daddydonuts Posted February 4, 2013 Share Posted February 4, 2013 Before I get blasted, I have searched HZ for the answer with no clear definite solution on what to do with the proportioning valve. Some say take the guts out of the prop valve, some say don't... My Car-73 240Z My Brake setup is the 81 280ZX 15/16 Master Cylinder, reman'd stock 240Z booster (I might upgrade to ZX later), 240Z stock proportion valve, 83 280 ZX rotors and calipers in the rear, 83 Toyota 4x4 front calipers that use the stock 240Z rotor direct bolt on caliper. My question is what exactly I should do with the proportioning valve to make this system brake properly? If I am missing some information that you need to make a clear definitive answer please let me know before posting. I am just trying to clear up some of the confusion that has been talked about on HZ for many years with different opinions on what works. I will not drive my Z until this is fixed. I will never race my Z in a competition, and will eventually run a modest N/A engine with triple carbs...so HP will never be over 220 in case people are wanting to know what kind of power I will need for stopping my car. Once again, I hate bringing up a topic that has been talked about many times, but I, and probably others, find many opinions on what to do with the prop valve when upgrading to disc brakes. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 4, 2013 Share Posted February 4, 2013 You have two options: 1. Leave the stock valve in place, unmolested. 2. Remove or gut the stock valve and replace it with an adjustable valve. In either case you need to take the car out on a straight, level road and safely test the brake balance yourself. Quote Link to comment Share on other sites More sharing options...
EuroDat Posted February 4, 2013 Share Posted February 4, 2013 I would go with John's first option. Test the car on a quiet road with the original PV. Then if the balance is not right, strip the guts out of it and fit an adjustable somewhere where you can get to it and not in the car where temptation to play with it is at its highest. Your PV is located above the diff which wont effect the dual system. If its on the firewall (like the 260 & 280z) you should remove it completly and fit unions. Stripping the guts out of the 260/280z type removes the safety features of a due brake system and makes the brake warning switch useless. Might not be legal. Remember: the system you replaced had a complete engineering R&D department team working on the design. Your on your own with this so take your time to get it right. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted February 4, 2013 Author Share Posted February 4, 2013 I was leaning more towards option # 1 above. One more response from a HZ member that agrees with that, and I will go that route...just want to do things right. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 4, 2013 Share Posted February 4, 2013 The OE proportioniong valve in the '73 is connected to both the rear and front brake circuits and uses the front brake pressure to act against the rear brake pressure in some manner for the proportioning action. If you gut the valve it will connect the front and rear brake curcuits defeating the saftey benefits of the dual-circuit master cylinder. Quote Link to comment Share on other sites More sharing options...
Nigel Posted February 5, 2013 Share Posted February 5, 2013 Daddydonuts, I understand your confusion. There is a lot of misinformation out there about brakes, with a lot of assumptions made about various components. Case in point, gutting a '73 240Z proportioning valve. I keep seeing this come up again and again. Beermanpete is right on. Don't do it! As for brake bias, unfortunately, it's difficult to calculate brake torque for a drum brake, since it doesn't increase linearly with pressure. So, it's hard to know what the stock 240Z brake bias is for comparison to your new setup. However, your new combo has ~64/36 front/rear brake torque split, which is pretty close to the ~63/37 split of a 280ZX. Assuming the weight distribution and center of gravity height are similar, then the two cars probably have similar brake bias requirements. The '73 240Z proportioning valve looks identical externally to the 280ZX valve, but the ZX valve might have a different curve. You could try swapping your stock valve for a ZX valve as an experiment, if you're not happy with the bias from the stock valve. Nigel Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted February 5, 2013 Author Share Posted February 5, 2013 Thanks for all of the knowledge Quote Link to comment Share on other sites More sharing options...
SlowRob Posted February 5, 2013 Share Posted February 5, 2013 I'm running virtually the same setup and left the prop in-place. Braking is quite even, locking all four wheels evenly. Don't forget that wheel/tire choice will also affect proportioning. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted February 5, 2013 Author Share Posted February 5, 2013 I'm running virtually the same setup and left the prop in-place. Braking is quite even, locking all four wheels evenly. Don't forget that wheel/tire choice will also affect proportioning. More than likely, a wheel and tire combo that will fit under stock wheel wells, my car has very little rust and no need for flares Quote Link to comment Share on other sites More sharing options...
Ben Posted February 6, 2013 Share Posted February 6, 2013 My recommendation - option 2; Lose the stock PV, and fit an adjustable inline one to the rear circuit. I've done just that (the setup was stock M/C, Hilux front, R31 rear), the bias was dialled in when the car was checked for compliance after the turbo engine installation. The front M/C circuit goes directly to a distribution block, and the rear circuit is directly connected to the Willwood PV. The OEM brake warning 'device' was that gummed up, that it would have never shown a failure anyway... You could always fit float alarms to the M/C reservoirs if you wanted to retain a warning system. The authorities were happy with the brake bias, but I wasn't so keen on the pedal travel. The car now sports a Z31/4Runner front and 1" M/C. I haven't driven it since the front upgrade, but the pedal was certainly firm with the 1" M/C! Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted February 6, 2013 Author Share Posted February 6, 2013 I think for now I will go with the stock PV, and test it as stated above...logically thinking, it seems I would have the same amount of fluid to move with the larger brakes compared to the stock setup, given that I have the bigger MC. Quote Link to comment Share on other sites More sharing options...
Nigel Posted February 6, 2013 Share Posted February 6, 2013 My recommendation - option 2; Lose the stock PV, and fit an adjustable inline one to the rear circuit. I've done just that (the setup was stock M/C, Hilux front, R31 rear), the bias was dialled in when the car was checked for compliance after the turbo engine installation. The front M/C circuit goes directly to a distribution block, and the rear circuit is directly connected to the Willwood PV. The OEM brake warning 'device' was that gummed up, that it would have never shown a failure anyway... You could always fit float alarms to the M/C reservoirs if you wanted to retain a warning system. The authorities were happy with the brake bias, but I wasn't so keen on the pedal travel. The car now sports a Z31/4Runner front and 1" M/C. I haven't driven it since the front upgrade, but the pedal was certainly firm with the 1" M/C! According to the specs I've found on the R31 rear brakes, they use 260mm rotors, and calipers with a 38mm piston. This will produce significantly less brake torque than the 280ZX rear brakes, which have 258mm rotors, and calipers with a 43mm piston. That being the case, this is not an apples to apples comparison, and probably not a good basis to make a recommendation. Also, the narrow 4x4 front calipers that the OP has, with the 43/34mm pistons, only have a slight increase in piston surface area compared to a stock 240Z caliper. So a 1" master cylinder, with it's 30% increase in piston area over the 7/8" master cylinder wouldn't be a good match. It'll only result in a rock hard pedal, and require way more effort to achieve the same brake force. The 15/16" master is better suited. The 15/16" master has been fine even with the V6 4-Runner calipers with the 43/43mm pistons, which don't have that much more surface area than a stock ZX caliper. I've found that you can't make any assumptions about the capabilites of brake components just by looking at them or the model of car they came on. I've seen what look to be huge, 6 piston calipers, but have turned out to only have 4, tiny little 34mm pistons in them! You have to find the specs and do the math to make any meaningful comparisons. Quote Link to comment Share on other sites More sharing options...
Ben Posted February 7, 2013 Share Posted February 7, 2013 For clarifications sake; The R31 calipers I'm using are the Australian PBR version, not the JDM version. The rear rotor I'm using is 258mm, the JDM HR31 would be a 290mm rear rotor. 15/16 '280ZX' MC's aren't available over the counter here anymore , Nissan don't stock them and the aftermarket have ceased production, so that removed my first preference. My point is that unless you have access to a brake testing rig to check, the bias could be all over the shop - it's not only the piston area that matters, the pad area and heat-shedding capabilities of the system are relevant too. An aftermarket PV gives you the flexibility to get it right, rather than being stuck with the original proportioning % numbers. That is, unless you are doing a full brake swap on a like-for-like vehicle (e.g. fitting R32 GTR brakes to an R32 GTS-t, including the M/C). Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted February 7, 2013 Author Share Posted February 7, 2013 For clarifications sake; The R31 calipers I'm using are the Australian PBR version, not the JDM version. The rear rotor I'm using is 258mm, the JDM HR31 would be a 290mm rear rotor. 15/16 '280ZX' MC's aren't available over the counter here anymore , Nissan don't stock them and the aftermarket have ceased production, so that removed my first preference. My point is that unless you have access to a brake testing rig to check, the bias could be all over the shop - it's not only the piston area that matters, the pad area and heat-shedding capabilities of the system are relevant too. An aftermarket PV gives you the flexibility to get it right, rather than being stuck with the original proportioning % numbers. That is, unless you are doing a full brake swap on a like-for-like vehicle (e.g. fitting R32 GTR brakes to an R32 GTS-t, including the M/C). Luckily Rock auto had a rebuilt Nabco 15/16 MC that I bought...yay me Quote Link to comment Share on other sites More sharing options...
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