Question for the pros concerning Anti-Lock brake and pad replacement

I forgot to mention:

He said this would not really be bleeding since pedal does not need to be depressed. Can I hook up a blastic bleeding tube over the bleeder screw anyhow to catch the fluid or should I just let it drip openly?

thanks!!!

The thinking is that with anti lock systems you want to bleed some of the dirty fluid in the caliper out BEFORE you push the piston back in because when you push the piston back in you push that dirty fluid up into the abs system controller. Supposedly you could get some dirt in the controller and screw it up. I'm sure it has happened to someone somewhere and it's not a bad idea to do what he suggests. My only concern is whether letting it drip like that instead of bleeding it by pressing on the brake pedal will let air get into the caliper. The other thing you don't want to do is get air into an ABS system because on some of them the only way to bleed them is to hook up the fancy dealership computer to control the ABS valves while bleeding.

the controller and screw it up. I'm sure it has happened to someone somewhere and it's not a bad idea to do what he suggests. My only concern is whether letting it drip like that instead of bleeding it by pressing on the brake pedal will let air get into the caliper. The

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I bought a little $6 one-person bleeder kit which contains a plastic tube and a little resovoir to catch the fluid. Are you suggesting that I remove the caliper and then at least hook the tube to it and maybe depress the brakes a few times to let the fluid run out and then let it drip until it stops?

He's saying to compess the piston while the bleeder valve is still open rather than closed.

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other thing you don't want to do is get air into an ABS system because on some of them the only way to bleed them is to hook up the fancy dealership computer to control the ABS valves while bleeding.

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The reason that step is not in the manual, and you won't find it any GM service manual, and I've never heard it taught at any of the GM courses that I've to in over 25 years, is because it's an absolutely useless step. I've never done it myself, and I've been doing ABS brake work since it came out on GM vehicles. I've never seen any ABS damage due to pushing caliper pistons back in without opening the bleed screw. I've never known any other techician that I've worked with experience any problems in this area. Another urban legend of sorts.

Ian

Ian, you're certainly more knowledgeable on these things than I am, but this very thing was covered in an issue of Motor magazine a few months ago. No, I don't remember the issue and don't have it anymore. I seem to remember it was in the help column and a mechanic wrote in about having to replace an abs valve module after a brake job. The advisor that wrote the column said it's possible to get fluid contaminated with rust particles and other debris pushed back up into the module if you compress the caliper pistons without opening the bleeder screws. He said the tiny orifices in the module simply cannot be cleaned and it'll likely have to be replaced if they get plugged. I've never seen it happen myself, and I don't do anywhere near as much brake maintenance as you. But it's not a lot of trouble to bleed them this way, and I've made a habit of it since reading the article as my wife's car and my truck have ABS. I just preload the pistons with a C clamp, open the bleeder screws, and then turn down the clamp. Probably one chance in a million that a person would ruin an ABS module the other way, but I'd probably be the guy.

Garrett Fulton

Believe me, if I thought I would screw up expensive ABS modules doing this, I'd change my way of doing things.

Whatever happened to the trans on your Aurora? I seem to remember that you were looking for some software update information. I mentioned that I could find that info, but never heard back. Did you manage to find that info?

If not, try this site:

Of course it does. Any time you compress a fluid and give it a low resistance path of escape, it's going to take that path.

You can do it either way, one of those ways might be slightly less messy.

Do what you feel confident doing.

$7? Vinyl hose is like 3 cents a foot at the hardware store...

No. There is no reason to pump the brakes with the bleeder open at this point.

Yes, when the master cylinder runs dry, but then you'll *really* need to do a full bleed!

if there is a pressure differential inside the caliper from

No, because fluid pressure inside the caliper is higher than the air pressure outside of the caliper.

Not so much "dumb" as it is scary.

You don't know where this alleged dirty fluid starts and the supposed 'clean" fluid stops.

You seem squeamish about the simple act of cracking open a bleeder screw, if that is the case, do as Ian suggests and just push the piston back in without messing with the bleeder.

Ian's experiences are not anecdotal, I also have been doing brake jobs on vehicles since the introduction of ABS and have yet to see where retracting a caliper piston without opening a bleeder has caused any sort of jam-up in the ABS valves.

In all due consideration, the situation mentioned in the Motors Magazine article could just as easily have happened anyway whether or not there was a brake pad replacement previously performed. No one can tell one way or the other...

When you do that, does fluid come out of the bleeder valve at that time? Do you put the plastic bleeder tube "over" the opened valve -or- do you just let the fluid shoot out?

Question for both of you!!!

I'm really confused then what I should do. I "know" how to change her pads and can do the steps. With such a difference of opinion on both of your parts (I respect truely the knowledge of both of you), what should I do?

Let me ask you this, I have the one man bleeder kit that I bought for $7. All it has is a little plastic flex tube that goes into a small plastic container. Should I just hook it onto the bleeder screw, open it up and pump the breaks a little bit to let some fluid run into it and then stop pumping? Once I stop pumping, will the fluid eventually "stop" dripping with the valve open? "Then", with the tube "still" over the "opened" bleeder valve, can I just compress the piston and then close the bleeder valve and put on the pads and then open the bleeder valve and let it drip again for a minute before closing it. Since I have the plastic tube over the valve the whole time, do I less run the risk of causing air to go into the lines?

Please help me on this question: "if" the bleeder valve is "still" open when I compress the piston, would that not cause air to come into the bleeder valve and work it's way up to the master cylinder when the piston is being compressed? Sorry if it's a dumb question. I don't know the internals of brakes. Never had "formal" training. Only have done brake pad replacements. If I bleed the system (ie, depress the brake pedal a few times) before I just let the fluid drip( from the open bleeder valve ) until it stops dripping, then would not just "clean" fluid work it's way back up to the master cylinder when the piston is compressed (with bleeder valve open)?

If this was my truck, I would not have a problem. This is my friends car and I just don't want to mess it up.

Same here, I've heard of this but I dont remember where, never done it, never a problem.

If you're really worried about it do what GFulton said, it wont hurt anything. Just remember to check the fluid level when your done. What you are trying to do is push the fluid out of the bleeder while pushing the piston in instead of up the brake line. No need to let it drip or any of that nonsense.

Just open the Bleeder screw and Push in the Piston. The Fluid will come out of the bleeder instead of up into the Brake system. When it's in all the way then close the bleeder. You won't loose a lot of fluid out of your brake system this way, and you won't put the dirty crap into your system. The last thing you want to happen is the Master to empty out. You want to keep it pretty much full. If your master ends up empty, your going to end up with Air in it, then Air in the ABS unit. It's just going to be a pain for you to bleed it out at that time.

Forget the one person bleeder kit. They don't normally work all that well. The bottle fills up to fast, and or the Hose Pops off and you end up sucking Air into the system. Just get a friend and have him sit in your car. Then Slowly Pump the brakes. I usually go with 3 times, at the third time hold the brake peddle down, then you open the bleeder and slowly let the Fluid out until it just about stops, then close it, and have your friend Pump another 3 times slowly, and do it again. Keep doing it however many times you need to. If the fluid isn't to dirty then you may only have to do it a couple times if you didn't let much air in to start with. Keep in mind to check the fluid level in the master so that it doesn't get to low.

Another good thing to do is put something under the Brake peddle like a brick or a block of wood so that the peddle doesn't go all the way to the floor when you pump it. This is because under normal conditions your brake peddle doesn't normally go down to the floor. After the Master has Aged, it's only been working from one spot the other spot in it's boor. If the master isn't in to good of shape past that point, and then you force the peddle to the floor. You could possibly cause the Master to fail. It does happen. A newer Car it normally isn't a problem.

If you have front ABS then you ALSO have rear ABS. There is NO Front ABS only cars out there. It's either REAR ABS only which is usually trucks because the rear end is normally so light so they end up locking up easily, or 4 wheel ABS. If you have drum brakes in the Back, then you have nothing to worry about. You don't have to screw with the Fluid unless you have wheel cylinders that are leaking. In which case Replace and bleed out like the front. Don't let the fluid run out of the master and empty out if your changing them. If you have Disk brakes in the Back, then it MIGHT be the same as the front. Depends on the Car/Truck.

Brakes are Series Business. You better know what your doing. I've seen many jobs come in from people NOT knowing what they were doing and it just ended up costing them more money to fix there're screw-up. You want to STOP and not step on the brakes and find that you can't.

Nope. I've set many a vehicle to gravity bleed, then taken a phone call that lasted too long only to come back to an empty master cylinder.

The bleeder screw is at the top of the caliper, I can't imagine how rust particles are going to defy gravity and magically find their way to the top of the caliper. besides, you have no way of knowing exactly what part of the system contains the rust that might cause a problem. Rust isn't reserved to only the caliper bores, the steel lines can have rust in them also. Corrosion from inside the master cylinder can just as easily find its way into an ABS modulator.

No you won't. Air can NOT get in where fluid is being forced out under pressure.

You could also cut a piece of two-by-four long enough to fit in between the seat bottom and the brake pedal such that it would keep the brake pedal depressed one to two inches, this will block all the fluid ports in the master cylinder preventing any fluid movement from or to the master cylinder (effectively locks everything out) then open the bleeders and push the pistons back, close the bleeder AS the piston is being pushed back, there is absolutely NO WAY that air can enter the system and no way the master cylinder can go dry.

Just as two GM mechanics with a combined experience of over 50 years have told you.

Son of a gun then. The guy made it sounds like it will "stop" dripping in a minute or so but the master cylinder will "still" have enough brake fluid in it.

How about if I just let a little fluid come out of the bleeder valve and then close the valve and then compress the piston? That way, any "dirty" fluid (and/or rust) should have dripped out and only the clean fluid will go back up?

I'll just have to make sure I top the fluid between installing the pads on the first and 2nd calipers because I'll need to drain the 2nd caliper slightly as well.

Sorry to ask all of these questions.

My friend just replaced the pads on his wife's car and she has ABS as well and he did not know about this bleeder valve step and he did not run into a problem.

thanks.