Master! Master! What's the bore that I've been after? (Master Brake Cylinder)
 

Our brothers in arms in the MX5 and FD3S, to some extent the FC guys also, have a few forum threads that cover going from a 7/8 (NA Miata) to a 15/16 or a 1". or the FDs going to a 1" 929 master cylinder. Some have added bigger aftermarket brakes, others prefer the firmer action they get when going with a larger bore. In my reading I have not found anyone who regrets this change. I am considering changing my brake booster to a dual diaphragm (8.75") and 15/16 or 1" master cylinder. The braking system is a GSL-SE and can see myself trying the 15/16 first. I'm kinda surprised why this isn't a common discussion in our first gen group. Any opinions out there?

For SA it would be the incompatible threads for the brake lines. Not sure about the GSL-SE. I think I've heard of folks doing this before tho.

I have all the SE hardlines, but am considering haven new made so I can go DOT5.

I wouldn't go with DOT 5. I'd do DOT 5.1 and use Motul.

I have read a bit on the different DOT ratings. Why would you suggest 5.1 over silicon?

Compressibility

One of the first disadvantages of silicone brake fluid is compressibility. You don’t want any compressibility in your braking system. This will cause your brake pedal to feel soft when you press it. Silicon brake fluid is slightly compressible and will cause this softer pedal more than glycol based fluids.

Moisture

All braking systems have moisture in them. Other types of fluid absorb water easily. Unfortunately, silicone brake fluid does not absorb water. Since the water does not mix with the fluid, it will descend to the lowest point and form a puddle. This can lead to corrosion in your hydraulic system and may impair the functioning of your brakes.

Compatibility

Another disadvantage of silicone brake fluid is that it is incompatible with glycol-based fluids. This means that you will not be able to mix the two types. If your car has used glycol-based fluids for a long time, you will have to flush and reseal the entire system to use silicone brake fluid.

Anti-lock Brakes

Silicone brake fluid also can’t be used with many anti-lock braking systems. Most systems are designed to work with glycol-based fluid. If you use silicone brake fluid instead, it may interfere with the mechanical valving found in some anti-lock braking systems.

Sealing

One of the final disadvantages of silicone brake fluid is sealing. Glycol-based fluids are easier to seal because they can’t pass through small pores in the system. Silicone brake fluid will pass through smaller pores in seals and gaskets. Therefore, it is much harder to seal effectively.

the Factory offered 15/16 and 1" masters for the competition setup in 1979, so i would say its been done. although i think the FC/FD guys change stuff, because they have a mushy pedal from the factory, and the GSL-SE doesn't

the FB master has a different bolt pattern than the FC, and FD is also different again. however the booster to firewall bolt pattern seems to be some standard, as basically every car uses it.

in the FC world, Clokker uses Subaru master/booster combos, the masters come in a bunch of sizes.

GSL=SE have best brakes of all 1st gens. With the exception of track duty,properly maintained oe brakes are more than adequate. Pedal feel is not an issue,modulation/feel can be improved by addition of Braided stainless lines. Switch from DOT3 to DOT4 fluid is a further upgrade.

DOT5.1 is also compatible with DOT3 and DOT4 .

So since it makes sense to use a GSL-SE master cylinder, does anyone suggest getting brake booster from an SE or stay with my SA?

If your SA booster is in good shape and functional,there is no benefit in swapping in a SE booster.

you need the FB booster, as the FB master will not fit on an SA booster

Oops,forgot about that...

And change all the fittings going to the FB master to the correct pitch.

Op says he has all SE hard lines.

What exactly is the difference in brake boosters? As far as I can tell the SA and FB look the same with the vertical master cylinder.

I think one difference, IIRC, is that the FB booster has an integral vacuum check valve.

SA's have a separate check valve in-line on the main vac hose.

Also keep in mind that the SA's never came with disc brakes, the PP Valve will have to be swapped over to a version that came with stock disc brakes. That is unless you like locking the rears up way sooner than you may need to.

for some reason i dont think the FB master will bolt up to the SA booster, could be wrong.

The Nissan Patrol M/C, Part No JB1419 has a 1" bore and bolts directly to the FB booster. The Aussies have done this and give it a positive review. I'm in the midst of this conversion; PM me if you have questions.

A+ on the topic heading! It got me to open it.

Yes, many people here in Australia go for the Nissan Patrol master cylinder. I'm not sure whether this is the same mode name and part number in the US, as sometimes the brake lines are swapped to the other side between LHD and RHD models. Some minor modifications are needed to fit to RX-7s, which are documented on AusRotary.com.

On our cars, you can fit the entire FD brake booster and master on an 84-85 model as a bolt on conversion, bbut not earlier as the clutch master cylinder is positioned much closer to the brake booster. The FD has the 15/16" master cylinder and the booster is a twin diaphragm model. The later series 7 and 8 boosters have a much more compact design. Fitting a FD booster opens up a whole range of options, as you can fit the 1" 929 master etc.

Personally, I don't see the need for a bigger diameter master cylinder unless you are fitting much bigger piston calipers. Even the Mazda 4 piston calipers from the FC and FD will work very well with a 7/8" master. While increasing the master cylinder size will reduce pedal stroke, it will also increase pedal effort.

The other factor to consider is that newer master cylinders, like the ones from the series 5 and FD, or the 1" masters from the 929, are made of aluminium. These are more expensive to purchase and generally cannot be rebuilt once the bore is pitted. The old trusty steel ones can be easily resleeved and rebuilt quite economically - for a lot less than a cost of a new aluminium one.

Man this is an awesome discussion going on here! I've been considering upgrading my whole front end (again) with TII front brakes and would love to do an upgrade. Good info in here!

Could someone have a 7/8" MC bored to a 15/16" and use a rebuild kit from a FD or such?

Yes I believe a small increase like that is possible, but it will depend on whether brake specialists your way offer the service. About 10 years ago, I had my whole master resleeved and rebuilt by a local brake shop, as the genuine master cylinder was over $600 here. The resleeve involved machining out the housing and installing a new stainless steel sleeve. I had the option of increasing internal diameter when doing this, and presumably they were going to fit a bigger diameter seal kit to suit. I doubt the FD kit would be suitable, but I'm sure a brake place would be able to supply parts to suit.

Forgot to mention that I have FC 4-piston calipers on the front. The pedal feels mushy to me with my 7/8" MC. I started a thread on this a while back, and I think you're the one that suggested the Patrol MC :)

Brake feel is subjective, and I'm probably spoiled by my other 2 cars, which have very firm, immediate pedals. YMMV