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Rebuilt Brake Master Cylinder

Discussion in 'Mondial' started by cockrill, Jun 2, 2015.

  1. cockrill

    cockrill Formula 3
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    I've had an issue with my 1984 Mondial Coupe that caused the brake pedal to slowly sink to the floor while stopped. I would have to pump the brakes once or twice to build the pressure back up. The issue was worse on hot days, and is a pretty classic sign of a bad Brake Master Cylinder.

    Before spending several hundred dollars on a new or rebuilt Brake Master Cylinder, I decided to try to rebuild mine. I bought a new gasket kit from Superformance for around $30. I'm happy to report that the rebuild worked, and my car now stops (and stays stopped!) better than ever. Since my results were so positive, I wanted to post the procedure I followed in case someone else wants to tackle this (relatively) easy task.

    Before I start, I do want to give credit where credit is due. A big thanks to Birdman for his tutorial on removing the Brake Master Cylinder (The Ferrari 308 master cylinder). I also referenced the following threads here on FerrariChat:

    http://www.ferrarichat.com/forum/308-328/272207-84-qv-master-cylinder-reservoir-question.html

    GTB QV 49461 refurb - Page 14 - FerrariChat.com

    http://www.ferrarichat.com/forum/308-328/301518-brake-master-cylinder-exploded-view.html

    Note that I will be referencing some of the photos from the three FerrariChat threads, as I didn't take a lot of photos due to my hands being covered in brake fluid.
     
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  3. cockrill

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    #2 cockrill, Jun 2, 2015
    Last edited by a moderator: Sep 7, 2017
    First, I drained and removed the Brake Fluid Reservoir. My car's reservoir has two chambers; one for the brakes and one for the clutch. I believe that the earlier cars have one reservoir for brakes, and a separate reservoir for the clutch.

    I used a couple of screwdrivers to remove the blue clutch fluid level sensor. There is a gap (marked in the photo) below the sensor's connector to insert a flat-head screwdriver. Gently pry up to get a small gap between the blue sensor and the reservoir big enough for a second screwdriver. Slowly work around, prying up, to remove the sensor. A second set of hands helps here.

    Once the reservoir has been drained, stuff a bunch of old rags/towels around the brake master cylinder, grab either side of the reservoir with your hands, and slowly but firmly pull upwards. The reservoir will pop off of the brake master cylinder. Don't twist. Just pull firmly straight upwards.

    After removing the reservoir, I used brake fluid to wash out the black sludge that had built-up on the clutch fluid chamber.
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  4. cockrill

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    #3 cockrill, Jun 2, 2015
    Last edited by a moderator: Sep 7, 2017
    Removing the brake master cylinder itself from the car is easy and less stressful than removing the reservoir. I disconnected the two brake lines and then used a ratchet wrench with a long extender to remove the four nuts.

    There will be some additional brake fluid drips from the master cylinder and the brake lines, so make sure you have the rags/towels in place to catch them.

    When I pulled my master cylinder from the brake booster the "plunger" came out with the master cylinder. The plunger is a valve looking piece of metal with a nut on one end and a flair on the other end. Do not mess with the nut! The nut is used to set the correct length of the plunger and, if you tighten or loosen the nut, you will alter the length of the plunger which will impact your braking.
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  5. cockrill

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    #4 cockrill, Jun 2, 2015
    Last edited by a moderator: Sep 7, 2017
    Using Snap Ring Pliers, I removed the retaining ring (or lock ring) from the master cylinder and pulled out the guts (i.e., piston shaft, seals, and springs). Note that there are two sets of guts in the master cylinder...
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  6. cockrill

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    #5 cockrill, Jun 2, 2015
    Last edited by a moderator: Sep 7, 2017
    In order to remove the second set of seals/springs from the brake master cylinder, remove the rubber plug indicated on the photo to access a screw. Remove the screw with a flat head screw driver.

    Note that some people posted online that, once the screw is removed, the seal/spring assembly will shoot out from the master cylinder; so be ready to catch it! Mine, however, did not. In fact, I had to use long needle nose pliers to reach down into the master cylinder to grab and pull out the rear set of seals/springs.
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  8. cockrill

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    #6 cockrill, Jun 2, 2015
    Last edited by a moderator: Sep 7, 2017
    After removing the master cylinder internals, I used brake cleaner and a toothbrush to clean all components. I then thoroughly inspected everything, looking for a possible cause to my fading brake pedal.

    The first thing to check for is pitting on the piston shaft itself. I had some stains on mine, but fortunately no pits that I could feel. I felt around inside of the master cylinder itself for pits, but didn't feel anything. If I had found any pits, then a new seal kit wouldn't have fixed the problem and I would have had to replace the master cylinder or send it someplace to have rebuilt.

    I did see one possible culprit to my braking problems. One of the seals had a small chunk of rubber missing!
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  9. cockrill

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    #7 cockrill, Jun 2, 2015
    Last edited: Jun 2, 2015
    Using the new seals from Superformance, I reassembled the master cylinder. I was more than a little nervous as the new seals were slightly smaller in diameter than the old seals. The size difference was small, but it was there. I'm guessing that the seals are made slightly smaller than needed so that the pressure of the springs can deform their shape to fit the cylinder.

    Reinstalling the master cylinder is the reverse of installing it. Just be careful not to cross thread the connectors on the brake lines.

    Note that the brakes will have to be bled after reinstalling the master cylinder. If you are going to bleed the brakes the old fashioned way (i.e., having your spouse or child pump the brakes), then you may want to bench bleed the master cylinder before installing it on the car. (I won't outline the procedure here, as I didn't do it, but there are plenty of videos demonstrating the procedure on YouTube.)

    I used a Motive brake bleeder and have Speedbleeders installed on my car, so bleeding the brakes was pretty straightforward. I began at the rear-passenger caliper, moving the rear-driver caliper. After the rears, the brakes were still mushy, and I was getting nervous. After a couple of seconds of bleeding the front-passenger line, however, a huge bubble of air came out and the brakes firmed up. I only got a couple of bubbles out of the front-driver side line.

    After cleaning up I took the car for a drive around the block. I'm sure that all of my neighbors think I'm nuts as I repeatedly stopped to check if the brake pedal would fade...
     
  10. cockrill

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    To sum up, I totally recommend rebuilding your brake master cylinder if your car is experiencing brake fade. It only cost $30 (plus two 32oz bottles of brake fluid); saving me hundreds. I did the work over a period of about four days, but the total time investment was less than 8 hours. (It would now only take me an hour or two to rebuild a master cylinder, so a lot of my time was spent researching, taking photos, etc.)
     
  11. FCnew

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    .

    Thank you for the documentation. The knowledge shared is much appreciated.
     
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  13. mulo rampante

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    Great description and instruction. Makes me think we should have a well-organized and well-managed thread that just contains pointers to threads like this.
     
  14. braq

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  15. mulo rampante

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    ^ That looks very well organized. Good call.

    But for starters, maybe a sticky that just contains links to common issues, etc. Just a thread with posts containing links to other threads. If I can get some time tonight I'll post a sample thread for the idea... don't want to derail Jeremy's topic here.
     
  16. Bell Bloke

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    Excellent write up and pictures, Cockrill old Chap, not many would have undertaken that job but very impressed.
    One for the archive, but not recommended for the novice.
    ;-)
     
  17. PV Dirk

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    Good work!
     
  18. MvT

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    Nice work Jeremy! That looks indeed not good! How did the cylinder look? was it smooth? This can happen is the inner surface is not smooth or just deterioration due the age of the rubber seal.
     
  19. cockrill

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    I got lucky and the cylinder was good. There are some stains on the shaft, but no pitting that I could feel, thank goodness.
     

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