Doing brake job with ABS

"Martin Lynch" wrote

There is nothing different that you need to do just because it has ABS brakes. If you do a pad replacement, there should be no need to bleed the brakes. Just push the piston back in to the retracted position and install your brake pads. If you start fooling around with bleeding the brakes....you may end up with more trouble then you want.

If it's rear disc brake pads you are replacing, there may be a procedure that you need to do in order to retract the piston. Usually it involves turning the piston while pushing it back into it's bore.

Ian

I'd personally vote for opening the bleed screws before pushing the pads back in, then topping up the MC when done. Don't want to take the chance of backwashing gunk into the HCU.

I don't even want to start the bleed/not bleed argument again - but I will say that bleeding on ABS does carry risks that don't exist without. So you makes your guess and you takes your chance.

nate

Nothing different about bleeding brakes in ABS cars (I've got two) - most cars should have brakes bled when pads are changed - this is an easy job and a good chance to flush the system.

Andrew

shiden_kai wrote:

"Nathan Nagel" wrote

I figured that this would come up. Personally, I think it's a fairy tale.....but if it makes a person more comfortable when replacing brake pads on an ABS equipped car, there is nothing wrong with that.

I worry that everytime you let a novice at something as simple as bleeding/flushing brakes, they inevitably end up screwing the procedure up. How, I don't know, as I do this all day long and never have any problems....but then again, it's my job. And since there is no "real" logic to opening up the hydraulic system when pushing pistons back in.....it seems safer to me to just avoid the hassle that might happen.

But of course this is an area of automotive repair where tech's fall into line on both sides of the argument...so it's best to do what feels good.

Ian

There's two wrong answers so far. You have no choice. Do it right.

Brake fluid is hygroscopic. It absorbs water over time. It also picks up dirt. Notice how the fluid in your master cyl is yellow, not the clear of new fluid. Guess what's in it ? You need to FLUSH the brake lines whenever you do a brake job. Don't do it cheap, do it right. If you have 50-60K miles you should probably rebuild the wheel cyl's, your call. If you have the rear drums I would definitely rebuild ($5ea) or replace ($12/ea aftermarket) the rear wheel cyls. They were seriously cruded up on my Quest.

Do the pads and disks/drums, reassemble. You should open the bleeders before retracting the pistons. Note that if you don't open the bleeders that the fluid will probably overflow back at the master cyl (if you've _ever_ added any fluid).

Fill the master, have an assistant pump it up, open a bleeder (with a hose attached in a jar of brake fluid) and let the pedal drop a reasonable amount. Close, pump, do it again. It will take 3-6 pumps per wheel, done in a couple of rounds around the car, to get clear fluid out. If you don't have an assistant then a "one man bleeder" will help you do the flushing. Once it's all clear, do a round of bleeding to make sure there's no air. (You still need an assistant for a final round of bleeding when done since air can leak in around the bleeder screw with the one-man approach.)

Bleeding for the ABS *is* in a different order for the Quest. The Haynes manual should list two different orders for with and without ABS but Haynes tends to slump when it comes to details that count. On my slightly older Quest the factory manual says it's LF, RF, LR, RR with ABS with the ABS unit disconnected. Without ABS, it's the usual RR, LR, RF, LF.

Bob

Well, the brake fluid (about 4 yrs old) looks extremely dark, so I think I do need to do the full bleed.

What is an HCU?

I'm using a Motive pressure bleeder kit, so will that eliminate the "risks" associated with bleeding ABS brakes?

Thanks again

Hydraulic Control Unit

IMHO the main risk is getting dirt in the HCU. I'd siphon out as much brake fluid from the MC reservoir as possible and also manually remove any dirt that you see in there before bleeding, if you're decided to go that route.

good luck

nate

Right. Don't do it right, do what Edward guesses you should do via "common sense".

It goes without saying, if you don't know what you are doing, then don't work on your car in any area that could affect safety. Now that we have the disclaimer done, let's get back on topic.

You really don't have a clue. Do you know what "hygroscopic" means ? Do you know why brake fluid turns yellow ? Have you seen what the seals and inside of a wheel cyl look like when someone has simply "changed the pads" at 50K and now they have 100K miles ?

It takes very little time to do it right and flush the system. At a minimum, you should inspect the wheel cyl's and calipers for leaks. You can rebuild a caliper in about 10 minutes with $5 worth of parts. You can rebuild a wheel cyl in about 3 minutes for about $5 worth of parts. If you are not comfortable with rebuilding a wheel cyl, then you can buy them for about $12 each.

For rear drum brakes, you also need to clean the assembly and grease the contact points. If he has 50K of more miles, he probably needs a shim kit and needs to clean the calipers too.

As to the rotors, you should either check them with a dial gauge or have someone do it. If they are out of spec, you can decide if you should turn or replace them. Drums are the same.

People like you who "put pads in the car and go on down the road" are not qualified to do brake work. Like you said, brakes are a safety item. It you don't know what you are doing, then you have no business doing it. I think that applies to you.

Bob

If you have a bleed kit, I'll assume that you are beyond these folks who tell you to just "change the pads" or "pay someone to do the work". According to the factory manual, there are no special procedures for ABS equipped vehicles aside from the change to the bleed order and the disconnection of the ABS unit during bleeding. I'll qualify that by saying that my car is a different year from yours, so you may want to get a proper manual.

If you open the bleed screws when pushing the pistons back, the fluid should go out the bleeder, not back up the line. Flush them first if you are really concerned. Fluid is only $4/quart... if you have to bleed again later it's no big deal.

BTW - if you have rear drums on a Quest- DO NOT adjust the rears using a spoon. Instead, bring them up to a reasonable distance from the drum during install, then use the "backup/pump" technique to force them to self adjust after you get the car on the road. Quest rear drums are known to lock up tight if adjusted in the lift.

Bob

Correction: Quest w/o ABS is RR,LF,LR,RF. With ABS is correct as posted above.

Bob

Is the "dirt in the HCU" risk specific only to ABS systems?

I've flushed brake systems in many non-ABS cars with a pressure bleeder system, with no problems.

Thanks

Unless you open up the brake lines, which you shouldn't need to do, there should be no reason to bleed the system.

----------------- Alex __O _-\

I would add that it is a good idea to get as much of the old fluid out of the reservoir before you start the process. Then wipe down the inside of the reservoir with a clean towel. By doing that you will spend less time, and fluid, getting the dirty old fluid out of the sytem and replaced with the clean fluid.

----------------- Alex __O _-\

just curious, how would a professional mechanic go about bleeding the system without getting dirt into the HCU?

Yes. I don't see any risk at all in flushing a non-ABS equipped car, other than the minimal risk of getting gunk in a prop valve if so equipped. In any case if the flushes are started early and done regularly there should be no problem. If you wait until the brake fluid gets all nasty, then you have to worry.

nate

"'nuther Bob" wrote

Actually, it's guys like you that want to "Midasize" every vehicle when doing a brake job that gives the whole industry a bad name. Perhaps you aren't actually a professional tech....but there are lot's like you in the trade.

I will agree with one thing you say, if people would have their brake fluid flushed on a regular basis, there would be less need for other component replacement down the road. But even on vehicles that don't have that regular maintenance.....there isn't any reason to be rebuilding calipers and wheel cylinders on every brake job, or even every other brake job. Typical shotgun approach. That's why people can't figure out why a brake job never is "$59.99".......because a lot of so-called mechanics want to "Midasize" the entire brake system.

Ian

BS. At around 4 years and 50K the seals are crusty and lack flexibility. The fluid is dirty and there's usually a little gunk in the cyl's. If you let it go, you have major junk at the next pad change at 100K. It costs about $20 to get kits for all four wheels and maybe an hour to rebuild them all.

This guy is in his driveway, not down at Midas, as are 99% of the people posting here. *Inspecting* wheel cyl's and flushing the system is part of any brake job. Since it takes very little time to do either it doesn't make sense to pull the brakes apart and skip the rebuild.

Bob

I'd like to see your 3 minute hone job. After you have wrung off the bolts and twisted the line in two or maybe just rounded off the fitting.

Still preaching without a license huh, well if the owners manual does not recommend changing or flushing brake fluid every time you replace the pads then why do you feel more qualified than the people who made and designed the thing. I am more than qualified about this and do not preach half as much. Take or leave it, the average brake job at 50,000 miles needs a visual inspection of the components and some pads if needed. Feel free to waste all the brake fluid you want...