Brake Bias Issue..? 96 Cobra - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 9 Old 12-09-2015, 08:47 AM Thread Starter
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Brake Bias Issue..? 96 Cobra

I have a 96' Cobra that I coyote swapped this past year.. in the course of the swap I also converted over to 04' IRS with FTBR bushings and deleted the ABS block as I was able to get nowhere in diagnosing it's non functionality other than I assumed the unit had went bad altogether..

Other changes to the chassis were 04' Cobra bilstein's all around, 04' Cobra Coupe springs cut one coil and finally no front sway bar due to my current oil filter arrangement.wheels are 18x9 and 18x11 with 245/35's and 295/35's

Onto the issue..

I have been driving the car for just under a month now and have had two situations where an emergency stop became necessary. Both situations have resulted in the front brakes locking up and me almost sliding to my certain doom..

I had the intentions of upgrading to S197 calipers before long but now have to back up maybe address other issues before I can do "cool guy" stuff like that..

My first direction I want to take is maybe my tires? fronts are some dry Pzero Rosso's...

Any help appreciated.


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post #2 of 9 Old 12-09-2015, 08:51 AM Thread Starter
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Just to add on...:

Battery is relocated to the rear as well.. could mr front spring rate be a contributing factor..?


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post #3 of 9 Old 12-09-2015, 10:57 AM
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A couple things to look at. Check the DOT date code on your tires. If they are older than 6-7 years, they have hardened and will need a lot more heat (hard to achieve on the street) to develop the usual grip levels. The older tires can really impact braking ability with non-abs.

Another thing is driving style. When driving a non-abs car, you have to allow a little time for weight to transfer before applying full brake, or the front will skid prematurely. With abs, we often develop a habit of stabbing the front brake in emergency situations and abs takes care of the rest. Instead, I would try a quick squeeze with rapidly increasing pressure over 0.5-1.0 seconds. That additional compression time can make a big difference on your car's ultimate stopping power. Try it on an empty road and test it out.

Stiffer springs and dampers will also impact weight transfer and weight transfer rate, but I would look at the other 2 items first.

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post #4 of 9 Old 12-09-2015, 06:17 PM Thread Starter
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Originally Posted by fast_frank_d View Post
A couple things to look at. Check the DOT date code on your tires. If they are older than 6-7 years, they have hardened and will need a lot more heat (hard to achieve on the street) to develop the usual grip levels. The older tires can really impact braking ability with non-abs.

Another thing is driving style. When driving a non-abs car, you have to allow a little time for weight to transfer before applying full brake, or the front will skid prematurely. With abs, we often develop a habit of stabbing the front brake in emergency situations and abs takes care of the rest. Instead, I would try a quick squeeze with rapidly increasing pressure over 0.5-1.0 seconds. That additional compression time can make a big difference on your car's ultimate stopping power. Try it on an empty road and test it out.

Stiffer springs and dampers will also impact weight transfer and weight transfer rate, but I would look at the other 2 items first.

Thanks,
Frank
I mean, let's be real here.. They're old.. I'll be the first to admit it.. I guess I kinda know the answer here.. but like typical I have to be told..lol.

I really need to start there, Any recommendations on tires..? It's a daily car that sees about 3K miles a month..

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post #5 of 9 Old 12-09-2015, 07:40 PM
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Aside from the tires, the ABS sets the knee-point bias on the car (essentially measures differences in slip between front and rear and adjusts to prevent rear lock before front lock). In addition, the IRS cars (later cars in general) had a slightly different anti-dive built in to account for the ABS. Since you appear to be running Cobra brakes front and rear the F/R brake torque bias appears correct. But if the ABS is disabled then I don't think there is a way for the system to adjust for panic stop situations. You may have to add a manual prop valve to the system or correctly diagnose and repair the ABS issue in order to get maximum performance out of your rear brakes.
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post #6 of 9 Old 12-09-2015, 08:28 PM Thread Starter
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Aside from the tires, the ABS sets the knee-point bias on the car (essentially measures differences in slip between front and rear and adjusts to prevent rear lock before front lock). In addition, the IRS cars (later cars in general) had a slightly different anti-dive built in to account for the ABS. Since you appear to be running Cobra brakes front and rear the F/R brake torque bias appears correct. But if the ABS is disabled then I don't think there is a way for the system to adjust for panic stop situations. You may have to add a manual prop valve to the system or correctly diagnose and repair the ABS issue in order to get maximum performance out of your rear brakes.
So in "Dumbass" terms.. the ABS unit acted as a somewhat variable Prop. valve..??

Yeah the ABS unit is long gone.. after taking care of the obvious deficiency I have in the rubber dept., I guess I may need to look into a prop. valve..

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post #7 of 9 Old 12-09-2015, 08:46 PM
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I wouldn't recommend using a prop valve to reduce braking pressure to the front axle, as it would mean all modest braking is being done with the rear axle. That's a recipe for a spin in low traction conditions.

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post #8 of 9 Old 12-10-2015, 02:54 AM
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Even the ABS equipped cars have a conventional proportional valve. It is located directly underneath the m/c in the combination valve. The combination valve is usually referred to as a proportioning valve. Is the combo valve the stock 1996 Mustang Cobra valve? The 1996-98 Mustang Cobra and 1999-2004 Mustang Cobra proportioning valves have significantly different curve shapes.

The IRS Mustangs brake systems were designed around front calipers that had 13% more area than what you have. This in combination with the different weight distribution from the Coyote engine and relocated battery is significant. All of these changes are going to affect the optimal brake bias. I think you are just going to need to disable the stock proportioning valve and install an adjustable valve. You will need to cut one nut off of the line going to the ABS replacement block and buy one line to do this.

Ford didn't incorporate EBD (Electronic Brake Force Distribution) into the ABS system until after 2005.

https://en.wikipedia.org/wiki/Electr...e_distribution
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post #9 of 9 Old 12-10-2015, 06:36 AM Thread Starter
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Yes. It has the stock 96' prop. Valve.. Man, I kinda knew better.. other gentleman had me actually thinking it was acting as some distribution block of sorts.. and I just somehow got lucky that I'm not stopping on the rears..lol!.

And thats kinda what the characteristics of the car would feel like if i were to put a finger on it, Like the rears calipers could do more than they actually are doing in this instance.

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