bigblockgq Posted August 12, 2013 Report Share Posted August 12, 2013 I've had the same problem with two 7/8 master cylinders know. What happens is the fluid from the rear master cylinder reservoir works it way into the front reservoir and overflows, It is a slow process. At first I checked the wilwood proportioning valve I installed and then double checked the line positions in and out. The p/v is clearly marked FI RI FO FO RO then I checked with wilwood's site and it states that the front and rear channels are completely isolated in the p/v. Everything looked good so I took the master apart and found nothing visually wrong, wtf. I bought a new 7/8 m/c installed and bleed and I'm back to the same concern the rear brake reservoir (front container) bleeds into the front brake reservoir (rear container) the brakes feel ok no pulling or anything strange, all look like they are wearing normal. I tracked the car for a day like this and just kept refilling the rear reservoir and wrapped rags around the front reservoir. The pushrod adjustment is good its not holding the m/c piston in or anything strange. I really cant see it being two new m/c ? The only other possibility I can come up with at this point is that the proportioning valve has an internal connection. Anyone seen this problem ? The picture below the front (rear brake) reservoir is below half and the rear (front brake) reservoir is filled to the top and seeping out. Quote Link to comment
datzenmike Posted August 12, 2013 Report Share Posted August 12, 2013 Well as long as brake performance is unchanged, just get a reservoir from an '82 and up 280zx. Part #46091-W1300 about $20... problem solved Quote Link to comment
bigblockgq Posted August 12, 2013 Author Report Share Posted August 12, 2013 Well as long as brake performance is unchanged, just get a reservoir from an '82 and up 280zx. Part #46091-W1300 about $20... problem solved I like that idea! I had a thought of running a piece of brake line between two new holes front and rear and my friend jb weld. The current reservoirs I have are clamped on the outer machined edge of the m/c. The reservoir you are suggesting looks like it is a internal press fit? will it work ? Quote Link to comment
bigblockgq Posted August 12, 2013 Author Report Share Posted August 12, 2013 The 7/8 master I'm using : 72-73 240z 74 260z 75-78 280z Quote Link to comment
datzenmike Posted August 12, 2013 Report Share Posted August 12, 2013 I like that idea! I had a thought of running a piece of brake line between two new holes front and rear and my friend jb weld. The current reservoirs I have are clamped on the outer machined edge of the m/c. The reservoir you are suggesting looks like it is a internal press fit? will it work ? . There are inserts that seat in the master and te reservoir pushed down into them. Maybe this won't work, but you get the idea. Maybe there are clamp on ones? Quote Link to comment
Ooph! Posted August 12, 2013 Report Share Posted August 12, 2013 I'm just guessing of course but something seems incorrect in you're system. The only way fluid from one reservoir can get to the other is to be pushed there, either something is connected incorrectly at the pv or it is leaking internally or the master is leaking back to front undoing any changes you make with the P. Valve. If it were mine I'd disconnect the pv and see if it continues, it seems you may have already eliminated the master by replacing it. Just my 2 bit's worth Quote Link to comment
flatcat19 Posted August 12, 2013 Report Share Posted August 12, 2013 Why do you have a proportioning valve? You're already rocking a disc/drum MC. Read this... http://www.pirate4x4.com/tech/billavista/Brakes/ Quote Link to comment
bigblockgq Posted August 12, 2013 Author Report Share Posted August 12, 2013 Why do you have a proportioning valve? You're already rocking a disc/drum MC. Read this... http://www.pirate4x4.com/tech/billavista/Brakes/ propotioning valve is mainly for track use for optimum balance ( fuel load) compound so on- I use track compound pads, more agressive. Quote Link to comment
datzenmike Posted August 13, 2013 Report Share Posted August 13, 2013 Depends on the PValve. I have one in my truck and it only tailors the pressure to the rear. Has no connection to the fronts whatever. Most cars have a pressure switch to warn of a loss of pressure in one of the two systems on a dual master. That's the closest the fronts come to the rears. As long as there is pressure in both systems when the brakes are applied the switch stays centered and off. If one system fails the pressure in the other pushes the switch over and grounds it turning the brake warning light on in the dash. Quote Link to comment
bigblockgq Posted August 14, 2013 Author Report Share Posted August 14, 2013 I have an adjustable wildwood poportioning valve, it has a brake pressure warning switch built in for a failure ( see picture) It is internally isolated front to rear hydrolic circuits but that is the only thing that I have not replaced to correct the problem. I'm thinking that the switch for pressure indifference valve that would trigger the light for failure may be leaking internally. I'm going to call wilwood tomorrow and run it by them. Depends on the PValve. I have one in my truck and it only tailors the pressure to the rear. Has no connection to the fronts whatever. Most cars have a pressure switch to warn of a loss of pressure in one of the two systems on a dual master. That's the closest the fronts come to the rears. As long as there is pressure in both systems when the brakes are applied the switch stays centered and off. If one system fails the pressure in the other pushes the switch over and grounds it turning the brake warning light on in the dash. Quote Link to comment
Mannyvig Posted August 19, 2013 Report Share Posted August 19, 2013 It is most likely leaking internally. Quote Link to comment
wayno Posted August 20, 2013 Report Share Posted August 20, 2013 If I were guess here, since the same thing has happened to 2 different masters, I would start looking towards the shaft from the brake pedal to the master since you have checked everything else, is it to long or to short, since you don't have a booster, it is connected directly. 1 Quote Link to comment
TheBirdistheWord Posted August 30, 2013 Report Share Posted August 30, 2013 I know this is a slightly dated thread, but have you figured this out? I was searching for some other brake related info and stumbled upon this. The current M/C on my 510 does this, its not stock, I bought it this way. I thought just replacing it would fix it, I'm thinking I might be wrong now. How could too long or short of throw or push bar damage the M/C? Quote Link to comment
bigblockgq Posted September 3, 2013 Author Report Share Posted September 3, 2013 It was not a push rod problem for me, that was one of the first things I looked at. I ended up putting a piece of brake line between the reservoir's to fix it, they now stay at the same level. I know this is a slightly dated thread, but have you figured this out? I was searching for some other brake related info and stumbled upon this. The current M/C on my 510 does this, its not stock, I bought it this way. I thought just replacing it would fix it, I'm thinking I might be wrong now. How could too long or short of throw or push bar damage the M/C? Quote Link to comment
c4ck4 Posted January 6, 2014 Report Share Posted January 6, 2014 I don't know if the 7/8" master cylinder is the same as on my 620 but I'm having this same problem. I put in a new master a few months back and only put 200-300 miles on it since then. Yesterday I felt the brakes kinda engage and then clunk a little bit so when I checked the fluid, the front reservoir was dry and the back one was over flowing! I do have the stock load sensing valve, is that similar in purpose to the proportioning valve you put in? Can you post pictures of your solution with the brake line connecting them? Did you just poke it through the plastic of the reservoirs and JB Weld it? Is something like the 280zx master above appropriate for 4 wheel drum setup? Quote Link to comment
datzenmike Posted January 6, 2014 Report Share Posted January 6, 2014 I do have the stock load sensing valve, is that similar in purpose to the proportioning valve you put in? The NSLV Nissan load sensing valve, tilts down slightly with the frame movement as more weight is added in the back. The more weight that is added the more braking pressure is allowed through to the rear tires. More weight = more traction so more braking can safely be added. Is something like the 280zx master above appropriate for 4 wheel drum setup? The zx master is 15/16" and much larger than your stock 3/4". To get the same brake line pressure you will have to step much harder on the peddle. Looks like 56% harder at all times. Your legs are quite strong and exerting 100 pounds on the brake pedal for a moderately sudden stop is easy. Now imaging almost having to push 160 pounds to do the same amount of stop. This makes driving a chore. I didn't have a 3/4" for my 710 sedan and used instead a 7/8" one. The pedal is noticeably much firmer. It's an automatic so you have to hold the brake at the lights. It isn't impossible but it is a slight bother. And this is only a 36% increase yours will be getting close to double that. In addition the zx master is set up for use with rear disc brakes... you have drums. You would need to swap your rear proportioning valve into it. Quote Link to comment
ggzilla Posted January 6, 2014 Report Share Posted January 6, 2014 Rear proportioning valve? Typically you remove the Residual Valve from a disk/drum master when converting to all discs. Doing the opposite (using all-disc master with disc/drum setup) means adding the RV. Or do nothing but keep the rear brakes manually adjusted. Quote Link to comment
datzenmike Posted January 6, 2014 Report Share Posted January 6, 2014 Ha ha yeah residual valves, my bad. All Nissan masters have residual valves in them for rear disc or drum brakes. Drums are for holding 6-8 PSI in the lines while disc are only 2 or 3 PSI to keep the pads against the rotor to keep them clean. Quote Link to comment
c4ck4 Posted January 7, 2014 Report Share Posted January 7, 2014 That all really helps me under stand the theory of braking and master cylinder size. Mostly though I'm just trying to figure out why my reservoirs are emptying and overflowing. And how to fix it. Could this happen if i reversed the front and rear lines? Maybe I installed it wrong Quote Link to comment
ggzilla Posted January 7, 2014 Report Share Posted January 7, 2014 Nope, reversed lines won't cause that. A bad mc is indicated. The seals were put in backwards perhaps. Quote Link to comment
c4ck4 Posted January 7, 2014 Report Share Posted January 7, 2014 Well since it was new, maybe I can still get an exchange for it. Quote Link to comment
Juanjoze Posted May 29, 2023 Report Share Posted May 29, 2023 On 9/3/2013 at 2:56 PM, bigblockgq said: It was not a push rod problem for me, that was one of the first things I looked at. I ended up putting a piece of brake line between the reservoir's to fix it, they now stay at the same level. Hello, I know it's been a long time but I have the exact same problem with a 7/8 master cylinder, I also have a proportioning brake valve. Did you find what was the cause? Quote Link to comment
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.
Note: Your post will require moderator approval before it will be visible.