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Which rear brake conversion to use?

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I am trying to decide between Maxima calipers and z31 rotors or a 280zx rear setup.

I am planning to run s12+8 brakes with drilled rotors in the front.

Which setup would be cheaper and easier to do? How would each conversion affect brake bias?

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Check out the Brake threads in the FAQ forum and all of the pinned threads in the brake forum.  You will see many complaints about degraded rear brake bias after doing the various rear brake "upgrades" using Maxima, 240SX or 280ZX calipers.  As you will see after reading about 100 threads they actually are not upgrades at all and people are frequently disappointed after removing their rear drum  brakes. 

 

Also, be warned that the stub axles were not designed for disk brakes. The flanges can get bent/warped which will cause the rotor to rub on the pads and overheat. You can have the flanges turned if they are not too bad.  Out of six old  stub axles, I was able to use one after turning it. New stub axles are NLA.  After-market stub axles are available, but run about $600 to $700  (see vendors forum).

 

Note: I have done all of the so called "brake upgrades" using the above rear calipers,  including front caliper, master cylinder and booster variations, and they are not upgrades all.

 

Go look at Arizona Z Car brakes if you want an upgrade in terms of performance.

 

Here are my brake bias (torque) calculations I did when playing around with different brake configurations:

 

Based on using a 1 inch Wilwood master cylinder

 

Stock front/ 240SX rear:  0.654 front  0.346 rear

 

Toyota solid front/ 240SX rear:  0.660 front  0.340 rear

 

Toyota vented front/240SX rear: 0.704 front  0.290 rear

 

Note: a proportioning valve will not correct the bias problem.

Edited by Miles

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Thanks for the info Miles. I am on a budget so I am not looking for a high performance brake setup. Just something a bit better than stock.

I am currently working on my suspension, tokico springs and struts and poly bushings. So i wanted to finish my brakes while I'm at it.

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280zx calipers are the only ones I would use as they have larger piston area than the 240sx and Maxima.  They are a pretty good match for stock fronts. With the early maxima bracket they are bolt on and are aligned correctly.  They feel great with the stock master cylinder.  I've been running the 280zx rear setup for 10 years now, and It's a good stock level setup.

 

If the 12+8 calipers have more piston area than the stock Z calipers I would think it's going to be too much front bias.  You'd be surprised how good properly setup stock brakes feel and perform, but the key is front to rear balance.  Don't bother with uber large master cylinders, brake boosters or calipers as they are not needed unless road or track racing.

 

The later front wheel drive maxima bracket is the one that is out of alignment, and needs proper machine work to get it done correctly.  Why bother with all that hassle for a smaller piston? 

Edited by rejracer

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Thanks, I am leaning more towards 280zx rear brakes as well.

 

12+8 will definitely offset bias towards the front and I don't know of any good ways to correct it. Maybe if I run wider wheels in the back?

I don't really plan on racing the car too much, maybe a track day every 2-3 months. At least for now.

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Thanks, I am leaning more towards 280zx rear brakes as well.

 

12+8 will definitely offset bias towards the front and I don't know of any good ways to correct it. Maybe if I run wider wheels in the back?

I don't really plan on racing the car too much, maybe a track day every 2-3 months. At least for now.

 

Please follow up this thread with how the 280ZX calipers work out.

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I still can't understand why folks would go with the S12+8 caliper in front.  If you are not going to a vented rotor there is no performance advantage to adding two additional pistons and weight to the front.  You are actually increasing braking distance by increasing front bias.

 

Go with the S12W caliper and vented rotor in front or just leave the stock part in place.  You'll save money.

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Wouldn't wide wheels help shorten braking distance? Also wouldn't wider rear tires help offset brake bias further back?

Besides larger caliper should help with brake fade.

 

Maybe for now I'll just do rear disc conversion and leave stock front calipers. Maybe i'll just get drilled front rotors to help with cooling.

 

Right now I should be close to 220hp at the crank. Once I get bigger injectors and ECU I'm planning to get to at least 300, so I would want to have bigger brakes at that point.

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No

No

No

Better read up on 'rotor mass in relation to braking efficiency'!

 

A more considered and prudent suggestion: Porterfield R4S pads and matching shoes in back properly adjusted, with Motul RBF650 fluid combined with those 'wider wheels/tires' and don't upset anything in the mix.

 

My stock brake system with the above combination can easily flat spot sticky "A" compound tires, 245 in front, 265 in back and pull my up onto the belts at 100mph with hard application after repeated stops. It has worked on mine pushing a bit more than 300 'at the crank'... Consider that John Morton was running the stock stuff in SCCA winning races with 325 crank HP... 

 

Most 'brake fade' in S30's is due to bad fluid, cheap pads, and misadjusted rear brakes.... Try those three first and be amazed. Unless you're running Lemans, or more than 30 minute track-day sessions you're meddling with a mix that works well when properly and competently maintained.

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I will chime in here.

 

I did rear disks on my car strictly for vanity reasons and left the front alone other than new disks/brake lines. I bought a "kit" with maxima rear calipers and 280zx rear disks. I didn't build it to be a track car otherwise, like Miles mentioned, go with a complete front/rear and MC kit as it will be a better balanced system to start with.

 

I'm not sure how to calculate brake bias as Miles mentioned, but my brake system seems to be fairly well balanced and the car will stop fast enough to lose your gum without locking up the rears. It's probably due to the near even weight distribution these cars have or maybe I just got lucky with my car weight, springs, weight transfer to match up with brake system I have.

 

If you read this Miles, what is a good brake bias for these cars and how to did you go about calculating it? I'd like to do it to my car as the %'s you show above really seem about right to me for a street car, but again I don't really know.

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Here is more info on brake bias:

 

Brake bias calculator: You can calculate bias manually or use a program for calculating it . I did mine manually and then used the calculator below and the results were very close. You need to collect all of the variables and then do your calculations. There are many threads on how to do the calcs. 

http://www.tceperformanceproducts.com/bias-calculator/

 

Discussion on various brake combinations and  resulting brake bias/balance:

http://forums.hybridz.org/topic/113398-toyota-truck-calipers-ventilated-brake-rotors-mm-rear-disc-brakes/?hl=bias

Edited by Miles

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Seriously, if John Morton could take National SCCA Titles using only upgraded Pads, Fluids, and the stock system.....

 

REALLY how much is your occasional track day poseur going to tax that same system?

 

This is a marketing perception, rather than an engineering reality.

 

The "shortfalls" of the stock system universally are due to people improperly maintaining the vehicle, and not due to an engineered shortfall or deficient braking system.

 

They are engineered to stop a vehicle TWICE the weight of what you have. That means MARGIN. If you are having problems of excessive pedal travel, 'brake fade' or etc....

 

Consider looking in the mirror at the maintenance you have not been properly performing, rather than blaming a system that will haul the car down from 120mph four or five times in rapid succession and STILL LOCK 245's.

 

If your stock system does not do that---you aren't maintaining it properly. Period.

Edited by Tony D

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Thank you everyone for your input. I'm not very familiar with braking system. I installed all new hard lines, they are larger in diameter than stock.

 

I think I'll stick with stock brakes for now.. maybe just a rear disc conversion.

 

Also after reinstalling my brake booster I noticed that I it's touching my custom downpipe.

Are there any smaller booster available for out cars or would it be easier to just bend the downpipe slightly?

 

sugh.jpg

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Early 240's have smaller boosters.

Is your check valve functioning properly?

Sending boost to a vacuum booster is a sure way to diminish braking assist...

 

Basic Hydraulic Theory states, the pressure in one section of the system (properly bled with no compressibles contaminating it) will be the same everywhere, regardless of diameter, cross section, height, shape, etc...

Larger diameter piping, properly filled and bled of air is transparent in terms of the system performance, it just adds volume incrementally.

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No idea.. I haven't driven the car yet. I am just finishing the project. Original booster was shot so I got one from a junkyard but I haven't tested it yet.

 

Aren't 240z boosters only smaller in diameter but are the same height?

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