Brakes or rather Not..

[Intouch]

thanks everyone for the kind input.
my engine is a 427IR, injected. according to chuck keene who built it, there is enough vaccum and the car brakes (or not) as any mkIII he's built.

i think we can conclude that the mkIII brakes are average/ok....well, with 550 horses that simply is not enough i feel.

i want my cobra to have eyeball popping braking just as it has mind boggling acceleration.....

[D-CEL]

I’m sorry it’s taken me so long to get this info out, I’ve been dealing with some of those life issues.
As the title of this thread states the factory SPF brakes aren’t what they should be.
My car #239 had the Olthoff big brake kit, and still they required way more effort than I felt comfortable with, so last year I started working to fix it.
I did what most people do when they think their brakes aren’t good enough, I threw calipers and rotors at the problem. And like most, I wasn’t happy with the result.
Then I decided, my failure was because of the master cylinder/power booster, so I fabricated a dual master cylinder mount with remote reservoirs to go in the stock location.
Cool!!
Yea not so much.. that was worse than the stock set up!
It serves me right, I should have really looked at the problem and taken it all apart, measured everything and then spent the money and built parts.
The issue with the SPF brakes is not caliper, rotor or solely M/C related.
The issue is the pedal ratio.
After all of this work, and dismal results, I looked at the only piece of the puzzle left.
The brake pedal…………
When I removed the brake pedal (a royal pain in the arse!!) and measured it, I found the ratio to be 3.6/1!!! That is roughly half of what all of the aftermarket pedals ratios are. (6/1 to 8/1) When you couple that with a large diameter M/C , motors with weak vacuum signal and you get what we all suffer from.
The fix is really a higher ratio.
So, just re-drill the hole for the brake rod 2 inches closer to the pivot to raise the ratio…
Now the problems:
Because the top of the Power booster is near touching the underside of the fender, it can’t be raised when you re-drill the pedal. That rules out using the stock booster.
Also the brakes rod to MUST stay as close to perpendicular to the M/C bore as possible.
So that rules out the stock mounting location.
The only option I see is to remove the booster and M/C assembly. Fabricate a new M/C mount like I did, but raise it to match the new hole in the pedal to keep the rod angle correct.
Here are some pics of how I got there.
I was able to get a 12.720x1.25 rotor and a Superlite 6R caliper inside the stock 15 wheel. I also swapped in a set of Wilwood’s forged aluminum hubs, which are considerably lighter. So all of the effort wasn’t a total waist
I wish I knew why the “power that be” at SFC felt it necessary to put a power booster on a car like a cobra.

Jason

[patrickt]

Jason, very nice explanation. Am I correct then that, had the pedal assembly been properly engineered from the outset, you wouldn't even need power assist for the brakes?

[madmaxx]

Nice work, so modifying the brake arm changes the fulcrum so you get a better mechanical advantage? Did you brake pedal stroke change, in other words does the brake pedal have to travel futher.

[D-CEL]

patrickt,

In my opinion, yes you are saying it correctly

I think it would have been a much better design had they built it without the booster.
I would guess that they payed no attention to the ratio for it to leave the factory like that.


Jason

[D-CEL]

madmaxx,

Yes, the stroke increases and you pick up modulation.

[D-CEL]

It was really a fun project, I wish I could spend more days doing that kind of stuff.

To add some more details.
The pivot rod that all the pedals swing from has a bolt on each end!
Yes that is correct, each end! So you need to be a contortionist to get the one on the fender side. You will also need to put a pair of vise grips on the shaft under the dash to keep it from turning.
I fabbed up a stainless “L” bracket that bolts to the top of the foot box to retain the rod when I put it back together. Just so I would never have to mess with that freakin bolt again!!

I had to machine a new pedal clevis and a mounting plate on the dash for the Wilwood balance bar assembly and adjusting knob (Blue)


Also, anyone who thinks about this type of mod should keep in mind that the foot box is made of relatively thin fiberglass. As you increase the pedal ratio, you increase the load and fatigue placed on the mounting area. I made the mounting face of my bracket bigger and added two extra bolts. When I build the next one it will be even bigger to distribute the load better.

I have all of the part #s for the Wilwood pieces I used, and I am a Wilwood dealer, so if anybody is interested in any or all of it, I’d be glad to help.

JASON

[D-CEL]

I do also need to comment on the statement that Ant made about the AP being superior to Wilwood, as I have had this discussion more times than I care to remember.

AP makes an excellent product, they work as they should.
However, the cost of a cast, aluminum body, 6 piston AP caliper kit is more than twice the cost of a Wilwood billet aluminum bodied kit. (You can get a billet bodied AP caliper it just comes in a whole different catalogue! And they are a whole lot more expensive. Not that cast doesn’t work, its just has more flex.)
The question I was always asked was:
“Why is the Wilwood so much cheaper than Brand X”
To that I would respond:
“We make money, at the price we sell at, your question should be”
“Why is brand X so expensive?” “what am I getting for my dollars?”

Are they good? Yes. Are they worth twice or three times the money?

That’s your call.
Ant say’s “yes! Because he likes the Yellow logo”

Fyi,
Wilwood does in fact have calipers with dust boots, if you place value on them.
Those are calipers targeted at the “street market” because somebody said “you need them” You will find that in a high temp applications, the boots will burn and fall apart. I have seen it many times in classes where you must use a stock caliper. The guys that must use PBR calipers routinely take them out because they catch fire. They do nothing when it comes to keeping the true enemy out of your brake system, moister. No seal can keep that out completely, that why the fluid must be changed regularly.

By the way, the AP replacement parts make the kit prices seem reasonable

JASON

[Ant]

Jason,

I dont disagree with a lot of what you have said, comparing cast to billet, I dont actually think caliper rigidity is a lot different between the two.
The wiper dirt seals on the AP's are in the piston bore (not exactly visible) and can heat transfer better and arent anywhere near as susceptable at burning off like old style boot seals that were just under the brake pads. Dirt seals arent really that necessary and if you clean the caliper piston before fitting new pads the seals should last a good while.

AP road calipers are of a heavier construction than their race calipers, coupled with the double lip wiper seals are claimed to be more durable, due to the fact they generally see less maintainance than a race caliper which is regularly serviced.

PBR caliper dirt seals and the design that AP makes on these calipers arent really the same thing. Moisture yes its always a good policy to change the fluid every meet.









[quote=D-CEL;935762]I do also need to comment on the statement that Ant made about the AP being superior to Wilwood, as I have had this discussion more times than I care to remember.

AP makes an excellent product, they work as they should.
However, the cost of a cast, aluminum body, 6 piston AP caliper kit is more than twice the cost of a Wilwood billet aluminum bodied kit. (You can get a billet bodied AP caliper it just comes in a whole different catalogue! And they are a whole lot more expensive. Not that cast doesn

[Ant]

Jason,

I originally wanted to use Wilwoods, as I have used the billet Superlite in the past with 1.88/1.62 these are just a little to wide for my application, so I then looked at the 6 pot calipers, I have a space problem and am limited in width, but the narrower SL6 would have worked, then I priced up some AP's (they are about twice the price) but are narrow enough, the upside to that the AP has a bit more pad area, coupled with 330 x 32 front rotors have a bit of heat capibility before parts get cooked. Also looked GN Wilwood but to wide, so I spent more money, which you dont get any prizes for.

You are right the down side with my internal wiper seals would be heat but most likely with my short races and light weight car hopefully not a problem, apart from regular maintainance. Corrosion with the design seal I have these will do nothing to prevent that, so change the brake fluid every full on meeting!

[PANAVIA]

Jason , very nice explanation and nice tube work, my compliments to your tube bender.

[D-CEL]

Ant,
Back in the “old days” the Wilwood stuff was aimed at Stock car or drag racing. The “street market” didn’t exist for them. They didn’t worry about tight packaging.
Having more swept area does have advantages, but it’s not what most people think.
Because the pads and rotors are bigger and have more thermal mass, they absorb more initial heat and exert less thermal shock on the rotor. Additionally, there is more pad material, therefore they have longer life.
It’s hard to look at a catalogue and not pick the biggest, raciest part (most expensive) part. I suffer from that disease. Those big calipers like the GNIII and huge rotors were designed for short track stock car applications. Arguably, one of the most brake demanding racing applications. 3600lb cars, 750-800hp, huge sticky tires and lots of down force with very little time between cycles. Huge parts with lots of area and mass are the only way that they would last an entire race. Street cars just can’t use that much brake even on the track.
However you do get points for having COOL brake parts! I would never say you did the wrong thing. If I had a connection at AP I would run them!! LOL
It’s like building and Aluminum big block. There are a lot of cheaper ways to make more power than you can use, but it’s what I wanted to do, so…..

Steve,

Thank you brother! I didn’t even have to throw any tubing away! I started with the long one, when I screwed it up, it became the short one! LOL

Jason

[WildBill1965]

Have you properly bedded the brakes? At first I complained to Dennis and that was the first question he put to me. So now the brakes are fine!

[Got the Bug]

Originally Posted by WildBill1965

Have you properly bedded the brakes? At first I complained to Dennis and that was the first question he put to me. So now the brakes are fine!

What steps are involved in bedding the brakes? Guessing that this would have to be done when the brakes are new.

[RonNichols]

Jason,

Check your safety wire. Interesting mod though. Does it perform like intended?

R