A One Inch Diameter Brake Master Cylinder for the S30 Z Cars
With the availability of the 280ZX 15/16 inch diameter master cylinder becoming limited there is now another option for a larger diameter master cylinder for the 1970-78 (S30) Z cars. Wilwood, long known for their automotive racing products, now makes a one inch diameter master cylinder that is almost a â€œbolt-onâ€, requiring only two minor modifications.
Why use a larger [one inch] diameter master cylinder?
The diameter of the brake master cylinder is determined primarily by the amount of fluid displacement that is required to move the caliper pistons against the brake pads so they contact the rotor surface. Other minor factors, such as the brake pedal lever ratio and the brake booster size, may be considered as well.
The diameter of the stock master cylinder on the 1970-78 Z cars is 7/8 inch. When Nissan introduced the 280XZ in 1979 they changed the brake system by going to disc brakes at the rear and added a vented rotor up front along with a floating caliper. The rear calipers and the new front calipers required more fluid and hence Nissan increased the diameter of the 280ZX master cylinder to 15/16 inch.
Brake modifications to the 1970-78 Z cars typically involve changing the rear brakes from drums to discs with calipers replacing the rear wheel cylinders. The front calipers are changed from the stock two-piston to a four (or six) piston one with increased piston area. Both of these changes require more fluid from the master cylinder and the change to a larger diameter master cylinder is always recommended as part of the brake upgrade.
The 280ZX 15/16 inch diameter master cylinder is typically used for the S30 brake upgrade, but as the supply of good used 280ZX master cylinders becomes scarce and the cost of NOS ones quickly increasing, going to an aftermarket one inch diameter master cylinder is a viable option. However, a larger diameter master cylinder will require more pedal force to build the same fluid pressure. Nissan used a larger diameter brake booster on the 280ZX to reduce the pedal force of the 15/16 inch diameter master cylinder.
The Wilwood one inch master cylinder
The Wilwood one inch diameter master cylinder which will work on the S30 Z cars is Wilwood part number 260-8794. There is also a 260-7563 part number which is the one inch diameter master cylinder but with remote reservoirs. The remote reservoir kit makes the 260-7563 slightly more expensive than the 260-8794.
The Wilwood one inch diameter master cylinder is available from Jegs, Summit, StreetPerformance.com, and probably others.
The Wilwood one inch master is a â€œvertical mountâ€ type and although it initially appears to fit the S30 brake boosters as is, you have to do a modification to it first. The center-to-center spacing on the S30 booster mounting studs (for the master cylinder) is 60mm whereas the bolt hole spacing on the Wilwood one inch master mounting holes is 57.2mm (2.25 inches). So, you will have to elongate (slot) the mounting holes on the Wilwood master with an end mill or a file. You could also drill out the mounting bolt holes (on the Wilwood master) to the next larger drill size.
The second modification allows the Wilwood one inch master to connect with the S30 brake lines. The Wilwood one inch master cylinder outlets are designed to be used with standard 3/16 inch SAE double flare brake line fittings which have 3/8-24 threads. However, you need 10mm x 1.0mm female metric threads to interface with the stock Nissan double flared brake lines.
Fortunately the SAE threaded outlet fittings on the bottom of the Wilwood master cylinder can be unscrewed and replaced with the Nissan metric ones off your old stock master cylinder. However, this only applies if you have a 1972-78 stock master cylinder as your donor.
The outlet fittings of the 1970-71 stock master cylinders are different and will not fit the Wilwood master. This also applies to most the aftermarket (i.e., the non-Nabco/Tokico ones) S30 master cylinders.
The stock outlet fittings on the bottom of the Nissan master cylinder are part number 46038-B5012 which is still available from Courtesy Nissan:
Note: Tighten the outlet fittings on to the bottom of the Wilwood master cylinder with 156 in-lbs of torque.
If you cannot locate suitable metric outlet fittings, then you can resort to cutting the metric fittings off your stock brake lines, installing 3/8-24 fittings, and re-flaring the ends of the lines. No manufacturer (that I am aware of) makes a single-piece 10mm x 1.0mm to 3/8x24 UNF brake line adapter.
Residual pressure check valves
According to the Wilwood 260-8794/260-7563 instruction sheet, the Wilwood one inch master cylinder contains internal residual pressure valves (for drum brake use only) which should be removed and not used in disc brake applications.
Adjusting the booster pushrod
The push rod projects from the front of the brake booster and activates the master cylinder pistons. The push rod length is adjustable and the push rod to master cylinder piston clearance (gap) should be checked any time the master cylinder or booster is replaced.
Problems can occur if the push rod is improperly adjusted. If the gap is too small (or non-existent) then the master cylinder piston will not return completely when you let off the brake pedal and there will be pressure remaining in the lines which will result in brake drag and premature pad wear. If the gap is too large then there will be a slight time delay in brake actuation, increased pedal travel and reduced pedal travel reserve distance.
The preferred push rod adjustment procedure is to use a special tool or gauge to determine the gap. However, if such a suitable tool is not available then an alternate method can be used (see the accompanying pictures).
Using a vernier caliper, measure the distance between the rim of the master cylinder bore to the mounting flange surface on the master cylinder (measurement â€œAâ€).
Measure the distance between the bottom of master cylinder primary piston to the top of the rim of the master cylinder bore (measurement â€œBâ€).
Subtract A from B to obtain the depth of the master cylinder primary piston to the mounting flange surface (measurement â€œCâ€).
On the booster place a precision straight edge across the face of the master cylinder mounting surface adjacent to the push rod. Measure from the top of the straight edge to the top of the push rod (measurement â€œDâ€).
Measure the width of the straight edge (measurement â€œEâ€).
Subtract D from E to obtain the height of the push rod (measurement â€œFâ€).
The push rod clearance (or gap) is determined by subtracting F from C. Adjust the push rod to obtain 0.3mm (+/- 0.2mm) of clearance.
Warning: When adjusting the push rod length avoid pulling the push rod out of the booster to prevent the reaction disc from falling down into the booster. The best way to prevent this is to place the booster facing up when adjusting the push rod length. If that is not possible (i.e., booster is bolted to firewall) then apply moderate pressure on the push rod in a direction towards the booster during the adjustment which will keep the reaction disc from moving.
* The stock Nissan reservoir caps will fit on the Wilwood reservoirs. Likewise, the Wilwood reservoirs appear to be identical to the Nissan stock ones so that they will even fit the stock master cylinder. The Wilwood part number for the reservoir is 260-3386.
* The Wilwood master cylinder has o-ring sealing where the reservoir mounts, a nice improvement over the stock master.
* Use silicone sealant to seal the base of the master cylinder to booster as it should be an air tight seal.
* Tightening torque for brake line fittings. As a general rule tighten the nut finger-tight until you feel it draw down tight, then tighten with a brake flare wrench approximately 1/6 to Â¼ turn more. Do not over-tighten.
* A nice explanation on the importance of the booster pushrod adjustment can be found here: