jayh

I did a shake down with the car at the track this weekend. I have the ABS disabled. I found under hard braking the front brakes would lock very easily. No matter how i tried to modulate the brakes they would lock.
Anyone ever run without the ABS system and have this problem?

Adax

iTrader: (2)

Yes. I'm chasing other brake problems so I am hesitant to attribute it all to the ABS absence but modulation prior to ABS engagement is harder without ABS and fronts lock easily.

John V

iTrader: (1)

ABS systems in modern cars are one of the ways the manufacturers control brake bias.

Why would you disable the ABS?

Adax

iTrader: (2)

Because I am allowed to be 56 pounds lighter without it.

John V

iTrader: (1)

56 pounds? That sounds like a really bad tradeoff.

Adax

iTrader: (2)

Not really. Very little time is gained under braking and most of us can threshold brake as well as ABS. Maybe a different story in the rain but baring a lock-up there's not much ABS advantage when it comes to lap times. 56 pounds though (2% of total weight) pays off in corners, under acceleration, and under braking so pretty much everywhere. When races are usually won by less than a car length, it matters.

John V

iTrader: (1)

I'm having trouble resolving your two statements. On one hand, you can threshold brake as well as in a car with ABS. On the other hand, you're apparently having problems with the fronts locking.

I'd postulate that some drivers can brake as effectively without ABS as they can with ABS... but that none can do so in every braking zone, on every lap. One mistake is all it takes to throw that miniscule (56 pounds) advantage out the window.

jayh

Sorry for the confusion But I originally posted the problem with the front brakes locking up. Then Adax also posted a reply.
To answer your question why I was running with the ABS disabled I damaged the rear sensor cable when replacing the rear clip. I thought I'd give it a try to see how it ran without the ABS but without the ABS system the hard braking was extremely bias toward the front. For me, I would need to install a proportioning valve or fix the ABS system. I'm inclined toward fixing the ABS. The weight is not an issue with me.

Adax

iTrader: (2)

Sorry, for the latter post I should have said "in general". True, if I can't get front bias worked out otherwise it will be better to keep ABS. If it gets sorted, I'd rather give up the weight. One of the many things in "development".

AC

ASH8

56 pounds, over 20 kg, you are dreaming mate, try about 18 pounds.
ABS Module, bit of wiring, and a tiny bit more of hydraulic line is not close to 25 KG.

Adax

iTrader: (2)

No, the rules in the class I race the car in permit a 2% weight reduction if the ABS is disabled.

Sorry for all the confusion I've caused.

AC

RE-Vision

Without the ABS you just have single channel brakes. RX8s have Electronic Brake Force Distribution so you'd need to add a proportioning valve.

trackjunkie

i feel like my car has too much rear brake bias with abs on. it feels like the rear abs kicks on when i threshold brake. im running DTC60 front and DTC30 rear

John V

iTrader: (1)

I would hope the ABS would engage when you threshold brake. That's kind of the point.

trackjunkie

I'm saying it's too much rear bias, so if the abs wasn't working, the rear would lock up and I wouldn't be able to threshold brake without flat spotting rear tires.

John V

iTrader: (1)

Try DTC-15 or -5 if they still sell those?

Mr. Pockets

I agree. You're trading a maybe a couple tenths of performance for consistency under braking and the margin of safety ABS provides.

There seems to be some suggestion in this thread that the ABS system does a fair bit of proportioning front to rear. I wasn't aware of that, if true.

TeamRX8

iTrader: (25)

Well just to summarize, the braking system from the factory has no mechanical brake bias other than the master cylinder and caliper piston sizing with the ABS system electronically providing the rear bias (called EBD, see attachment at bottom of this post) as dictated by the wheel sensors. It’s one of the reasons I generally recommend using the same brake pads front and rear; the ABS system will just work against that to tune any forced bias out, at least within it’s adjustment capability range. So you can’t just disable it and expect to have proper bias. Other changes are required to compensate for removing the programmed electronic balance.

trackjunkie

it seems like the rx8 asb engage ice mode much easier than in my Evo. so far in 5 races with the rx8, i've hit ice mode 3 times during race. i tracked the Evo for 8 years and only engaged ice mode once, when i hit the brakes while the tires was still off the ground from a jump.

problem with using same compound front and rear and relying on abs to control the bias is that you still have an uneven bias during non threshold braking. like during trail braking where you're not on the brake at full force, so the abs is not engaging to control the bias. and you'll end up with too much rear bias.

on my Evo, i had too much rear bias for my driving style, that i end up using high performance street pads for rear and dtc70 for front. on my rx8, im now running dtc60 front and hp plus rear, and it still have too much rear bias. i can feel the rear abs engaging before the front. and during trail braking, when the rear abs comes on, the rear will snap out unpredictably.

Adax

iTrader: (2)

Is your abs working with the Adaptronic ECU? if so, what ABS controller are you using? Mine will not work with either manual/stabilty control or auto/stability control ABS controllers. Plan to contact them Monday.

AC

heavy85

ABS related ... I've searched and cannot find definitive info just a bunch of conflicting back and forth. I just built an engine swapped RX8 for time trial and hill climbs and I want the ABS to work. I've read that the ABS can run stand alone all it needs is power and wheel speeds. Wheel I have power and wheel speeds but the ABS wont work. I'm running no factory Mazda PCM or modules at all except for the ABS unit. It was a DSC car but the DSC sensors have been removed. I did keep the stock dash harness intact although I dont use it for anything but plugged it in and at least got an ABS light. Just ordered a fancy ABS code reader so hopefully that will help.

The only fact I know is a member here broke his steering angle sensor and it disabled DSC/TCS but kept ABS alive. This is why I removed the DSC sensors and wiring but kept the ABS sensors.

I've read it has to have signal from the PCM to work and I've read it doesn't. Dont know where else to look and so am asking if anyone has successfully run the factory ABS as a stand alone system?

Thanks
Cameron

ASH8

From a US Racing prospective TEAM (Mark) is the man who knows.

I am pretty sure you are chasing your tail trying to change or disable/modify Brake Bias rear or front, unless you can FFF0 FFFX, code write save etc with the correct dump/write interface.
ABS was and is standard equipment on All RX-8's sold, only some early models had DSC as 'feature option' that then became mandatory standard equipment from about 2005 MY onwards.

Mazda still uses Ford IDS system, but is now separated for the past 4 years.
But the issue as I see it is how do you prevent the PCM/ECU from hand-shaking/communicating with ABS, IC, SRS AB, DSC modules as they all speak to each other and hold event data, writes and holds DTC's and if events are serious enough can or will put car ignition into limp home mode, when warnings are ignored, max speed is limited to a crawl.

I could be wrong but I am pretty sure to 'control' all of these modules effectively you have to abort/remove All of the OEM Mazda equipment and then install a proven aftermarket control system,

ASH8

Just throwing this out and not new but would 'inserting' a brake fluid restricting orifice devise on the front hydraulic brake lines create the rear brake bias desire you want, without any major electronic module changes, and would it be race legal?

heavy85

Blackwell

I am running a haltech standalone and am having the same issue with no abs. Unfortunately the abs computer seems to run the speedo on the factory dash. I have plenty of spare outputs I could use to trigger to abs module if its that easy. I feel like they were talking over the CAN bus though. The haltech has CAN support for NC mx-5's so that is running my tacho and temp gauge, I still get an abs light and the dsc squiggles.