Improving the ABS

[Brianmoooore]

Can't see any obvious reason why an E36 ABS setup wouldn't work with the signals from E30 hubs, although if the frequency generated varies by much, then the comments above would apply.
Should be possible to add frequency multiplier/dividers to the ABS sensor lines.

[suzie650]

so what exactly are you trying to change about the abs system? the % of slip the wheels are allowed to have under braking before the abs cuts in and takes over??
the e36 system will be essentially the same, in the way it deals with you blindly clamping your foot on the brake as a cat runs out into the road.
m3 might be programmed to allow more slip before it cuts in? but not much, cus bmw still want you to have as much steering capability under braking as in a 325i.........
later systems are able to chatter the brakes in and out faster but still come in at around the same detected slip %.......
(...)

The abs on an e30 is mapped for tyres/wheels/brakes it left the factory with. I.E, the maximum deceleration allowed by the abs is lower than the maximal deceleration possible with a modified car. I'd like the abs to perform with these modified bits, and if possible be mapped a bit more aggressively as well

Can't see any obvious reason why an E36 ABS setup wouldn't work with the signals from E30 hubs, although if the frequency generated varies by much, then the comments above would apply.
Should be possible to add frequency multiplier/dividers to the ABS sensor lines.

Good idea with the frequency dividers. Also goes in Turbo-Brown's direction, and might avoid stripping the hub if that's the way I end up going.
I'll have to find a picture of E30M3 and E36 abs triggers...

[sean_318i]

I fitted a switch to the abs on my 325i touring it cuts the current that switches on the abs relay so its a small current and used an extra rear window heater switch on the dash to switch it off. To switch it back on you must turn off the ignition for about three seconds (can be done while car is moving) and turn it back on again. ABS light comes on on dash to warn that its off. e36 sensors are different to e30 ones they are much longer and made of plastic.

[suzie650]

Thanks for that sean.
I am most likely to put a switch anyway (would allow some testing as well), but would like the abs to work better when switched on.
IIRC, if you switch the ABS off after starting the car, you don't have to switch the car off to turn it back on again. Can you confirm?

and turning the ignition off while driving ain't a good idea...

[HairyScreech]

long shot and i havent realy considered this very much but i know the late 90s fors abs system is a stand alone unit that uses a 4 way split and has braked traction controll below 30mph, self contained unit and are cheep as feck.

[suzie650]

Do you mean ford abs? As fors doesn't return anything on google...

[ShakeyC]

Mapping ABS

All it does is compare wheel speed against other wheels, when braking if one slows faster than the rest the ABS pumps that caliper until wheel speed is matched left to right, back to front. This is only complicated by traction control systems integrated into a single ECU. Think you mean the traction threshold delay which is the trigger for the ABS to kick in, increase the threshold longer the wheels are allowed to lock under braking before the ABS pump is triggered. BMW ABS is renowned for not kicking in too early, any later think even the best driver will be in trouble.

[sean_318i]

On my car the feed to the abs relay only needs to be broken for a second to turn the abs off and to turn it back on the ignition has to be turned off for three seconds. This could be due to the way I wired it but it works fine for me and is rarely switched off anyway. I only fitted it because if I spin while drifting a roundabout I roll slowly backwards into the kerb, if my wheels are locked I will keep going sideways in a similar direction to the one I was traveling in.

[murran]

Mapping ABS

All it does is compare wheel speed against other wheels, when braking if one slows faster than the rest the ABS pumps that caliper until wheel speed is matched left to right, back to front. This is only complicated by traction control systems integrated into a single ECU. Think you mean the traction threshold delay which is the trigger for the ABS to kick in, increase the threshold longer the wheels are allowed to lock under braking before the ABS pump is triggered. BMW ABS is renowned for not kicking in too early, any later think even the best driver will be in trouble.

i was just thinking this today.....
youve got the system over complicated in your head......
e30/e36 systems are basic..... no traction, esp. acc. sensors. theres really nothing to reprogramme except the % of slip the wheels are allowed compared to the other wheels before the abs cuts in. (for example your doing 100 mph and you brake hard the wheel begins to lock the % of allowed slip is 20% then the wheel can effectivly be doing 80 mph compared to the others before the abs pump starts doing its stuff on that brake, if you get me?) the system just picks up the wheel speeds from the 4 sensors, if when you brake too hard a wheel locks the sensor picks it up cus the other wheels are turning, the valve for that wheel in the abs pump will pump the brake in and out several times a second to keep it at the said 20% slip programmed into the ecu.......
dont know where you get the idea that the system can only work with the original wheels tyres brakes etc. as this is wrong! all the system knows is this slip %!! you could put 135 section tyres on the car, the system will work exactly the same, just with less available grip the abs will come in much sooner cus the 20% slip threshold is met despite their being less retardation of the cars speed.
upgrade the tyres and brakes then the car will be able to retard its speed faster without aproaching the 20%.

ive no idea what the fukk i just waffled on about........ does it make any sence?

[suzie650]

Not quite...

The abs effectively "senses" the wheel speed, but what it does with this information is down to its mapping, where a lot of parameters go into. Weight transfer and maximum available grip (with stock tyres) to name the most important. Change this, and your abs is not on known territory anymore. Might not change a lot, but it's not ideal any more

Then comes the fact that, as mentioned by ShackeyC, I might like to change the triggering threshold (although if all the parameters are corrected in the first place, this shouldn't be too important, as the BMW factory threshold is probably not bad. Just nice when you go on the track and like placing your car on the brakes.

Then, as I will be using bigger caliper piston diameter, comes the problem that what the abs does might not have the effect it wanted. If for instance the abs calculates that to "unlock" your wheel, it needs to release the pressure during 5ms, which works perfectly with stock calipers, this will not work any more as the same pressure decrease with a bigger sized piston means that more fluid needs to be evacuated and that the pressure might have to be released for 7ms. (obviously, the values are just examples). More annoying is if you go for smaller size pistons, as the release will be too important and you will not even stay on the maximal braking set in the abs.

Even old systems are more complicated than just a speed comparison and max speed difference allowed setup.

This page might expain it a bit better than my bad english. Look under tech info and abs.

[dannyboy759]

On my M3 I put a switch in the centre consol, one of the window cut switches with the markings rubbed off that turned the abs off when i wanted to.
The reason for doing this was i found that with the Group N pads I had the abs cut in far to soon and was completely useless.
The only way around this was to get a Group N abs ecu but it just wasnt worth the 3000 odd euros so the kill switch worked quite well.

[murran]

Not quite...

The abs effectively "senses" the wheel speed, but what it does with this information is down to its mapping, where a lot of parameters go into. Weight transfer and maximum available grip (with stock tyres) to name the most important. Change this, and your abs is not on known territory anymore. Might not change a lot, but it's not ideal any more

Then comes the fact that, as mentioned by ShackeyC, I might like to change the triggering threshold (although if all the parameters are corrected in the first place, this shouldn't be too important, as the BMW factory threshold is probably not bad. Just nice when you go on the track and like placing your car on the brakes.

Then, as I will be using bigger caliper piston diameter, comes the problem that what the abs does might not have the effect it wanted. If for instance the abs calculates that to "unlock" your wheel, it needs to release the pressure during 5ms, which works perfectly with stock calipers, this will not work any more as the same pressure decrease with a bigger sized piston means that more fluid needs to be evacuated and that the pressure might have to be released for 7ms. (obviously, the values are just examples). More annoying is if you go for smaller size pistons, as the release will be too important and you will not even stay on the maximal braking set in the abs.

Even old systems are more complicated than just a speed comparison and max speed difference allowed setup.

This page might expain it a bit better than my bad english. Look under tech info and abs.

ah i see. so have you experinced these issues yourself?

my boss runs an audi rs4 its superchipped, modified wastegates milltek system with high flow cats, fully adjustable fk suspention etc. for the ring weekenders he goes to.
standard untouched abs esp system runs the standard 18 inch wheels with road legal track tyres. but brake wise its got brembo 6 pot porsche gt3 front calipers and 4 pot brembo ones on the back with a separate little hand brake one too.
not a problem. abs works fine........ i know its not the same system but just an example.

[suzie650]

piston size might be close, or the system might be different... Not very knowledgeable about VAG cars... apart from my mkII golf sh*tter.

More modern abs don't have fixed mue curves, but they're worked out by the sensors (long. and lat. g-force, gyroscopic, ...) Basically, they do it through the esp. These systems are great when you disconnect the "touchy" traction control.

Funnily enough, I know that when a very experienced mechanic (Ken' Brown, in Scotland) put a PCCB system onto a 996 turbo that only had "standard" 4 pot, he had to swap the abs ecu as well, as it wouldn't run properly on track. More than enough on the road though.

[suzie650]

On my M3 I put a switch in the centre consol, one of the window cut switches with the markings rubbed off that turned the abs off when i wanted to.
The reason for doing this was i found that with the Group N pads I had the abs cut in far to soon and was completely useless.
The only way around this was to get a Group N abs ecu but it just wasnt worth the 3000 odd euros so the kill switch worked quite well.

I was chasing that Gruppe A / Gruppe N abs as well, but found the same price problem as you.
The latest Bosch Motorsport ABS is the M4... 4000 Euro, and you go nowhere if you don't know how to map it...

[HairyScreech]

yes i did mean ford and i normaly proof read my posts as well.