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Thread: ABS Research, Mazdaspeed LSD Compatibility

  1. #1
    Comp Engineering Student Riot_Polizei's Avatar

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    ABS Research, Mazdaspeed LSD Compatibility

    Hello guys,

    Lately, I've been looking into some wiring and set-up differences between a Protege5's open differenatial speedometer-gear transmission and a Mazdaspeed Protege's LSD ABS speed-sensor transmission. Ultimately, I'm trying to see if it's possible to retain the speedometer's functionality without having to install a speedometer gear in a dropped-in Mazdaspeed transmission. Theoretically, this could be achieved by some ABS speed sensors, but we'll see why it's probably not that simple.

    The big difference of concern is how the speed is relayed to the ECU. We know that non-ABS Proteges utilized a speedometer gear on the differential, and that ABS-equipped Proteges had magnetic speed sensors within the wheel hubs. Thus, anyone who wants to drop in a Mazdaspeed tranny into a P5 (such as myself) would completely lose the speedometer without installing the speed gear in the Mazdaspeed transmission.

    However, all Protege5 hubs have bolts and holes for ABS speed sensors, regardless of whether they have the ABS hydraulic/control unit. A proper speed sensor will drop right in, which presents an opportunity to install a Mazdaspeed LSD without needing to rip it open and install the speedo gear. There's definitely some hope, but the hard part is indeed getting the speed sensors to talk to the ECU without some sort of ABS control unit.

    Take a look at this diagram:



    As we can see, all wheel speed sensors are hooked up directly to the control unit, which only through it may the speed data be sent to the ECU (PCM in the diagram). This is further supported by the fact that the data is purely in the form of sinusoidal waves, which depending upon their descriptive variables, activate ABS at various wheels and times.

    Example:



    So, even if you bundled all the ABS speed sensor wires together and soldered them into the respective port on the ECU, I don't think the car would know what to do without the speed gear.
    What do you think guys? Do you think there's gotta be another way around having to rip open the Mazdaspeed transmission and dropping in the speedo ring?

    Surely, there's gotta be some sort of aftermarket speed sending-unit that could interpret the data from each hub speed sensor.
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  2. #2
    Registered Member STudMUffin1177's Avatar

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    Wow you went deep on this, I'm not too good with computers and all that crap but could you just swap out the ecu from a p5 that came with ABS? If you install all the wheel speed sensors and all the appropriate wiring and such wouldn't the 'new' ecu read everything as normal? I never realized how tricky ABS systems were, hopefully someone has some good input.
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  3. #3
    The Diagram Dude pcb's Avatar

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    I think you might be out of luck. Completely !!

    It's sounding like you can't even install a speedo gear in a mazdaspeed diff.
    There's no spot for the gear ??

    https://www.mazdas247.com/forum/show...eedometer-gear
    The Diagram Dude

  4. #4
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    Is retrofitting possible? sure. is it cost and time prohibitive? definitely.

    In a vehicle (not just Mazda, but most all automobile manufacturers work about the same way) the 4 wheel speed sensors talk to the ABS ECU. Speaking generically, as I don't 100% know exactly how the MS system works (and really don't feel like taking the time to research specifics)...

    If 1 speed sensor is bad/missing the whole system goes into failsafe and the dash lights up like a christmas tree. If any part of the system is not present or malfunctioning, the system goes into failsafe. The ABS ECU pulses the brakes to help the vehicle regain traction so you would also need to replace all of the brake lines and components as well, because If the ECU sees the vehicle stopping but does not see the pressure increase in brake lines, again it goes into failsafe and you've got christmas tree syndrome. This is also why it usually requires a factory scan tool to bleed the brakes in one of these cars.

    The ABS ECU talks via data to the engine ECU and the instrument cluster. For speed signal specifically, most will talk directly to the instrument cluster, and the cluster talk to the ECU but the "order of reporting" may vary.


    The only way you will be able to make this work correctly, the way it is supposed to work, would be to have a donor vehicle and swap everything over. brake lines, ECU, wiring harness, speed sensors, etc. There's a lot more to it than just adding some wheel speed sensors and calling it a day.

    At that rate you may as well just buy a mazdaspeed and call it a day. While it is POSSIBLE to retrofit the entire ABS system over to a P5 to make it work, it's not a task I would personally want to undertake considering all of the time and expense to make it happen. And the reliability of a retrofitted ABS system, just doesn't sound like a good idea to me from the standpoint of safety. I wouldn't want to be driving that car, and I certainly wouldn't feel right about ever selling it to someone else when it comes time to buy a new car. I don't know that it would technically even be legal to sell it in many jurisdictions...
    Last edited by pb4ugotobed; 06-14-2019 at 10:22 AM.

  5. #5
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by pb4ugotobed View Post

    The ABS ECU talks via data to the engine ECU and the instrument cluster. For speed signal specifically, most will talk directly to the instrument cluster, and the cluster talk to the ECU but the "order of reporting" may vary....
    That's true but our car can also receive speed info from a speedo gear in the transmission that goes directly to the engine ECU then the ECU sends speed info to the cluster.

    Roit is just trying to get speed info to his ECU but not convert his car to ABS.

    From that thread I posted and a link within it, it sounds like the LSD is problematic especially if driven hard and it needs to be welded inside to provide more reliability.

    You may want to just keep the tranny you've got and spare yourself the headache and expense of an LSD.
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  6. #6
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    Quote Originally Posted by pcb View Post
    That's true but our car can also receive speed info from a speedo gear in the transmission that goes directly to the engine ECU then the ECU sends speed info to the cluster.

    Roit is just trying to get speed info to his ECU but not convert his car to ABS.

    From that thread I posted and a link within it, it sounds like the LSD is problematic especially if driven hard and it needs to be welded inside to provide more reliability.

    You may want to just keep the tranny you've got and spare yourself the headache and expense of an LSD.
    Understood, but looking at the diagrams above, "Q" is the speed sense output from the ABS ECU and goes directly to the cluster. The cluster would then output that signal to the engine ECU and cruise control ECU's. Either way, the speed signal is processed within the ABS ECU and output from there. Same as I described above.

    But..

    If there is nowhere to put the gear for a speedo signal in the trans, then he's got no choice but to add the wheel speed sensors, which would also require adding everything else in the ABS system as well to make those work. Even if you didn't want to add the ABS it wouldn't work because the ABS ECU talks to the speed sensors, and if you don't have EVERYTHING hooked up, the ABS ECU will be in failsafe and the engine ECU will know it as well and you'll have more codes than you can count.

    I'm pretty sure the main wiring harness in the vehicle would also have to be changed, as I am sure none of the wiring is present either.

    If you insist on LSD, then I would look into swapping internal parts from the differential instead of the whole assembly, if they're that similar you could bolt in the other trans, then they're probably common across both platforms.

  7. #7
    The Diagram Dude pcb's Avatar

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    Some guys swaped in the LSD and everything worked fine because they had ABS.

    Other guys swapped in an LSD and everything worked fine except the speedometer wouldn't work until the gear was installed in the transmission.

    But in that thread it looks like all mazdaspeeds had ABS so there wasn't even a space to install the speedo gear in the transmission ??

    I'm almost positive that our ECU accepts speed info from either the speedo gear or the ABS headunit and it recognizes which is being input and works accordingly.

    Apparently the speed info from the wheel speed sensors is more accurate so the car uses that info if it's available.
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  8. #8
    The Diagram Dude pcb's Avatar

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    Some inputs and outputs are bypassed depending on where the speed info is coming from.



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    like I said, I don't know the specifics about this car, and really don't feel like researching it since it's info i'll never need or use lol. so was speaking generically amongst all cars.

    Either way, the wheel speed sensors won't interface directly with the cluster. They need the ABS ECU to work. And without everything in the entire ABS system connected, the ABS ECU won't work properly either since it would be in failsafe mode. so my original post still stands to be accurate. unless he switches everything and converts to ABS, there really is no way of making a wheel speed sensors from an ABS car work in a non-ABS car, even if the only thing you want out of it is to make the speedometer work.

  10. #10
    The Diagram Dude pcb's Avatar

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    I found these two different speed signals.



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  11. #11
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by pb4ugotobed View Post
    Either way, the wheel speed sensors won't interface directly with the cluster. They need the ABS ECU to work. And without everything in the entire ABS system connected, the ABS ECU won't work properly either since it would be in failsafe mode. so my original post still stands to be accurate. unless he switches everything and converts to ABS, there really is no way of making a wheel speed sensors from an ABS car work in a non-ABS car, even if the only thing you want out of it is to make the speedometer work.
    Agreed.

    What he may "possibly" be able to do is instsall a single wheel speed sensor and toothed gear and run that info through some sort of "emulator" device to convert it into a signal that mimicks the speedo gear signal.

    I don't know if that's possible though ??
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  12. #12
    The Diagram Dude pcb's Avatar

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    @Riot.

    It's sounding like you'll need to open up your differential anyway to have it welded, so you could install your speedo gear at that time, if you can actually install that gear in the mazdaspeed transmission ?
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  13. #13
    Comp Engineering Student Riot_Polizei's Avatar

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    Oh yeah, ultimately, putting in the speedo gear in a mazdaspeed transmission is ultimately the only way to get speed readings on a non-abs car. Gotta get it machined on the LSD, unless you get an aftermarket LSD with the gear option.

    I'm still looking into bypassing a complete ABS ECU/ABS control unit swap-in, though. No breakthrough's going to happen anytime soon, but if those speed sensors send information in the form of oscillations, there's definitely a way to perhaps find or program a microcontroller to interpret this data. If one can do that, then all that remains is finding a way to get this info to speak to the ECU.

    With the way this research and data sounds, I might try to make this my senior design project lol
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  14. #14
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Riot_Polizei View Post

    I'm still looking into bypassing a complete ABS ECU/ABS control unit swap-in, though....
    there's definitely a way to perhaps find or program a microcontroller to interpret this data.


    With the way this research and data sounds, I might try to make this my senior design project lol
    That sounds kool !!

    It should'nt be that hard to do and it's right up your alley.

    I found this and it looks like the sensor ring has about 40 teeth on it, so about 40 pulses per rotation of the axle.
    And it is a sine wave.

    I don't know how many pulses you would get from the speedo gear but I assume about 2-10 pulses per rotation of the axle.

    So your home built controller would receive 4-20 pulses to give out one pulse. (roughlyish)

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  15. #15
    The Diagram Dude pcb's Avatar

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    I was just thinking...

    I don't know if you've changed/upgraded your ECU or not but it may not be able to receive speed data from either an ABS or speedo gear input ??

    I'm 98% sure the factory ECU works with both and works with either standard or automatic transmissions.
    The different systems just plug in differently and the ECU knows how to deal with it all.
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