Brake Master Cylinder

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7/8" bore

Replacing a Master Cylinder on Federal

There are major differences between the North American (NA) (also know as Federal) and the Rest Of the World (ROW) master cylinder. The NA version has three (3) pipes, other have four (4) pipes. There is also a great amount of difference between Left and Right hand drive cars. The remainder of this portion will deal with the Federal version.

It is difficult to remove the master cylinder due to stuff in the way. I am writing this after just completing the removal.

Info non-talk.png "The direction conventions are based on sitting in the drivers seat. That is, right front means the right front of the car when sitting in the drivers seat. Not back left as if you were standing in front of the car bent over the engine compartment!"


The first few steps are to gain access to the master cylinder and reduce the amount of fluids to spill.

  1. Remove the inlet pipe that goes between the intake manifold and the inter-cooler. Play it safe and tape up the inlets.
  2. Drain the radiator – on NA cars there is a drain on the lower left. Don't forget to tighten this back up. Be careful when tightening this piece it is plastic and it is a Lotus only part.
  3. Remove the overflow bottle
  4. Remove the overflow bottle retain bracket. Don't worry the nuts for the 3 small bolts are an integral part of the frame and won't move or fall out.
  5. Remove the vacuum hose - I had to cut mine off, don't worry it is a standard 7/16" vacuum hose.
  6. Remove as much of the brake fluid as you can.

Removing the low brake fluid sensor

  1. Unplug the low brake fluid sensor from the harness
  2. Pry off the black plastic cap. Be careful it pops right off. - I still haven't found mine. It is only available by purchasing a new reservoir.
  3. Pull the guts of the sensor straight up. Only the black plastic cap holds in on so this is easy.

Level Sensor 2688.jpg

Separating the Reservoir from the Master Cylinder

On Federal cars the clutch cable passes between the master cylinder and the reservoir. Now the real fun starts!

Insert picture of the cable passing between the 2 components.

It would probably be best to remove the reservoir at this point. I didn't do it until I had freed the master cylinder and reservoir as a unit. It took considerable strength to hold the master cylinder while applying a pry force. My Internet search suggested placing the master cylinder in a vice for this operation. If I were performing this repair again I would attempt to remove the reservoir at this point.

The reservoir is held in by the 2 rubber gaskets. Separating the reservoir from the master cylinder involves lots of wiggling, brute strength and a tool to pry the 2 pieces apart. Note that the rubber gaskets stay with the master cylinder.

Attempt to break the seal between the rubber gasket and the reservoir. Wiggle the reservoir around a bit. Gently pry between the plastic reservoir base and the rubber gaskets. Insert a tool (I used a ratchet handle) between the 2 parts forward of the forward most gasket and apply force. The forward part of the reservoir will pop out. Swing it out of the way and pry more toward the back gasket. A fair amount of force was necessary to achieve separation.

Undoing the Hydraulic Pipes

Breaking the fittings free required that I use "Flare Nut Wrenches". When I tried a standard open end wrench all I accomplished was to start rounding off the corners of the fitting.

Once you have broken all 3 fittings free it is probably best to move on to the 2 nuts that hold the master cylinder to the vacuum booster. I didn't and I buggered up one of the threads while loosening a nut holding the master cylinder.

Unbolting the Master Cylinder

This was another tough job. The nuts are a thin variety of lock nut. The right nut was easily accessible. The left was blocked by 2 of the brake lines.

The lock nuts looked good until I removed them. They were a bit chewed up looking after removal. I replacing them with elastic stop nuts 8mm x 1.25

Removing the Brake Lines

If you left the brake lines attached while unbolting the master cylinder now is the time to finish removing the brake lines. There are two sizes of fittings. The big fitting is 12mm x 1.00 and the two small fittings are 10mm x 1.00

Removing the Master Cylinder

My master cylinder was stuck to the brake booster due to leakage induced rust. It took a bit of convincing to let go but once the seal was broken it came out easily.

Rebuilding the Master Cylinder

New Federal master cylinder are not available. I was unable to find an acceptable GM replacement. I sent out my old unit to White Post Restorations for a rebuild. They are a reputable company with fast service.

Note: When sending out the master cylinder don't send anything that is not intended to be rebuilt. Remove plungers, seals for the reservoir and etc. It is easy for a re-builder to loose these items.

Cleaning up the Rust and Flaking Paint

I cleaned the old brake fluid and gunk with a rubbing alcohol. Remove the plunger from the vacuum booster prior to attacking the area with a wire brush. A wire cup mounted in a drill did the trick. Next I did a bit more cleaning followed by a coat of Ospho to neutralize the rust. A bit of semi-gloss black paint made it nice enough to make the show and shine happy.

Putting it all back together

To be continued.

Bleeding the Brakes

Possibly I should have bench bled the master cylinder but I didn’t. I don’t know if I could have fit the cylinder with reservoir back into the car. Maybe someone can give it a try and add to this section. Do an internet search on “bench bleed master cylinder” if you are interested.

To bleed the system I ended up loosening both side mounted brake pipes until fluid came drooling out. After tightening these brake pipes I gravity bled the system by going around the car to each caliper in turn and:

  1. Applying caliper grease around the threads of the caliper bleed nipple
  2. Attaching a hose leading from a caliper bleed nipple into a catch can
  3. Loosening the bleed screws

I then waited until a fair amount of brake fluid had accumulated in the catch can. This took about 15 minutes for each caliper. Fortunately I have a lot to work on with the car so I wasn’t just sitting and waiting to top up the reservoir.

Also See

Master Cylinder in the WIKI.

Brake Master Cylinder Reservoir Cap

Cross reference

Make Model Year Application

PONTIAC Asuna (Canada) 1990-1991 4-1.6L F/inj. (6)

PONTIAC Asuna (Canada) 1989-1990 4-2.0L F/inj. (K) w/ Power Brakes Stamped 2631

PONTIAC Lemans-FWD 1990-1993 4-1.6L F/inj. (6)

PONTIAC Lemans-FWD 1989-1990 4-2.0L F/inj. (K) w/ Power Brakes Stamped 2631

PONTIAC Optima 1990-1993 4-1.6L F/inj. (6)

PONTIAC Optima 1989-1990 4-2.0L F/inj. (K) w/ Power Brakes Stamped 2631

Possible US sources

AC-DELCO 174-812




BECK/ARNLEY 072-8751


CENTRIC 130.36002

EIS E150607


ITM 25-01609


NAPA (BRAKE) 39869


From GLS Autoparts

Possible UK sources

Unipart Brake Master Cylinder:

Product Code: BUYOUT0014957

Description: FPSPMH392 MASTER C

Price incl VAT: 110.09 GBP (2007 price)

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