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PostPosted: November 16, 2015, 6:12 pm 
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Location: White Rock, BC, Canada
Hey guys.

My cars brakes are not strong enough to lock up the race tires. It takes a huge amount of pedal effort to get it to slow down about the same as a normal production car. Pedal travel is minimal. I flat out do not have room for a booster of any sort. So the plan is to reduce the M/C bore sizes to increase the pressure unless someone has a better idea. I was thinking buying a 0.625" and swapping the 0.75" to the front. This would give me ~80% more pressure which would probably be fine?

Current specs:
-1" bore for front
-0.75" for rear
-6:1 pedal
-remote bias adjuster
-miata front 10" rotors, 2.01"(?) piston.
-drums in rear (it's what I had)

I haven't had a chance to play with the bias much, but I think it's heavily biased towards the front currently. It may be a better idea to wait until next summer when I can try it out. I should also point out that I was injured when driving it last, and unable to push as hard as normal. In summer when (hopefully) 100% I will find it easier.

Basically I'm not too sure what sizes I should try, and I'm getting tired of buying master cylinders (one had a flawed case which leaked.... and no warranty :BH: ).

Thanks for any help.
Cory

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PostPosted: November 16, 2015, 7:00 pm 
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Considering the master for the mustang rear is larger than the one you are using on the front, the master for the miata is smaller than the one you are using on the front, compounded by a lower than stock pedal ratio and a lack of boost, I'd just swap the ones you already have to .750 front/ 1.0 rear and see how it works.

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PostPosted: November 16, 2015, 7:11 pm 
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Miatav8,MstrASE,A&P,F wrote:
I'd just swap the ones you already have to .750 front/ 1.0 rear and see how it works.


Thanks. That is a great idea, and I will start with that. This is why it's good to have someone else's input; I was stuck on replacing stuff, but this will at least let me test the fronts with no extra cost. Feel a little dumb for not thinking of that myself to be honest.

It's been too long since I did the math for my brakes. No idea why I went with the sizes I did. Who knows, maybe I mixed up the masters when I installed and it will be perfect when I switch (how's that for optimistic?).

Cheers.

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PostPosted: November 16, 2015, 9:56 pm 
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Master cylinders are expensive. I'd play with the pedal ratio first.


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PostPosted: November 17, 2015, 3:17 am 
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Have to second TRX's suggestion.

Had pretty much the same problem. Super hard pedal, no travel and couldn't lock the brakes unless you really stood on them. Bad pedal ratio. Re-did the pedal mount to achieve a ratio of near 7-1 and viola! Great brakes.

Might mention the system is Miata master cylinder and calipers with fabbed pedals. YMMV

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PostPosted: November 17, 2015, 7:57 pm 
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I bought a brake bias adjuster they are not really expensive and a great tuning tool.
http://www.speedwaymotors.com/Wilwood-2 ... oC0q3w_wcB
I use it to dial in the brakes usually adding as much from brakes as possible without locking the tires. On concrete you can more a little more pressure forward on asphalt a little less etc. It would help in your case to see how close you are to locking the tires.

When you are applying pressure is the pedal too hard to push to get enough pressure? Do you have good brake pads? You might want to get high performance pads which will have a lot more bite. Also check that all brakes are functioning correctly and that you do not have a blockage.

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PostPosted: November 18, 2015, 12:11 am 
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Thanks guys. I'm pretty much stuck with the 6:1 pedal ratio, and it's going to be cheaper/easier just to buy another M/C once I figure out what size I need. I do have a bias-bar but can't set it up since I can't induce lock-up.

Swapping to the 0.75" M/C up front should make a huge difference. Then hopefully I can sort out the rear size from there.

Cheers.

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PostPosted: November 18, 2015, 7:43 pm 
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I noticed your pedals were floor mount and not much you could do, plus the bores were opposite what they should be.
I'm anxious to know how that works for you with equal balance.


You could also raise you feel with a heel board, which raises the ball of your foot, allowing the pedal pad to be raised, increasing the ratio and leverage.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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PostPosted: November 19, 2015, 12:38 am 
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Quote:
I noticed your pedals were floor mount and not much you could do, plus the bores were opposite what they should be.
I'm anxious to know how that works for you with equal balance.


Yeah, I'm pretty curious as well. I will switch them soon, but won't be able to test until summer likely. I'll update here when I do.

Quote:
You could also raise you feel with a heel board, which raises the ball of your foot, allowing the pedal pad to be raised, increasing the ratio and leverage.


I could, but I'd also have to cut my toes off :mrgreen: I already don't have much room for my size 11 feet. Pedals are currently really comfy for me, so would like to keep as is.

Cheers.

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PostPosted: May 26, 2017, 10:01 pm 
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Bit of a delay but I've switched the M/Cs and the pedal is better. Pretty sure this is what I had intended but mixed them up somehow. It's better, but still not good enough. My right leg is sore from driving the thing and autoX may be a bit much. I've just ordered some Hawk HP+ pads which are supposed to be very grippy, and a 1/2" bore M/C to try. It's the smallest one available, less than 1/2 the area of the 3/4", so it should make a noticeable difference. If it give me good feel on the fronts, I'll swap it to the rears and try it there then order yet another M/C when I know it works.

Cheers.

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PostPosted: May 26, 2017, 11:42 pm 
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i had similar and just swapped out the miata MC for a datsun 120( centric (130.42001) brake master cylinder) now have great brakes. its the mc that most downunder guys are using
john


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PostPosted: June 17, 2017, 7:38 pm 
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Sorry, I'm late to this Cory, but is there room to increase the lever arm of the brake pedal? I'm not familiar with your setup, but if you went from something like 5:1 to 6:1 that could help as well, couldn't it?

Cheers,

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PostPosted: June 18, 2017, 5:01 pm 
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So you swapped the 3/4F and the 1"R and it got better you need to play with the balance bar and see if it is still offset to one end.
that will tell you if you have the split right.
A 5/8 F and a 3/4 R might be better to lower pedal effort, remember though lowering pedal effort will increase travel.
A 1/2" MC sounds real small, thats even small for a motorcycle.

Also if you are drum rear it is easy to swap wheel cylinders, a smaller cylinder will reduce rear braking power and increase effort to lock.

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PostPosted: June 18, 2017, 8:01 pm 
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AFAIK, 5/8" diameter is the smallest standard master cylinder size.

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PostPosted: June 18, 2017, 10:45 pm 
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Hey guys.

Pedal ratio is 6:1, and has to stay there unless I want to do a major re-work (Hint: I don't). If I were to do a major re-work, I would include a brake booster.
Fooled around with the balance bar to get the best braking I could. Didn't look to see what direction I am biased in. I can get decent lock-up from one end at a time, but getting both to lock at 80kph takes all my leg can put out. This is a street and race car so need a little more finesse than that.

I've yet to install the 1/2" M/C. Maybe tomorrow. Not concerned with pedal stroke because at this point it basically does not move at all.
Cheers.

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