ReubenH

Brake master cyls, to 1-1/16”, or not to 1-1/16”

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So i’ve Upgraded the brakes on my BC. Factory non ABS, so has the 1” 4-port master. The other option for these cars was ABS, same design, but the two bottom ports are blanked off, and it has a 1-1/16th” bore.

 

Now on the BC with the old 277mm 2-pots, I had added a BH large brake booster, and the pedal feel was great, nice and firm, very responsive (it’s a great upgrade for first gen owners with stock brakes) Now though, after upgrading to 4-pots, the pedal feel has gone back to what it felt like from factory... a bit spongy (not bad, just not as nice).

 

i assume this is due to the fact you gotta send more fluid into the 4-pots? So you need a longer strike to get the same pedal feel? Am I also right in assuming that going to a 1-1/16” would compensate nicely for this?

 

thats why I’m here asking, I don’t know if that’s going to do anything, by stepping up to the next larger master...

 

Next question is, does anyone know what master came on the non ABS 4-pot equipped GC’s? Was it 1” or 1-1/16”? If it was larger, and had the 4-ports off the master, easy, I just need one of them... if not... we’ll there is a place I can send a 1” non ABS master to get bored out to 1-1/16, and then re-sealed, they quoted about $200, which I thinks pretty reasonable.

 

So brake experts please advise, is the bigger bore a worthwhile upgrade to suit my new 4-pots?

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Seems promising. Might have to get it customised too, it’s starting to look like 1-1/16” is ABS only.

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Well stopping force is fine, they can lock up if you stomp it hard enough. Pedal feel is more what I’m shooting for, I figure bore size will have more affect on pedal feel than pad material. But I may be wrong? I’m certainly no expert on this matter.

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Pedal feel is hugely affected by the pads...give racebrakes a ring to discuss before changing the cylinder.

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gc8 4 pots always seem to have rubbish feel, interested to see how you get on if you do play around with the master cylinder. 

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I was thinking about giving racebrakes a call anyway to bounce ideas off them. Might just do that.

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Just checked my spare and current 4 port master cylinders, and they are both 1 1/16 inch. Both v5/6 Type R.

Edited by Loren

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My BC5 with ABS has always been pretty spongy with 1 1/16" - 4 pot front 2 pot rear.

Cert guy wanted it firmer and more travel once firm for the cert and suggested the master cylinder to be replaced. A brand new cylinder netted the same result.

I'm wondering if the firewall flex has something to do with it.

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I don't think it's the firewall flex as the sponginess is present even when lightly pressing the brake pedal... and there is always quite a bit of

travel before it firms up. Compared to my BP5 pedal that is rock solid an practically no travel at all.

 

Could be related to the relative work done by mechanical leverage verses the booster?

Edited by Loren

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Go back to basics,check brake hoses,caliper piston seal leaks and sticking pistons.Bleed brakes with front of car elevated in correct sequence.Check wheel bearings,can cause brake pad knock off.I have done three Subaru 4 pot caliper conversions 94 Wrx,94 Legacy Rs and Legacy 2002 Gt and one Brembo conversion a 2007 Legacy Bl.None of these cars required a master cylinder upgrade.

Edited by Dre
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1 hour ago, Loren said:

I don't think it's the firewall flex as the sponginess is present even when lightly pressing the brake pedal... and there is always quite a bit of

travel before it firms up. Compared to my BP5 pedal that is rock solid an practically no travel at all.

 

Could be related to the relative work done by mechanical leverage verses the booster?

Good point. Also from memory it's not spongy without vacuum (car running), even the initial sponginess isn't as prevalent.

 

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Dumb question, how do you identify whether the master cylinder is 1" or 1 1/6"?

I'm curious to know what I have on my be5.

Sent from my E5823 using Tapatalk

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