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
Parts list;
M3 brake booster (part # 131010-15210)
With alu spacer block!
M3 master cylinder (part # 47201-B1020)
With reservior!
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.
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.
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.
7/8" is bigger than 13/16" so it will reduce pedal travel and make for more effort to pull you up. To reduce force on the pedal go to a smaller master cylinder or bigger pistons in the calipers or wheel cylinders. I’d call 3/4" an upgrade.
If you go up in caliper piston size you can go up in master cylinder size. With my Subaru I kept the std NA Liberty master cyl when the Brembos went on. I did measure stroke volume of the master cyl to ensure it had capacity for the greater caliper piston volume.
I did the same on my rs turbo when going brembos, but the master was actually the same bore as the STi version and i only changed the booster over
I was mainly thinking going from sirion to copen calipers would have been an increase in piston sizing ao would warrant a larger master, but i may be wrong it may only be the disc diameter/thickness?
I’ve done the L200 to Sirion to Copen upgrade once. The master cylinder didn’t need the upgrade. The Copen caliper was physically bigger but I can’t remember and difference in piston size though I would assume some increase.
I have since swapped back to the smaller m100 brake booster and adapted the m300 master cylinder to it.
Also worth mentioning that there are at least two different master cylinder sizes for the m100.
I have also welded the hole in the brake pedal closed and drilled a new hole about 1cm further down.
All this in an attempt to improve pedal feel, but it’s still squishy as hell, no matter how I bleed it. Nothing is leaking.
I am assuming one of the valves in the abs block is not seating properly, so that’s next to be replaced.
I will possibly attempt to overclock the replacement abs to improve regulation speed.
The brakes seem to be the weak point of my M101 Sirion Rally 2, having very long pedal travel and not a lot of assurance that they will actually stop the car! It feels like I have about 50bhp too much engine for the brakes.
I’ve recently replaced both front calipers and thoroughly bled the system but there is still a lot of pedal travel before anything happens, and then generally wooly-ness.
I notice upthread, someone mentions adjustment at the pedal, how is this done please? I wonder if there is slack in the pedal causing the initial 1" or so of pedal movement where literally nothing happens.
EDIT - I’ve had a good look and there is no slack on the pedal - The pedal is a bit of a wobbly fit onto the pushrod of the master cylinder, but not a major cause for concern - there is about 5mm of play at the pedal while this is taken up, then the pedal immediately starts acting on the pushrod of the master cylinder on my car. So it looks like this is working normally, but there is a lot of pedal travel before meaningful braking is achieved!
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