Intro

Installing & Removing the brake master cylinder isn't covered very well, so here's a writeup to compliment what's already been written. Feel free to add your thoughts as well.

This is for 1989-1991 Non-turbo RX-7s. For other years/types check your service manual for differences.

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Also checkout my other writeups:
Transmission Removal/Install - www.rx7club.com/showthread.php?t=352505
Waterpump replacement - www.rx7club.com/showthread.php?t=481877
Speed-bleeder Coolant Flush install - www.rx7club.com/showthread.php?t=362904
Torn Brake Piston boots replacement - www.rx7club.com/showthread.php?t=366651
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Key Search Terms
Brake Master Cylinder, Saggy Brakes, Pedal Sink, Pedal Sinks, Brake Pedal Sink, Brake Pedal Sinks, Pedal Hill, Brake Pedal Drops, Brake Pedal Falls, Soft Brakes, Brakes Sag, Brake grip, Mis-spellings - Break Master Cylinder, Saggy Breaks, Pedal Sink, Pedal Sinks, Break Pedal Sink, Break Pedal Sinks, Pedal Hill, Break Pedal Drops, Break Pedal Falls, Soft Breaks, Breaks Sag, Break Grip


Setting Your Expectations
For novices & semi-pro mechanics, this is a 6-9 hour job. This should really be done in the daylight hours. Yes a basic set of tools plus a few others will work, but there's nothing more annoying than NOT having the right tool for the job. Below I've listed the tools I ended up using.

NOW!!!! is the time to replace those old vacuum lines around the brake booster, before you have further problems. Also replace the "squeeze style" hose clamps with some nicer "screw down style" hose clamps. Check with www.mazdatrix.com or your dealer for pricing & availability on these.

Mazda Part # Description
FB01-43-640 Hose, Vacuum
FB01-43-836 Hose, Vacuum

Also I HIGHLY RECOMMEND replacing your stock bleeder screws on the calipers with SPEED BLEEDERS. This will ensure air won't leak back into your brake lines when you bleed the system, which causes your brake pedal to be "spongy" and "move excessively" when stopping. Details & where to order is here:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/speed-bleeder-sizing-203961/
(you'll thank me later )

What's involved
You'll be removing the brake master cylinder, proportional bypass valve (PBV), bracket, fluid level sensor, bench bleeding the master cylinder, and finally bleeding your brakes.


General Troubleshooting
If your brake pedal is sinking to the floor, first determine if you are loosing brake fluid (aka hydraulic fluid).

Checking for Leaks:
Fill the brake fluid reservoir with dot3 brake fluid, re-tighten the cap, and wipe down the master cylinder and the brake lines around it so they're nice and clean. Pump the pedal with the car running so it sinks to the floor a bunch of times. If the fluid level doesn't change in the brake fluid reservoir, then lets doublecheck there is NO fluid leaking. First look at the brake master cylinder & lines you just cleaned for leaks. If no leaks, let's move on to the rest of the braking system. Loosen the lug nuts on each rim (use penetrating oil on them first), then jackup the car and put it on jack stands. Remove each wheel and check the brake lines on each wheel for seepage. Check the flexible brake line cracks for seepage at each caliper. Check the brake calipers and the brake piston boots for fluid leaks. Check both sets of bleeder screws on the rear calipers (top & bottom) and the single set of bleeder screws on the front brakes. Check the junction box for the rear brake lines in front of the gas tank. Follow the brake lines until they disappear next to the transmission. If you don't find any seepage, then chances are it's the brake master cylinder that is worn. You have an internal leak only, the brake fluid is leaking past the pistons in the master cylinder and you're loosing hydraulic pressure.

There IS a 2nd possibility besides a bad master cylinder, but you can verify this when removing the master cylinder. If you remove the master cylinder and find lots of brake fluid behind it around the brake booster rod & rubber seals (the big donut behind the master cylinder), there may be a chance the leaking brake fluid has eaten into the rubber diaphragms inside the brake booster (aka power brake unit). If HOWEVER all you see is white grease behind the brake master cylinder, then it's probably a bad brake master cylinder and your brake booster is fine.


Tools
Don't EVEN THINK about using a standard open ended wrench on the brake lines, you'll need a 10mm flare nut wrench (partially closed end) as shown below.



For handtools:
- A metric 3/8" and 1/2" socket & drive sets wit 3" & 6" extensions. 1/4 inch socket & drive set wouldn't hurt either.
- 1/2" torque wrenches (you need to measure foot pounds when tightening these bolts/nuts).
- Good screwdriver seat (3 short, long, stubby sizes - 9 total). The best screwdrivers are made from harden metals and have grooves cut in the phillips & fat heads tips to hold the screws better.
- Metric Wrenches (open & closed ends)
- Flare nut wrenches (10mm)
- Flat style prybar
- (optional) Dremel Drill with 4 foot drill bit extension. Mini dremel wire-wheel brush, both flat & cone shaped brushes.
- Bench Bleeding kit for the brake master cylinder (see picture below).

For Sprays:
- WD-40, PB-Blaster, Brakeparts cleaner
- High temp spraypaint (optional)

Oils:
- dot3 brake fluid (preston is good).

Other Items:
- Fender & Bumper Covers (scratch protection, you'll need it). Get those at autozone/walmart.
- Portable Ramps, jack & jackstands. Buy at autozone/walmart
- (Optional) Painters tape (paper or plastic). Buy at lowes, homedepot, wal-mart.
- (Optional) Creeper. Buy at autozone or walmart.
- Shop towels


Stuff to order
- New or remanufactured brake master cylinder WITH reservoir included. You DO NOT want to bother with rebuilding your own master cylinder unless this is a project car, then by all means do it and learn how to do it. Same applies with getting the reservoir already being attached.

Your local autoparts stores do not stock these, so check www.mazdatrix.com, www.atkinsrotary.com, or another rotary website. If you get stuck, I know oreilly auto can order these. I'm not sure if advance autoparts or autozone can get the FULL remans with reservoir included, but I know orielly auto parts can.


General Recommendations
- Take digital pictures of everything before you uninstall stuff. Take pictures as you go.
- Don't leave bolts/nuts loose, re-install them when you take stuff off
- Labels parts and loose hardware as you take them off.
- When you torque a bolt, mark it with a red paint pen so it's easy to spot bolts you missed torqueing down.
- TRIPLE CHECK the factory service manual diagrams, it's easy to confused foot-pounds and inch-pounds. You don't want to strip threads or break a bolt by accidentally over-tightening. I can already tell you the manual says "foot pounds" incorrectly with the master cylinder.
- Download the service manual from here:
http://www.teamfc3s.org/main/factory_service_manual/
- Print off the brake system pages you'll need to reference. It's handy to have them readily available.
- When reading the service manual pictures, notice the last set of numbers on each bolt & nut are the US units of ft-lbs or in-lbs. Be sure to NOT confuse the two.

Prepping
- Put the car on jackstands (2-3 notches is good) & put on the fender/nose covers
- Cleanoff excess grease or fluids with brakeparts cleaner. Avoid spraying this on the master cylinder's fluid level sensor, use a shop rag when wiping down the reservoir.
- Spray PB-Blaster on all the master cylinder bolts (some are hard to see), brake line fittings, and caliper bleeder screws (2 sets in the rear, 1 set in the front).
- Keep 2-3 paper towels underneath the master cylinder & proportional bypass value to catch fluid leaks.


Dis-assembly
Drain the master cylinder with a hand vacuum pump or bleed the brake lines until dry (aka pump the brake pedal).

Next remove the fluid level sensor, but don't follow the manual's directions of detaching the wiring harness connector. Just take 2 flathead screwdrivers and gently squeeze the other end of the sensor until it's loose. Then pull the sensor out of the underside of the reservoir and let it hang there.

Two bolts hold on the master cylinder, but you'll need to remove the proportional bypass valve (PBV) first. Use your 10mm flare nut wrench to remove the brakeline fittings (after soaking them with PB Blaster). You'll need to grip the valve with your hand to prevent bending the metal lines. If you bend one, it's going to be 500 times HARDER to line up the metal fittings during re-assembly.

After the valve is removed, you only need to remove two of the brake master cylinder lines to remove the master cylinder. Re-install the bolt on that PBV valve bracket so you won't loose it.

Cleaning
The new brake master cylinder may have been painted or have an anti-rust agent on it. Use a scrubbing pad and dish soap to clean it and spray the MC with some black paint. Be sure to tape off the reservoir, brakeline fitting holes, and back of the master cylinder so no paint gets in there. It may take 2-3 hours to dry and 12-24 hours before the paint hardens.

Scrub clean, dremel wire wheel brush clean, & re-paint the PBV valve bracket and the bolt head (not the threads, just the bolt head). Scrub & clean the loose metal brake lines as well.


Prepping
You need to bench bleed the master cylinder before reinstalling it. All three holes/fluid passages in the brake master cylinder have to bled at the same time, so you can use the 10mm plastic adapter that came with the bench bleeding kit (see picture below) and the existing metal lines. The bleeding kit should have a softer and harder plastic hose. Use the softer hose on the metal lines and the harder hose on the plastic 10mm adapter.

Put your master cylinder in a vice (use a shop towel) and gently squeeze it with the vice. Fill the reservoir with .dot3 brake/hydraulic fluid, attach the hoses, and attach the hose-reservoir fill neck adapters. Insert your LARGER phillips head screwdriver into the hole in the back of the master cylinder. For the first "pump" press lightly on the screwdriver and slowly build pressure with your hand until the screwdriver & piston moves. For the first 6-12 pumps just press 1-2 inches. For the remaining 12-24 pumps press all the way in. You'll still get some tiny air bubbles, but once the larger air bubbles are bled out, you're done.

To "pinch off" the fluid lines, I pushed those "insert-able" hose adapters from the bench bleeding kit into the plastic lines. Note you need to stop-up the insertables with bits of paper towel first so they don't leak.


Re-installing
Now that the lines are pinched off and your master cylinder won't leak, re-install it. You may want to clean all the brakeline fitting threads with brakeparts cleaner first. As you put the PBV valve bracket and master cylinder on, you may want to cover it up to prevent "splashback" or fluid leaking and ruining your new paintjob.

Note the torque on all the brakeline fittings is measured in inch-pounds and the master cylinder mounting bolts are measured in foot-pounds. I put about 5-6 foot-pounds (72 inch pounds) of torque on all my brakeline fittings.

I would tighten & torque the master cylinder mounting bolts first, but you may find loosening these to install the PBV valve is necessary. The "mounting bolt" in that bracket for the PVB valve is going to bump against the left master cylinder nut.

It's a pain to install the brakeline fittings into the proportional bypass valve (PBV). Don't bolt the PBV down until all the fittings are installed. Use your fingers to install the fittings, DO NOT attempt to use force the nut in if the fittings don't thread correctly. It's a bit challenging to line up the threads. I did the bottom two first and then the top two last. When bolting down the PBV valve to the bracket, you may need to "pull up" or "push down" on the PBV valve so that bolt will turn freely.

Once the PBV valve is partially installed, then carefully remove the pinched off plastic lines and install the remaining metal brake lines. Your towels underneath the master cylinder should catch any dripping fluid. Don't forget the metal brakeline underneath the brake master cylinder. I used my flat style prybar to help brace the PBV valve when tightening the fittings.

Once all the lines & fittings are hand tightened, then use your flare nut wrench and lightly tighten them down (5-6 foot pounds). Be sure to QUADRUPLE CHECK the torque on all the metal lines.

Finally re-install the fluid level sensor that you left hanging. Be sure to wipe it down first.

Note if the rubber shielding on the master cylinder metal brake lines is peeling off, you may want to spray paint or "rubber coat" those lines, once you clean them.

Bleeding
Now that you've bench bled the master cylinder, finally bleed all the brake lines. Start with the passengers rear caliper (both sets of bleeding screws), then the drivers rear. Next do the passengers front & then drivers front. Hopefully you bought the speed bleeders I recommended so this is a snap. The $5 crappy autozone bleeding kit may work somewhat, but without speed bleeders you'll need a friend to pump the brake pedal while you open & close each nipped between pumps.

Fill the master cylinder every 3 pumps, and pump each caliper 6-8+ times as needed. Once you've bled the brakes, be sure to crank the car up and doublecheck the pedal is stiff and does not sink/loose pressure.

Note if you are missing the nipple covers for the bleeding screws, autozone sells these.

Afterthoughts
I didn't check or adjust the brake booster (aka power brake unit) push rod length like the manual says. I assumed the piston depth & travel on the new/reman brake master cylinder was the same.

Once you confirm you're pedal is stiff (no air in the lines) and doesn't sink, then replace those brake booster vacuum hoses & clamps I mentioned, part FB01-43-640, FB01-43-836.

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Notice below the sensor in my hand, the white greese behind the master cylinder, the brake master cylinder bleeding kit, and how I am using the bleeding kit.

 

Awesome writeup, I vote for archive.

 

jesus. how can a flat rate mechanic survive when they only pay 1.5 hrs to replace the master cylinder. just playing. all in good fun. GREAT WRITE UP.

 

back from the dead

this should have been archived. And note that adjusting the brake booster pushrod really should be done. It will make your brake pedal catch much higher. I noticed a world of difference when I did it on mine.

 

im going to put this back up top so that it can be archived.... or at least a reason why its not archived.

Brian

 

You're correct, Aaron Cake has not archived this particular one.

 

well, it calls for a 6 to 9 hour job. If it takes 9 hours then there are some serious issues. If it takes an hour and a half I would be surprised.

it shouldn't take 6 hours even if include the time it takes to drive to the local autoparts store for brake fluid and a new master cyl.

And you don't remove the brake proprotioning valve. You un bolt it and move it out of the way, you don't have to disconnect the valve from the brake lines at all.

 

Yeah I forgot to do that to, and my pedal travel is a bit too much.

Also I'm noticing stronger pedal pressure is needed at lower speeds... which probably means the booster vaccum line needs replacing and/or booster rebuild.

 

+1 for archive