240z Master Cylinder Upgrade

Suspension, including wheel, tire and brake.
steve3510
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240z Master Cylinder Upgrade

Post by steve3510 » 05 Oct 2013 16:13

Hey everyone... I just installed a 240z master cylinder on my project 510.. I was bleeding the brakes today and when I got to the drivers front caliper I blew out both rear wheel cylinders. Is there a wheel cylinder upgrade to go along with the master cylinder that I need to do?? Also... The car has been sitting for 20 years and hasn't been driven... I am also figuring that could be the problem but I just wanted to check..

Thanks in advance..
-Steve

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okayfine
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Re: 240z Master Cylinder Upgrade

Post by okayfine » 05 Oct 2013 19:21

Z master isn't really an upgrade, just a slightly bigger bore that will stiffen the brake pedal feel somewhat. No upgrades to the rear wheel cylinders are necessary (only if you change the front brakes might you need to change the rears to suit). Car been sitting 20 years I'd change out all the rubber lines (and all the other rubber bits everywhere else) while you're changing out the wheel cylinders.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson

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jason
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Re: 240z Master Cylinder Upgrade

Post by jason » 05 Oct 2013 23:20

I upgraded to a 200sx 13/16" master cylinder in my 4 door this year and had a rear wheel cylinder let go about a month later. I figure the higher pressure blew out the weaker seal. Waiting on the other one to go now ....
Jason

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Dave Patten
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Re: 240z Master Cylinder Upgrade

Post by Dave Patten » 06 Oct 2013 07:17

Like Okayfine said, you need to go thru the brake system. The rubber parts are going to be pretty well used up from just sitting.

Regarding your “Upgrade”, the 510 master is 3/4" bore and the Z car master is 7/8”. By increasing the master cylinder bore diameter you push more fluid, but at a lower pressure for equal pedal pressure.

Example of the Change in Master Diameter:
With 100# of pedal pressure and a 5:1 pedal ratio it puts a 500# force on the master cylinder. The fluid in the brake system must react against the piston with equal force or 500# over the surface area of the master cylinder piston.

Math:
Force applied to the master cylinder / area of piston in inches = Fluid Pressure in the brake system (PSI)

The 510 master:
500# / ((.75”/2) x (.75”/2)) x 3.14159 = 1,132PSI in brake system

The 240Z master:
500# / ((.875”/2) x (.875”/2)) x 3.14159 = 832PSI

Clamping Pressure at the caliper, based on brake system pressure:
510 Front Caliper, Piston Dia. – 2.008” (51mm)

Math:
Brake System PSI x Area of caliper piston

510 master, 510 caliper:
1,132PSI x ((2.008/2) x 2.008/2)) x 3.14159 = 3,585#

240Z master, 510 caliper:
832PSI x ((2.008/2) x 2.008/2)) x 3.14159 = 2,635#

So by increasing the master diameter from 3/4” (510) to 7/8” (240Z) with no change in pedal pressure, you decrease braking force by 26.5%.

To have the same braking force means you need increase pedal force with the 240Z master by 36% (from 100# to 136#).
Dave Patten
http://www.FutoFab.com
Dunbarton, NH

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two_68_510s
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Re: 240z Master Cylinder Upgrade

Post by two_68_510s » 06 Oct 2013 07:32

Dave this is a treasure! Thanks for the technical insight, really helps with decision making.
(Not to mention it is well laid out and very informative)
Joel

2 '68 510 2 door sedans
'95 240SX


“We will either find a way, or make one.” – Hannibal

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jason
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Re: 240z Master Cylinder Upgrade

Post by jason » 06 Oct 2013 09:30

Well that makes sense, thanks for clearing that up for me too!
Jason

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StrutlessWonder
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Re: 240z Master Cylinder Upgrade

Post by StrutlessWonder » 06 Oct 2013 12:30

Thanks Dave!

Larger MCs resulting in rock hard pedals with no feel that require massive quad strength to stop the car are no fun.

If any of you want to learn more about brake bias:
http://sports.racer.net/brake_bias.htm

And if you know your brake piston diameter, pedal box ratios, master cylinder, disc diameter, and other specs, there are Excel Brake bias spreadsheets on the web you can use to play with your intended changes before you spend your cash:

http://sports.racer.net/docs/brakes.xls
http://www.tceperformanceproducts.com/bias-calculator/
www.vitessesteve.co.uk/Resources/GTBrakingmodel.xls
Kurt Hafer
'70 2dr VG30et "Strutless Wonder"

steve3510
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Re: 240z Master Cylinder Upgrade

Post by steve3510 » 06 Oct 2013 19:47

Wow thanks Dave! This forum is awesome! Ok next question... What do you all suggest I do? I am in the early stages of my project and if I need to change something now is the time. I appreciate all of your input thus far!

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okayfine
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Re: 240z Master Cylinder Upgrade

Post by okayfine » 07 Oct 2013 05:46

Tough to say, for we don't know what your plans, goals, or budget are.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson

steve3510
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Re: 240z Master Cylinder Upgrade

Post by steve3510 » 07 Oct 2013 05:57

True.. My bad. I am putting in a L18 block with a A87 head, Subaru 4:11 rear end, 240z 4 speed, dual side draft mikuni 44's, I plan on driving it around in nice days and auto crossing the car. Anything else you would like to know.. Just ask

steve3510
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Re: 240z Master Cylinder Upgrade

Post by steve3510 » 07 Oct 2013 06:06

Oh and I also, (down the road) plan on upgrading the front brakes and doing the caliper conversion on the rear. But like I said.. down the road..

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okayfine
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Re: 240z Master Cylinder Upgrade

Post by okayfine » 07 Oct 2013 06:16

If that's the plan, you might want to move up the time table. Mainly because you're going to be replacing some bits now based on your OP, but then replacing those same bits again (anything you do at the rear, and likely your BMC) when you go to rear disc.

The Z BMC swap is because the BMC in the car is bad? Could it merely be opened up and cleaned out? Rebuild kits for the 3/4" BMC come and go, as do rebuilt parts.

Given the performance potential of the L18, stock brakes (or upgraded stock brakes, say with Porterfield pads/shoes and some aluminum drums) would be more than fine for street and A/X.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson

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Re: 240z Master Cylinder Upgrade

Post by Byron510 » 07 Oct 2013 06:18

The 7/8" 240-280Z master works quite well on a 510. As you already know, the pedal effort will be greater. However I've used this MC on many of my own cars and found it to work just fine and the extra effort to not be excessive nor is there a loss of pedal feel.
This MC will also work well with your later upgrades to larger brakes all around.
For the rear, just get some new 510 wheel cylinders, for simplicity sake. The rear brakes are just along for the ride and really don't work that hard. It's the front brake upgrades which really make a difference - unless you're going to participate seriously in track days my vote would be to leave the rear brakes stock for now. Get the car going and enjoy it. You probably need to spend the money elsewhere on the car.
Post some pics.
Byron
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because the opposite never works.

steve3510
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Re: 240z Master Cylinder Upgrade

Post by steve3510 » 07 Oct 2013 06:28

I do have aluminum drums for it also.. I installed all new braided brakes lines. Yes I installed the new master cylinder because my original one is bad. And it was only $50 through my work. (I manage a parts store). I ordered new wheel cylinders for it yesterday. That is my goal now, just to get it one the road so I can enjoy it. I have more money to spend on the paint.. The brake disc upgrades will come after everything else is done.
I'll get some pictures up soon!!

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two_68_510s
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Re: 240z Master Cylinder Upgrade

Post by two_68_510s » 07 Oct 2013 07:29

[quote="steve3510" (I manage a parts store). [/quote]

Nice!
Joel

2 '68 510 2 door sedans
'95 240SX


“We will either find a way, or make one.” – Hannibal

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