..in anticipation of going to the track (road course).

A friend of mine went once without changing his brake fluid (at least 8 years old) and boiled the heck out of them and then having to sit on the sidelines the rest of the day. I didn't want that

So... this is what I did:

I used a baster type syringe to suck out the old fluid to the extent possible.
Then I pumped the brakes and heard the master suck in some air. (oops)
I figured that bleeding would get the air out.

I filled the master up with Prestone DOT3 synthetic... Then I filled up the power bleeder with about 64 ounces of the same.

Hooked up the power bleeder and pumped it up to 20 psi. I opened the rear passenger bleed screw and watched the fluid flow out. I waited till the fluid was clean and clear with no bubbles. Did the same at each corner.

After running at least half of that fluid through the system, I emptied the power brake bleeder and poured in Motul600 fluid.

I sucked out the master to the extent possible and poured the Motul in there as well. I bleed the brakes with the motul till I see it at the bleeder screw (it's darker than the clear prestone)

I go around the car about 3 times to get out as much of the prestone as possible. I run a liter through the car and master.

On the road: The car now has spongy brakes. It's like there is air in the lines. Did sucking air into the master get it stuck in there? Jeeze - there was at least half a gallon of brake fluid that went through those lines!!! Do I have to tilt the car up so the master is perfectly level? What the heck did I do wrong?

 

I am guessing that air in the master didn't help. When you bled the brakes did you follow the proper sequence?
I just put stainless steel lines on all calipers and bled with speed bleeders by myself. Was worried about it a little since I hadn't done them on this car yet - the pedal is rock hard after. Never let master get low and followed proper sequence.

 

Bleed the right rear first, then left rear, next would be the right front and then last would be the left front.

Not to insult you if you did the process this way. But some people bleed there brakes incorrectly. It is safe to say that there is air in the system. Before you started, there was no problems. There could be one other problem but you would have picked this up. It would be if one or more of the bleeders are leaking.

Hope this will help you.

 

Most likely you now have air in the BPMV (Brake Pressure Modulation Valve). The BPMV consists of a pump and a set of valves that are commanded by the EBCM for the purpose of controlling brake pressure at each individual caliper.

You need to locate someone with a Tech2 (a handheld computer that can diagnose/control GM vehicles) because that device can command the BPMV to run and pump air/fluid through the system.

As you have already guessed, letting the Master Cylinder reservoir run out of fluid was not a good idea.

Some Corvette service shops have a Tech2, dealers have to have a Tech2 .... most likely you will be visiting your local dealer to fix this problem.

 

Wow! That can really happen??!?! What do people do when they change masters??!?

Before I go down this path, I'll do a bench bleed on the master and try again. Holy crap!!

Thanks for the info though. I'll repost this weekend when I get to it.

 

I don't see how you can have air in the master if you were pressure bleeding...

As stated, you have pumped air into the BPMV.

You could try going to a safe area and doing heavy ABS activations, followed by a rebleed.

Good Luck!

 

I have changed a master cylinder on my Z06, and if you do not bleed the air out of the master cylinder and ports, you will never get all the air out.
I would try holding the pedal down, and cracking the rear brake line fitting at the master cylinder until you get the air out. Then do the same for the front brake line port. It may also help to let some fluid gravity feed out the port, tighten the fitting, push the pedal, then crack the fitting again.
I am thinking that the active handling and ABS circuits are normally closed, so you do not have air in the circuits that require the TECH II to bleed. You should be able to manually bleed the brakes without getting air in the normally closed circuits.

By the way, if you change out a master cylinder, bench bleed the cylinder, and bleed the ports as described above, you should not even have to bleed the rest of the system. I had a firm pedal immediately, but I went ahead and bled the calipers just to get clean fluid in the system. I also found that when you bench bleed the master cylinder, if you are patient and just let the MC gravity bleed until fluid runs out the ports, it only takes a couple of pumps to push most of the air out. Putting the cap back on the MC will help stop the fluid from continuing to flow out the ports until you can get it on the car.

 

think you will need your ABS Control unit bled - don't do it yourself. I wouldn't even attempt it...get a quote, or somebody you know that can help that has done it before.

 

Once the air was sucked inside the master you had the potential to force air into the BPMV. Anytime you have air in the brake circuit upstream of the BPMV you stand a high risk of getting air into it when bleeding the brakes. This is what the Service Manual says about this situation when bleeding the brakes:

Important
If it is determined that air was induced into the system upstream of the ABS modulator prior to servicing, the ABS Automated Bleed Procedure must be performed.

This procedure uses a Tech 2 scanner to operate the BPMV valves so air can be bled out of the unit.

Bill

 

Recently power bled the brakes and 1L to flush is about what I got. Was able to borrow a Tech2 to do 'automated bleed procedure' for EBCM. Was surprised how dirty the fluid was - nearly as murky as fluid from 1st flush. Took another 1L of fluid as well.

I would definitely get the EBCM done with the Tech2.

 

Your answer is the one that I like the most... Nothin like telling me what I want to hear!!!! I just hope you're right. I'm off to take off the master, bench bleed it and put it back.

The tech2 sounds like a cool device - but I HATE the dealer and that tool is like $4G.

It's worth the first try for free.

 

I believe someone else mentioned bleeding correctly as stated above and then going out to safely get ABS to engage. If you can do that followed by another bleed sequence maybe you can luck out. I have never done that but sounds logical.

 

I have never had a problem getting air out of the BPMV. At a slow safe speed, hit the brakes hard and make the antilock brakes do their job (the pedal will pulse.) After a few times, it will feel like new again You are essentially doing the same thing the Tech 2 will if you go to the dealer

Just make sure you are at a slow enough speed that you feel safe hitting the brakes as hard as you can. I like to go a little faster than needed, then ease onto the brakes so it isn't a sharp jolt when you hit them.. Ease onto them like normal and when you are getting close to stopped, hit them hard to make the ABS work.

 

The Tech2 auto bleed runs the BPMV for about 15 sec at each wheel, plus the bleed valves are held open about another 30 sec. Another interesting fact is the bleed sequence is changed to LR, RR, RF, LF.

 

Huhhhhhhhh ????????????

Where does the air go when the BPMV pumps ????

When the dealer uses the Tech2 to force the BPMV to run they have the bleed screws open at the calipers so the BPMV can pump fluid/air out of the system ..... your "technique" can't get the air out of the system .... so I have no idea how you think it "works".

 

Try it out sometime That's a pretty aggressive response for simply not "understanding" how it "works."

If there is a LOT of air, of course it won't work as well. If you get a little air bubble caught that you can't get out, it's the easiest and best way to do it in many cases. I'm sorry if you don't like the logic, but it has been done MANY times for line lock installs and in situations like the OP is in etc.

 

FWIW: The master bench bleed fixed the problem.

 

It won't get the air out of the system but it may transfer it to the lines where you can do a normal bleed afterwards. As for his comment that it works without doing further bleed operations it may be that there was no air in the BPMV to begin with.

As for applying the ABS I haven't had do it yet but I would go out to a non-busy highway, check to make sure nobody is close behind get up to 60 and nail the brake pedal as hard as I could and hold it till the car almost comes to a stop. That way all 4 wheels ABS and the pump and valves run for a couple of seconds. The car will come to a straight stop. When autocrossing at a certain Go Kart Track I do this from close to 70 mph everytime I come down a long straight so I know C4s and C5s are well behaved under these conditions.

Bill

 

What is that? Excuse my ignorance, but like to know what was done.

 

A bench bleed on the master cylinder:
1. remove master
2. connect fittings and flex line to run the outlets back into the reservoir.
3. depress plunger several times and change the angle of the master while doing it to get all the air out of it.
4. Put the cap back on the master, reattach brake lines to master and mount to the brake booster.