: Do you have to do anything with Stabilitrak to bleed the brakes?



bpitas
04-15-10, 03:45 PM
I need some help understanding how the braking system works and more precisely, where you can get bubbles that would cause a spongy pedal.

My understanding is that the ABS system uses solenoids to cut braking pressure to individual wheels to prevent lockup, and Stabilitrak uses some sort of accumulator to build hydraulic pressure so it can apply the brakes without you pressing on the pedal, so at some point there have to be some Stabilitrak solenoids inline and sharing fluid with the braking system, right?

I'm asking because Sunday night I had my "check brake fluid" indicator come on while going around a tight corner (Stabilitrak tried to come on while I was trying to get my left-hand G's up in the DIC since I got my summer tires put back on last week - only got .92g though) and immediately after the "check brake fluid" I got the "service stability system" message too. Sure enough, when I checked, my brake fluid was way low, so I added some within 5 miles or so, once I could get to an AutoZone with DOT4, but before I got the new fluid, both messages came on another 2 times I think. Adding brake fluid made the message go away, but this morning I started noticing that the pedal feels a little spongy. No puddles on the garage floor, so I'm trying to figure out if I really have a leak or if the thing just needs to be bled because I got air into it while cornering with the reservoir really low.

I had last topped off the brake fluid reservoir in the fall when I put my UUC flywheel in, and had the brake fluid out to bleed the clutch, so wouldn't expect it to be that low - so it's possible I have a leak somewhere... So I'm going to do a flush this weekend and identify whether I've got a leak or it mysteriously evaporated or something. But when I bleed it, is there anything special I should do to make sure I bleed out any air that's in the stabilitrak system? I think I remember on my old WRX there was a jumper you could pull (or put in, I forget) that would get the traction control solenoids to duty cycle for testing and bleeding purposes - is there anything similar you can do with the Stabilitrak to bleed any air that's in that system? Anything else I should be wary of other than starting with the farthest away rear caliper, doing inside before outside, and working until the fluid is clear? Doing a search on "bleed" and "stabilitrak" gave me about 500 threads on bleeding the clutch (and after my UUC flywheel install I know how to do that ad nauseum!) but nothing on stabilitrak... I'm convinced the reason people (myself included) have such an issue with bleeding the clutch is that there are bubbles that aren't just sitting in the lines, but are attached to the diaphragm in the master cylinder or somewhere else in the mechanism, so the only way to get them out is by working the whole apparatus - you can't just pressure or vacuum bleed the air out, because the air bubbles aren't out in the flow, they are attached to stuff.

I'm picturing the way the bubbles in my soda always gravitate towards anything non-smooth (the straw, ice cubes, etc), and thinking if there is an accumulator for the stabilitrak or somewhere else where bubbles can hide, then I want to work those bubbles out all at once rather than having to bleed multiple times. I'm convinced that's why the clutch is such a bitch to bleed - you can pressure or vacuum bleed all you want, but the bubbles are safely hidden away in different chambers and the only way they come out is from regular usage. I believe I was even told once by an older mechanic that it's sometimes worth lightly rapping each caliper with a plastic hammer while bleeding if you can't get a firm pedal, because it'll help dislodge the bubbles and get them to float to the top where they can come out the bleeder.

Anyway, thanks in advance for any pointers!

nikon
04-15-10, 03:59 PM
The service manual doesn't mention anything special about bleeding the brakes, other than the order and to do the inside bleeder before the outer bleeder. I'm guessing you now have air in the system due to it being low...I'd bleed the system and see how it feels...and if your doing it by yourself the motive bleeder is a worthwhile investment.

As far as a leak, check to see if you have any corrosion around your calipers (inner/outer bleeders) if not it's probably just low due to worn pads.

PISNUOFF
04-15-10, 04:22 PM
I've noticed that when I had really bad fluid and bleed the system the brakes will work great until the ABS kicks in. I haven't figured out a way to open the solenoids, so I just flush/bleed the brake system then take it out and get the ABS to kick in (which makes the pedal a little spongy again) then bleed again.

Bleed the inner then outer of each caliper in this order per the service manual. Right rear, left front, right front, left rear.

If you think you have air bubbles attached to the insides of your clutch line you can hook up a handheld suction bleeder to the resevoir and put a vacuum on the system and let it sit for a while to see if any air escapes.

bpitas
04-15-10, 05:55 PM
Great - thanks for the feedback guys! I put new Hawks on it last Spring (I think) with new rotors, so *hopefully* the pads didn't go down that much, but now that you mention it, I have been hearing a slight squealing as I'm approaching a stop lately. I used to have that all the time with my PF pads, so I don't think much of it, but now you've got me thinking that maybe I have a stuck caliper or something and it wore down one of the pads!

Man it sucks having an "old" car. :-) I don't think of my '04 as "old", but let's face it - it's about 6 years old now!

bpitas
04-15-10, 05:57 PM
If you think you have air bubbles attached to the insides of your clutch line you can hook up a handheld suction bleeder to the resevoir and put a vacuum on the system and let it sit for a while to see if any air escapes.

That's what I have actually, a vacuum bleeder, and I couldn't get my clutch to feel good using it. The only thing that made it feel right again was tons of pedal-pumping by my girlfriend while I bounced between the vacuum pump and the reservoir to make sure it stayed topped off.

POS VETT
04-15-10, 06:23 PM
AFAIK, Tech II can cycle the ABS valvebody on C5 and C6 Corvettes. My Corvette god actually uses that method to flush brake fluid. I have no idea whether Tech II can do that on a CTS-V, but I'd be hard pressed to believe it doesn't.

nikon
04-15-10, 07:14 PM
That's what I have actually, a vacuum bleeder, and I couldn't get my clutch to feel good using it. The only thing that made it feel right again was tons of pedal-pumping by my girlfriend while I bounced between the vacuum pump and the reservoir to make sure it stayed topped off.

Out of this I read.....I must have a sick mind :)

bpitas
04-16-10, 10:40 AM
LOL I knew that was coming as soon as I hit "Submit", but editing it would only draw more attention to it. ;-)