Howard Coleman

iTrader: (6)

this is just a heads up for interested parties...

with the completion of my methanol injection system (see new section Auxiliary Injection) i am getting down to my last few major projects and since my car is up on jackstands for the wisconsin winter it's time to straighten out the brakes.

i removed the ABS a few years ago and run AP5200 front calipers on 13X1.25 rotors. the rears are stock. i retained the "proportioning valve" sub assembly. bottom line, not much in the way of rear brakes currently. i run 18X8.5 245s up front and 18X10 285/30/18s in the rear.

having seriously raced for 22 full seasons, having built 3 tube frame RX3 chassis and won a number of races i know that most road races are won in the rear of the chassis. the driver who can put the right pedal down first exiting a corner has the advantage. think rear grip. ditto under braking and here again one of the suspension design objectives is to be able to transfer as much brake torque under control as possible. you adjust rear brakes up til the car becomes out of control. then back off a smidge.

i plan to do more tracking next year and run the Silver State Classic so it is time for the brake system to get overhauled.

i will remove the power brake diaphragm and master cylinder. i plan to use two Tilton short "75" series masters... only 3.25 inches long. i will use a Tilton adjustable brake bias bar, and build a bracket that bolts to the firewall using the same 4 OEM holes. it will also provide the mount for the master cylinders and the bias assembly.

since the stock pedal is around 4.5 to 1 leverage i will need to add some leverage at the bias assembly. 7 to 1 works for me.

of course all of this is nothing new. Damian has a similar setup on his track fd.

you may be asking what the XXXX do i need this for w ABS. could i get along without it? sure. i will tell you though as one who has had alot of experience racing that the ability to fine tune the brake balance is probably of far far greater value than you might think. once you've had it... it is hard to live without.

so i am not wishing a debate re ABS here, it is fine for some.

the purpose of the post is to let interested parties know that i am on the case and will share anything i learn and will post pictures of my setup once it is completed.

i will be doing a 2 piece 13 inch rear rotor and 4 piston caliper too...

the right brakes can make you go really fast.

howard coleman

sereneseven

Hi Howard,

one thing you may be intersted in is the 996 RSR has a pretty sweet little dual set-up that mount's in place of the booster I believe it was an AP or tilton part that porsche hemoligated into they're own you might want check with BSR or possibly motorsports spares about it, might save a lot of work.

i'll check with a few friends and see if i can find a p# or picture.

Black91n/a

Tilton, AP, Wilwood, and others have pre-assembled dual MC pedals, but what Howard wants to do is keep the stock pedal and the stock mounting points, which won't be possible with the other setups, hence the custom route.

sereneseven

^ yes i understand this thats why i was reccomending the RSR setup because it bolts in-place of the booster which the gt-3cup is equipted with while maintaining the same brake pedal... the main differences between the 996 and the rx-7 would be bolts hole locations on the firewall and the push rod length other than that it should fit very well.

Howard Coleman

iTrader: (6)

yes, one of my design parameters is to retain the very neat OEM pedals. i do appreciate any help, pictures etc. i searched for an hour or so to find any pics of the brad barber/damian setup to no avail. i think jim lab might have his setup... i do have a pic or two and it is slick as to how the additional leverage was engineered in.

i am mainly looking for ideas as i weld/machine and for the first time in quite a few winters don't have alot to do on my car (dangerous).

i may design and build a remote brake fluid reservoir in part of the space below the wipers out of the engine compartment.

damian is using 3/4 and 5/8 masters but i have forgotten what he is using for brakes so i will check in w him.

i have spent most of the last 2-3 years perfecting my twin T04 turbosystem along w lots of neat engine related stuff and it is refreshing now to get back to the systems that make the FD so special... in that it is first and foremost a track/circuit car not a drag car.

i am changing wheels to Enkei NT03+Ms. 18X8.5 front. 18X10.5 rear. lots lighter than my Enkei V1s that came w the car.

howard coleman

DamonB

But you would agree there is absolutely no advantage to be had by people doing this to their street cars, yes?

I only mention that because many readers fail to realize that a car built for the track and a car built for the street are different animals. It will only be a matter of time before they feel their street cars need it because Howard said so

I look forward to seeing your project.

Howard Coleman

iTrader: (6)

yes

limbar85

iTrader: (21)

i was also recently searching for a dual master cylinder setup. i dont remember where i found this pic, but yeah.....maybe itll give u an idea

sereneseven

^ AHA!!!! thats almost identical to the 996 RSR set-up i was talking about. and right now there are probably a bunch of RSR units floating around since evryone is running the 997's

the_glass_man

iTrader: (2)

A-Spec supposedly has one that looks just like that. I inquired about purchasing one, but they told me I would have to bring it there in order for them to install it.

Looks like one in the same to me. I'd like to see a limited run of these remade.

jgrewe

iTrader: (1)

Not an FD but here is what i did on my FC.
I had to reposition the hole in the pedal up about 3/4" to get the pedal pressure I wanted so I then had to lower the pedal mount that far to keep things in line.

Check the Tilton website, they have a cool form you fill out with info about your car, brakes etc and they will recommend masters for you.

Howard Coleman

iTrader: (6)

thanks for all the comment and pictures.

i really hate engine compartments cluttered w non-essentials. look at the pic of Damian's car and all the brake fluid reservoirs. i am going to make one remote reservoir to service all three cylinders and it is going to hide in the space under the wipers, not in the engine compartment..

as to bracket... i want the bias bar as close to the firewall as possible. i don't want the masters sticking too far forward. i will be using the shorter Tilton masters.

finally the 64 dollar question is can you build in enough mechanical leverage to properly pressure the pads to stop the car. reading thru old posts david breslau was commenting about this. of course you can add as much leverage as you want but as you add leverage you add pedal travel. the whole deal is a balancing (bad pun) act.

thanks again for the pics and any advice.

howard coleman

jgrewe

iTrader: (1)

Shoot for about 70- 80 lbs of pressure needed at the pedal. Above 90 gets a little tiresome after a while.

I have my reservoirs inside on my dash bar just off to the right of the steering wheel.

Tilton will tell you everything you need in their tech section on the website. You can even choose your pedal ratio to work from.

Howard Coleman

iTrader: (6)

a few days ago i filled out the tilton spec sheet and as soon as i hear back from them on master cylinder sizing will order the parts. as to pedal ratio i plan around 7 to 1. the car is a street track car. i don't have a problem pushing on the pedal. i converted to manual steering back in 99 and it is one of my favorite mods.

howard

sereneseven

worst case you'll have to get smaller masters if the pedel is to stiff.

WidefootRacing

iTrader: (3)

Hi Howard,
I never did the full math/design work to figure out (my) idea twin MC setup,
but keep in mind that you may be able to find pads (or get some made) with
a high enough Mu (friction level) to cut down total fluid pressure needed,
while not having to use extra small MC bores and long pedal strokes. Just
make sure the cold stopping properties aren't too poor, not as big a deal
for a real race car like yours, but anyone who drives on the street needs to
keep their brakes working right...

Other stuff I know you're aware of:

1) Stiffness counts - reinforce the firewall mounting area, make sure the
MC brackets are extra stiff to cut down on excess pedal travel.

2) Keep all flex lines short as possible - a setup a friend made for some
cars used long runs of flex line, and while I respect his abilities I felt this
wasn't the best choice. Flex lines will inevitability expand more under
brake pressure than hardlines, again losing pedal travel.

3) Choose MC bore sizes that keep the balance bar as close to centered
as possible. If you can, spec the strongest balance bar you can find, and
keep the MC's as close together as possible to reduce the bending
leverage on the balance bar arms.

4) Spec the stiffest calipers you can find - again, flex in the caliper means
lost pedal travel means less braking.

5) Be careful where you place remote reserviours, try to keep them high
enough that there's no "S" bends in the feed hose, and the hose should be
as short and straight as possible. Anything that impedes the flow of fluid
into the MC's is bad...

6) Proper brake ducting and keeping the calipers/rotors from overheating
is important. Without the extra fluid and pressure available from a large,
boosted MC, if you boil the fluid in your lines you'll have less chance of
recovery in emergency situations with non-power brakes.

I listed a bunch of obvious stuff for other folks checking out the thead.
Good luck with your project, and if I can be of help please feel free to
email me at widefoot@comcast.net. I don't check out the forums as much
as I'd like (too busy with the mechanical design/consulting/fab end of my
business), but I'm a fan of really good brakes... ;-)

David Breslau
Widefoot Racing Co


D'Oh! There's a "7" (of course) - Make sure to route hardlines in as short
a path as possible, but much more importantly avoid extra rises and falls
in the lines. You want to minimize the risk of air being trapped in the lines,
and if possible allow provision to "back bleed" from the calipers up to the
MC's. This is only safe if you make sure to keep the calipers well flushed
with clean fluid, but since it's (almost) inevitable that the MC's will be higher
than the calipers, one of the easiest ways to really flush the lines of air is
to power bleed from the caliper.

Only do this if you're properly skilled, it's easy to screw-up the brakes by
getting dirt into the MC's. Do not do this at all if you're still running an
anti-lock system. I'm not responsible if you do something silly (like follow
my advice...).

David

Howard Coleman

iTrader: (6)

thanks david.

i do feel you raise the key consideration... does the proper mechanical advantage end up w too much pedal travel. compared to engineering my twin garrett T04s it will be a fun challenge. i may or may not succeed of course.

but i did sleep in a holiday inn express last night and as a matter of fact my son graduated from the same school you did. a point about which that i am both very proud and jealous.

thanks lots for your contribution. rest assured my system will be stiff and all SS lines.

regards,

howard

Black91n/a

You may want to be careful that the MC's aren't too short to be able to pump enough fluid to satisfy your calipers.

Let me explain. My dad's freind Jeff races a BMW 2002 in GT3 and SPU, I help crew for him when I can. He's got a Tilton pedal setup with dual MC's. He was having lots of problems with fade (or so he thought). We'd have to constantly bleed the brakes because he'd complain about a soft pedal. He then changed his MC's to a larger bore and all "fade" problems disappeared. We'd then be able to ignore the brakes all weekend without issue.

We figured that the MC's were nearly bottoming out trying to move enough fluid, so any little bit of boiled fluid would cause the MC's to bottom, leading to all kinds of brake problems.

Howard Coleman

iTrader: (6)

yes, thanks, absolutely the cylinders need to move X amount of fluid. i haven't heard from Tilton so i will call them monday and pass on the info.

howard

Howard Coleman

iTrader: (6)

i had an interesting talk w a tech guy at tilton today...

i had been planning to make a mounting bracket that added a bunch of mechanical leverage to the power braked pedal which due to the assist is around 5 to 1 leverage.

it now appears that the sole reason that the leverage is needed is because of the modest piston area of the rear brakes. he also felt that i would probably burn up the rears going full tilt on a road course w my 54% rear weight and 285s on the back.

if i were to put a set of 4 piston calipers on the back i could probably run a pedal ratio of 5, or at the very most, 6 to 1.

should i do that, which i will, i would initially use a 5/8 on the front and a 3/4 on the back.

if i were to run the stock rear caliper i would need 7 to 1 and would run 3/4 front and 5/8 rear.

the 75 Tilton master cyclinder is shorter because the spring is recessed into the piston. cool. sign me up for some of those. another factoid: the master cylinder piston moves 1/2 inch in the front and 1/4 inch in the rear system.

i am going to put 13 inch rotors on the rear w a 4 piston Wilwood caliper.

tomorrow i will measure the exact OEM pedal ratio (anybody know?), pick out some Wilwoods, and find some rear rotor hat makers.

howard coleman

WidefootRacing

iTrader: (3)

Hi Howard,
Don't know the value off-hand, but measure to slightly above the center of the
pedal itself when getting the "pushrod to pedal" distance. It's best to be a little
conservative, and I also think that the natural motion of the pedal when it's being
pressed on leads to the foot contacting it a little higher as it's pressed further
down. Also make sure to get the relative angles of the distances, to make any
corrections for "non-normal" (perpendicular) forces.

Interesting comments from the Tilton guy. Does this: "the master cylinder piston
moves 1/2 inch in the front and 1/4 inch in the rear system" mean Tilton's
recommended twin MC's, or what the OEM MC is doing? If it's such a difference
of motion for a twin MC setup, to my mind that's bad, as it means the balance
bar will be constantly rocking whenever the brakes are used. My understanding
is that you want MC output flow to balance the demand from the front and rear
calipers, so the actual stoke depth is as close to identical as possible.

Did he recommend a piston area for the rear calipers to work with your current
fronts? Why are you going with Wilwood's for the rear? To match the fronts?
(not sure of how your car's currently set up).

David Breslau
Widefoot Racing Co

Howard Coleman

iTrader: (6)

Hi David,

thanks for the useful comments.

i will be conservative as to pedal ratio and your point is a good one as to determining the actual length of the lever v the pedal surface and contour.

i do agree that the goal should be to have equal strokes and will further discuss it w him.

i did check out various Wilwood 4 piston calipers... i will probably go w the Forged Billet Superlite. piston size options range from 1.375 to 1.75 and are four in number so i should be able to find the proper size to reduce or eliminate bias bar movement.

i run AP 5200s in front. they are 1.625 and 1.5 sized pistons.

i used Wilwoods during the last 6 years of my racing and found them to be excellent as to performance. Wilwood, as you may know is/has been big in circle track racing. i have always always kept close attention to what goes on in that area as they know alot about going around corners... i, for instance, was the first to adapt a quickchange rear end to my GT3 car. i ran wide 5 hubs before anyone. i used an onboard rideheight adjuster on the RR to raise the corner near the end of the race when i had burned off 65 pounds of gas. i ran tire bleeders and used tire softener... all from the circle tracks. as well as Tilton twin masters and a bias bar

now i have to settle on rotor size and find someone to make me the hats.

it will be quite interesting to determine how much pedal leverage i will ultimately need given i will be adding quite alot of additional rear piston area...

regards,

howard

.

jgrewe

iTrader: (1)

Having the balance bar pivot all the time is not a big deal. They ride in a spherical bearing. Just adjust the push rods so that when the pedal is depressed and the masters squish in the bar is perpendicular to the push rods. The master that travels more gets a longer push rod.

DamonB

The Saturday night shortrack oval dirt and asphalt crowd is an excellent source of knowledge and parts, trouble is the far majority of roadrace guys instantly snub them. I laugh all the time at seeing the same products in a circle track catalog selling far cheaper than they do to the roadrace crowd. I guess it makes the aristocrats feel better to pay the extra money

Howard Coleman

iTrader: (6)

^
right-on...

for example the tri-point swaybar is just a Speedway Engineering garden variety swaybar (PN 608-188-35) w bent trailing arms and a few tweaks. i think the bar is about $80 and the arms are about $80. there's a bit of hardware. Tripoint sells it for around $500. i highly respect their suspension expertise and they deserve a pat on the back for doing it right.

but

if i do change bars guess whom i am going to call..

howard coleman