CANbus speed limiter hack

Ryan Holton · **Posted:** Wed May 07, 2014 12:55 pm

Vincent Keene wrote:

What? Cash's 6 is NOT AWD.

Ohhh I thought it was a Mazdaspeed6 :stick:

Richard Casto · **Posted:** Thu May 08, 2014 9:32 am

Cash Davidson wrote:

Richard Casto wrote:

First option is to intercept the signal off each wheel and cap the output that is sent to the ABS ECU to show the car not going any faster than 120 MPH. Basically read in the sensor pulses and create an adjusted output.

I had exactly the same idea - kind of a pulse converter - take in two pulses, output one. It would take some work, but I think this is doable.

Cash,

I had another thought. I looked at the other thread and saw the mention of removing every other tooth on the ABS sensor. My concern with that approach is that such a large adjustment to the pulses per second it might have a significant negative effect on ABS performance (if you want ABS to continue to work)??? Another idea is a custom ABS toothed wheel.

It did some quick Googling and it looks like the 03 Mazda6 has the ABS reluctor ring on the hub and based upon the photos, it looks like it might be pressed on. This is similar to what I have found on my old Honda Civic in that the ring was press fit onto the stub axle that is part of the CV joint. And on the Honda, that ring can be removed/pressed back on. I don't know the tooth count, but I did see some other replacement reluctor rings for other Mazdas having 44 teeth. I don't know what the top speed of your car is without the limiter, but lets say it is 150 MPH. 120/150 = 0.8 Apply that same factor to the toothed reluctor ring and you get 44 * 0.8 = 35.2. So a 35 toothed reluctor ring should provide the about the same number of pulses per second at 150 MPH that a 44 tooth would at 120 MPH. In effect you are getting a 0.8 correction factor for your speedometer (actually 0.795 for a 35 toothed wheel). 150 will indicate 119 MPH. And the difference may not be enough to cause wonkyness of the ABS (if that even would exist).

You would just get a hold of a spare Mazda 6 reluctor ring, measure it and have someone machine the custom ones. There is a potential that Mazda might have different tooth count versions in their inventory, but likely they have standardized on a specific tooth count. Another idea is that someone (other than Mazda) might make a ring that has the right tooth count but with a roughly similar outer ring diameter. So by a combination of machining an adapter, or minor machine work on the ring itself (likely much less machine work than a totally custom ring), you might be able to use that ring on the Mazda6. Depending upon the outer ring diameter, you might have to adjust the sensor location as well.

Richard

Cash Davidson · **Posted:** Thu May 08, 2014 2:48 pm

Richard,
We need to quit thinking alike.

I had done the same thing - looking at other ABS rings of similar dia but different number of teeth. Yes they are just pressed on. I have an extra set of rear ones and will check to see if they are different from the front. I'll be putting a clutch in soon, so that would be the time to change the rings if I can find alternates with fewer teeth.
Thanks!
Cash

Richard Casto · **Posted:** Thu May 08, 2014 4:05 pm

I found this UK company....

http://www.reluctorrings.com/

They say they make custom rings.

I did a quick scan of some of what they offer (OEM style replacements). I didn't see any with low tooth counts. I suspect you may not find any. I would expect that higher tooth counts improves speed measurement accuracy as lower speeds (approaching locking).

I also wonder what would happen if you just remove a specific number of teeth (such as nine in my example above). You could space them out on the ring (remove about every 4th or 5th tooth), but I can envision measurement methods by the ABS ECU that might not be happy with a non uniform tooth pattern. Or it might work just fine.

Regardless... Post back here if/when you solve this.

Richard

JamesShort · **Posted:** Thu May 08, 2014 4:12 pm

Here is a solution:

Cash Davidson · **Posted:** Thu May 08, 2014 4:34 pm

JamesShort wrote:

Here is a solution:

Don't laugh! I did the math and 29" dia tires would do it. :lol:

Of course I'd have to remove the fenders and quarters. With my terrible gear ratios, I'd need 4 miles to get up to speed, but eventually I'd get over 120. :sing:

Cash Davidson · **Posted:** Wed Aug 26, 2015 8:39 am

Update:

I think I finally got this working last night. Lets just say there are a bunch of wires going to that controller. Details to come!

Cash

Cash Davidson · **Posted:** Fri Aug 28, 2015 8:48 pm

So harken back to last spring when we were talking about defeating the speed limiter:

I have finally gotten around to actually doing it.

DISCLAIMER: This is shared for entertainment purposes only. I do not advise you to modify these systems. I am not responsible for you burning up control modules, making your car unusable or you crashing your car and dying.

Here's what I did - keeping in mind that my intuition nearly makes up for my poor judgement. :lol:

I unplugged the 28-pin connector to the ABS controller.

I stripped back the harness covering so I could get to the wiring:

After much testing and analysis, I determined there is one wire that when interrupted, the car will continue to accelerate past 120mph. Here is the pin and the wire with blue tape:

I cut the wire and extend the two ends into the drivers compartment:

I ran the wires thru a normally closed pushbutton mounted on the dead pedal:

Re-install the dead pedal in the car:

How it works (theoretically):
As I approach 100mph, I step on the pushbutton (breaking the circuit to the ABS).
The speedometer drops to zero, the ABS and TCS lights come on.
The car continues to accelerate past 120mph.
As I lift from the throttle, I also release the pushbutton.
The speedo snaps back to life and the ABS/TCS lights go out.

It seems to work in the driveway, but I couldn't get quite to 120mph. Who wants to be my instructor at VIR in a couple weeks when I test this? :mrgreen:

Thats it! Wadaya think??

Cash

Vincent Keene · **Posted:** Fri Aug 28, 2015 9:13 pm

Sounds like it will work, but I wonder if you can devise another electronic means to engage the switch at the predetermined point? If you could get it to work with the final gear only, a RPM window switch would do the trick.

FrancisChan · **Posted:** Fri Aug 28, 2015 9:26 pm

Does the car have a cruise control disable switch on the brake pedal?

Maybe that and a GPS speed switch (http://hmbe.com.au/products/gps-speed-switch-2) could create an automatic system that disables the ABS/TC when approaching 120mph and depressing the brake pedal then overrides the GPS switch and brings the ABS back online?

Chad Culbertson · **Posted:** Fri Aug 28, 2015 10:01 pm

This reminds me of a floor mounted high beam switch for some reason. Those things were so awesome.

George Bright · **Posted:** Sat Aug 29, 2015 10:56 am

Now to help you get to 120 MPH.

Add another switch.

FrancisChan · **Posted:** Sat Aug 29, 2015 11:04 am

I heard somewhere that you'd need 2 of the big bottles to break 140mph...

Scott Johnson · **Posted:** Sun Aug 30, 2015 1:53 pm

Optical switch on the speedo. As the needle hits a certain speed it stops the ABS signal, when you hit the brakes and the speedo sweeps beach by the ABS is turned back on.

Alternatively, put the switch under the gas pedal, how often are you NOT full throttle at over 120? Floor it and ABS (with speed limiter) is shut off. Get off throttle and the ABS comes back on.

Cash Davidson · **Posted:** Sun Aug 30, 2015 5:38 pm

Scott Johnson wrote:

Alternatively, put the switch under the gas pedal, how often are you NOT full throttle at over 120? Floor it and ABS (with speed limiter) is shut off. Get off throttle and the ABS comes back on.

I was gonna do this, but I'm at WOT quite a bit when I'm no where near 120mph - I didn't want to be cycling the ABS/TCS controller on and off constantly.

George - the car could definitely use some help getting to 120. If I get a good run out of hogpen, I just hit the limiter a second before I lift for T1. The back stretch is longer and I usually get to the limiter as I crest the hill.

To Francis' suggestion about the brake pedal disengage - you really want the controller back up and working BEFORE you step on the brake.

Thanks for all the input!! We'll give this a try in a couple weeks and report back!

Cash

THSCC Forums

CANbus speed limiter hack

Who is online