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Front and rear caliper/cylinder ratios should match the application of the car weight bias, brake and tire sizes. Otherwise, a brake proportioning valve will be needed to prevent premature lockup of the rear brakes (the valve reduces pressure to the rear brakes). Early Datsuns used fixed proportion brakes (with no valve), but in the 1970s some were fitted with a Load Sensing Valve Assembly called the NP-Valve. This allows good braking whether fully loaded or empty. The 1200 got a load-sensing valve in October 1989.
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Overview
The ratio of the brake piston diameter to the master piston diameter gives you the mechanical advantage.
But what about the front/rear proportion? You use a smaller mechanical advantage on the back to get the brake force distribution right. You want the front to lock slightly before the rears, and you can use this to tune the brake balance. This rule hold for all hydraulics by the way.
The same size caliper will stop the car faster with larger rotors. So caliper size alone doesn't determine the balance.
Factors * Rotor diameter * Drum diameter * brake pad/shoe material * Front/rear tire size difference (if any) * Caliper bore size/wheel cylinder bore size
Start with your desired pedal pressure (i.e how much foot force you want on the pedal), pedal ratio and work out the required master cylinder size. Lastly, you need to ensure that the stroke of the master cylinder can move enough fluid for the brake size, so work out the total displacement of fluid required. The government regulations specify the maximum leg effort required. Nissan already worked this out by providing the 11/16" master cylinder (easier to press than a larger 13/16" unit, and generates more pressure than a smaller 5/8" unit).
But what about varying loads? A heavily loaded car, with weight in the trunk, will need more proportion to the rear wheels than a lightly loaded car.
Make a full-braking hard stop:
- If both front and rear tires lock up at the same time, this is optimal for braking efficiency. For a margin of safe handling, the front should lock up slightly before the rear.
- If the rear brakes lock up before the fronts, squirrely handling is the result. In this case an Adjustable Brake Proportioning Valve can be added, to cut down on the rear pressure until the fronts lock up first.
- If the front brakes lock up long before the rears, the car won't be stopping as quickly as it should. Adding a Brake Proportioning Valve won't help fix this problem. You can add more tire to the front (e.g. wider tyre), or use larger wheel cylinders on the front (or smaller on the back) in order to make the brakes more rear-biased. Or,changing to a less aggressive front pad will move the bias rearward and thus enable quicker stops.
The other issue with proportioning for a street car is due to weight transfer: Less than a full-braking-force stop will transfer less weight to the front, so more rear brake force can be used. For this reason Brake Proportioning Valves (both factory and aftermarket) don't start restricting the rear brakes until a certain hydraulic pressure is reached. This is what is "adjustable" in some of the adjustable valves, and so won't help with full-force braking.
B110
Datsun 1200 sedan/coupe/wagon does not use a brake proportioning valve. Instead the front and rear working cylinders are sized to achieve a good balance. The maximum weight loading of the car is restricted to 600 pounds passengers + cargo.
Compared to Datsun 1200 drum brakes, the disk brakes require a higher line pressure (harder pedal push) to make them work & this means that the rears would have a greater tendancy to lock up, so the factory fitted the rear wheel cylinders with a smaller bore size to balance the brakes out. Thus a correct proportion is achieved, which is different from the all-drums proportion.
If you fit stock 1200 type disc brakes, then modify or change the master cylinder (remove the RV from the front circuit) AND replace the rear wheel cylinders with 11/16" disc brake units.
All Drums Front: 13/16" wheel cylinders Rear: 13/16" wheel cylinders Disc/Drum Front Front: 1.894" caliper cylinder with 212.5 mm rotor Rear: 11/16" wheel cylinders
Not to be confused with the Brake line pressure differential Warning Light Switch
Brake Upgrades
So you've changed brake types, now has the front brakes are locking up well before the rears come into play. How can this be cured?
Changing master cylinders may change pedal feel but will not change bias. A master with larger diameter cylinder will result in a harder pedal, but less pedal travel. By contrast, a smaller diameter master cylinder will reduce required pedal foot pressure, but will increase pedal travel for a given result. Most Nissan master cylinders from the same era (1971-1982) interchange. You can locate almost any size with a cruise through your local junk yard (sizes are cast on the side of the cylinder).
There are options for changing the brake bias:
- Change rear brake wheel cylinders (larger or smaller). Alternate sizes are available from Nissan motorsports. Or from stock applications. For example, the 510 rear cylinders are 7/8, but bolt in place of the stock 1200 13/16 cylinders. Note that 1200s with drum brakes already have 7/8 rears.
- Changing master cylinders will not change the bias
- Use an appropriate factory bias valve (aka NP-valve or "proportioning valve"). Note that Datsun 1200s don't use one but B210/B310 did.
- Maybe the easiest would be to buy a brake bias controller valve.
- These are available thru your local high performance shop or mail order thru Jeg's or Summit, etc. for around $50 USD.
- Some Volvos also have an adjustable valve you could use
Wilwood adjustable valve
NP-Valve
The NP-valve used with USA B210 and USA/JAPAN B310 is integrated into the splitter and so serves as the circuit pressure loss safety switch.
It is functionally normally if -- during a 50km/h quick stop -- the rear the wheels lock simultaneously with front wheels, or front wheels lock first. Danger if rear wheels lock first.
Location of NP-VALVE in B210
Specifications
See: Brakes#Specifications
Part Numbers
46234 CONNECTOR [brake splitter] 46224 BRAKE INDICATOR SWITCH [combo splitter+switch] 46400 LSVA * 46: Master cylinder, pedal &, piping group * 400: Load Sensing Valve Assembly
Japan
B310
All use NP-Valve except some A12 DX/STD models which use only a splitter.
46400-F2300 46400-F2310 46400-R3001 46400-R3011
Late Sunny Truck
B120 Sunny Truck 46400-G1500 VALVE ASSY 8910- 46405-G1501 BRACKET-VALVE 08630-81851 BOLT Bolts to Lower Back Panel
PB110
OPTIONAL for PB110 was a Proportioning Valve. It was placed in the line to the rear brakes.
46400-A1100 "P" VALVE ASS'Y (op.) DX
* Same as JDM Datsun 510 1970-1972
* "ASS'Y-VALVE, proportioning (op.) S&C"
* In the 510, it replaced the 2-way connector which all 510s have
46400-H1005 "P" VALVE ASS'Y (op.) GL,GX
46364-H2600 JOINT-union GL,GX 2
S30 (240Z) to 0672 USA 46400-E4100 <> 46400-E4101
North America
B210 46400-U0506 ASSY-NP VALVE 4WAY SWI,FRA,GER,SWE DEN,NOR,BEL,HOL,L UX * also used by early 610 46400-H7200 ASSY-NP VALVE 4WAY 0974-0777 * also used by A10 wagon 46400-S0801 ASSY-NP VALVE 5WAY 0877- * also used by S110 0381-
B310 46400-W5000 VALVE ASSY-NP 5WAY EUR,COM(A14,A15) OP COM(A12) * also used by 910 0780- S
610 46400-U0506 ASSY-VALVE NP, 4 WAY -0775 46400-N3700 ASSY-VALVE NP, 4 WAY 0875-
A10 46400-N3000 NP VALVE ASSY (4-WAY) SEDAN & HATCHBACK 46400-H7200 NP-VALVE ASSY WAGON
620 starting 1976, about 1/2 way back 0276- 46400-B1900 ASSY-VALVE LOAD SENSING (L.S.V.) DX 0875- 46400-B1900 ASSY-VALVE LOAD SENSING (L.S.V.) Truck 0876- 46400-B1901 ASSY-VALVE LOAD SENSING (L.S.V.) 0877- 46400-B9800 ASSY-VALVE LOAD SENSING (L.S.V.) $667 USD
720 VALVE ASSEMBLY [also called load-sensing valve, under bed] 2WD 0679-0681 46400-05W00 0781-1181 46400-03W00 0781-1181 46400-05W00 HD/T 1281-1282 46400-34W00 0183- 46400-10W00 DUAL WHEEL 46400-10W10 0183- 46400-20W10 0183- 46400-81W00 HEAVY DUTY 46400-81W10 4WD 0679-1181 46400-45W00 1281-0785 46400-30W00 <> 46400-30W01 <> 46400-30W10 0885- 46400-30W11 46400-45W00
46400-03W00
