Master Cylinder Installation

Last updated: March 22, 1999

Rob has this on his web site, so go there for the "real" version. I am just putting this here as a "copy", but he may update his, so go there. --Steve

Date: Thu, 18 Mar 1999 19:56:23 -0500
From: "Rob Robinette"

929 Master Cylinder Install for 3rd Gen RX-7 (for big brakes)

Why would you need to upgrade the master cylinder?

When you upgrade to larger brake calipers your brake pedal movement may increase because more brake fluid has to be moved to power the bigger (or more) pistons. Upgrading to the Mazda 929's master cylinder (MC) can bring the pedal movement and feel back to stock (or better than stock). The only difficult part of this mod is the fabrication of a 12 inch length of brake line which can be done pretty easily if you have a pipe cutter and pipe double flare tool. You can always take the 929 master cylinder to a brake shop and have them fabricate and install the brake line. You could do everything else and save some cash.

What You Need

• A 93 Mazda 929 master cylinder (ABS version) - I got mine from Jeff Haas Mazda for $170 (that's a 25% discount for ordering from their 800 number: 800 233-2991). Pep boys wanted $214 for it. I don't know what Mazda Comp charges. The stock master cylinder is 15/16" in diameter, the 929's is 1" in diameter and about 1/4" longer. That 1/16 of an inch larger piston pushes quite a bit more fluid.
• 12 inches of 3/16 inch brake line ($2 auto parts store)
• 2 new copper crush washers for the MC's banjo bolt $1
• a pipe cutter ($7 Home Depot)
• pipe double flare tool ($40 Pep Boys)

Removing the Master Cylinder

Warning

Do not attempt this modification yourself unless you are a very competent mechanic. A short brake line will have to be fabricated and a single point failure in the brake system will result in the total loss of brakes and possible damage/injury/death! A brake shop can fabricate the brake line and hook it up to the new master cylinder. Before you remove any of the brake fittings, carefully clean all around them, so that dirt can't get into the system as the fittings are opened.

Start by putting some rags below the master cylinder (hydraulic fluid will bubble and peel your paint very quickly). I recommend getting a pack of various size vacuum plugs for this purpose. I put plugs on each of the two brake lines and one on the hydraulic clutch connection to prevent excess fluid drippage. Use a 10mm wrench or the SST (Special Service Tool) the RX-7 Workshop Manual calls for to loosen the brake lines that go into the double brass fitting next to the filler cap (item C in the first diagram below). A 10mm brake line tool will help you torque the brake fittings properly (it's hard to do with a 5 inch long 10mm wrench). By disconnecting the brake at the brass double fitting, very little fluid will drip out. I put vacuum hose caps on the brake lines once I got them loose. Remove the two nuts that hold the MC to the brake vacuum chamber. Remove the large vacuum line running to the vacuum chamber to relieve the vacuum pressure and remove the MC. If you don't release the vacuum you will have trouble getting the MC out.

You'll have to swap the master cylinders' reservoirs because the 929's doesn't have an hydraulic clutch connection. Remove the Phillips head screw below the reservoir and pop off both reservoirs and then swap them. Use a little hydraulic fluid on the rubber seals to make the installation of the reservoir easier. Reinstall the phillips head screw to secure the reservoir.

The 929 MC has a fitting for one of the two brake lines on the wrong side (engine side, rather than towards the fender). One of the brake lines is a perfect fit. Use two new copper crush washers and bolt the banjo bolt on the new MC. I don't know what the torque value for the banjo bolt is but I had to tighten it as tight as I could with a 8 inch ratchet to stop it from leaking.

The other line on the MC is too short to reach around to the other side of the MC. A new, slightly longer brake line will have to be fabricated to run the line from the engine side of the MC to the brass double pipe connector. I bought a prefabricated, 12 inch long 3/16 inch brake pipe, cut off one end, removed the flare fittings, put on one of the original metric flare fittings from the old line, bent it over a 2 x 4 railing to get a nice 180 degree bend, cut it to fit with a pipe cutter, put the other original metric flare fitting on and double flared the new pipe. See Photo. See the Brake Proportioning Valve Install How To for instructions on how to double flare a brake line. Connect the new brake line and torque the connectors to 113 to 190 inch pounds (10 to 15 foot pounds).

Bleeding the Master Cylinder

I highly recommend this procedure--if you bleed your master cylinder you will minimize the amount of air you push through the brake lines and ABS. If you don't do this you may have a really tough time (and use lots of brake fluid) getting the air out of the brake system (you may suffer a spongy brake pedal for years!). This procedure is well worth $10 and a little time.

I got my master cylinder bleeding kit at Mechanics Auto Parts, HELP! part # 13999, Metric Master Cylinder Bleeder Kit, $9.49. The kit consists of several plastic fittings and rubber hose. Mount the master cylinder in your car by securing the two nuts and connecting the hydraulic clutch line but don't hook up the brake lines yet. Screw the correct size bleeding kit fittings into the two line connectors at the double brass pipe fitting and run the hose from the fittings up into the master cylinder reservoir (the fluid loops around from the master cylinder's outputs back into its reservoir). See photo above. Fill the MC reservoir with brake fluid and pump the brake pedal until you don't see any more bubbles coming out of the hoses. It took me about 5 minutes of pumping. Remove the bleeding hoses one at a time and hook your brake line up quickly so you'll limit the amount of fluid that runs out. Torque the brake lines to 113 to 190 inch pounds (10 to 15 foot pounds). Bleed the brake system and do a pressure check. I had very little air in the brake system, the MC bleeding worked. See the Brake Bleed How To. My brake pedal is firmer now and there is less pedal travel than with the stock MC. Be careful during your test drive, your brake vacuum will take about 30 seconds to replenish itself.

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Date: Fri, 19 Mar 1999 07:27:31 -0500
From: "John Levy"

> The only difficult part of this mod is the fabrication of a 12 inch length of brake
> line which can be done pretty easily if you have a pipe cutter and pipe
> double flare tool.

I found that it is not necessary to cut the straight 12 inch line - use the full length and carefully form it using the proper tool. It is best done working the shape a little bit at a time first from one end then the other.