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Comments
The ABS system is exactly the same in the Automatic-WRX but the way the ABS interacts with the underlying AWD system is completely different.
If you go through the following link, you will find the following excerpt:
http://home.attbi.com/~eliot_www/awd.html
The VC's rotational sensing characteristic initially caused lots of problems for the engineers. Anti lock braking systems rely almost entirely on speed differences between the 4 wheels to detect a locking wheel. Thus, when the transmission tries to force 4 wheels to rotate at the same speed, it creates serious difficulties for the ABS system.
The engineers had to use a variety of hacks to get around this problem. Mitsubishi delayed ABS for a while for its first generation GSX, then finally decided to make ABS and rear VC limited slip mutually exclusive options. The VW syncro system simply disconnected four wheel drive the moment the brake pedal was stepped on via a secondary clutch. Most other vehicles using this implementation of VC have a very similar disengage feature. The very successful World Rally Championship Lancia Delta Integrale even went as far as to apply a little bit of power (via the engine computer) to reduce the drag of the VC when the brakes were applied! Some very crude systems used a overrun device that is conceptually similar to the bicycle crank. This meant that while four wheel drive was disengaged during braking it was also inoperative when reverse was engaged!
The easiest hack was to reduce the effective viscosity of the fluid in the coupling, so that the drag was reduced. This also meant that the VC's locking effectiveness was reduced, which is probably quite acceptable for a vehicle intended primarily for paved roads. The VC's attraction is its simplicity and cheapness, not its sophistication.
Later...AH
The way ABS detects a locking wheel is by employing an individual speed sensor at each wheel. The wheel speed is then compared to the vehicle speed, and if it finds acceleration, (the wheel is slower than the vehicle, or sliding) the system will reduce brake to that wheel.
Otherwise a sufficient explanation. Also, this is the reason why a Torsen center diff (Ala quattro) is a better system for managing this, although they also will lose ABS on locking either front or rear diffs, the only advantage is they can potentially still have ABS functioning on one axle.
You do not have to go outside the Subaru fold to get this Torque-sensing center differential (even though Subaru/Quaife etc does not use the term "Torsen" to define this, since "Torsen" is a brandname of a company that markets one of the the torque-sensing/biasing differentials available)...you need to look only as further as the Automatic-WRX (or VDC Outback), which has, in addition to the Torque-sensing planetary gear center differential, a multi-plate electro-mechanical clutch-pack for transferring torque rapidly front/rear rear/front. This is also employed in the World Rally conquering Subaru Rally cars.
The article in the link mentioned, does not mention the VTD-AWD (of Subaru employed by the Auto-WRX), since it was written prior to the VTD-AWD of Subaru coming into production vehicles.
Later...AH
If I slam the brakes on a wet railroad track or other metal surface (manhole cover, etc.), sometimes the brakes go to the floor. Same thing happens in deep snow or even hitting potholes. It doesn't happen often though.
I'm not saying anyone is wrong, but I feel that this is "normal" since it's been happening to me the same way in my OBS for 5 years (and in my Neon, prior to the OBS). It's just something that I got used to.
Maybe it's more prominent on the WRX because people might tend to drive it harder.
-Dennis
- Hutch
Probably a good move just to pull the fuse like you did.
-Dennis
Road no longer turning wheel + brake pressure = locked wheel so the ABS engages.
Since the WRX abs is four channel ABS and only the wheel that was off the ground was affected, i didn't experience any loss in stopping distance.
I was driving on ICE (yes pure ice) last night (turned my 30 minute drive from my parents house to my apt into 2hr 10 minutes) and while the ABS engaged, I didn't experience any pedal to the floor effect.
In fact, every time ABS has engaged on me, I've expericed the opposite effect of pedal to the floor. The pedal pushed back at me.
I've got a question for the people this as occured with, what do you normally do with the clutch while you are braking? Personally, i leave it engaged until the car is about to stall, then disengage it. I've noticed that if you disengage the transmission from the engine (no matter what the gear you were in) stopping effectiveness goes down the tubes quickly.
I could be costing to a stop from 60 mph and I will leave it in 5th until I'm almost stopped, i wouldn't, say, disengage it at 20 mph and use the brakes to stop me the rest of the way on their own. Even though there will be very little engine braking at those low speeds in such a high gear, I find it makes a HUGE difference in stopping ability.
Here's my take.
As far as I know, the jury's out on this one. Some drivers downshift almost to a complete stop and then put the tranny in neutral and use brakes the rest of the way, and some leave the car in whatever gear they're in until almost stopped and then put it in neutral and use brakes.
One method puts more emphasis (and wear) on the brakes because you're not getting as much engine braking; another advantage is that, if you suddenly have to get back on the gas again you're already in the appropriate gear. The other method can cause tranny trouble if your shifting technique is bad (ie downshifting at excessive speed) but, if you're almost stopped in a high gear and suddenly need to accelerate, you'll have to shift down and some trannies don't like to be shifted out of a high gear at a very low speed.
When coming to a I personally downshift through the gears (making an attempt to rev-match) until I'm in 2nd gear and almost completely stopped (my Neon's gearing is really, really short so 2nd gear is only good to about 10 mph, and I can't get the tranny into 1st unless the speedometer has stopped registering!) and then use just the brakes. After 70K miles I've felt no change in the tranny's behavior. I also like (mentioned above) having the ability to mash the gas if I need to accelerate again. It's saved me from an accident a few times when some jerk tries to cut behind me at a toll booth; I've been able to get ahead enough to avoid him.
DjB
I was referring to the people that take the thing completely out of gear when they come to a stop (I know some people do it, i've watched them). If they see a stop in front of them they push in the clutch immedatly while braking no matter how fast they are going (basically they don't like to downshift and they push the clutch in way too soon). I'm wondering if it's those people who are having the abs trouble more than the people that have the transmission engaged.
Basically, was the clutch depressed (or in neutral) when you experienced the wierd ABS trouble?
I suppose there could be an emergency situation where you might need to do that, but if you know the road at all, I don't think it would be the "norm".
I tried to reproduce the problem with mine yesterday as I went over several sets of RR tracks, I could not get it to do anything out of the ordinary. I suppose if you aren't accustomed to anti-lock brakes, and they are set off, they alone can surprise a person. But if you know what to expect, I can't see that it's a problem.
That's just my own opinion, and I do not conclude that there isn't a possible problem with some vehicles.
Ken
-mike
Some have reported experiencing this problem after rumble strips just prior to a toll booth (rolled right through ..) small road bumps, railroad tracks, and various road anomalies. Going out and speeding over bumps/RR tracks and slamming on your brakes will most likely not create the conditions necessary to experience the failure. I was lightly depressing the brake pedal when it happened to me. The pedal felt like mush.
I've tried repeatedly to reproduce the experience and could not. It only happened once .. that was quite enough. Until this issue gets addressed the ABS stays off.
- Hutch
-mike
Here it is in a nutshell:
step on brakes = no reduction in speed = problem
BTW did you ever test the auto WRX to see if power braking would achieve 3k+ rpms at a stop?
- Hutch
-mike
On the brake issue, I think it is a VERY serious matter. A second or two going 40 MPH is a very long distance - almost 60 FEET or about 4 car-lengths. Tell me thats not scary! There is a nasty strip of road near my house that has ALOT of potholes/bumps/warped concrete - now that I KINDA know how to induce this problem, I think i'm going to try to check it out.
Also, what does SoA say about this? I am assuming people have compained about it. Are they lookin into it? Do you think its might be a probelm with WRXs made before a certain date (as if a certain shipment of sensors/parts/whatever were faulty?). Or do you guys think its a faulty design. I have only had my car for 2 months, and i am HOPING that maybe it was an issue with ones made earlier. Sorry for all the questions.
HAZDAZ
Or at least, this is the comment from SOA. However, IIRC, the issue is now being investigated by NHTSA. I dont know of any "fix" or "recall" action..my dealer says they have been alerted to the "situation" but that there is nothing they are supposed to be doing at this time except checking the brakes for proper operation if a customer complains of brake problems such as this one.
We are tracking the issue. The problem we are having is duplicating it. Some folks that have said they could "make" it happen have tried for a dealer, but to no avail.
I'm still tracking it and we do have other folks looking at it. We have not had any of our vehicles in our test fleet that have had a similar complaint.
I understand the frustration with this. If we could duplicate it, we could look into a remedy. While we have reports of "soft" feeling brakes, etc., they have all been deemed within range. No duplication of "brake pedal dropping".
We know it is important to all of you.
Patti
Coming up to a stop sign, there was a break in the concrete (expansion joint?) with a drop of an inch or so, probably 20 feet from the intersection. Upon hitting the drop - no brakes, although don't remember the pedal going to the floor. The brakes reappeared in time to stop me with my hood in the intersection. It's important to note that I was not braking in an agressive manner and have never had such a thing happen on any of the other 5 vehicles that I have owned with ABS.
Since this occurred, I have been keeping an eye on the same topic on the I-Club board and plan on pulling my ABS fuse if it occurs again...
Craig from Seattle
Stephen
Fortunately I had time to pick a line around the corner that allowed me to hang out the tail and scrub off some speed, otherwise I would have gone right off the road.
Ive never actually tried to duplicate that exact experience. I did test the ABS on flat, smooth pavement just to make sure the system was working..and it worked fine. But I wont be going out looking for places to make it happen again. One close call is enough for me.
There is a problem with the ABS and I'm confident that in time the source will be identified and corrected. Sooner would be better than later. For now, I'm keeping fuse #8 out.
I don't need no stinkin' ABS anyway. (said with a bad Mexican accent)
- Hutch
Anyway, I wondering, given the sensitivity of the paint that I've heard about what cleaning products people are using to wash, wax and polish and what is being used to apply them..i.e. sponge, etc. Any suggestions would be appreciated so I can keep my car shiny and new looking.
Oh, side note..I'm curious if any people with auto WRXs have experienced the ABS problem.
Eric
I have a full kit Stongard clear bra on my car, and it's worked pretty well. I also get it washed and waxed nearly weekly. People ask if I keep it garaged, when it truth it's entirely street parked.
Personaly, I use Meguiars myself, the professional line.
Every two months I use the show car glaze and the #7 yellow wax. One a week I wash with Meguiars soft wash gel. I finish up the job with Meguiars final inspection spray, makes it real shiny. The spray works well to maintain the wax between waxings.
Sorry if I sound like a commercial for Meguiars, it's just that it's the stuff I use and about the only stuff you can find in professional grade in the stores. The last thing you want to do is use an all in one wax, they usually contain cleaners or abrasives that can cause swirl marks.
Craig from Seattle (OK, Kenmore...)
Stephen
Hutch-
may come as a surprise; the characteristics you've mentioned, IIRC I've had 5 encounters with it on my... '98 OB in my 4 years of ownership. Yes '98 OB.
My experiences were pretty much what you've described - Lightly on brakes to slow down then light final push to get car to stop (routine). What wasn't routine, at final push of the brakes car continues forward likes brakes aren't there. Apply force on the brake pedal (not stump), felt the pedal sag a little and then the ABS kicked in.
Sad to say that the condition(s) has to be precise to duplicate. I would agree with Dennis, who mentioned earlier, that it may be more prominent with the WRX as the tendency of driving it harder.
These are the conditions I've encountered:
Once going over rumble stripe. Gone through numerous rumble stripes thereafter, hasn't occur again.
Once over uneven paved road (dry).
Once over uneven paved road with icy patch (right tires) and nicely paved no ice (left tires).
Hasn't happened again to date.
Twice stopping in sleet/snow on unevenly paved road.
Not expecting it to happen again. Giving myself plenty of buffer and let the car roll to a stop without the brakes.
None of the above qualified the 3rd characterization
Patti-
Hope I'm not fueling the fire here. Just thought I share and maybe help shed some light.
I didn't see the need to report any of my experience since none of the occurence were in emergency situation. Just thought it as the ABS way of doing its thing, though unusual, but thought nothing more of it. However, when I really needed it (I had a few of them too) it hasn't failed me yet.
-Dave
Let us know how it goes.
Bey
There's a little Edmunds/i-club drive coming up this Sunday. We'll be hitting the twisties of Eastern PA/Western NJ. Keep your eye out in the future (i-club Tri-State and Sube Crew/Events) if this one is a little early in your break-in period.
-Dennis
-mike
Can't make it tonight Mike, I'm doing Small Claims at night this week, so my work "day" is just getting started. Keep me posted on anything that comes up in the future.
Dennis, I think I'll hold off until the break in period, might not be able to contain myself, but also keep me posted of future events.
As for washing, I guess I should get on it, if I want to do the weekly think..Sunday will be a week.
Time to work...
Eric
Bey - I remember seeing the same post on the I-Club thread for ABS problems. I'll try to find it and report back...
Craig from Seattle (OK, Kenmore)
On the "ABS ~~~~Dirty Draws" thread in the General Community>Maintenance section, "duckboy' found the sinlge bolt that fastens the ABS sensor bracket to the hub loose. After tightening it, his problem apparently went away.
Within the same thread, there was reference to another thread, "My ABS is Fixed!" in the General Community>New Age section - "toby" said the dealer replaced his ABS actuator (later refered to as 'module') and that took care of things. In the same thread, "Storm Racing" said his dealer first replaced the 'brake booster', later replaced the 'ABS module', and finally found a 'faulty left front wheel sensor' that was apparently providing errant readings...
Craig from Seattle
-Kevin
I got mine at Welsh Subaru in Limerick. They hooked me up with a black sedan and had it ready for deliver in 3 hrs. (Credit check at 9am, approval at 10, pick up at 1pm). They've been great so far. I live in Limerick April-Nov and Colorado Nov-April.
Ryan
You can give Alex Leist a call at (908) 782-2025 and tell him that bluesubie sent you.
I started going there for service about a year ago and they're no pressure and no b.s.
You can post here or email me with any questions.
Good luck and hurry and get the Rex!
-Dennis
Happy driving...
Eric