Problem:
My '99 M3 has always had a much softer brake pedal than any of the '95 M3s I've driven (even when using the same pads, etc.). The pads have always been well bedded (both street and track) and the fluid has been well bled. I was hoping that installing stainless lines might improve things but in the process of installing them I drained all the fluid out of the system. Now my pedal is unacceptably low and soft no matter how often I rebleed and probably indicates that my problem all along was air in the system that I can't bleed out using normal means.

Details:
I can pressure bleed each corner (at 10-15psi) for 15 seconds without any bubbles, but if I cycle the ASC by putting the car on jack stands in gear while running (thereby making the ASC apply brakes to the rear wheels to try to make them match the stopped front wheels) I can get a tiny bit of air out when I rebleed. After repeating that process several times I was able to bring the pedal up far enough to drive the car and even brake hard enough to get into ABS, but the pedal still goes almost to the floor with no feel. FWIW, I also tried having someone pump the pedal while bleeding but that made no difference (as expected).

Questions:
I have no use for ASC on my car. Can I just remove the hydraulics for it? Is there a DIY way of getting the air out from before the ASC pump (as cycling the ASC as above has yielded only limited improvement and I certainly don't have a BMW diagnostic computer)? Surely anyone who club races a '96-'99 M3 has gotten rid of the system or at least gotten around this problem. To clarify, this is unrelated to any talk of bleeding ABS (or anything relating to the ASC throttle body delete). Any help would be appreciated!!

As far as I know ASC is tied in with your ABS. You would have to change out your ABS pump if you want to get rid of ASC to a non-ASC pump.

Have you checked your master cyl.? This sounds a bit more like a master cyl problem than a ASC.. Course I could be completely wrong.


You can also find a mechanic with a MODiC comptuer and they can put the asc system into bleed mode btw.

The only way to properly bleed the ABS system is to open the valves with a tool like the BMW GT1 or an Autologic like I have. Typically you don't need to bleed the ABS. IMO take somewhere and have it done as I stated above.

E46Sev-

I'm sure it isn't the master cylinder especially since all my new problems occurred without even pumping the pedal once (I did pump it after the intial bleed out of desperation, but it didn't make a change).

folsom330ci-

As I said in my original post, I don't care about bleeding the ABS. I want to bleed the ASC. They may be interrelated by BMW's choosing, but they are theoretically completely independent.

I did find some useful info from a post back in 1998 (emphasis in bold is mine):

The difficulty with bleeding brakes on ABS and ASC+T equipped cars is that there
are passages in the control unit that the brake fluid doesn't pass through during
normal braking...

If you are careful not to let the fluid reservoir run dry, you can bleed the
brakes using conventional methods without any problems. The fluid remaining in
the valve body won't be changed...

For ABS cars without ASC+T, the ABS pump and valve body can be cycled by turning
on the ignition and pumping the brake pedal while a bleeder valve is open. This
needs to be done for both front wheels and one of the back wheels so that all
three channels of the ABS unit will be flushed.

I don't yet know of a non-MODIC workaround for ASC+T cars, but I do have a couple
of ideas.

If anybody knows how I could spend a day with a MODIC, I think that it would be
very easy to reverse engineer a method of cycling the ASC+T unit.

The first, and perhaps more elegant way, would be to capture the pattern of the
bit streams between the MODIC and the car while it's in its service mode, and
then programming a device to replicate the sequence.

The second, and perhaps more practical way, would be to disconnect the ASC+T
valve unit (it has a nice convenient round connector) from the car's wiring
harness and manually jumper in power to operate the pump and valves.

I already know that there are five pairs of wires going to the ASC+T valve unit.
One pair is power to the pump motor. Each of the other four pairs operates a
solenoid valve for each wheel. I think (but need to verify) that these operate
on straight 12V power.

The sequence might be as simple as supplying power to run the motor, and the
applying power to the valve for a wheel at the same time that wheel's bleeder
screw is open. It may or may not be necessary to pulse the valve. It might also
be important to limit the time the motor runs so that it doesn't overheat.

These questions could be easily answered by watching the signals applied to the
ASC+T valve unit while a MODIC was running the service routine.

This is a basic service requirement of our cars that for all practical purposes
BMW is trying to restrict our ability to perform. Even most independent service
shops are unable to implement this most basic of procedures. There is no good
reason (other than trying to monopolize the service business) that they needed to
make the use of a MODIC necessary to bleed the brakes.

I think that BMW is making a big mistake by ignoring the fact that a big part of
enthusiasts' involvement with their cars includes working on them. Since they
appear unwilling to help, we need to work around this problem.

So... anybody got a MODIC?

Brian Brown.
'96 318tiS w/ASC+T
BMWCCA #130878

Any advice other than 'bring it to the dealer' would be appreciated. No one has taken all the extra, useless junk (i.e. ASC) out of their '96 or later brake system?

No one has taken all the extra, useless junk (i.e. ASC) out of their '96 or later brake system?

Try posting on the forced induction forum. I know some cars remove the ASC throttle body to make room for supercharger installation.

When people delete their ASC all they are doing is removing the secondary throttle body. The hydraulic system is left intact...

BTW: The ABS unit is the ASC hydraulic unit. They are one in the same, the ASC module will modulate the rear brakes only. If that doesn't do the trick it will close the secondary throttle body.
It is not senseless junk, it serves a purpose. If you need to bleed your brake system then get it done correctly. It seems like your cutting off the head to cure the problem. You don't need to go to a dealer either anyone with the proper equipment can do it.

I've read that there is a way to cycle the ABS pump by shorting one of the ABS relay terminals. If you do a search on "ABS" and "relay" you should be able to find it.

folsom330ci-

You use the ASC system on your IP racecar?! If not, then it's just weight and complexity you don't need, right? When I've 'used' the ASC I thought it was mediocre at best and with the throttle body removed or the system manually turned off it's all just a bunch of useless componentry. Maybe I am asking how to cut off the head to solve the problem, but I'm also asking how to solve the problem without paying someone less competent $100 an hour to do a task I should be able to do myself. Surely you find all the extra junk on your IP car annoying compared to your SpecE30?

4ZPN-

The ASC system is actuated independently of the ABS and while air in the ABS will have no effect on braking without ABS, air in the ASC screws up normal braking. Cycling the ABS won't help - I want to cycle the ASC! Searches only turned up recommendations to go to a dealer (or anyone with a modic / dis system) and some mentions of the ABS relay which I believe is independent of the ASC.

Thanks for your ideas.

JD

folsom330ci-
4ZPN-

The ASC system is actuated independently of the ABS and while air in the ABS will have no effect on braking without ABS, air in the ASC screws up normal braking. Cycling the ABS won't help - I want to cycle the ASC! Searches only turned up recommendations to go to a dealer (or anyone with a modic / dis system) and some mentions of the ABS relay which I believe is independent of the ASC.

Thanks for your ideas.

JD


I was under the impression that the ASC works together with the ABS. I'll have to take a look under the hood again and trace the path of the brake lines.

I know that it seems like any air in the ABS system shouldn't affect the feel of the brakes when the ABS isn't engaged, but this has not been my experience. I also have the low brake pedal "bug", but right after activating the ABS numerous times the pedal height is back up to "normal" and the pedal is firmer. During ABS activation I can feel the pedal working it's way back up.

I know that it seems like any air in the ABS system shouldn't affect the feel of the brakes when the ABS isn't engaged, but this has not been my experience. I also have the low brake pedal "bug", but right after activating the ABS numerous times the pedal height is back up to "normal" and the pedal is firmer. During ABS activation I can feel the pedal working it's way back up.

Interesting - thanks. I haven't personally experienced the same thing - I've used tons of ABS at wet track days and the pedal never changes - but I'm at least glad to hear someone else is annoyed with their pedal height / feel.

The ABS hydraulic pump IS the ASC hydraulic pump. They are the SAME device. Bleeding the ABS/ASC pump is the same since it is the same device.

For now only the ASC secondary TB is removed from my IP car. When I get motivated I will be removing the entire ABS /ASC system but quite frankly it doesn't matter either way to me.

What's wrong with paying soemone to do it for you? They would have the correct equipment and training.

I am a little offended by the "competent" comment since I am one of those "less competent" individuals you are referring to. And I am not less competent than you are by a LONG shot. I bet there are things that you know more than me, this is def not one of them.

I had alot of problems with my E36 ABS a few years back. I did alot of research on it.. I have the techinical manual which goes over the whole Teves mark IV system.

Im going to post the PDF for you here, you can decide yourself. I've seen both ASC and non ASC cars. If I remember right, the ASC cars just had a different ABS pump that had more stuff on it. There isnt an independent unit. Come to think of it, I've never seen a BMW with traction control that has 2 different modules, 1 abs and 1 asc as you say. I could be wrong though.

Im gonna dig up that manual for you.. and we can settle this once and for all


http://personal.linkline.com/sevan/photos/teves.pdf

hope this helps

Damn.. looks like most of that manual requires a tool. It mentions the TRACS system. Which I'm readnig right now to see if it's a seperate module...


See? I think I was right here... The TRACS (ASC) equipped pumps have 4 valeves instead of 3... Check out Page 4 of the manual.. Kinda vague ..but..

"The hydraulic part of the system includes ana electric pump, which provides high pressure brake fluid for building up the pressure after the pressure reduction phase. When the ABS is combined with TRACS an additional valve is included for this function. The system has two or four wheel speed sensors"

page 44 has a hydralic diagram of the entire system. I dont see a secondary pump there.. Could be referring to a NON TRACs system though

Im going to have to go with Folsom330CI here. He seems to know what he's talking about too.

folsom330ci-

First off, please accept my apologies for the unintended insult. I don't currently have a BMW mechanic I completely trust and it's been years since I was friendly with any local dealers' master techs. I'll leave it at that. Furthermore, I'm a design engineer by day and I work on cars enough for it to be a part time job, so I refuse be ignorant of the technical aspects of a car I work on regularly.

That being said, have you used the computer to bleed the system on an ASC car? And ABS and ASC bleeding is combined into one option in the computer system? Have you ever seen or heard of a car that appeared to be perfectly bled (before computer hookup) with a lousy pedal that had air trapped somewhere in the system that only cycling the ABS / ASC with the computer could fix? I've drained the fluid out of a number of ABS equipped cars (including two '95 M3's) and never come across this problem, so even if the ABS and ASC are tightly coupled it is certainly unique to this particular hydraulic system.

It's my understanding that the ABS system has a pump to move fluid back to the master cylinder from an accumulator when bleeding pressure off the line to a locking wheel. It seems that the ASC would need a pump that served a different purpose of building pressure to send to the rear brake lines.
[edit - the Teves document says the pump is for building pressure so I'm wrong there] Even if I knew the working details I might not know enough to see how air gets trapped in the system.

As to why I wouldn't pay someone else to do it, if they incorrectly assess the problem and tell me the problem is something it's not, it will cost me alot of money and waste a bunch of my time. That is more likely if my circumstance is really uncommon, even if I have a sharp technician. If you tell me this is a common problem and my symptoms exactly match your understanding of the system, then I'm happy to bring it to you or any other expert. However, I haven't heard that yet so I'm trying to understand what the problem or the solution might be, first.

Thanks again.

JD

Im gonna dig up that manual for you.. and we can settle this once and for all

http://personal.linkline.com/sevan/photos/teves.pdf

hope this helps

Awesome. Many thanks!

It looks like running the (one and only) pump on both the front and rear lines will get rid of fluid upstream of the standard lines (that wouldn't normally bleed out). I can also see that the outlet valves might get some air stuck downstream of them, too (so they should be turned on while the system is pressurized by the ABS pump, although that's probably more difficult). Now I know what to try.

JD

No problem, mate :) let me know what you discover and I hope it helps

<3 to bimmerforums, glad I can help

Subscribed. Same problem here -- I've definitely felt the ABS push the pedal up on occasion, especially when the car is light while driving over a crest. ASC could certainly have to do with this. Soft pedal feel on E36 M3s is certainly not a rarity, as a simple search for "soft pedal" reveals. I replaced the Master Cylinder without any noticeable difference. The booster is still not out of the equation, as the pedal holds pressure much better when the engine is off than when it is on: When holding pressure on the pedal while starting the engine I can feel the pedal go down by at least two inches. I can hit the floor with the pedal when the car is not moving, but not when the car is moving. The car certainly stops all right and there's not much fade with the Porterfield R4 pads, but it feels to me like the rear pads are wearing faster than the fronts, especially at the track. Bleeding the brakes with the calipers off and pistons compressed revealed some extra air, as did bleeding with the ABS in bleed mode. However, if there was any temporary relief to the soft pedal feel it certainly didn't last long. Any additional help on this matter would be very much appreciated, as this is the only thing that bothers me about my otherwise excellent car.

-FDj

jdmorris: No worries... trust is a BIG issue in my business and for good reason. There is an option to cycle the ABS valves which we do use in extreme cases where we can't get the pedal to firm up. It is rare but it does happen. While I would never condone shorting wires on a harness there are ways of holding the valves open in this manner.

IMO if the pedal is softer or lower after the new lines were installed I would recommend a complete system flush with the proper equipment as a starting point.

Again, apology accepted but not necessary. There are alot of Internet heroes that muddy the waters. I wanted to clarify that, while I am not correct all of the time, I was not one of "them".

jdmorris: No worries... trust is a BIG issue in my business and for good reason. There is an option to cycle the ABS valves which we do use in extreme cases where we can't get the pedal to firm up. It is rare but it does happen. While I would never condone shorting wires on a harness there are ways of holding the valves open in this manner.

Is that referring just strictly to E36's or later models, etc.? Reason I ask, I took our E46 to the dealer for the brake flush as I thought they use their software due to DSC. If they don't use it unless it's an extreme case than I wasted some money haha.

It's been a while and I never posted a follow up. My brakes were unacceptably terrible after completely draining the system, even after pressure bleeding thoroughly and raising and spinning the rear wheels to get the ASC to apply rear brakes. After reading the Teves manual, posted above, that explained that ASC and ABS were one and the same, I was sure that the only possible problems could be air in the ABS pump line before it merges with the main line, or air in the pressure release valve lines. I ran the ABS pump using the instructions found in a search (pull the relay and short the pump line). This improved the pedal slightly, but it was still mediocre (I'd already bled air out of the ABS pump line when I previously cycled the ASC and rebled). I was hoping to have a friend with a BMW interface put the system into 'bleed mode' which would cycle the valves while running the pump, but never got around to it. Instead, NorCal got some rain and I had the opportunity to go out and do 4 wheel ABS stops. Every time I had the opportunity to lock up wheels the pedal feel improved. Now the pedal is as good as or better than it ever was (this problem all started when I installed stainless lines - UUC's made by Technafit are excellent, BTW). The result matches my hypothesis that the release valve lines on the ASC equipped cars hold air if the system is ever drained and only opening those valves under pressure to get the air back to the resevoir will fix the problem. I'll likely try the BMW diagnostic computer and pressure bleed the brakes some time in the future and will post any additional findings at that time.

glad I could help :wave

The ASC/ABS hydraulic unit differs from the earlier ABS units in that they have extra valving that ports the pump flow TO the brakes for ASC function, in addition to the normal flow to the MC for ABS function. This extra valving and hydraulic circuitry can not be bled by normal means and ABS stops. Believe me, I've tried. You will get your pedal back if you have it bled with the right equipment that cycles the pump and valves in a manner that gets all the air out. Just cycling the ABS function with relays or hard stops will not get your pedal back 100%.

Rich