General musings on 4-piston brake upgrades

So the brakes on my car are at best adequate and more accurately described as spongy/crappy. I've been considering an upgrade since the car came into my possession in December. It's pretty well sussed out at this point but after a talk with JVL today he suggested I throw this up for all to see (the depths of by brilliance or stupidity have yet to be determined because it's not done yet)

Anyway my plan is to do a knock-off of the Group A setup shown in the rally parts catalog with cheaper Wilwood stuff. I have the rotor and caliper I plan to use on the way. All I need is a custom brake hat and caliper mount. So, I did this a few nights ago. We start with a spare front spindle/hub assembly:



And then after about 2 hours (with stops for beer) of careful measurement and CAD work we get this:



I did learn some interesting things along the way. There are a lot of very nice round English (not metric) dimensions on the assembly...weird. Things like the wheel mounting face being exactly 1.75" away from the face of the caliper ears. I plan to measure a rear hub/spindle sometime next week as well as getting the new rotor and caliper into the computer. Then it's just a matter of connecting the dots between them.

I still haven't completely settled which calipers and bore sizes to use yet. I'll clean up my spreadsheet with the calculations and post that soon. For now the best guess is UL-HP rotors (266 x 29.2) all around and radial mount DynaPro calipers 1.62" bore in front and 1.25" in the rear. More to follow...

Here is the spreadsheet:







Edited 1 time(s). Last edit at 03/23/2007 08:48PM by Tim Taylor.

Mazda is like that, a lot of their suspension/brakes are English measurement instead of metric. The brake hydraulics are *all* English, your wheel bolt pattern is 4x4.25, pads and calipers are standard English measurement parts, and so on.

I "heard" that FC RX-7 calipers are trivial to install on a 323 spindle. Aluminum 4-piston, usually on eBay for $50/pair if you can't find them locally.

---

Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

Pete Wrote:
-------------------------------------------------------
> Mazda is like that, a lot of their
> suspension/brakes are English measurement instead
> of metric. The brake hydraulics are *all*
> English, your wheel bolt pattern is 4x4.25,

no, 4.5" PCD



pads
> and calipers are standard English measurement
> parts, and so on.
Calipers and hydraulic is mostly Lockheed built under licence.
>
> I "heard" that FC RX-7 calipers are trivial to
> install on a 323 spindle. Aluminum 4-piston,
> usually on eBay for $50/pair if you can't find
> them locally.

Uhhh no way.
>
>
> Pete Remner
> Cleveland, Ohio
> 1985 RX-7 rallycross rustbucket/experimentation
> thingus
> 1984 RX-7 reshell
> 1978

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Ha, I just found this...it's already what I was doing but it's still an interesting read.

http://www.rallydesign.co.uk/catalog/pdf/designing_4_pot_brakes.pdf

You should have no issues making this setup yourself. I've seen you capabilities.

The thing I wonder about is the master cylinder capabilities. It seems that any real race upgrade I've ever seen has had the ability to change the bias front to rear.

That rallydesign stuff is a good read and a good find. They are the company that won't sell to US or Canada due to liability that I spoke to. Good luck and post pics of your progress.

---

Grant Hughes

Yeah, so space isn't a little tight on a GTX hub...it's silly tight. Lots of parts are trying to co- habitate the same physical space. I still don't have my sample parts in hand yet but I roughed them out based on the mounting drawings on the Wilwood website and experience with others I've used in the past. I'm trying to use no more than 3/8" of wheel spacer for clearance. Right now the nice green caliper sticks right thru the wheel. Not so good.



The radial mount DynaPro calipers just don't look like they're going to fit. So, now I'm looking hard at the Billet Dynalite calipers. The narrow mount variety makes the mounting bracket easier but is 0.46" wider due to the huge pads they hold. I'm actually giving serious thought to cutting down the brake ears and making my own mounting points on these fixture pads in the casting.



Nothing is certain until I get the actual parts in my hand. I was unable to convince anyone at Wilwood to save me some time and give me a generic CAD model of their caliper…like I will steal their design from an .IGS file of the outer surfaces. Last time I did this sort of thing I wanted to modify the mounting ears on a caliper for more clearance. I talked to the head engineer at this company http://www.thebrakeman.com/calipers and he gave me the native CAD file of what I needed. BTW they make really nice calipers (similar to the old 4 piece Girling design but forged sides and hard anodized) and I would be using them again if they made the bore sizes I needed. So the game continues...

Yeah clean those pads, use one and make the little triable thing I wuz telling you I did for Dereks.
And recall that I used a 1" spacer.

We should team up and make a few of the triangle things for a few other guys.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

NoCoast Wrote:
-------------------------------------------------------

> The thing I wonder about is the master cylinder
> capabilities. It seems that any real race upgrade
> I've ever seen has had the ability to change the
> bias front to rear.

I think full race dual master cylinders are great but the thought of all the surgery to make it fit in my car makes me wince. The spread sheet I posted above actually has the bottom of it cut off. It’s really incomprehensible without the ability to look in the cells at the formulas. I went thru the whole brake formula for a stock GTX to back out the brake bias.

Torque created by the caliper on the rotor (at the wheel) = TW
TW = PS x AP x μ x 2 x RE
PS = Pressure of system (instantaneous circuit pressure at the caliper);
AP = Total area of pistons in one half of caliper (one side of opposed type or active (piston) side of sliding or floater type);
μ = Friction coefficient of the pads against the rotor;
x 2, since there are two sides of the rotor that the pads are exerting force against;
RE = Effective Radius of clamping force

End result is that it has about 60% front bias until the stock proportioning valve kicks in at a line pressure of about 430 psi and the bias goes to 70% front. I'm headed for as close to 60% front bias as I can get by sizing the piston bores and I'll fix the rest with an aftermarket proportioning valve. The last column in blue shows the ratio of the piston areas to the master cylinder to make sure I wouldn't run out of fluid volume.

john vanlandingham Wrote:
-------------------------------------------------------
> Yeah clean those pads, use one and make the little
> triable thing I wuz telling you I did for Dereks.
> And recall that I used a 1" spacer.

I'm still going to make the attempt to pull it off from the stock ears, without the big spacer and changing all my wheels. I'm also starting to warm to the idea of a billet dynalite caliper with the bridges remade in steel (both to accommodate my rotor thickness and for overall stiffness). I started with the intention of not making this to much of an ordeal...seems to have snowballed.


> We should team up and make a few of the triangle
> things for a few other guys.
>

Sounds reasonable, I don't know any other people willing to do this silly of an upgrade though. Might be a really, really small market. Most of the GTX people I run into are all about bolt on stuff. The idea of taking the hub apart to machine it frightens them. I don't scare easily I'm to dumb.

In return for your invaluable help consider yourself the sole distributor of the Sooooper Bitchin GTX brake upgrade to the rally community. You're in charge of painting them green though.

You guys are too hightech, I'm having difficulties following everything.

John splain me all this in a barbaric language pleeeeeeez.

---

Cheers
M.Samli
Phoenix AZ
Gaylant VR4
EVO III GSR (Stolen)


Rallies are no place for traitors

I'm not quite as adept in barbaric language as John but here is a Cliff notes version let me know if I make it better or worse and I will attempt to clarify:

First off you can ignore all the brake formulas. I just used them to get an idea of what the stock brake bias in my car was. The thing to take away is that it's around 70% on the front when you're stopping hard.

Grant asked why I wasn't using a Soooper Bitchin' fulls race ready dual master cylinder setup like this:

http://www.wilwood.com/Products/005-PedalAssemblies/002-FSMP/fsmtmc/index.asp

The answer is I'm to lazy to cut up my car and move around enough stuff to make it fit. No question that it's a better setup but I can make it work more easily by changing to a bigger master cylinder and adding a proportioning valve like this to the rear brakes.

http://www.wilwood.com/PDF/ds488.pdf

He also asked if I was going to run out of brake fluid volume. This is a real concern when you add bigger calipers because standard practice it to go bigger on the piston bores (this means more "leverage" i.e. longer and softer pedal travel) for more stopping power. It's very easy to go overboard and the result is that the pedal hits the floorboard before you have moved enough fluid to make the pads contact the rotors. That's why I have a column in the spreadsheet (F+R)/MC. This is the ratio of the piston areas to the master cylinder area. You can see that the stock ratio is very close to the NDL ratio.



Beyond that we're just talking about packaging 5lb of brakes into a 3lb sack. There are lots of clearance problems with my current wheels. This is a section view with a NDL caliper and 1/2" of wheel spacer.



John solved (feel free to jump in here John) this by going to 1" spacers with 15" rims, then cutting down the stock brake ears and mounting to the two casting pads circled in red in the picture above with his "triangle things".

I just decided yesterday that there's no clean way to make my current rims work. I'm waiting for the drawing but it looks like Compomotive TH3's are going to work nicely. They have a nice bulged profile to clear calipers that you can see in this picture I nabbed from the UK website.



I wandered away form barbaric there...sorry...did I make it any clearer?

Tim







Edited 1 time(s). Last edit at 04/02/2007 08:23PM by Tim Taylor.

Tim Taylor Wrote:
> I just decided yesterday that there's no clean way
> to make my current rims work. I'm waiting for the
> drawing but it looks like Compomotive TH3's are

That's too bad the brake solution has grown so large, because those mazda rotary phone dial wheels are strong and oh so cheap. I've beaten the living daylights out of those very rims with my crappy driving at (broken) Rim of the World, and they always held up.

The car looks like its shaped up really well. you'll have to rally it some day.

Chris

Yup,

Now it's crystal clear to me.........................NOT !

I applaud the effort.

---

Cheers
M.Samli
Phoenix AZ
Gaylant VR4
EVO III GSR (Stolen)


Rallies are no place for traitors

sagsert Wrote:
-------------------------------------------------------
> Yup,
>
> Now it's crystal clear to
> me.........................NOT !
>
> I applaud the effort.

Moosie, ol boy, you know me, I say get the details, source the nearest thing we can that works the same that we can afford , build it, try it and then go and see WHY it works correctly.

Tim has ready access to sooooper bitching modelling and graphic tools, this can change the order one can approach a problem.

He's been making heroic efforts to do something I wouldn't want to attempt: build really good brakes withou eeither brake calipers or alternate discs in hand and do it under existing 14" wheels.
When I did the Sooooper bitching set up for Derek Bottle's 323 I knew I would cause I knew I had 15' wheels to play with and I knew the original GpA set up used very thick spacers, so i could too.
As for sizing, I work from the piston sizes I've measured off of old Escort MkII Gp4, Sierra 2wd, Sierra 4x4, Escort Cossie, Subabrat, and VW.
Good enough for "them"

In essence I say I work from " praxis" and he's working using his noodle.
That's fine if you have a noodle to work with or noodle-extenders like 'pooters and graphics.
I have neither.
(But I do have a good eye.)


Hey, you gotta call and rant about the slime-ball politics you merely hinted at here.
>
> Cheers
> M.Samli
> Phoenix AZ
> Gaylant VR4
> EVO II GSR
>
>
> Rallies are no place for traitors

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Tim, you're in SF? I'm in SJ. I have GOT to stop by and buy you some beers and convince you to show me how you make those lovely CAD drawings.

---

Self-righteous douche canoe