Brake Proportioning

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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.

B110

Datsun 1200 does not use a brake proportioning valve. Instead the front and rear working cylinders are sized to achieve a good balance.

Datsun 1200 disk brakes require a higher line pressure [harder pedal push] to make them work & this means that the rears have a greater tendancy to lock up, so the factory fitted 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

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

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.

Specifications

See: Brakes#Specifications

Part Numbers

46234 CONNECTOR [brake splitter]
46224 BRAKE INDICATOR SWITCH [combo splitter+switch]
46400 NP-VALVE

North America 

B210
46400-U0506 ASSY-NP VALVE 4WAY SWI,FRA,GER,SWE DEN,NOR,BEL,HOL,L UX
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