BIGJIM Posted March 11, 2004 Share Posted March 11, 2004 OK, Helped a freind install toyota 4x4 calipers on the front of his z 6-8 months ago. it has pretty much sat in his garage since then. we installed the 4x4 toyota calipers, 300zx rotors, 280zx master cylinder, and 280z power booster. everything was new. cant get a decent brake pressure, idle surges when the brake is pressed in and this thing has got me totally stumped! i dont know what else to do. it has no air in the lines since i have bled them more than 30 times. help! i did notice that when i tired to bleed the master cylinder, the front reservior bled no fluid when the bleeder was open and the res was full of fluid. could this be the problem? im lost here. wish we had left em stock! Quote Link to comment Share on other sites More sharing options...
j260z Posted March 11, 2004 Share Posted March 11, 2004 the master cylinder should be bench bled before it is installed and then there is an order you have to bleed the brakes in. i can't remember what it is but will try to find it for you. when you mentioned idle surge, did you mean that the engine idle surges when you depress the brake? another thing to check is whether you have the one way valve in properly on the vacuum line to the booster. Quote Link to comment Share on other sites More sharing options...
Guest ZmeFly Posted March 11, 2004 Share Posted March 11, 2004 The order is furthest from the mc starting to the closest, ie rr lr rf lf. Hmm is the check valve good? Quote Link to comment Share on other sites More sharing options...
BIGJIM Posted March 11, 2004 Author Share Posted March 11, 2004 tried 2 different check valves, isnt the problem. im stumped! Quote Link to comment Share on other sites More sharing options...
materchan Posted March 11, 2004 Share Posted March 11, 2004 is your brake booster new, if not then you might have just gotten unlucky and got a bad brake booster. get your head down near the pedal and with the car on depres the pedal, if you hear any hissing or somthing like that then you brake booster is bad. Quote Link to comment Share on other sites More sharing options...
Guest bluex_v1 Posted March 11, 2004 Share Posted March 11, 2004 I had a similar problem when I was still driving my 260... IIRC, the only thing the check valve does is prevent fuel/air mixture making its way into the booster, so it is just a one-way valve and should not cause these symptoms (unless the clamps on it weren't tight enough). I'm pretty sure it has to be a bad diaphragm. I had thought about spraying starter fluid near the booster while having the brake pedal depressed...as in how you can look for intake leaks and stuff. I don't know if the fluid could possibly damage the booster diaphragm, but I assume it is so volitile that its not going to be in contact with it long enough to matter. (never got around to trying it though because I picked up a 280 junkyard unit instead) Quote Link to comment Share on other sites More sharing options...
SpeedRacer Posted March 11, 2004 Share Posted March 11, 2004 Actually, I think you will find that the check valve is there for two reasons: 1) To prevent damage to the brake booster diaphragm if there is a backfire and, 2) To prevent the loss of vacuum in the brake booster when the engine loses vacuum (i.e. at wide open throttle). First, check to make sure that the check valve is not installed backwards. Next, since the idle surges when you depress the brake pedal, I would guess that the brake booster diaphragm is leaking. This allows additional air to enter the engine and is a bit like opening the throttle valve. To check this, turn the engine off and, after a couple of minutes, step on the brake pedal. You should still have vacuum and it should be easy to depress the pedal two or three times. If it's hard to depress the first time then the vacuum has leaked out and you need to find out where. You didn't say if it was every working correctly right after the conversion. So, it may be caused by the significant travel in the brake pedal. Check the rod between master cylinder and the brake booster. It's possible that it is too short. The spec for the rod length is in the shop manual. Also, the front reservoir (on the later cars) is for the rear brakes so check the brake bias (proportioning) valve and see if it is stuck. Good luck and please let us know what happens. Quote Link to comment Share on other sites More sharing options...
TimZ Posted March 12, 2004 Share Posted March 12, 2004 What SpeedRacer said. Small detail on the bleeding order - because of the way the brake lines are routed, the left rear is actually the farthest from the MC, line length-wise. So, LR, RR, RF, LF Quote Link to comment Share on other sites More sharing options...
Ben Posted March 14, 2004 Share Posted March 14, 2004 If the master didn't bleed properly, then the corresponding circuit certainly has a large amount of air in it.... Since you know that there is an issue - fix your bleeding problem & take it from there. The Z brakes will not purge all air unless the master is bled. Quote Link to comment Share on other sites More sharing options...
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