Sirion M1 Master cylinder and brake booster upgrade

How to guide for brake booster/ master cylinder upgrade on a Sirion M1.

I did this upgrade after installing Copen front brakes and Applause rear brakes on my Sirion. I found the standard 3/4” (19mm) master cylinder just wasn’t moving enough fluid and I had too much travel in the pedal. After a bit of research I found the M3 Sirion booster/MC assembly could fit. It has a 13/16” (20.6mm) bore and the booster is also larger providing more assistance. I did this conversion on a LHD Sirion, I am not sure if it will also work on the RHD Sirion. If you try it please share your results :slight_smile:

Parts list;

  1. M3 brake booster (part # 131010-15210)
    With alu spacer block!
  2. M3 master cylinder (part # 47201-B1020)
    With reservior!


  1. Remove brake booster and master cylinder
  2. A small section of the firewall needs to be cut out (or hammered in :upside_down_face: )

  1. Shorten the threaded rod from the brake booster by 1cm to prevent fouling on the brake pedal. Fit the fork from the original brake booster.

  1. Install the new brake booster and master cylinder. The brake lines can be slightly bent and moved to fit the master cylinder with minimal effort.
  2. Fabricate a mounting bracket for the reservoir. In my situation I had to extend the hose between the reservoir and master cylinder due to the location of my strut brace. I welded a small bracket to the charcoal canister mount for the reservoir.

  1. The pedal free-play will need to be adjusted and the brake system will need to be bled. Refer to workshop manual.

I’ve been following this thread for a bit and find it interesting that you changed the master cylinder. I’m running a standard L60 booster and master cylinder that go to stock VN discs and calipers all round. IIRC, the Vn was a 13/16" bore and the daihatsu was 3/4" bore. Even with the smaller master there is plenty of pedal and I can lock up the brakes fairly easily.


How did it all end up? Interested

Been driving with this setup for years, I wrote the guide long after the conversion. It works great :+1: