out of its pocket in the booster. I had exactly the same condition in my 78. When I disassembled the booster I found the disc lying in the bottom. I put a small amount of silicone grease on the disc to hold it in place and when everything was reassembled the brakes worked great. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 7, 2005 Share Posted November 7, 2005 I completly flushed the brake system so all new fluid there and I have new steel braided lines on all four corners. I am also running the original size booster for the early model 240Z. Did you delete the stock perportioning valves? I did, so I have no perportioning valves at all. I am going to try and rebleed the brakes again. I went thru 4 ZX master cylinders trying to find a good rebuilt one. Did you use a new one? Mike Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 7, 2005 Share Posted November 7, 2005 I bet skipzoomie is right. Typical reaction disk thread is titled: "I've bled the brakes 173 times and the pedal is still soft." I didn't recognize it until he said it, but that definitely sounds like the problem in this case. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 7, 2005 Share Posted November 7, 2005 Definetly a possability, I will check it out tomorrow. Thanks for the help/tips Guys! Mike Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted November 8, 2005 Share Posted November 8, 2005 Definetly a possability' date=' I will check it out tomorrow. Thanks for the help/tips Guys! Mike[/quote'] You would know if it was the reaction disk by a soft pedal accompanied by little to no stopping, followed by an extremely hard brake pedal and a jarring stop with the wheels locked. Atleast thats how it normally goes from what i read. It basically makes the brakes "on or off" so to speak. I think it might have something to do with your proportioning valve removal. Everyone I asked says keep it, atleast for the 4x4 front and 240sx rear swap. I would imagine letting more pressure to the rears to allow a totally equal distribution of pressue is a bad idea (this is assuming you have the 280zx booster w/o internal proportioning, i believe there is one, or maybe that is 300zx). Also, did you switch the lines from front to back on the M/C? Pretty sure that the 280zx's had the fronts and rears switched in relation that the 240z stock setup. Side note, i don't believe the 240z had a front proportioning valve, you may be talking about the warning light thinga ma jigger. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 8, 2005 Share Posted November 8, 2005 Right you are it was not a perportioning valve but I gutted it anyways. The back one was removed and I just used a union fitting to tie the two lines together. I am using the stock booster for a 1971 240Z, I put a rebuilt one in 2 yrs ago. I also switched the lines when I swapped to the 280ZX master cylinder. Damn, running out of idea's. May need to take it to a brake Guru! Mike Quote Link to comment Share on other sites More sharing options...
Tim240z Posted November 8, 2005 Share Posted November 8, 2005 Mike, I had terrible luck with the rebuilt masters and finally bought a brand new one .... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 8, 2005 Share Posted November 8, 2005 It sounds like you didn't bother checking the reaction disk. I'd still suggest you take a look in there. Easy enough to look. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 8, 2005 Share Posted November 8, 2005 Actually I do plan on checking it. I just have not had the time the last couple of days, maybe friday if all goes well. Mike Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 8, 2005 Share Posted November 8, 2005 Jon, What am I looking for when I check it out? I know the plunger has a bushing/seal on the back of the rod to the master cylinder so I was wondering? Thanks, Mike Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 8, 2005 Share Posted November 8, 2005 Pull the master, pull the pin, should be a ~nickel sized 3/16" thick rubber disk in there. If it isn't stuck to the back of the pin it probably fell into the booster. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 9, 2005 Share Posted November 9, 2005 Damn, it's there. Would have been an easy fix though...cries! Next step? Mike Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 9, 2005 Share Posted November 9, 2005 Hmm... Sometimes internet diagnoses are frustrating. This appears to be another "there's nothing wrong with my braking system so how come it sucks" threads. Something has to be wrong... All I can suggest is take a step back, look at each individual component and see what you come up with. If it's not the reaction disk, then I'd suspect the brake lines and/or the bleed. Tim mentioned the master cyl. Did you test that? Usual test is soft constant pressure on the pedal. If the pedal slowly sinks, the master is bad. Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted November 9, 2005 Share Posted November 9, 2005 Ok found one problem. The brake line from the master cylinder to the front brake is leaking under pressure at the union, line and master cylinder. Would this allow air into the brake system as well as fluid loss? It was not leaking at the shop the other day and when I looked closer when checking the booster diaphram I notice a very small wet spot but when I pumped the brakes several times hard it would drip from the line below the master cylinder. I loosened and retightened the line and it still leaks. Will try to fix this and then recheck it all again. Mike Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted November 9, 2005 Share Posted November 9, 2005 ok this is a very basic test, but want I've always done is pump the brakes rapidly several times until they build pressure, then just stand on the pedel. press it down as hard as you can and hold it. If there is a leak, as you are holding it, you will feel it slowly leaking down. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 9, 2005 Share Posted November 9, 2005 Ok found one problem. The brake line from the master cylinder to the front brake is leaking under pressure at the union' date=' line and master cylinder. Would this allow air into the brake system as well as fluid loss? It was not leaking at the shop the other day and when I looked closer when checking the booster diaphram I notice a very small wet spot but when I pumped the brakes several times hard it would drip from the line below the master cylinder. I loosened and retightened the line and it still leaks. Will try to fix this and then recheck it all again. Mike[/quote'] Yes, a leaky fitting will allow fluid out and air in, and will cause a spongy pedal. Did you flare your own lines? The key thing I had to figure out about flaring brake lines is to chamfer the line before you flare it. I just use a big drill bit that I spin by hand, like a 1/4 or 5/16. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.