jbotstein1

I have the Wilwood 4-pot kit and rear rotors, pads and lines. I got it all in a Spugen group buy about a year ago. Anyways, I noticed that when stepping on the brakes fairly hard, but not slamming on them, the ABS would kick in prematurely. My understanding of ABS is that at a certain amount of brake pressure, the ABS will kick in to avoid skidding. With bigger calipers and steel braided lines wouldn't the pressure to activate ABS come from less brake pedal effort?? I removed my ABS fuse. Is that stupid. I feel that the car does stop better cause I can step harder on the pedal without locking up, whereas ABS would have kicked in otherwise. What do y'all think?? Did that even make sense??
Jonathan

jbotstein1

guess not

Cubs2k

ABS works by measuring wheel rotation not pressure. There is a magentic sensor on the wheel hub that measures wheel rotation. I think that the Wilwoods are just very powerful and are probably grabby, thats why the ABS kicks in.

slipstream444

I don't think it's as simple as that. ABS does measure wheel speed, but also senses a speed differential above a certain threshold between wheels, and/or all out wheel lockup in order to activate the ABS. The parameters and code written for the computer is actually quite complex.

If you research the Willwood 4 puck calipers on this site, you'll actually find they have a lower clamping force than the stock calipers ... due to the fact the overall piston area is slightly less than stock. The Willwood calipers are pressure cast (what Willwood claims to be "forged") and not true forged, which allows for more caliper distortion at high temps. Since the force is distributed over a greater area, there's a greater propensity for caliper distortion. This, coupled with the unknown variables involving your rotors, pads, and tires ... makes it difficult to determine the best approach to solving your problem.

There are several things that may be causing your problems and it's going to take a lot of work on your part to sort it out.
I think the possible sources may be (without amplifying info from you): possible caliper flex, overly aggressive pads (assuming - you didn't say), weak rubber (assuming again - what size and type/brand of tire are you using?), system in need of a good bleed to eliminate clamping force variability and the resultant wheel speed variation between corners, possibly worn tires, and/or any combination of the above (and more). The fact your ABS is activating prematurely is a sign there's a problem somewhere in the system. If your ABS light hasn't come on, there's a problem with your brake/wheel/tire setup. Remember - they all work together and a change in one affects them all.

I personally spent the extra cash and bought the Pinnacle brake system from Rick's. There's a HUGE difference in braking performance (even with some pesky residual air in the system), and while my stopping distances have measured a solid 30-35% shorter than stock (consistent), I have to absolutely smash the brakes to get the ABS upset. With a few more bleeds ... the system will be perfect. I use Hawk HPS pads with very good results overall (fade, modulation, control, wear, dust, and noise). They're the most balanced pad I've tried to date - considering all variables for street/mild track use. I have 225/45-17s GY F1GSD3s fronts and 255/24/17 rears. The brakes stay ice cold even after mashing on them at 120+ MPH on repeated passes. The calipers are ultra light and true forged and the modulation is as precise as laser surgery. The best $2900 I've spent on the car. They guarantee I can go deeper in the corners than any other brake system out there.

The Willwood system is lighter and much better looking than stock, and a bargain at $1000 (as far as brakes go), but the research I've seen points to premature failure and average performance on the Willwood 4 puck system. That alone may be your issue.

Good luck

Nobody

Interesting info, slipstream. I want to believe it, but my grounding in reality prevents such fantasy--you're braking in distances that are 65% of stock and your brakes are ice cold--and you can't figure out how to get air out of your calipers? 65% of stock wouldn't put you in F1 territory, but god damn, you'd be outbraking every car known to consumerdom by a considerable margin.

RACER

The size of the piston does not necessarily dictate overall clamping force but dictates the amount of sensitivity or feel in the brake pedal. For example, the larger the piston, the more flow and less pressure you have, hence less brake pedal feel. This means you would have to press harder on the brake pedal. The smaller the piston, the less flow and more pressure you will have, hence more feel and sensitivity in the brake pedal. This means you won't have to press as hard on the brake pedal.

RACER

[QUOTE=slipstream444,Oct 5 2004, 08:03 PM]while my stopping distances have measured a solid 30-35% shorter than stock (consistent), I have to absolutely smash the brakes to get the ABS upset.

slipstream444

Ice cold was a right out exaggeration ... I know - I know (I figured people would realize it was a figure of speach).
However, when you can touch the rotor surface less than 7 minutes (bare hands ... and I don't have lepracy) after romping on them at 118 MPH and 116 MPH within a couple of minutes of each other (120 MPH was another slight exaggeration), that tells me the brakes are shedding the energy extremely efficiently and quickly. The speeds were distance limited. One thing that helped is the fact the dust shields have been removed increasing airflow.

slipstream444

The total surface area of the caliper's pistons (on the inside of the caliper) relative to the master cylinders determines the force applied ... i.e. the total clamping force. It's the priciple that works in every hydraulic system. Since the Willwood system doesn't change the master cylinder or booster, those components are held constant when computing clamping force. Therefore, if the total surface area of the four pistons in the Willwood system are less than the stock caliper, the total clamping force is less ... that's a fact. There are a lot of good articles and books that outline this. The formulas I used came right from my old fluid dynamics text. It's a rather simple principle.

slipstream444

[QUOTE=RACER,Oct 6 2004, 01:53 AM] The tires play a major role in an automobile's braking system.