Abs braking systems

[Graeme Stebbing]

Hi Guys, I am still beavering away on my project with the brake /upright change, I have a set of Supra uprights, that have the ABS toothed wheel mounted behind the drive flange, it has 96 teeth, and I have the original Soarer upright, that has it's toothed wheel behind the axel shaft it has 48 teeth I would prefer to use the Supra upright as the steering arm is 25mm shorter than the Soarer version.
Does anyone know what the change from a 48 to 96 toothed wheel will do to the ABS the pitch and size of the teeth are the same, it's just the Supra has double the number.
Does the ABS computer just expect to see a pulse at a constant rate, so when the wheel locks up under braking the ABS ecu just pulses the brake peddle until the pulse returns from the wheel, so the number of teeth is not important or will I have to install a pulse divider circuit to fool the computer into thinking it only has 48 teeth as original, I have followed out the wiring diagram and the ABS ecu seems to take a speed signal from the cluster so I wonder if the ecu will be confused by the extra teeth, when it is taking a reference speed from the cluster. I have spent hours trawling the net for an answer without luck, does anyone have any knowledge or experience on this subject.

Best Regards
Lambo

 

[Randy V]

Graeme,

Unless there is one tooth or gap that s a different length than all the others, I don't believe the computer would know the difference between the two 48/96 wheels.. Now where it would make a difference would be a different number of teeth from side to side and possibly front to rear..

 

[Graeme Stebbing]

Thanks for the quick reply Randy, I have been reading up on ABS systems in Toyotas, the car does have separate sensors on each of the back wheels, I suspect the ECU does not count the pulses just, knows when they stop this is an interesting pdf from Toyota but still not that much wiser what would happen through. Lots of good info on this site as to how Toyota stuff actually works.
http://www.autoshop101.com/forms/brake09.pdf

Best Regards
Graeme

 

[David]

It gets wheel speed from the sensor. So it knows how many teeth it should have and the wheel diameter. It'll also work out the speed difference front to back so will be very confused. It also knows the wheel inertia, car weight, brake response times (and fluid amounts) along with the quickest possible time the car can stop. So you're really going to mess with it's programming by sticking better brakes and wider stickier tyres on. IMO you're better off getting a very simplistic ABS, a very advanced programmable one (eg Bosch M4) or leaving it out altogether.

 

[Roark_John]

Hi Guys, I am still beavering away on my project with the brake /upright change, I have a set of Supra uprights, that have the ABS toothed wheel mounted behind the drive flange, it has 96 teeth, and I have the original Soarer upright, that has it's toothed wheel behind the axel shaft it has 48 teeth I would prefer to use the Supra upright as the steering arm is 25mm shorter than the Soarer version.
Does anyone know what the change from a 48 to 96 toothed wheel will do to the ABS the pitch and size of the teeth are the same, it's just the Supra has double the number.
Does the ABS computer just expect to see a pulse at a constant rate, so when the wheel locks up under braking the ABS ecu just pulses the brake peddle until the pulse returns from the wheel, so the number of teeth is not important or will I have to install a pulse divider circuit to fool the computer into thinking it only has 48 teeth as original, I have followed out the wiring diagram and the ABS ecu seems to take a speed signal from the cluster so I wonder if the ecu will be confused by the extra teeth, when it is taking a reference speed from the cluster. I have spent hours trawling the net for an answer without luck, does anyone have any knowledge or experience on this subject.

Best Regards
Lambo

Can you provide photos of your uprights? If the bearings are the same size, just swap the drive flanges from your Soarer uprights to your Supra uprights, then you've got the "right" toothed wheels on your uprights.

Are you using the ABS system from the Soarer? I'd be sorely tempted to use the MR-S (3rd Gen) system as it's already setup for the proper mid-engine weight distribution (47/53) and approximate weight threshold (23-2400lbs) for a replica.

 

[Roark_John]

It gets wheel speed from the sensor. So it knows how many teeth it should have and the wheel diameter. It'll also work out the speed difference front to back so will be very confused. It also knows the wheel inertia, car weight, brake response times (and fluid amounts) along with the quickest possible time the car can stop. So you're really going to mess with it's programming by sticking better brakes and wider stickier tyres on. IMO you're better off getting a very simplistic ABS, a very advanced programmable one (eg Bosch M4) or leaving it out altogether.

This is erroneous on many counts and has been covered elsewhere.

If actual wheel/tire size were dictated by programming, then there would be no aftermarket upgrades for rims & tires. Since almost every style of car in the world has been modified, you'd see warranty denials for this & you don't. It's simply a non-issue.

Same goes for uprated brakes. Along with weight increases/decreases...which varies based on intent. "Thumping" stereo systems add alot of weight...as do multiple passengers and heavy loads. Stripped-down "track" cars don't suddenly lose their ABS capability - unless some eager owner has "light-weighted" the wiring harness & pump.

The important issue is weight bias and approximate weight threshold. A system that is geared towards a front weight bias is going to be less-than-ideal on a rear weight biased vehicle...and vice versa. But as long as the system is seeing the inputs it needs (based on operational requirements) then it will still function as programmed. This includes systems that have been "upgraded" with larger rotors, bigger calipers, and different bore master cylinders.

 

[Graeme Stebbing]

Hi guys thanks for the replies, I have included some pics the first are the Supra the second the Soarer, the two uprights over all measure within a few mm of each other, but the biggest difference is where they put the stub axel relative to the kpi viewed from the inside, the Supra axel centre is about 15mm in front of the kpi, and the Soarer is 10mm behind, so given the bottom and top suspension arms stay in the same place this would have a major effect on the wheelbase, this is not a problem through as the bottom and top arm can be moved to correct that.
I originally measured from the centre of the axel to the pivot on the steering arm and the Soarer measured 140 mm and the Supra 110mm, but I wasn't till I put the two side by side to take the photos, I realised the distance from the kpi to the steering arm pivot was identical at 130mm so there is no advantage to use the Supra upright to get quicker steering because relative to the kpi they are identical. so I think I will make life simple and just use the Soarer upright. I just wish I knew why the axel is in a different position.

WYLD, Your suggestion to use the MR-s is a good one, it makes sense with the weight distribution, as I wrecked an entire Soarer and never throw anything away lol, I now need to find out the type of abs in a Soarer relative to say an MR-S I have a service manual for the MR-S and Soarer and the picture of the MR-S abs sensor is a bit unclear, it looks like it is similar to the Supra in that the sensor appears to point towards the outside of the wheel and not sideways at the rear of the stub axel as on the Soarer, and so perhaps a large toothed wheel, I need to find a MR2 that has the toothed wheel behind the centre of the axel and of course with 48 teeth. I don’t think my chances are good, and I thought building this car was going to be easy, and one thing you really don’t want to get wrong is brakes.

best regards
Graeme

 

[Cliff Beer]

This is erroneous on many counts and has been covered elsewhere.

If actual wheel/tire size were dictated by programming, then there would be no aftermarket upgrades for rims & tires. Since almost every style of car in the world has been modified, you'd see warranty denials for this & you don't. It's simply a non-issue.

Not so. Far from it.

The programming is static in that the ecu is programmed to read a relative rate of rotation between all four wheels based upon relative rolling distances associated with known and programmed tire sizing front/rear. If that relative tire sizing (ie. rolling distance...) is changed by using different aftermarket wheels and tires then the ECU starts to think there is wheel slip and then you're in for a whole world of trouble simply operating the vehicle going down the road. And when you get to the dealer to complain about the ABS operation they'll look at the non-standard/OEM wheel and tire sizing and tell you there ain't warranty coverage for that. Happens all the time. Ask any service manager at a new car dealership.

Of course, it's possible to maintain the right relative ratio with non-standard wheels and tires. However, the margin of error is very small, in the neighborhood of 2-3% typically with most ABS systems and most aftermarket wheel/tire combinations go beyond this limit.

 

[Damian]

Cliff I can say that in my personal experience you are wrong. I took an e46 M3 down to 2100lbs from 3400lbs and went from 18" stock heavy rims to 19" LIGHTWEIGHT rims that were over an inch wider just in the front not to mention the Alcon BBK (15" front and 14" rear) which all in with the rims weighed less than the oem tires and rims alone. NEVER NOT ONCE EVER did I have any issues withthe ABS either on or off track NOT ONCE!!!!!! Now I did do my best to keep the circumference of the tire as close as possible BUT with a lowered car on super agressive coilovers (750lbs front 1100lbs rear springs) again there was never any issue.
Now my wife is a service advisor at a dealership and when I told her about this thread she darn near LOL. A lot of misinformation going on here. Lets just say her shop has NEVER turned down warranty work because of bigger rims and wider tires EVER!! Might just be the back woods dealerships you go to but around these parts that has never been heard of. Again guys I'm just sepaking about my own real world experience with a car I built. Maybe I was the exception to the rule but than again every race preped M3 in Orlando (admitedly mine was one of the most radical) acording to your sumation should never be able to run the ABS and well lets just say that there are PLENTY of BMW's down here that must be exceptions as well.

 

[Damian]

Also lets not forget the guy that put the ABS from a vette into his 69 camaro which was posted in the other thread who seems to have it working just fine although he does turn it off on the track as it RARELY activates early but it is on an on off switch that he pushes when on or off tack. On teh street and the point of this thread it works as if were in the original car. Again it must be another exception. Here is the artricle: http://www.hotrod.com/techarticles/hrdp_1108_abs_for_hot_rods/viewall.html

Here is an an example of where theory doesn't match reality:" It is theoretically possible that high-friction compound brake pads could cause wheel lockup before the EBCM pump generates enough pressure to prevent skidding, but in the real world many stock-class road racers are running race pads without serious issues." Again theory and reality are two very different things


Read more: http://www.hotrod.com/techarticles/hrdp_1108_abs_for_hot_rods/viewall.html#ixzz2VNTqTn2k

 

[David]

Did you actually read the article you linked to?

It doesn't "work as if it was in the original car", what a stupid statement. When driving normally it doesn't appear to make things worse would be a better statement.

Yes it works to a certain extent but still has issues enough to have to turn it off and there is no back to back testing to see what difference it makes. Does the ABS actually work?
Does it actually shorten brake distances or increase them?

Also part of that article is is crap as the ABS ECU doesn't "predicts and eliminates brake lockup using an algorithm based on the brake system’s downstream (post-EBCM) fluid volume.", it predicts brake lockup by monitoring wheel speeds and detecting a wheel slowing faster than it (thinks) is physically possible, the reason the downstream fluid volume is essential is because the ECU needs to know how much pressure to release to remove enough pressure off the brakes to allow the wheel to speed up again. It does take into account the brake fluid pressure though.

But anyway, it still mentions all the reasons for not just picking any random ABS ECU

Currently the EBCM can’t be reprogrammed. You’ll need to find a donor car with similar overall weight, front/rear weight distribution, center of gravity, roll rate, and wheelbase.

Yet despite that and using half of the donor car it still doesn't work properly.

As for the M3, that is a very special case that (depending on spec) actually comes with a special ABS ecu that can cater for track use so it's a pointless example. That it *does* come with a special ABS ECU should tell you everything you need to know.

By all means go ahead with playing but it should not be undertaken lightly and should be with a lot of care.

 

[David]

This is erroneous on many counts and has been covered elsewhere.

If actual wheel/tire size were dictated by programming, then there would be no aftermarket upgrades for rims & tires. Since almost every style of car in the world has been modified, you'd see warranty denials for this & you don't. It's simply a non-issue.

When you replace an Audi ABS ECU you have to program it with the wheel size/brake setup. If it doesn't matter why do they bother?

Same goes for uprated brakes. Along with weight increases/decreases...which varies based on intent. "Thumping" stereo systems add alot of weight...as do multiple passengers and heavy loads. Stripped-down "track" cars don't suddenly lose their ABS capability - unless some eager owner has "light-weighted" the wiring harness & pump.

It has an effect, the ABS ECU is incredibly robust in its programming to take care of that. Stripped down track cars are most likely to suffer but not by losing ABS, more not slowing down as much as they can.

The important issue is weight bias and approximate weight threshold. A system that is geared towards a front weight bias is going to be less-than-ideal on a rear weight biased vehicle...and vice versa. But as long as the system is seeing the inputs it needs (based on operational requirements) then it will still function as programmed. This includes systems that have been "upgraded" with larger rotors, bigger calipers, and different bore master cylinders.

Basically modern ABS does not 'just' detect a locked wheel, it constantly monitors wheel speed and if it detects that a wheel is decelerating faster than it believes is possible, well, well before it locks, it isolates that circuit (so to prevent pulsing in the pedal) and releases pressure, just enough (and this is where the brake characteristics comes in) to let the wheel re-accelerate up to the speed it feels it should be, once back up to speed it then re-pressurises that circuit (this is where the pump comes in) and un-isolates it. This then keeps going until a low limit (say something like 5mph) at which point it stops working.

The issue with transferring from one vehicle to another is that those parameters are screwed, even changing wheels/brakes will screw them up, Audi for example (and it's probably common across the VAG range) do it by having multiple configs stored in the ECU, if you replace the ABS ECU you have to log onto it and 'tell' it which model with which brake setup you have. This is the way for example the monster braked massive wheel RS4 can share an ABS ECU across the range with the S4 and plain cooking A4. In addition you have to 'pair' it with your powertrain ECU but that is for the DSC/TCS/eDif functions.

If your 'maximum possible deceleration' is wrong then it will either prevent the ABS from kicking in until its too late (so lots of locking up) or it will kick in too early (so restrict the maximum deceleration).

If your 'brake characteristics' are wrong then the ECU will either waste cycles bleeding additional pressure and adding additional pressure to either get the wheel to stop slowing down or to re-accelerate it, or it will over release pressure, let the wheel accelerate too much and have to re-apply pressure. Either way it will increase braking distance.

Now there *is* some learning going on with these systems but AFAIK its not 'saved' so has to be re-learnt every power on.

The ABS *will* work but it will not work well.

 

[Damian]

correction my car was 2900lbs.
now aside that it did work as per the original ON THE STREET. it only had infrequent interference (to early) on the track which prompted him to add the on off switch. short story unless under extreme track conditions the system worked as well as could be expected. your are correct though it didn't act 100% you got me ( but it came pretty damn close for a home brew system)