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280Z-LS3

Let's talk brake system design

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Gathering parts for my 1975 280Z build and time to get the brakes sorted out.  Been hunting around the web for brake parts from the major aftermarket players, in particular Wilwood, AP Racing and StopTech.  Don't really want to just buy a "kit" from a Z car vendor,  purchase parts for custom setup or swap an OEM system without understanding what I am getting and how it will fulfill my requirements and expectations which is performing under road course track duty.  I am honestly new to performance brake theory and hope to learn enough to talk intelligently with brake vendors to hone in on a properly designed and balanced brake system.  For starters would like to understand how to choose piston sizes in calipers and relation the front calipers piston size have to rear caliper piston size to produce adequate brake torque for S30 chassis.  Floating vs bolted rotor ring pros and cons.  Proper rotor thickness front and rear, assume starting with 1.25" width up front.  Brake pad choice is easy to get into ball park with recommendations.  Going to be using a dual M/C to maximize tuning of brake bias.  Street legal 275 R17 autocross/track tires are planned.  I believe the only item that may need to be custom fab'd are radial caliper mounts which confident I can handle.  All other parts should be off shelf from Wilwood, they post extensive product into on their webpage as does AP Racing but they are Euro based thus harder to source.  StopTech I have found to be lacking in product description.  Hope this is enough info to get the conversation started.  Any words of wisdom truly appreciated! 

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With a 17" wheel you have lots of options for calipers.  Google what others use and you could design your own brackets?  A few calipers people use are the brembo sti calipers or the Cadillac sts calipers? Sts seems to be every ones favorite for cost.   Then you could use a willwood proportioning valve to get your bias dialed in?  Nissan R32 calipers are also popular.  Tons of options unless you want to clear a 14 or 15" wheel.  

 

I have the Zcargarage which is a stoptech kit that was designed with the automotive engineers, the bias is about perfect.  It's expensive, but I think its worth it. I wanted 15" wheels and a parking brake, plus as good of stopping as I can find.  

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Most of the so called brake upgrades are not upgrades at all.  The popular upgrades tend to result in too much front brake bias creating an unbalanced brake system.  Many people regret "upgrading" their brakes after discovering that their brake modifications did not improve braking.

 

Stock brakes are designed as a system.  Changing one braking component has an unplanned  domino effect on the rest of the system.

 

I recommend that you you spend a lot of time reading all of the "brake upgrade" posts before making a decision to modify your car. Look at the posts that deal with brake bias.

 

Well maintained stock brakes are fine for most 240Z applications.

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Most of the aftermarket brake companies, be it Wilwood, AP Racing, or whatever manufacture calipers intended for front wheel applications, and others for rear wheel applications.  The rear oriented calipers will have smaller overall piston area to give you a default "bias" that is in the ballpark for most cars.  The bias is fine tuned/corrected with either dual master cylinders and a balance bar, or with an adjustable proportioning valve.  Each method has strengths and weaknesses.  In general racing/track cars would be best served by a balance bar, and street cars with an adjustable proportioning valve.

 

The relevant data are combined (assuming multiple piston calipers) piston size for each front caliper, combined piston size for each rear caliper, brake disc diameter front/rear, and tire diameter.  With this information, companies like Tilton Engineering can make sound recommendations for front/rear master cylinder sizes.

 

None of this is rocket science, but there is a lot of data and arithmetic involved in sizing everything correctly.

 

I agree with the prior post that many brake "upgrades" are actually not always true performance upgrades.  People get away with just bolting on huge discs and 4-piston calipers on the front brakes only, because generally such a mod just dramatically increases front brake bias.  Front brake bias is "safe" (it won't cause the car to spin), but many of these aftermarket front brake upgrades will actually increase stopping distance from stock.

 

To do it right, brakes need to be a system involving front/rear, master cylinders, and proportioning systems.  If this is done correctly, you can dramatically improve on the stock brakes in terms of weight, "feel", stopping distance, and fade resistance.  

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1 hour ago, Ironhead said:

 

The relevant data are combined (assuming multiple piston calipers) piston size for each front caliper, combined piston size for each rear caliper, brake disc diameter front/rear, and tire diameter.  With this information, companies like Tilton Engineering can make sound recommendations for front/rear master cylinder sizes.

 

None of this is rocket science, but there is a lot of data and arithmetic involved in sizing everything correctly.

 

To do it right, brakes need to be a system involving front/rear, master cylinders, and proportioning systems.  If this is done correctly, you can dramatically improve on the stock brakes in terms of weight, "feel", stopping distance, and fade resistance.  

Thanks Ironhead, these comments are exactly my thinking.  So i guess my issue is where to start.  Since I have rim size limiting rotor size do I just maximize rotor, say at 12.88" or 13" with 1.25" width for front then choose front caliper size then match rear rotor/caliper accordingly?  From what little I understand the larger the piston size the greater the torque for a given pedal effort.  Found this little nugget on the web:

 

"All things being the same.... a 1.25" bore FSL generates 2531"lbs of torque at 509psi and 60lbs of leg effort.

Moving to a 1.375 FSL-
Same effort and same pressure: 3062"lbs of torque. +17%

Moving to a 1.625 FSL-
Same effort and same pressure: 4278"bls of torque. +40%"

 

FSL is Wilwwod Forged Superlite.  How much torque is too much, that's the question.  All the rest can fall into place


 

1 hour ago, Ironhead said:

 

 

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You could just call Wilwood, Stoptech, or Essex Parts (AP Racing distributor), tell them the weight of your car, how you will be using it, and what size wheels the brakes need to go under.  Budget will be a huge consideration too.  Of the three Wilwood will definitely be the most affordable.  AP and Stoptech components range from somewhat reasonably priced to astronomically expensive.  AP Racing parts go all the way up to F1 components...you can imagine what that costs.

 

Anyway, they could recommend compatible front/rear disc and caliper combos suitable for your use and budget.  They could also suggest pedal/master cylinder setups...or you could just shop around after you decide on discs/calipers.  I really like Tilton pedals and master cylinders.

 

Coleman racing can machine custom brake hats reasonably inexpensively once you know what you need.  I personally would go with floating discs in front, not so important in back because the rears generally see far less heat.

 

 

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Posted (edited)

I spoke with Wilwood, StopTech and Essex and here is a bit of a review of experience.  Wilwood was the most helpful but clearly wanted to steer me to pre-assembled kit only because I mentioned was employing 2015 Mustang Super 8.8 rear and possibly 2018 Mustang front spindles.  Felt the tech really wanted to help but I needed to give him more info which is why I started this thread.  StopTech did not want to give me the time of day, buy a kit or go away was basically my options.  Essex was wanting to be helpful but also said buy a kit because of their "limited stock".  He did offer to sell me anything from AP Racing's extensive the Euro catalog, which he emailed over, but I was to be "on my own" choosing parts.  I will crack this "black box" lol

 

Thanks for the heads up on Tilton for pedal and M/C. 

 

I am hoping to design a system utilizing standard stocked hats from one of three above.  I have the rears covered with Wilwood hat 170-14430 but will be locked into using a 12.88" rotor ring which is the smallest diameter offered compatible with 2015 Mustang hat which is machined for 12x8.75 rotor bolt circle.  Thinking this should be ok since the 12.88" ring is offered in 0.81",  1" and 1.1" widths.   One of these should match well with 13.06"x1.25" front rotor  #160-8165 if I can find a hat.

   

I am shying away from the 2014 Mustang spindle swap because it moves the wheel 3/4" forward in wheel well.  Arizona Z Car and Techno Toy Tuning both offer 5x4.5" hubs for stock spindles which match the rear 2015 Mustang hub pattern.  Hopefully either companies will share the hat off set used in their BBK before I buy a hub set to check hat availability.  If not may just gamble by buying a set and hope I can find an off the shelf hat.  Or, last resort, have a pair machined by Colman Racing.

Edited by jsulse
correction

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Agree with Ironhead. If you're trying to figure out master cylinder sizes and that sort of thing, both Tilton and Wilwood can help with that. In the meantime you're asking an extremely open ended question: "I don't know what suspension I'm going to use, but what brakes are going to work with it?" is an impossible question. 

There are several spreadsheets that you can find online which will allow you to plug in a pedal pressure, rotor diameter, pad size, number of pistons, etc and figure out the resultant brake bias, but last time I looked, about 10 years ago, they were all wrong. Every one of them that I looked at.

As to the single vs two piece rotor thing, a two piece rotor is more likely to have issues with pad knockback, although I'm currently having issues with that on one piece rotors. Haven't figured it out yet, my guess is that it's a result of axle shaft movement in the rear in my case. I have anti-knockback springs, but need to disassemble all of the calipers to install them, which I'm not looking forward to.

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I plan on using the stock suspension design modified with coil overs, rod ends, swap bars, camber plates, etc.  Don't know if that clarifies the suspension question though.  Does eventual shock valving, spring rates, ride height will need to be factored into initial brake system design?  If so, that's really starting to look like a "chicken or egg" conundrum lol.  I will continue learning about brake bias via piston sizing front and rear calipers and matching rotor sizing, both diameter and width,  front to rear.  A real world description of how a car was setup would be helpful, I learn best by example.  Would like to add learning this stuff is half the fun, maybe more recalling times of frustration while wrenching.

 

The knock back issue has been on my mind.  If I recall correctly the AP Racing calipers Essex offers have knock back springs.  Will inquire if Wilwood offers knock back springs for calipers that are of interest for my application.

 

 

 

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ride height very much so effects the brake setup. longitudinal load transfer takes place when you apply brakes... that is, weight from the back of the car shifts to the front of the car. This transfer of weight is based on the reduction in speed in the form of -g's, the wheel base of the vehicle, and the height of the center of gravity.

The suspension plays into this calculation because the center of gravity is changed with the suspension. from my research, the center of gravity should be about 3/4 the way up up the block.

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Choosing your brakes, as with many mechanical systems in the car, is part packaging and part math. You can only exert so much force on the pedal and have so much pedal travel available, these are the bookends of your master cylinder size. On the wheel end, as rotor diameter increases, piston size and/or pedal force/g decreases but wheel diameter requirement increases. Rotor thickness depends on how much thermal mass you need for the intended duty cycle of your system, cooling can help here.

 

As for the dynamics, brake balance depends on CoG, wheelbase, and available grip and is determined by effective piston area, effective rotor radius, and pad friction. Dual masters or a proportioning valve is typically used to adjust, although prop valves can make more efficient use of the brakes (less wasted area under the ideal brake distro curve).

 

That's the high level, the rest is in the details.

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Posted (edited)

I used this setup from Arizona Z car for one of our 240Z' and found it to be a great street and mild racing use

http://www.arizonazcar.com/brake.html

front4lug3.jpg

 

frontrotor1.jpg

 

I also bought the new master they recommended and left the rears with the stock drum brakes and the setup works great.

 

There are also good kits from Techno Toys and Silverline so why re-invent the wheel when those are proven to be ready to bolt in and fit without issues. Also unless you are racing or have really big horsepower you really do not need disc brakes in the rear...

mini-ZXMASTERCYL1A.JPG

Edited by primaz

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Silvermine has a BBK kit using 12.88" rotors up front which is interesting.  I believe it uses a 2004 STI rotor with 1.18" wide.  I am looking to use a slightly larger diameter hat and rotor 13-13.2" and 1.25" wide to take advantage of all clearance in 17' wheel.  Not really trying to reinvent proven systems but just design a system within parameters of my build.  If need be will head over to friend's shop to use his Bridgeport to fabricate custom bracket which should allow me to mount almost any appropriately sized caliper/rotor combo up front.  The rears are easy because of the 8.8 swap uses 2015 hubs, plenty of off shelf brake options. 

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What's the percentage range brake bias that is generally seen suitable for a s30? I've been thinking about making my own brake kit as well using ap racing 5200 calipers. I've seen that the usual Toyota and maxima upgrade combo results in around a 66% front bias which is too much. 

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