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**TobyB** · 09-14-2015, 07:11 PM

My solution was to remove ABS from racecar, and use 318i master cylinder and bias valve. There. I've outed myself.

Yes, the E36 ABS recirculates fluid to some extent. It's how you get fresh fluid into
the system- tell it to open the valves, and run the pump.
At least over here...

hth,

t

**Bimmerman325i** · 09-14-2015, 09:45 PM

E36 ABS takes care of proportioning brake bias, pressure, and flow between front and rear brakes, as well as side to side (for 3-ch, fronts only).

A bias bar is not a great idea. The ABS unit needs equal pressure input from the MC, as the front and rear brakes run through different pumps internally.

The ABS unit modulates deceleration and lockup by varying brake pressure from full brake pressure to zero pressure (by closing the valves), many times a second. This system depends on a constant input pressure to both halves of the unit.

A bias bar is a whole lot of work for no gain; if you want to be able to set f/r brake bias, remove ABS. Otherwise, use full stock system.

The ABS also absolutely recirculates brake fluid, one byproduct of which is how you bleed the master cylinder from the factory.

**catboy** · 09-15-2015, 05:08 AM

Guys, firstly thanks for the replies.. I'm trying to get my head around the system as much as possible so I appreciate your inputs.
Apologies if some of the replies below sound a bit odd - i'm not trying to have an argument, I'm just trying to explain my situation, my current understanding, and respond to your comments so we might have a discussion and figure this out between us..

My solution was to remove ABS from racecar, and use 318i master cylinder and bias valve. There. I've outed myself. Yes, the E36 ABS recirculates fluid to some extent. It's how you get fresh fluid into. the system- tell it to open the valves, and run the pump.
At least over here...

I have a bit of an issue removing ABS because the car is going to run wet and dry (im in the UK so some might say mostly wet!). The ABS is worth a lot of time under those conditions here (around 2-3sec a lap around somewhere like donington park, in wet conditions, with the gp-n ecu mapping in my experience in other cars)

E36 ABS takes care of proportioning brake bias, pressure, and flow between front and rear brakes, as well as side to side (for 3-ch, fronts only). A bias bar is not a great idea. The ABS unit needs equal pressure input from the MC, as the front and rear brakes run through different pumps internally.

there's only 1 pump, but there are different valves controlling front (in), front left (out), front right (out), rear (in), and rear (out). on the 4 line system there's an r/l and r/r out in place of the single rear (out)

the standard master cylinder(s) actually give 2 different pressures, one for front and one for rear.. this is achieved with one m/c but two different size bores internally and 2 outlets, one for front (in) and one for rear (in) at the ABS pump. The same pump and ECU numbers can be seen to be used across a variety of models where there are different size master cylinder pistons (f/r), so I don't believe this to be the case - the pump will not be getting the same pressures on any vehicle, and the pressures (f vs. f, or r vs. r, aswell as f vs. r) can be different from vehicle to vehicle also.. prime example, pre 1995 325i vs. M3 where the master cylinder sizes are different, and even the f vs. r are different ratios from one car to another

The ABS unit modulates deceleration and lockup by varying brake pressure from full brake pressure to zero pressure (by closing the valves), many times a second. This system depends on a constant input pressure to both halves of the unit

I get the basics of the operation, except if the above was true I don't understand what the pump is for? in the situation as you describe above the max brake pressure would be the pedal input pressure from the driver and so the pump is effectively redundant, unless it actually pressurises the pedal 1/2 of the system?
If the system only relied on the pedal pressure then as it bled pressure away from the calipers to unlock the brakes the brake pedal would effectively "ratchet" towards the floor as the oil was pushed from m/c to caliper?

If the pump "pumped it back up again" that might work? And in that case I guess the ABS reservoir would run dry and the pedal/mc reservoirs would overflow based on my original question/concern?

A bias bar is a whole lot of work for no gain; if you want to be able to set f/r brake bias, remove ABS. Otherwise, use full stock system. The ABS also absolutely recirculates brake fluid, one byproduct of which is how you bleed the master cylinder from the factory.

I will run without ABS in dry conditions, and just use the bias bar - there is a benefit to me for this, and the bias pedal box is in the car already, so no work there. even with the ABS in place and functioning there is a benefit though, as you can use more braking on the rear (wet) or the front (dry) prior to lock-up.. with the gp n abs software its looking at relative wheel speeds, so without a bias bar you're effectively leaving braking performance on the table on one or the other axle..

In terms of recirc, this is the bit im trying to get my head around - which oil goes where.. I am not convinced there's as much interaction on an e36 between the brakes and the abs as there is on a modern car - i think that if you bleed the brakes without bleeding the ABS then the brakes will be fine until the abs is triggered, which leads me to believe the ABS pump is little more than a "straight through" manifold block until its actually triggered?

As I said, I'm not trying to argue, just trying to have a discussion to figure out how this works without spilling loads of brake fluid or putting the car in a wall! I appreciate a lot of these internet discussions descend into bickering, and I don't want that - I don't do a lot of posting on forums specifically to avoid it.. I also appreciate ABS is a subject that's historically been ripe for opinion!

TobyB - 100% understand why you ditched ABS, not sure I'm ready to do that yet (also it raced with ABS "in period" so im a bit restricted if I want to run in classes which require originality

Bimmerman325i - 100% understand why you suggest ditching it either or running with a standard m/c and ABS too, I just want to get my head around it completely and understand for myself how the systems (hydr. vs. ABS) interact

**catboy** · 09-15-2015, 05:44 AM

bit more info I've come across during my reading at lunch..

system works as a normal non-abs system when ABS is not triggered - I need to read more into brake bias-ing within ABS pump specific to the 3-line e36 system

when it is triggered, the ABS pump/valves do the following..

reduce pressure from the pedal to the caliper by bleeding fluid off
hold pressure by doing nothing
increase pressure by supplimenting the pedal pressure with the pump

..it seems like the reservoir for the pump is literally that - it just supplies the additional fluid, or a space for returning fluid - during the above operations

Also I found the following interesting (for me atleast - perhaps I need to get out more) information..

slip ratio = wheel speed / vehicle speed (not sure I completely agree with the following maths but the concept is correct)

when slip ratio = 0% vehicle speed=wheel speed
when slip ratio = 100% wheels are completely locked
optimal braking occurs between 10 and 20% slip ratio
ABS attempts to achieve 10-20% slip ratio for optimal braking

I also found out that on newer systems (with DSC) when the front wheel(s) lock and are being controlled by ABS, the pump will increase rear brake-line pressure to reduce stopping distance.. This I believe is what people refer to when they talk about the ABS controlling brake bias, but I'm not sure whether this is the case on the older systems without DSC / ASC / Traction control.

I need to find out some more about the 3-line ABS only system (referred to as ABS-ES on the ECU and in the part system) as I have a feeling this relies wholly on the master cylinder sizing for bias and the car does not attempt to change this or alter it based on braking conditions

ACTION ITEMS FOR ME:

- Does ABS-ES control bias in any way?

- Does ABS operation cause movement of fluid from reservoir to reservoir (in a system where the standard single res. is gone) - I don't think so, not enough to matter on track, but will test

Guess I might have to risk spilling some brake fluid after all ;)

**catboy** · 09-15-2015, 10:41 AM

for future reference, ABS-ES (pre '95 abs only system) controls brake pressure proportioning to the rear only. This means pressure in to the rear circuit is reduced by a fixed percentage, front always receives 100% - they're equal to around 25bar (ie rear brakes receive 100% of the rear line pressure) then a reduction of around 30% is applied to the rear only - its not a bias of % (front vs rear) modification. This is a "fixed proportioning valve" ie the point at which proportioning takes place is fixed at 25bar as is the %

from what I can find you should not fit a proportioning valve after the ABS unit - its possible, but this is like fitting two proportioning valves in series, and you end up with double-proportioning.. eg if you set the second valve at 50bar and 80% proportioning

0-25bar = 100%
26-50bar = 70% (30% reduction)
51bar upwards = 80% x 70%

If the second valve is under the 25bar "fixed proportioning valve" setting then you get a reduction there, so for example if its set at 20% reduction at 10bar, you get..

0-10bar = 100%
10-25bar = 80%
25bar up = 70% x 80% (about 55%)

This is all a massive headache to work out, and its not worth anything..

On a standard car, the rear receives a different pressure than the front at 0-25bar based on the master cylinder sizes. Above 25bar, the rear has a larger reduction vs. the front due to the proportioning valve but the pressure in is still driven by mc size
A proper balance bar (between 2x master cylinders) effectively changes the master cylinder diameters relative to each other - this effects the pedal pressure going to front and rear circuits PRIOR to the ABS system, and so effects the input values.. you still get the 30% proportioning of this specific value to the rear above the 25bar "knee" value, but you have the ability to alter the value going in..

example..

balance bar positioned to front (ie lower rear pressure)
1000N pedal pressure = 100bar * 0.7 = 70 bar rear brake circuit pressure
1000N pedal pressure = 200bar * 1 = 200 bar front brake circuit pressure

balance bar positioned to the rear (ie higher rear pressure)
1000N pedal pressure = 200bar * 0.7 = 140bar rear brake circuit pressure
1000N pedal pressure = 100bar * 1 = 100bar front brake circuit pressure

these are extreme examples, but to try and prove the point (for me to understand). I think this is correct (theory) and so using a bias pedal box still gives benefits for f/r balance and adjustment for different tracks and conditions and doesn't screw with the proportioning valve in the ABS system like putting a proportioning valve on the rear line would..
If someone can confirm my understanding is correct that would be awesome - assuming it is correct, I just need to figure out about the reservoir :)

So the rules appear to be..

Bias pedal box + abs is ok
Bias pedal box - abs is ok assuming mc sizes are correctly calculated
Bias pedal box + proportioning valve - abs is ok
Bias pedal box + prop valve + abs is not ok as proportioning can get screwed up badly
Standard pedal box - abs with no additional proportioning valve = potentially weird depending on mc sizes

..what I have is..

Correct sized mc's w.bias pedal box + abs with no external prop valve which means I can run with or without ABS switched on provided I leave abs installed
Should I remove abs completely then I might need to reassess rear mc size or fit an adjustable proportioning valve in the rear line

Hope this is useful to someone - definitely helped me! I will report back on reservoirs!

**TobyB** · 09-15-2015, 03:35 PM

when slip ratio = 0% vehicle speed=wheel speed
when slip ratio = 100% wheels are completely locked
optimal braking occurs between 10 and 20% slip ratio
ABS attempts to achieve 10-20% slip ratio for optimal braking

Yeah. And that's where we ran into real problems with early ABS-
R-comps (racing tires(tyres)) have a lower optimal slip percentage.

So the ABS gets confused, and DRY ABS- activated braking distances go up, unpredictably.
More modern ABS figures out what the hell's going on, compensates, and you're fine.

In the wet, I won't argue- almost any ABS that isn't going into 'ice' mode
will save you lap time.

And if I had to choose between ABS and a proper dual- master balance bar, I'd
take the balance bar any day. And it rains like crazy up here, too...

I'd agree- as long as the biasing system's purely mechanical, not hydraulic, it
should get along with ABS just fine.

And yeah, hell, try it and see. One or two ABS activations won't pump ALL your fluid
out onto the track- just enough to spin you! (heh)

As to your observation about how the system uses the pump when ABS is 'pretty active'-
to me, it FEELS (and yes, by this, I mean, feels in the pedal, not "I think" as the vernacular has become)
like the system is doing a dance with supply- the overall pedal height DOES move,
as in, it sinks as I push harder into ABS, but the pump is also pushing back as I modulate
out of it- the pedal 'kicks back' up more than it does when ABS is not active.

It's fun stuff, and if you play with it on test days and such, it's not going to kill you.
Might spin you... but probably not.

Keep us updated!
t

**Wh33lhop** · 09-15-2015, 07:54 PM

Originally posted by catboy View Post

system works as a normal non-abs system when ABS is not triggered

Yes.

when it is triggered, the ABS pump/valves do the following..

reduce pressure from the pedal to the caliper by bleeding fluid off
hold pressure by doing nothing
increase pressure by supplimenting the pedal pressure with the pump

Partially correct. There are basically three states of operation for each channel:

1. Normal/pressure increase. This is where your pedal is directly connected to the caliper.
2. Pressure hold. Your pedal is isolated from the caliper which becomes a sealed line with a constant pressure.
3. Pressure decrease. Your pedal is still isolated from the brake circuit, and pressure is bled off of the circuit into the accumulator/reservoir.

The pump is not used to increase brake pressure--that's up to your foot. This early-style ABS will only limit the amount of brake pressure, never increase it. The pump is merely there to empty the reservoir back into the portion of the line before the ABS. When you feel the pedal "pushing back" against your foot, that is the pump forcing the fluid in the accumulator back into the line between the pedal and the ABS unit.

Here's a cool video to illustrate the principle of operation--start it at 0:40

Also note the one-way valve between the solenoid and the pedal side line. If you reduce braking pressure at your foot beyond line pressure at any point during operation, this will equalize pressures and resort to state #1.

..it seems like the reservoir for the pump is literally that - it just supplies the additional fluid, or a space for returning fluid - during the above operations

Yes, it's just an accumulator.

I also found out that on newer systems (with DSC) when the front wheel(s) lock and are being controlled by ABS, the pump will increase rear brake-line pressure to reduce stopping distance.. This I believe is what people refer to when they talk about the ABS controlling brake bias, but I'm not sure whether this is the case on the older systems without DSC / ASC / Traction control.

Yes. This is a feature of DSC-era ABS (MK20/MK60), if it feels you are panic braking it will also increase pressure to ABS threshold for you.

That said, I believe there is a proportioning valve in E36 ABS as when it fails, the cars will lock the rear wheels before the fronts. You seem to have found this in the next post.

- Does ABS operation cause movement of fluid from reservoir to reservoir (in a system where the standard single res. is gone)

Good forward thinking. You can slap dual masters into an ABS-equipped E30 without issue (I've driven one and abused its ABS) so I wouldn't worry about it.

Originally posted by TobyB View Post

Yeah. And that's where we ran into real problems with early ABS-
R-comps (racing tires(tyres)) have a lower optimal slip percentage.

So the ABS gets confused, and DRY ABS- activated braking distances go up, unpredictably.
More modern ABS figures out what the hell's going on, compensates, and you're fine.

[long winded nerd alert] Yes, rudimentary ABS like in the E30 and early E36 doesn't adapt very well to conditions. I've noticed when I have race pads and all seasons on the car, the ABS will tend to increase stopping distances; sometimes dramatically (scary). Since the system is calibrated for stock pads, when you put high-mu pads it will bleed off way too much pressure when it activates since it operates based on line pressure.. which is proportionally much smaller for a given deceleration with high-mu pads. So every psi bled off with race pads will be equivalent to 2-3 times the brake force of that with street pads, and it winds up bleeding off way more than it needs to, whenever you hit a little bump (stiff suspension) it will freak out and bleed a ton of pressure off.

Interestingly, I've noticed that on a smooth track with r-comps this isn't nearly as much of an issue, since there are no bumps and you have way more grip. I haven't once felt the need to pull the ABS fuse on track, which was unexpected. But as soon as you hit bumps it gets annoying as it's slow to react.

As to your observation about how the system uses the pump when ABS is 'pretty active'-
to me, it FEELS (and yes, by this, I mean, feels in the pedal, not "I think" as the vernacular has become)
like the system is doing a dance with supply- the overall pedal height DOES move,
as in, it sinks as I push harder into ABS, but the pump is also pushing back as I modulate
out of it- the pedal 'kicks back' up more than it does when ABS is not active.

I had fun with this awhile back when I thought I needed to bleed my ABS and wired up momentary switch to each of the solenoids. Activate the solenoids and the pedal freezes in place, pretty cool. :)

**catboy** · 09-16-2015, 04:15 AM

awesome info thanks guys! So I guess over time if the pump is "refilling" the brake line between the pedal and the ABS unit, the ABS reservoir will empty into the brake reservoirs. Given the tiny amounts of fluid though, this is going to take a while, so practically I could get away with having independent reservoirs per m/c and a twin reservoir for the ABS.. I may look into joining the three together however I expect this to be more work than makes sense as my ABS pump is in the passenger footwell and my m/c's are in the engine bay infront of the driver..

I get what you're saying re: r-comps and high mu pads which is why I've specifically gone for the 3-line system from the euro m3 (im in Europe so was easy). I think this doesn't have "ice mode" or similar, and so shouldn't have a complete melt-down if you exceed its parameters! Also you can have the ecu remapped - mine is done with the gp-n / factory race car software which was designed specifically for slick tyres and sticky pads. im not 100% sure what this does, however I think it relies only on wheel speed and, the thresholds for slip ratio are reprogrammed as you mentioined

However its done, I've driven a couple of cars with this software and its night and day on track vs. standard. Its also nice to have as a safety net when its cold and damp first thing on an autumn track day! Looking forward to getting my car back in one piece so I can try it out.. :)

**Axxe** · 09-16-2015, 07:14 AM

How does one get this software onto their ABS ECU? What piece of hardware do you need to support it? This is for a 94 325iS, have 97m3 ABS pump available and 96 ABS ECU.

**Wh33lhop** · 09-16-2015, 10:10 AM

Originally posted by catboy View Post

awesome info thanks guys! So I guess over time if the pump is "refilling" the brake line between the pedal and the ABS unit, the ABS reservoir will empty into the brake reservoirs. Given the tiny amounts of fluid though, this is going to take a while, so practically I could get away with having independent reservoirs per m/c and a twin reservoir for the ABS.. I may look into joining the three together however I expect this to be more work than makes sense as my ABS pump is in the passenger footwell and my m/c's are in the engine bay infront of the driver..

I get what you're saying re: r-comps and high mu pads which is why I've specifically gone for the 3-line system from the euro m3 (im in Europe so was easy). I think this doesn't have "ice mode" or similar, and so shouldn't have a complete melt-down if you exceed its parameters! Also you can have the ecu remapped - mine is done with the gp-n / factory race car software which was designed specifically for slick tyres and sticky pads. im not 100% sure what this does, however I think it relies only on wheel speed and, the thresholds for slip ratio are reprogrammed as you mentioined

However its done, I've driven a couple of cars with this software and its night and day on track vs. standard. Its also nice to have as a safety net when its cold and damp first thing on an autumn track day! Looking forward to getting my car back in one piece so I can try it out.. :)

Yeah, if nothing else it's nice to know you're not going to flat spot your high dollar r-comps :) I don't know much about the euro M3 ABS, but it's sweet that you can get it remapped. I get frustrated with the stock primitive ABS and aggressive pads on the street, but on the bright side it's more motivation to stay out of ABS and brake smoothly.

Originally posted by Axxe View Post

How does one get this software onto their ABS ECU? What piece of hardware do you need to support it? This is for a 94 325iS, have 97m3 ABS pump available and 96 ABS ECU.

FYI- early (through 95) E36s have 3-channel ABS, and late (96+) E36 have 4-channel so you will have to add another hard line and convert your chassis to 4-channel if you want to use late model ABS hardware in an early model E36. It's doable, just not a cake walk. Bimmerman325i I think just completed a 4-channel conversion to his 95 M3, so he can tell you more about it if you're serious about doing this.

**Axxe** · 09-16-2015, 10:59 AM

Originally posted by Wh33lhop View Post

FYI- early (through 95) E36s have 3-channel ABS, and late (96+) E36 have 4-channel so you will have to add another hard line and convert your chassis to 4-channel if you want to use late model ABS hardware in an early model E36. It's doable, just not a cake walk. Bimmerman325i I think just completed a 4-channel conversion to his 95 M3, so he can tell you more about it if you're serious about doing this.

Not going to bother for this car, just curious about the mapping. With that said, can the 3-channel E36 system be adapted to fit an e30?

**Wh33lhop** · 09-16-2015, 04:03 PM

Originally posted by Axxe View Post

Not going to bother for this car, just curious about the mapping. With that said, can the 3-channel E36 system be adapted to fit an e30?

I would say it's likely. Both E36 and E30 use VR sensors, it may very well just bolt up or possibly (unlikely but I don't know for sure) even be the same unit. I don't know if the euro m3 units are different either, but people do e36 5-lug swaps and retain E30 ABS, so I would guess the reverse is possible quite easily.

Fun fact, the e30 iX has a 4 channel ABS, though not the M3. Don't know if it's any better with r-comps but I'd guess due to the all-weather nature of the iX, it's more adaptable to a broad range of conditions, so it's likely.

**catboy** · 09-17-2015, 03:20 AM

I have a feeling the "abs only" (labelled ABS-ES on the ECU) 3 line system fitted pre-1995 was the same on the Euro M3 and 325i as their US equivalents, but i'm not 100% positive on this so you may need to do some research on realoem or similar to check part numbers - everywhere I've read about it its referred to as Euro M3 but unsure if its because US M3's has ABS+ASC or something as standard across the board?

Either way, what you need is a 3-line pump as below..

..which has 5 ports - 2x in from m/c (top left in photo) and 3x out (bottom in photo, for fl / fr / rear). You also need to know the german words for front, rear, left and right to plumb it in!
The correct ABS ecu looks like this..

..there is another version of this which looks exactly the same but doesn't have the cooling fins on the side - this is the same part number and works fine; not sure what its from (mabe an e38 or something?)
There's another "green label ECU" which looks like this..

..and that is no good! its for the 318 I think which has a different system and can not be remapped. It may also be the same one used in the e30? Im not sure..

I have heard any 3 line pump will work fine, however I can not confirm this and as the parts are cheap and readily available it makes sense to get the "right parts" which are..

34521138219 - ECU
34511162291 - Pump

..there's also another pump which I think ends '94 which I know works too, however it doesn't show up in realOEM at all. This is a more common pump and much easier to find, which makes me think this is the original factory fit pump which was no serviced, and the '91 pump is the field service/replacement unit (hence rarer and harder to locate)

In terms of fitting it to other cars, this system of the "euro m3" pump and ecu can be run as a standalone and fitted to a multitude of other vehicles - I've found reference to people using this in e30's, e46's, even e90 touring cars in Europe, inplace of the very expensive bosch motorsport abs systems. I've also seen threads where people have fitted it to things like TVR's, Ultima's and Nobles and other high performance kit cars / production which didn't have factory ABS
The wiring information is in the early e36 electrical troubleshooting manuals, and basically it requires power/ground/ignition, wheel speed sensor inputs, and some additional wires if you want to connect it to the diagnostic connector, abs light on the dash, etc.. I can't comment on compatibility with e30's, but I think I read somewhere that the e30 has the same number of "teeth" on the wheel speed sensor rings as the e36, so it might be fine, or work with just a swap of the sensors..

The 4-line e36 and e46 system can be adapted, however I think there's much more interaction between ECU and DME so that's a more complicated to do and I'm not sure there's a massive benefit vs. a remapped 3-line system.. I also don't think the 4-line system can be remapped, however that's just based on me not finding anyone who can do it during my research

For 3-line remaps, I only know of one person who can do this and he's a) in the UK, and b) pretty damn hard to pin down as he's always busy doing more important things such as mapping race cars for (very) high level European motorsport teams! If anyone is serious about getting an ABS ecu remapped drop me a PM and we can discuss details - pay particular attention to the word SERIOUS, and be pre-warned its not cheap (although a lot cheaper than buying a gp-n ecu or a bosch motorsport system! )

hope some of that helps someone :)

ben

**nando** · 09-17-2015, 06:02 AM

Originally posted by Wh33lhop View Post

I would say it's likely. Both E36 and E30 use VR sensors, it may very well just bolt up or possibly (unlikely but I don't know for sure) even be the same unit. I don't know if the euro m3 units are different either, but people do e36 5-lug swaps and retain E30 ABS, so I would guess the reverse is possible quite easily.

Fun fact, the e30 iX has a 4 channel ABS, though not the M3. Don't know if it's any better with r-comps but I'd guess due to the all-weather nature of the iX, it's more adaptable to a broad range of conditions, so it's likely.

it's actually still 3 a channel pump. but the ix has 4 wheel sensors plus the deceleration switch.

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e36 ABS Standalone w/dual master cylinders - reservoir question

e36 ABS Standalone w/dual master cylinders - reservoir question

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