Spongy Brakes - Air - Bleeding - How to tell?

Where did you learn how to read?

He stated he had the repairs done in 'reply' to my post, not in the original post.

Mike

jim wrote:

I thank you as well Mike for trying to help.

Uhuh, one can deduct from my posts that two mechs already found nothing wrong with the system short of the first one who DID replace the Brake Pads (something I omitted from my post, sorry. But I did so merely because all I needed from here was the answer to my original question). BTW, I respect the inputs of folks like you on the Net BECAUSE you've nothing to lose and aren't looking to get a buck out of me. Thx!

As for this character Jim, I've seen from some of his other posts on Usenet that he's the occasional loser with the knack for insulting others on a whim.

You asked only one question:

The only answer you will accept is they have to drive the car to determine there is air in the brake lines. That's stoopid. Driving the car isn't going to tell you anything about air in the lines. It wouldn't be a bad idea to drive the car to give a general diagnosis but for answering that one single question, no it is not necessary. They obviously drove the car after doing the brake job and they obviously know about whatever it is you are whining about and they obviously have told you something. But you aren't going to present any of the facts because you are far more interested in getting the one single answer you want. If there is anything wrong with your brakes finding some idiot on Usenet to agree with you isn't going to get them fixed. You are to dumb to realize that maybe if you presented all the details in a factual manner you might actually get an answer that works in your favor (or at the very least keeps you from wrapping your car around a big oak tree).

The answer to your question is yes if all you want to know is is there air in the lines all you have to do is get in the car and pump the brakes. The reason you can tell the difference between air in the lines and the various other problems that would cause a low pedal is because air is the only thing in the brake system that is truly compressible (well, there are other things that have small amount of give but nothing even close to air for compressibility). As a result, if there where air in the line it takes more brake fluid pushed out of the master cylinder to compress that air, and consequently it takes more time for the fluid to return to the brake reservoir. Someone with experience can tell the difference between air in the lines and the various other possible problems that would cause a low pedal that pumps up.

-jim

The best way to tell is to do a proper bleeding procedure on the system. Some ABS brake systems require a scan tool to bleed. Also you may need a pressure bleeder. One of the first test is with engine off pump the brakes to remove vacuum from brake booster and see how the brake feel. You should then have a full firm pedal. Do you?

Tips on getting a good answer to your questions. People trying to answer your question do not have a crystal ball. So give them all of the info you have like year make and model and engine and transmission and mileage. Also cars engine and transmission service history or any recent repairs or problems. Also a description of your problem and what it is doing or not doing. If you have codes give up the code no. And remember a code does not say replace the part but only points to the problem that you have to check out. So to better help you give up all of the info you have on it. MT

Tips on finding a good mechanic/repair shop. Check around Ask around Word of mouth. Family friends coworkers neighbors business people and delivery people. Mailmen and parcel delivery people get around and notice a lot of stuff. Even a good parts house knows what shops are good and not good. Chamber of commerce and better business bureau and city hall. If you find a good referral to a repair shop go look them over and talk to them. Look for a clean looking busy place with nice people running it. Ask a few questions and ask about their qualifications and training. Not all places have trained tech/mechanics. If they do not find a place that does. Even all dealers do not have all trained techs/mechanics.

and you're too much of a friggin jerkoff to realise that the more you insult a person the more you'll be thought of as a LOSER!

....and no! They did not drive my car. I mentioned that!

....and no! I'm not looking for anyone to agree with anything I have to say! I'm only looking to see if the guy at the front desk WHO IS NOT THE MECH (I mentioned that as well) knows what the heck he's talking about! He's almost reluctant to bleed my system based on the actual mech's findings WHO ONLY went by the very little information he got from this guy at the front desk. 'And how do I know that? I WAS THERE!

Again, re-read and maybe that thick brain of yours will jar into working order.

end of story!

Well that was my point he didn't reveal that so you are off trying to figure out how air got in the lines. He won't say what the shop did or what their opinion of what the current condition of the brakes is.

-jim

So why hasn't the mechanic driven the car?

Maybe you can't tell by other means. Maybe it's just the simplest and most direct way to tell. So have them drive the bloody thing and know for sure.

when the master cylinder started leaking on my race car, it was firm, firm, floor, firm, firm, floor.

And the replacement one was borked out of the box - went to bench bleed it and it was leaking past the seal.

Ray

Yes, and replacing the master cylinder would be a terrible diagnosis for a pedal that gets firmer with each depression.

I had just purchased a car that had a spongy brake like you describe, and the mech at the dealer said "they all are like that, get used to it". So, I drove the car like that for a few years and had to replace the front calipers myself and after bleeding the brakes - holycow! The car suddenly had a firm pedal and brakes that would stop a tractor trailer! Moral of story - you can't trust mechanics all the time.

Your vehicle is not one of them, but some newer models have ABS that greatly complicates getting air out of the system if lines are replaced or similar large repairs. Some have tedious procedures for bleeding that many folks would probably screw up.

My van had out-of adjustment rear brake shoes when I got it (too much space between the drum and shoe), and until I adjusted it properly, the pedal would sink to towards the floor and it would only stop with the front brakes. You could possibly have this.

Your little 4x4 is so light, it should stop on a dime. Good luck. Brakes are really pretty simple.

That doesn't mean it had air in the system. It could just be the calipers had to move farther due to the difference in compliance of the pad material or due to uneven wear on the pads or other causes.

If there was air in the lines you would think you would have very quickly figured out that hitting the brakes twice (or more) would greatly improve the stopping capability. I mean think about situations come up all the time in city driving where you need to apply, release, apply the brakes in rapid succession. A couple hours of city driving and just about anybody would learn that pumping the brakes improves the braking capability. Although the designed firmness of the brake pedal varies a great deal from one type of vehicle to another, there are no vehicles that require pumping the brakes by design. That is, none of them are like that.

-jim

Air in the system or moisture in the brake fluid will give problems. That is why it is best to change brake fluid ever so often. It can draw moisture and boil into steam and is as bad as air in there. Also old brake fluid gets strong and is hard on all brake rubber parts. If you are not sure about the condition of brake fluid or air in the system. Have it pressure bleed and new brake fluid added. Your brakes will love you for the new fresh fluid. MT

Old brake fluid is pretty hard on metal parts, also. Acids will form that pit master and wheel cylinders and cause leaks in brake lines. Flushing out the old brake fluid is certainly a good idea after a few years.

-jim

I'd sure like to know why that is. I'm also curious as to why it's more pronounced on some cars than on others, even on similar models; my '89 Grand Marquis does that more than my '91 GM. (Both have new brake fluid.)

You would like to know why what is?

Does pumping the brakes improve the braking capability of your cars? It isn't supposed to. If that is your question then the 2 most likely causes are out of adjustment rear brakes and/or air in the lines.

-jim

It sounded like you were saying this is normal in the first quote. Anyway, they don't improve a great deal, but it is noticeable. Rear brakes are adjusted fine, and brake fluid is new and as air-free as I can make it. No ABS so no fancy bleeding procedures involved.

And again, I've noticed this on every car I've driven; again, it's not a pronounced effect, but it's noticeable. The pedal also firms up a little on the second or third push.

In general if everything in the brake system is working as it was designed to work the brake fluid that gets pushed out of the MC should return back to the MC at least as fast as the pedal returns. So what you describe indicates a problem - particularly if you notice the bakes stop the car better (on dry pavement) when pumped.

Is this with the car running or after you have turned it off?

-jim

It isn't so much that they stop the car better as it is that the pedal has a firmer feel and seems to give better control. The brakes on my '89 need a little work soon, but those on my '91 are outstanding since I changed the brake fluid; yet the pedal gets a tad firmer and more precise with a pump or two.

Running.

No this does not happen always. It only when when the pressure in front of the seal is less than the pressure behind. That will not be the case if the system is working as designed.

There isn't supposed to be any air. The system is designed to only push out so much fluid when everything is operating properly. That amount of fluid will maintain pressure and return fast enough so that the pedal return does not draw any additional fluid past the seal. This will only be true if everything is working as designed.

-jim