redtopz

I've been thinking about safety lately and one thing that has been concerning me is what happens if we have a brake bleeder screw or line failure at one of our calipers. Will we lose complete braking or does the stock abs system in C5 and C6's still provide braking to the front or rear calipers without the failure? Thanks.

davidfarmer

I know this is true of most years, not a 100% sure if all, but the OEM master cylinder is divided into 2 parts, front and rear. If you have a caliper leak, a line fail, etc, your pedal will get soft, but will still have some brakes. Also, in most cases, it will slowly leak out as you use the brakes, so you will notice a progressive loss of brakes, not a sudden failure.

I had exactly this happen in 2003 during a World Challenge race. A bleed screw was slightly leaking, and the brakes got worse and worse. Eventually, the pedal went to the floor, but I could pump them on the straights and still stop the car using the axle that wasn't leaking. I only ended up losing one position because of the leak (to Boris Said if I remember correctly)

0Brakemotive

That's why our C5's came with such effective and reliable emergency brakes

Jason

Those are on the excess parts pile.

redtopz

Thanks for the explanation David. Pretty gutsy to keep racing and only lose 1 position. That is what I thought, but I wanted to make sure before I went sailing off the track. My e-brakes are also on that pile in the shop.

0Brakemotive

I forgot I was in the RR section

BEZ06

Like David said, look in the m/c and you'll see a partition across the middle that divides it into 2 chambers. When you pour into the rear chamber, when it fills up high enough it spills over into the front.

I don't know about the C5, but the C6 Service Manual tells you the proper sequence for bleeding brakes is RR and LF, then LR and RF - that's because those are the circuits that are on either the front or rear chamber in the m/c.

I you had a RR line leak or bleed valve leak on the RR caliper, you'd lose the RR and LF brakes, but hopefully the other diagonal circuit would allow you to have LR and RF brakes to get you stopped.

If you use a Tech 2 for bleeding/flushing it might be important to do the sequence like the Service Manual says - especially if you're using the Tech 2 procedure for opening the valves to bleed the ABS lines.

However, I just always bleed/flush the old fashioned way - farthest from the m/c first, next farthest second, etc, i.e., RR, LR, RF, LF. I've never had any problem doing my C6 that way.

Bob

Bill Dearborn

Doesn't have anything to do with the ABS it is part of the base brake system. All cars have had to have a dual brake system for many years. Early C5s had front and rear brake while late C5s and C6s and a lot of other GM cars have dual diagonal braking which is one front brake on one side and one rear brake on the other side for one circuit and the opposite for the other circuit.

Bill

travisnd

Yep... GM just wants you to bleed each circuit at a time... which is the reason for the X pattern.

If I remember correctly the service manual states LR, RF, RR, LF. That way you bleed the LR/RF circuit, then do the RR/LF circuit and finish with the wheel closest to the master.

In reality I just work on the car one corner at a time when track prepping... inspect hub flanges, nut/bolt suspension, lube caliper slide pins, flip pads, put it all back together, hook up the motive and bleed the corner, then move on to the next.

MistressMotorsports

I don't want to scare you, but depending on the exact type of failure, really bad things can still happen. Even with diagonal braking, if you are braking hard and have a catastrophic failure (rotor or caliper comes apart, sudden fluid leak, etc,) the car is going to change directions very quickly. Or at a minimum, you will have severely reduced braking performance, which means you may not have room to react and correct before solid objects appear. This is really no different than other non-braking failures that could cause a loss of control, like scattering an engine and putting several quarts of oil under your rear tires, having a wheel come apart, etc. Some things just have no contingency plan available while on track. The best insurance is to do really good inspection and maintenance of all your critical systems. No solution is perfect, but you certainly can lower the chance of something bad happening by insuring your equipment is in top shape every time you hit the track.

Mike

Olitho

My neighbor Mike is correct. I have lost brakes completely twice and had a diagonal type failure a third time. All three occurences happened at Auto Club Speedway going from 128 MPHish down to the 45 MPH right corner after passing under the foot-bridge.

I will elaborate later this weekend when I have more time to write. I was lucky all three times that I did not have traffic immediately in front of me and that it is not one of the walled corners/turns.


Oli

flink

It's always going to end badly when you lose braking from two wheels, but the difference between half-braking and no-braking is tremendous.

Next week I'll be testing my car: open a bleeder to simulate a line failure, drive it at 30 mph in the paddock then hit the brakes. I'd encourage you guys to try the same thing.

A local C5 owner had a rear line fail at the track a year or two ago. He came in complaining that the brakes were a "bit soft". He didn't actually know that he had a real problem until I pointed out the puddle of fluid and his low-fluid light came on. That's really impressive.

And as we all like crash videos... a local AIX Camaro had a front line fail last year:



Photographs here: http://forums.rennlist.com/rennforum...47-post85.html