sperkins

I have a problem in my '99 FRC with having air trapped inside the ABS pump/module. At my last track event, I was having a long, mushy pedal that would not go away with typical bleeding (stock calipers - Carbotech pads). A couple of knowledgeable buddies helped me purge the ABS by raising all 4 wheels, cracking 2 opposing bleeders and running the rear wheels until the ABS engaged. It worked really good - for one session. The track (CMP) is pretty hard on brakes and I was into the ABS pretty hard every lap for at least 2 of the 14 corners (2 TT laps max per session).
So the question is - is it possible that when the ABS pump activates that the fluid is being churned into cavitation creating bubbles inside the pump?

Last C5

Cavitation?? Hadn't considered that, but I've had the same problem a couple of times on my Z at the track. The first time, after rebleeding the system, I went out and got into the ABS hard about 4 times and the problem went away. The second time I had my tuner hook up his Tech II and activate the ABS system - instant fix. Since activating the ABS system seems to fix the long/soft pedal I don't think that using the system would be the cause of the problem. But, I don't have a better explanation of the problem either.

2K3Z06

guessing your boiling the brake fluid. use the tech2, open the valves and flush with some good fluid. motol600,etc.

might use temp. paint on the rotors to check how hot they are getting.

good luck

froggy47

Not cavitation, but you might have an air leak at the abs, my friend (t1 racer) had that, new abs fixed.

Jason

I always chalked it up to caliper spread and learned to live with it until I can afford fresh calipers. As long as you get to the abs before the pedal gets to the floor, that's all the brakeing you're going to get.

wallyman424

I had the symptoms scott is talking about a couple years back. I chased it around like an idiot, replacing master cylinders, getting tech 2 bleeds, etc...

it was tapered pads and spread calipers.

Unless its doing this w/ brand new calipers and brand new pads, then I'd put my money on them being the culprits.

drivinhard

he's just rubbing it in he cleaned up the CMP TT field WITH brake problems

Jason

No brakes = fast

96CollectorSport

Spred calipers could be the cause, but if the problem shows up all of a sudden it's more than likely air trapped in the ABS unit itself.
When you engage ABS the valves inside move back and forth rapidly, if you have air in the system at or above the ABS unit that air can get trapped on one side of a valve. (And there is a total of 12 valves 3 per wheel) You bleed the brakes and get all of the air out of a closed system, but next time you activate ABS the air trapped on the other side of the valve is released into the system and you get the long pedal. That is why a Tech 2 bleed will take care of the problem, as you bleed you're sure that there is nothing but clean air-free fluid on both sides of the valves. If you perform a Tech 2 bleed and the air is still there look at the calipers.

PushinTheLimit

This is the same problem I've had since I bought my car. I thought that the calipers were trash (and they are anyways) but I still have a mushy pedal in the car. If bleeding them doesn't work this time, looks like I'll be buying another master cylinder.

sperkins

Makes sense. I'm going to re-do the poor man procedure in the hopes that I didn't flush it good enough the first time. I seriously doubt I've boiled the fluid in 2 laps, but I guess anything is possible.

davidfarmer

cavitation is the same thing as boiling, just due to "low pressure" instead of "high heat". It might be worth having a Tech2 Bleed done!

AU N EGL

Time for new Brake Calipers ?

96CollectorSport

The thing about the "poor man bleed" is that it's almost impossible to get all of the air out of the ABS unit, before we got a Tech 2 I would bleed the brakes, drive the car and initiate ABS, bleed the brakes, drive the car and initiate ABS and continue the process until the pedal gets firm or you run out of brake fluid.
Typically when you boil brake fluid it won't make it all the way back to the ABS unit, so you typically only have issues if you replaced a master or had to disconnect lines from the ABS unit.
Another option is to wait until the Dec. Road Atlanta event, Raftracer typically brings a Tech 2 along with him, you might be able to borrow it from him at the track. Just a thought. Danny's a good guy if you send him a PM and ask it may take care of your problem.
On piece of advice, if you do perform a Tech 2 bleed have a battery charger connected - the ABS pump sucks a lot of juice and you don't want to stop half-way through the procedure. I've even used a jumper pack at the track to give the battery a little extra capacity.

sperkins

Thanks Joel. I may have to talk to Danny about that. Been meaning to meet him anyway.
Here's the process I did at CMP that worked well for a little while. Maybe I need to do it more thoroughly making sure to flush out all 12 valves.
1. All 4 wheels off and on jack stands.
2. Pressurize M/C with motive bleeder.
3. Crack L/F and R/R bleeders
4. Put car in gear and run up the speed until ABS kicks in (due to front wheels not turning).
5. Crack R/F and L/R bleeders and do the process over again.
6. Removed Motive and did a manual bleed with someone in the car.

davidfarmer

I don't think that procedure would completely cycle the selenoids. I know the Tech2 procedure takes forever, and it seems to cycle them over and over and over. Plus, it seems like you would only be cycling the rear selenoids.

I wish there was a way to fully cycle the system sans Tech2..........

96CollectorSport

That's a pretty good way to do it "poor mans" and all, definatly a lot easier than the way I used to do it. But if you keep having problems then the Tech 2 may save you a lot of time and brake fluid.
I'm sure Danny will be more than willing to drink beer and pump the pedal while you do the grunt work.
Just watch out for those other TTA Mafia members, although the way the car's working with the crappy brakes they may want you to fix them.

drivinhard

I'm gonna bring some of these decals and put it in that livery, because he's gonna have a big 'ole bullseye on him

ScaryFast

There are actually 2 valves per wheel, plus a pressure build and pressure isolation valve (x2 for front and rear circuits). The isolation valve can take the MC out of the equation, causing the system to use only pump pressure. This is probably why the tech 2 bleed procedure works, you can freeze pressure in the system, then cycle the build and dump valves at the wheel to force fluid from the resivoir into the system, and I suppose air out of the valve block itself.

An ABS only system only has MC pressure (and 8 valves), so the question is: does the C5 system use the iso valve to close off the block from the MC in an ABS event, or does it act like a simple ABS only system if there is no ESC involved? I'll have to check. If it's blocking the MC during ABS then applying pressure with a bleeder tool at the MC is irrelevant.

SouthernSon