Guest ZonRed Posted October 4, 2007 Share Posted October 4, 2007 Hi Everyone, Just got a 75 280z and in the process of fixing it up. I decided to update the brakes to 4 wheel disc with the following: 1) 280ZX REAR CROSS DRILLED/SLOTTED BRAKE ROTORS 3) FRONT NON VENTED CROSS DRILLED/SLOTTED BRAKE ROTORS with reman stock calipers and semi-metalic pads 2) STAINLESS STEEL BRAIDED BRAKE LINES 3) REAR 6061 T-6 ALUMINUM REAR CALIPER ADAPTOR BRACKETS 4) USED MAXIMA 4 DOOR SEDAN CALIPERS THAT ARE CLEANED,CHECKED with semi-metalic pads reversed install so bleeder is facing up 5) 280zx 15/16 MC and 8 inch brake booster System was installed and power bleed, but pedal feels good but brakes will not engage until pushed almost to the floor and randomly the brake light goes off and on. The rod was adjusted to no effect. Pedal acts like there is pressure but gradually goes down like air may still be present. Shop says they guarantee there is no air, but are questioning the stock proportioning valves and tell me the reaction disk is OK. When brakes engage they do evenly and if I do a quick double pump they will lock up. There seems to be equal pressure before and after the valves but that is just a visual. This problem is keeping me from getting pass the state safety inspection so appreciate any guidance as I've read alot of threads about brake issues but I am missing something. Appreciate any advice. Quote Link to comment Share on other sites More sharing options...
smoorenc Posted October 4, 2007 Share Posted October 4, 2007 You sure your booster's bladder isn't popped? Mine went bad once and it was hard to stop. Quote Link to comment Share on other sites More sharing options...
Guest ZonRed Posted October 5, 2007 Share Posted October 5, 2007 You sure your booster's bladder isn't popped? Mine went bad once and it was hard to stop. The booster is new so I hope not, pedal seems to have a good feel to it just the brakes are not engaging well unless pump the brakes Quote Link to comment Share on other sites More sharing options...
Roostmonkey Posted October 5, 2007 Share Posted October 5, 2007 Bleed them again...and again. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 5, 2007 Share Posted October 5, 2007 If you're saying that you can put your foot on the pedal when stopped, and the pedal gradually sinks down, then I'd focus on the MC. I can't tell from your description if you replaced it or not. Also, did you bench bleed the MC before installing it? If not, probably no amount of bleeding in the car is going to get rid of the air. Do you still have the stock proportioning valve installed? If so, it needs to come out as you now have 4 wheel discs. The stock prop valve is set for drums in the rear, not discs. I doubt that's the cause of your issue with the sinking pedal, but you'll need to remove it none the less. I'd suggest installing an adjustable valve, but I know others have just left it out and have been happy with the results. Quote Link to comment Share on other sites More sharing options...
Guest ZonRed Posted October 5, 2007 Share Posted October 5, 2007 The MC was replaced with re-man, and that does concern me as some folks have mentioned that they have gotten bad re-mans. Luckily this one has a lifetime warranty, so I can excahnge it if needed. In regards to bench bleeding, I did it on the car which I later find out is not a good thing to do as it doesn't push the plunger all the way to the stop. The shop that power bleed the system tells me it should of taken care of that, but I,m willing to do it in a vice if you tell me otherwise. In regards to the prop valve, it is stock and the shop thinks it the problem as well. The question is which one? There is the one just under the MC that has the brake light sensor and then there is the one on the firewall that feeds the RF and rear. I read some people say to gut the distrubition valve but according to the shop manual it states the one on the firewall is a NP valve, is this the same? If adjustable prop is the way to go what one do you recommend for this, and any indication on where in the system it needs to be installed would be appreciated. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 5, 2007 Share Posted October 5, 2007 http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=adjustable+proportioning&category0= Any of these would work as a replacement for the prop valve. You'll see that there really are only 2 models available, just branded with different names. It should be installed in the rear brake line anywhere after the what you are calling the "brake light sensor". BUT - changing the prop valve will not fix a sinking brake pedal!!!!! Also, if I were you, I'd be concerned that the shop isn't able to tell the difference between the brake light sensor unit, and the prop valve. Also, that they think the prop valve is the source of your sinking brake pedal is another concern for me!!!! It tells me that whoever you're talking to has very little understanding of braking systems. Perhaps they can put a more experienced person on your car? On my 73, the prop valve is on the firewall near the brake booster. The "brake light sensor" unit is on the left front fender below the MC. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 5, 2007 Share Posted October 5, 2007 I'd double check the reaction disk and while you're in there, check the length of the pushrod that actually engages the master. Quote Link to comment Share on other sites More sharing options...
Guest ZonRed Posted October 6, 2007 Share Posted October 6, 2007 Went ahead an order a adj prop. I think that is what is going to get it working. The shop was just a local Goodyear as it was close to the house and I could drive through the subdivision to get it to them. When I first went to them the pedal was sponge and they power bleed it with not much difference and told me the MC and booster were bad. Replaced them with the 15/16 setup after reading threads on Hybridz. The pedal diffently got better but still had to put extra force and push the pedal past the resistance at halfway down to get any form of light braking. Double pump to lock it up The second time I took it to them they bleed it, adjusted the rod, and though it got a little more harder to push down it still behaved the same and the brake light frequently fluctuates on and off though less frequently. I am curious about some threads talking about gutting the distribution block for the rear drums. I've read the manual and besides the NP (Prop) valve and a 3 way connector in the back I don't see it on the 75. Maybe my ignorance as I haven't worked on a car in over 20 years and some terminology slips me. Always wanted to get one of these cars as a teen, so really looking forward to driving it like it was designed to be driven . Thanks all for the help, will let everyone know how the outcome goes. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 6, 2007 Share Posted October 6, 2007 I think some people have gutted the drum prop valve to remove its function from the circuit, but not have to deal with finding metric threaded unions for the brake fittings that would be needed if you took the whole prop valve assembly out. Quote Link to comment Share on other sites More sharing options...
Guest ZonRed Posted October 10, 2007 Share Posted October 10, 2007 If possible can someone send me pics of how they setup the adjust prop valve? Thanks Quote Link to comment Share on other sites More sharing options...
Guest ZonRed Posted October 11, 2007 Share Posted October 11, 2007 If possible can someone send me pics of how they setup the adjust prop valve? Thanks Or better yet can someone clarify on this. The new adj prop vavle replaces the rear control for the stock and goes inline where those lines connect. Where I'm needing clarification is with the front line that goes through the stock as well. Can I leave that alone or do I need to create a bypass connection and remove the stock valve all together. If I can leave it do I need to look in plugging the ports where the rear lines connect? It hard to tell from the manual if there are shared components/fluids between the front and rear or it seperate just in the same housing. Thanks, Quote Link to comment Share on other sites More sharing options...
MrFancypants Posted October 11, 2007 Share Posted October 11, 2007 You should remove the stock prop valve entirely and replace it with the adjustable. Some also recommend removing the brake warning switch as well. - Greg - Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 11, 2007 Share Posted October 11, 2007 Just to clarify, the front line does NOT go through the stock prop valve (although it might look like it does - check it out up close). The brake differential switch (I think that's the proper name) is mounted on the driver side fender not far from the MC. All this does is sense if there is a significant difference in pressure between the front and rear brake lines and if there is, a switch closes and lights the brake light up on the instrument cluster - like you wouldn't already have noticed that the pedal went down further and your brakes don't work so well Of course, both the front and rear lines need to go through it, but there is no reason to remove it unless it's leaking. Quote Link to comment Share on other sites More sharing options...
MrFancypants Posted October 11, 2007 Share Posted October 11, 2007 ^^ Yeah I didnt see the reason behind removing the "brake differential switch" but since I was redoing my entire brake system I removed it anyway. That's good info on the prop valve. If it's just a straight pass through for the front lines then you should be able to just bypass the rear line. But given that the front lines are the easy ones to redo, I would just pull it out because it's ugly - Greg - Quote Link to comment Share on other sites More sharing options...
Zmanco Posted October 11, 2007 Share Posted October 11, 2007 If it's just a straight pass through for the front lines then you should be able to just bypass the rear line. On my 73 the front line runs underneath the prop valve, but is not in any way attached to it. Quote Link to comment Share on other sites More sharing options...
GrommitZ Posted October 11, 2007 Share Posted October 11, 2007 I still think your current master cylinder is bad. I bet fluid is making it's way past one of the two seals, causing the low pedal, slow sinking and brake imbalance(light). Quote Link to comment Share on other sites More sharing options...
Clifton Posted October 11, 2007 Share Posted October 11, 2007 I'd double check the reaction disk and while you're in there, check the length of the pushrod that actually engages the master. I would do this too. The 15/16 MC's I've seen have a different insert were the push rod hits it. On my 71' I had to lengthen the rod quite a bit. Also The factory prop valve is not your problem as far as a soft pedal. Quote Link to comment Share on other sites More sharing options...
Guest ZonRed Posted October 13, 2007 Share Posted October 13, 2007 The 75 stock prop valve diffently has the RF line going through it. Here is a pic from the manual that shows a cutout. http://louque.homeserver.com/photos/280z/img002.jpg If I completely remove it I have to somehow reconnect the front line, anyone suggest what type of connector I should use? The local auto parts store are at a lost as all their pressure line joint connectors are male not female. It almost like I need a junction box but all the ones I can locate are 3 ways. By the way the pedal is not soft any more just the brakes are not locking up unless I double pump. Someone else told me it's because my stock prop is for rear drums and will not work. I either have to gut it or go with the adj prop is what I am finding out. Quote Link to comment Share on other sites More sharing options...
Clifton Posted October 13, 2007 Share Posted October 13, 2007 Someone else told me it's because my stock prop is for rear drums and will not work. I either have to gut it or go with the adj prop is what I am finding out. I run a stock prop valve with rear disks and have no problems locking the rears up first if I want. Quote Link to comment Share on other sites More sharing options...
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