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ABS was optional on my car, and most of the readily available replacement master cylinders are marked either "ABS" or "non-ABS". The "ABS" units are rare and are "remanufactured" only.

I've been warned off of "remanufactured" units, and I want a new master cylinder.

I'm trying to understand how important the "ABS / non-ABS" issue is. What exactly does the master cylinder do differently for an ABS system?

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    I really don't know if there is a difference, but that probably depends on the manufacturer. As far as whether to trust OEM vs remaned, I've never had a problem trusting remaned anything. Most of them come with a warranty, which means if they're bad, you can get them replaced FOC (except your time). I've found most rebuilders are pretty competent.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented May 24, 2021 at 2:52
  • For what it's worth, I canvassed four auto parts chains (NAPA, Autozone, O'Reilly and Advance) and made a spreadsheet of each of their master cylinders (typically 4: 2 new 2 remanufactured). All the "for ABS" cylinders are 0.875" diameter and all "non-ABS" cylinders are 0.812" (13/16") diam.
    – Harper - Reinstate Monica
    Commented May 25, 2021 at 21:00
  • You've got too much time on your hands :o)
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented May 25, 2021 at 21:22
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    @Pᴀᴜʟsᴛᴇʀ2 I only did it because the application/fit data I was getting from my first choices of vendor (NAPA and Amazon) was disturbingly inconsistent and incomplete. Once I checked the other 3, everything made sense.
    – Harper - Reinstate Monica
    Commented May 25, 2021 at 22:21

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The ABS system moves brake fluid around independently of the driver, so it may need a bigger internal cylinder volume to reduce the amount of "kick back" at the brake pedal.

On some car models, the internal bore of the ABS and non ABS cylinders is different to accommodate the extra fluid volume, and the mounting points may also have different locations to prevent fitting the wrong type.

Some car manufacturers have avoided the potential confusion of the names ABS/non-ABS cylinder, by renaming the ABS master cylinder as a "hydraulic pressure modulator" or something similar.

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