tytek

Yeah, but there is no trail braking this early into T1 at Putnam Park - to drop 50+ mph in 150 or so feet, you need to initiate the braking process well in advance, in the straight line.

As best as I can recall, I was not into ABS at this point on the track, as the R888 provided good level of grip. I was threshold braking (as best as I can ) and the sudden loss of electronic braking systems must have adjusted the bias to the rear, like others earlier have pointed out. With the back end being light, as it happened after I already slowed down some, the rears locked up like someone put the handbrake on... except I was totally not expecting it to happen. I do think that it is a dangerous condition, because if happened elsewhere on this track, or most other tracks, the car would have been toast, and possibly so would I. I intend to fix it, just not yet sure how.

Does anyone know what the default proportioning is between front and rear, if ABS module is not controlling the pressures? Would putting a master cylinder with a mechanical proportioning valve provide a predictable safety net when/if the ABS failure were to occur again in the future? I can imagine that even though the brakes would have locked up at some point, it wouldn't have been heavily biased to the rear and would have let me just slide straight off the track into the grass, instead of pirouetting like Katarina Witt during the 1988 Olympics. My BMW friends have already labeled my car a hazard

flink

ABS intervenes much earlier and more often than drivers think. And we have evidence of that here: you thought you weren't using ABS but as soon as the ABS stopped working, full pressure went through to the rear calipers and around you went.

Heavily rear biased. Which means you are utterly dependent on correct ABS function to avoid looping the car and crashing Given the frequency of ABS failures, this is crazy. Which is why I suggest that the brakes should be modified to be safe (ie: front-biased) in the absence of ABS.

And driver should spend a couple of test sessions with the fuse pulled, to get an understanding of the behavior and to learn how to manage front lockups.

lol. I've been racing with no ABS for five years and only really became confident with braking this year.

Precisely.

Bill Dearborn

Were you experiencing any brake thumping before this happened? As explained in the Stoptech Warped Brake Rotor Myth whitepage the thumping comes from varying amounts of friction around the brake disk. Without ABS functioning you may have had the brakes applied hard enough that a spot with increased friction was encountered by the pads resulting in the wheel slowing too fast thus causing a rear tire to lose its grip and start the clockwise yaw.

Not sure how heavily rear biased the base brake system is. First, the front rotors are larger in diameter than the rear rotors. That automatically gives you front bias, then the piston area for the front calipers is larger than the piston area for the rear calipers which gives more front bias. The front braking capability is ~ 2.66 greater than the rear. However, if the ratio of grip from the front to the rear changes due to tire size selection that could result in more rear bias. When I was having the C1214 issue with my 03Z I found the first few times I hit the brake and downshifted that I had a tendency to lock the rear wheels as I let the clutch out and that wouldn't happen if the ABS was working. My analysis of that problem was I had gotten lazy on my downshifts and the increased drag on the rear tires from letting the clutch out caused a compensating reduction in rear brake force to keep the tires from locking. When the ABS went south that didn't happen and I had to adjust my heel toe technique. I never had an issue with the rears locking at corners similar to the one the OP was entering where no downshift was required.

Bill

Olitho

It is my experience that the car behaves very differently with a failed ABS vs. when the ABS fuse is pulled. I can drive my car both ways and in some races I have had to make the adjustment. It is much harder and more unpredictable to drive when the ABS fails. The bias is not too bad when the fuse is pulled.

Recently, the California T1, GT2, ST2 racing contingent came up with an idea... actually it was FatBillyBob. The idea is to put a switch in the car for when ABS does fail to flip a switch and cut power to ABS and thereby go fully manual. I think that is a great idea as it removes the randomness of a partially functioning/erroring ABS system. I plan to do that.

sleeperstyle

op- glad that wasn't any worse, i have heard of that same thing happening more than i'd like to hear.

after a few abs failures, but thankfully no spins because of it.. i like the idea of a proportioning valve setup more and more.

i had the ebcm fail, and the wheel speed sensors/wires break and fail. flat spotted tires suck, luckily i am not THAT fast and pushing that hard to where i got out of control..

i did a whole weekend with no abs and it was a big learning experience, by the end of the weekend i had pep boys pads on the back to keep the rear from locking up - i am on street tires/ rs3's- i believe there to be too much rear bias on my c5.. running a square tire setup could make this worse, compared to the stock staggered setup.

can anybody link us to or share their proportioning valve setup? any suggestions on parts/ vendors? pictures? any info appreciated- for those who don't know much about it.

tytek

I did not feel any thumping and the previous 4 laps felt great under braking. Didn't have ABS come on at all, as I was trying to get used to modulating the brakes on this car.

Plan to pop by (not pun intended) Danny Popp's shop tomorrow to talk about options and such. I think that a cage is on the horizon for me too, as ext time I get off like that, I may not be as lucky.

Apocolipse

Redo all the lines without the abs module, just like old cars used to be, and have an adjustable prop valve for the rear. Lighter and simpler

Or do as I am doing and run a custom pedal setup with dual mc for the brake and a bias bar.

I usually test the brakes in the rain to see when rear locks up when adjusting the valve. This way you are not going as fast to cause the lockup. You want the front to lock before the rears do otherwise....weeeehoooo

C5Z06CE

This is what I would say. I think your video suggests rear brake bias was too high for some reason and you had a slight wiggle of the steering to the left a split sec before *** went around. If rears lock up then a slight bump in the road or cross wind is all it takes to go around. I suspect you hit a small bump as the rear wheels locked and you lost it. I wonder if the prior owner changed brakes significantly and you didn't know about it. May want to pm them and ask. Either way I think a new MC or dual MC is the best option here.

SouthernSon

I wish you guys a lot of luck on rerigging the brake system. 3 of us are still trying to get the proportioning correct with a 3rd gen. Camaro. Yes, have tried wildwood adjustable, 3 different M/C's, different pads, different oem proportioning and 1LE valves. Not a linear exercise as one might think.

C5Z06CE

I can not speak about a 3rd Gen Camaro but this is what I would use if I were going to do this. I have been eyeing this for some time as I plan to upgrade the brakes for the track.


http://dougrippie.com/products/drm-c...ster-cylinder/

Olitho

Try pulling the fuse and driving the car before you go to a lot of expensive and exotic solutions.....

jtmck

If you can not pull a fuse, unplug one of the wheel speed sensors, which will give you standard brakes.
Drive the car 5 to 10 mph on somethig slick, like gravel. Lock up the brakes. I think you may find you have no REAR brakes.

KNSBrakes

I have the same issue. I did make contact though -luckily not too bad but scary.

In my case - ABS worked for about 5 cycles 0 and then the front right locked up. YOu could clearly see the skid mark - it was dot dot dot dassssssssh.

All 4 wheel bearings are (now) new SKF's. In order

Check wiring to sensors
Send ECBM to ABS fixer
Scratch head

Car definitely slows quicker when not ABS - but that is not easy to do. Worth the practice for sure.

2MCHPWR

it does look very much like my spin at the glen.
After the spin, I found the right front ABS wheel speed sensor wire was melted against the exhaust.
•C1226 h - rf excessive wheel speed variation
• C1333 h - rf wheel speed circuit open or shorted

tytek

I appreciate all the input and analysis. Next step for me is to swap in my good spare EBCM and see if any codes pop up. Danny suggested I trace the ASR Desired TQ input to check for 5VDC signal. I am worried that the intermittent TCS Nocomm has something to do with a connection somewhere, and not the module being bad. But we shall see by next weekend. I have noticed that the issues surface when it is wet outside... or when the car has been rained on. Not sure if it is really true, but that could indicate a bad connection issue.

tytek

I saw that video on YT last night when I was looking for ABS failure videos. It does look very similar... Sucks that the issue is so prevalent.

My codes are different though. Just the P1571, TCS No Comm, U1040.

Olitho

The last time I replaced my harness was after a wet drive BRP. It was huge puddling and deep water all over the track. Even the paddock had foot deep water I drove through to get to the track. The car never ABS'd right after that until I replaced the main harness. All this talk is bringing back the memory.

Olitho

Your account represents the unpredictability of the result of the ABS failure. Many here have spoken of rear wheel lock-up and that seems most common, but anything can happen in ABS failure. That is why pulling the fuse when if fails is best. That is why I plan to add a cut-off switch so I can manually shut it off if I wish/need.

I have had rear tires lock. I have had front tires lock.

Life is like a broken C5 ABS. You don't know what you are gonna get until you slam on the brakes.

AND0

Adjustable proportioning valves are a less then ideal solution. Their proportioning is not linear, the pressure reduction varies with pressure. The best solution is the traditional dual master balance bar. Pretty difficult to accomplish in our cars though.

The EBCM's brake balancing comes into play quite often, more often then people realize I think. Seems like anytime you approach threshold braking the computer is doing something.

Seems like the easiest fix would be to completely disable the ABS and change to rear calipers to a smaller piston size and get closer to the natural hydro-mechanical balance of the car.

ABS is nice, when it works, but most of us have been driving at the limit with out it for years, and the C5's near 20 year old design just doesn't seem well suited to the demands of racing.

SouthernSon

Wow! I likee. Since it is a matched set and, especially, being from DRM it is probably a very good setup. I have always wanted a little more rear bias. I may have to try this. Got some stuff in the works with Randy at this time. May have to order this, too.