Brake pedal to floor. Have I wrecked my master cylinder?

  1. My model of MX-5 is: ND 2016 sport nav
  2. I’m based near: Southampton
  3. I’m looking for technical help or recommendations on: master cylinder

So I’ve had a slightly sticky caliper for a while. Today I removed it to refurb it with a new piston and seals.

The old piston is stuck pretty much fully extended but can’t get it out. It looks cruddy all around the seals so will probably just replace the caliper.

For now, I have reattached it. I pre-filled it and put it back on without the pads. I have bled it, using the buddy method. Fluid flows when the pedal is pressed and no more air is coming out.

Stupidly, I didn’t put a block under the pedal, so buddy was pushing all the way while bleeding. Now that everything is buttoned up, the brake pedal still goes to the floor, and pumping it doesn’t firm it up at all.

Have I wrecked the seals in the master cylinder? Could it just be air in the ABS?

I’m trying to get a new caliper but I’m nervous that once fitted I’ll still have this problem.

I’ve bled all four corners, and at no point did the master cylinder run dry…

Pushing the pedal all the way to the floor should not have wrecked the master cylinder.

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That happened to me on my NC in 2022.
Like you I “thought” the Master Cylinder had gone.
On the safe side I ordered a new one but then thought this can’t be right as you can’t really go too far to damage the seals due to its design.

I took the MC off checked it.
Basically draining what came out.
Does the ND utilise the MC for the clutch or is it cable.
Took all that off.
As that’s when the problem arose.
Put all back on and eventually the pressure came back and all was fine.
Luckily could cancel the new MC.
Been fine ever since.

I suspect air did get in and would use a pressure bleed device next time and not SWMBO, (buddy).
Try that.

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Had the same with my clutch, you probably ran low of fluid and will need a pressure bleeder now to ‘recharge’ the system with fluid. Pedal should then come back, clutch pedal did immediately.

Sure the poster won’t mind and might benefit too. :slightly_smiling_face:
Seems a few of us have had this issue, (only ever on my MX 5 mind).
Plenty of pressure brake bleeders out there, but can anyone recommend one that does the job and won’t break the bank balance?
As it’s not something we would use every day.

I have always preferred vacuum bleeding - you can get the small manual vac bleed kits quite cheap.

Now I have moved on to a compressor powered vac bleeding system.

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Which one have you got?

Just a gunson eazibleed, got it last year when the missus pressed the pedal unprompted whilst helping me bleeding it and I lost the pedal completely. This did the job spot on but as most kits is a little overpriced for essentially a plastic bottle, some caps and some tubing…