Proportioning on 510 with zx frot brake and 240sx rear

[Topher88]

From what I have read and heard with the stock 510 set up the rear will lock up so dose anyone have suggestions what I should do for the proportioning on my 510?

[rpowell25]

I am using a 15/16ths ZX BMC on my car that has 280ZX front and Maxima rear with great results.

[DISLEXICDIME]

x2

[datzenmike]

From what I have read and heard with the stock 510 set up the rear will lock up so dose anyone have suggestions what I should do for the proportioning on my 510?

 

The 15/16' master is designed for and has residual valves tailored for use with both front and rear disc brakes.If you have zx front and sx rear disc brakes you are probably just fine. What you may be referring to is a 15/16" master overpowering the stock 510 drums on the back.

 

Take your car out to a secluded highway and at about 25 or so, brake progressively harder until the brakes lock to a stop. Look at the rubber marks. If there are only marks from the rears then you have severe rear bias which is very dangerous. With the rears locked there is a tendency for the back to 'come around' like severe oversteer. Once the rears lock up, that's it, they will travel in the direction they are going. Imagine braking in a right hand turn, the front continues around the curve, the backs slide in a straight line crossing the center line. Ideally you would want to see the tire marks begin together on all four wheels.

 

Brake bias is usually designed in at the factory by increasing or decreasing the rear wheel cylinders. This may not be possible so the last resort is an adjustable proportioning valve where you can dial back the pressure to the rear calipers. These are not strictly street legal but uncontrolled rear lock up and severe oversteer is way worse. You will need to mount the valve in line with the rear brake line. I put mine under the hood so I wouldn't be tempted to mess with it while driving. I found that on my truck with 15" of lift the weight transfer to the front when braking lifted a lot of weight of the rear axle and the tires would lock. I installed a Willwood adjustable valve and removed 60% of the braking to the rear to fix it. Before, under even moderate braking on dry pavement the brakes would lock just as you came to a stop. Very embarrassing at lights and anywhere in town. I started leaving 3 car spaces so I could brake more gently and was petrified of a panic stop. Now I can jack on the brakes with confidence and because it won't lock up I can really stand on them if I have to.

[Topher88]

Thanks a munch guys. I'm still a few months out till I'm running but I'll definatly hit a road and see if I need that adjustable Proportioning valve. I have one more question. The factory brake lines kinda twist an wrap around, my question is would it mess up the system If I ran a new hard line in a much simpler cleaner location just to make it look cleaner.

[Uber Deaf One]

Interesting... I'm running a 15/16" master cylinder with 280ZX front disc brakes and stock 510 rear drum brakes.... all 4 tires lock up at the same time in a straight line. In Autocross I am often wanting more rear brake bias because I keep locking up the inside fronts. I do have a slotted rear crossmember with a proper alignment though... I'm wondering if having normal camber (-1.5 degrees as opposed to 2+) in the rear is helping with the rear grip under braking....

[DISLEXICDIME]

when i ran a stock master with zx fronts and stock rears my car barley used the drums

[Uber Deaf One]

when i ran a stock master with zx fronts and stock rears my car barley used the drums

 

EDIT: nvm I thought you had a 15/16" master cylinder.

[69datsun510]

From what I have read and heard with the stock 510 set up the rear will lock up so dose anyone have suggestions what I should do for the proportioning on my 510?

 

 

I suggest putting in an Adjustable Brake Proportioning Valve. You can pick one up at Motorsport Auto, located in Orange, Ca or on line at The Z Store, their website. Once installed you can dial in as much front or rear brake as you want. You can plumb the valve so you can have it inside the car and adjust it on the fly too.

[DISLEXICDIME]

EDIT: nvm I thought you had a 15/16" master cylinder.

 

I do in my currant car but it has disc brakes

[Uber Deaf One]

I do in my currant car but it has disc brakes

 

I'm running a 15/16" MC with 280ZX brakes up front, and stock 510 drums in the rear. I find myself wanting MORE rear brake bias at pretty much every AutoX event....

[jesusno2]

I have zx fronts with wilwoods in the rear car stops pretty good with the 15/16 M/C

[yellowdatsun]

You don't need a proportioning valve on a street car, unless you use components so horribly incompatible that they shouldn't be used to begin with. I bought a real proportioning valve some time back to install in my cars, and have never needed to put it in.

 

 

For years I used 280ZX front, a Z master, with drums on the back. No lockup problems.

 

Then I made brackets to add Maxima discs to the back, still no problems.

 

Then added a 300ZX Z31 master, no problems.

 

Then used VG200sx struts brakes up front, and 300zx Z31 brakes out back, still no problems.

 

Then added Z32 4 pot brakes up front, and Z31 out back, Z31 master, no problems.

 

Then switched to Z32 all around, still using the Z31 master, STILL no problems.

 

 

We also just switched my GF's car to 280ZX up front, and drums out back, no issues there either.

 

 

So if you DO have lockup problems, something probably isn't working right, or so out of balance with everything else that it should be changed anyways.