Folks, my brake pedal hit rock bottom again a few days ago, not sure why. Fluid is full in the master cylinder, and we bled the brakes twice on Saturday, all to no avail. The pedal still hits rock bottom and now has an obvious air-suction sound when you push hard.

Where else could air be getting into the system?

How old is the MC? Sounds like a classic seal failure inside. Fluid will be fine, but the pedal sinks.

ya, it sounds like it's time to overhaul , or replace the master cylinder.

And check to see if it leaked into the booster, if so replace that as well.

Master Cylinder is only two years old, but booster is probably 42 years old. Anyone have a link to simple instructions for booster replacment?

Also just remembered - Last week I replaced the front wheel bearings, may have accidently touched the pads or drum liner. I know thats not good, but what are the symptoms of getting oil or grease on the pads or liner?

The pedal won't go to the floor if there is grease on the drum, you just won't be able to stop as quickly.

The booster won't cause the problem you are experiencing. I've seen master go bad in less time. For as much as these cars sit around it wouldn't surprise me, seals can go bad from lack of use as well.

Same with the Booster leaking, the MC will still work and it would not go to the floor.....sounds like the MC to me...

Jon, I'm coming your way next week. Need some help? I've done the booster on mine...

Greg, give me a call and let me know of your travel plans. As always, we'll buy you a good meal if you come to town. 931-378-2060.

I went to a few websites this morning and many of them say a bad GM booster will, amongst other things, cause the pedal to go to the floor. There is an obvious, loud suction sound coming from the (booster?) when brakes are applied.

John:

M/c's have been crappy since the day I started driving a 9. I have been through so many m/c's on the car it isn't funny. You might recall a few years back I mentioned that I was given the wrong m/c for my car. The problem is that everyone else, now including me, has the wrong m/c on their 9's. The crappy replacment m/c syndrome is the reason I know that my car use to have the correct cylinder. Simply I had put on a dozen or so cylinders on the car for 26 years, without part's ordering issues. Suddenly after a quarter century 'my car's configuration is incorrect,' and all those high-end part-man professionals of days gone by, all lucked out and gave me the wrong one every time.

But how would I know about about how my car was made?

Your correct John and have been fishing in a much richer pond. A bad booster will allow the pedal to go to the floor. The only requirement needed to see how this is possible is to have a basic understanding of how a booster works!

The catch is that a bad m/c will make the booster sound-off as you say.

I use a different process than most when I'm troubleshooting. I know it isn't half the fun and half as impressive, but I like to start with the basics and conduct a few go/no-go tests. The real killjoy is that these tests ususally don't cost any money.

First of all, test your booster because it's easy, it's free, and it offers you a good starting point.

Disconnect that vaccume line from the booster and pull a vaccume on the booster. How you pull the vaccume is up to you. (I guess a pansyass--you know someone with a shocked look on their face say "Do you know what MOFO stands for?"--might have a problem with the test tools, but I disconnect the hose from the intake, and suck on it. Block it with the toung, and see it holds vaccume.) It's dealer's choice how you pull and maintain vaccume. The thing is that you're pissing in the wind if you start throwing parts at the car without verifying the booster holds vaccume.

If it doesn't hold vaccume, you need to repalce it. If you need to replace, you do not need to remove the hood. All it takes is a Craftsman brand 9/16" combination wrench, the one in even the most green shade-tree mechanic's tool box.

Here's a huge problem, and it may be the root/cause of yours.

I don't know why, but almost every pedal pumper applies a thousand times more pressure on the pedal than it takes to lock up the brakes, causing catostrophic failure to boosters, m/c's, w/c's calipers and brake hoses.

Update your post after you test the booster.

Also check the vacuum line that goes to the booster. I had one that collapsed internally. When you let off the gas, expecially when you are at higher rpms, the vaccum spikes. This will suck the hose closed so the booster sees no vacuum.

That hose needs to be replaced ever so often.

Merv, your eloquent responses and advice are always enjoyed by all. Ok, will test the booster and vacuum hose.

Pulled the MC off last night and there was fluid all around the mating area between it and the booster. Removed the four nuts from the booster mount (man what a PAIN!) and then called it quits for the night.

Next is to disconnect at the brake pedal connection, but is it the pin/nut hardware easily seen and accessed, or is it further up under the dash area where you disconnect?

Hmmmm...sounds like a bad master cylinder. Good, that you are replacing both.

The connection is right at the pedal itself and readily accessible.

Got the whole job finished tonight, just need to do the total Brake bleeding tomorrow night.

Even without that, the pedal movement is dramatically better (harder) and there is no "sucking chest wound" sound anymore!

Glad you have this one almost done, brake issues truly suck. And bleeding them can be a blast as well. Good luck and hopefully this will solve your problem and be back up and running...

Bummer, minor set-back. Maybe I didn't bleed the new M/C enough. Once we bled the front left and right wheels and cranked the bird up to apply some "power assisted" help, the pedal went right back to the floor again!

Shut the car down, and began bleeding the front again, and there was air to be bled. Quit after that for the night, and will do the rear tomorrow. Might have not done the "bench M/C bleed" to standard?

The bench bleed is key. If the wheels aren't bled up to par you will just end up with a soft pedal but if the bench bleed isn't done right you know what you end up with.

Also you need to bleed the farthesy wheel from the master first. rr lr rf lf in that order.

sounds like you are having the same problem I do with my TR6....I replaced everything up front ,calipers, rotors , pads hoses, still had 'bad' braking...replaced rear brake shoes ,adjusted...took it to shop, b/c it was still not braking right...if I hit the pedal fast (like a panic braking) pedal was up high and firm, if I hit t slow pedal slwly goes t the floor, I could pump it up, but a slow braking it would go down...I told mechanic I thought it was a bad booster...they tested it ,said ,no a bad MC, they replaced it...I picked the car up...it was the same, brought it back...they said , maybe a bad MC (the manuf has 25% return on these!), replaced it for another, picked car up, still the same, now they tell me I need a new booster! LOL...will order one monday , we`ll see...
Does Lucas make boosters?? LOL

I am about to give up on this brake project! Man, I just took the new MC off again and bench-bled again, re-installed and bled all the lines. There is no air in the lines! The pedal starts to feel hard after bleeding, but as soon as I start the engine the brake pedal sags like a limp noodle.

New Booster, new vacuum hoses, new M/C, new fluid.

What would cause this?

Are you using a bleeding tool or just doing it manually?
I assume you have two people doing the bleeding.
I saw a tool you can get at CI that makes the job easier and one person can do it.

Did you bleed them back to front in the order Vikky stated?

Have you successfully bled your brakes before?
Do you have someone close have a look at what you are doing. A second eye sometimes helps.

Are you refilling the master cylinder every time?

I'm assuming your bleeding correctly but I will state the procedure I do to see if we are both on the same page.

1. Driver pumps up the brakes, tells dude at RR to to bleed
2. Driver tells dude to close b4 the petal hits the floor
3. Move to LR and do same thing
4. Move to RF and do same thing
5. Move to LF and do same thing

You need to add fluid if you get low in the m/c while bleeding. Start over if m/c goes dry.
Always collapse the rubber in the lid b4 putting lid back on.

Start the car and test.

Pumping up the pedal should be done very gently. If you are too agressive you will break up all of the air into tiny bubbles. I usually have the wrench and my wife in the car. I have a clear platic tube I attach to the bleeder. My wife keeps light but constant pressure on the pedal all of the time. Simply hold light pressure and open the bleeder. When the pedal hits the floor close the bleeder. let it up, repeat. Continue until no bubbles. Check the master often! Drop a couple extra bucks for the good stuff too! Have heard dot 3 holds moisture. Again work farthest to closest.

Just wondering the condition of the hoses? I would suggest you have somone hold heavy pressure on the pedal while inspecting all rubber hoses. Think you said all the lines are new? If not follow all of them looking for leaks. No rubber splices no compression fittings, just double flares and metal.

Sorry Not Vlkki but I did teach brakes for a short time. I sure do like the color of her car! Along with my wife, neighbors, and a few friends, Vikki's pics talked me out of the blue.

Yes to all of the above. I've bled brakes on this car and my old 68 camaro many many times in the past and never had a problem. Something is not right. Remember, this all started last week when suddenly the brake pedal went to the floor while driving. No fluid leaks anywhere.

What orher vacuum failure possibilities could there be? I have a new hose from the booster to the intake manifold fitting. Seems strange that the pedal gets even softer once you start the engine.

Sounds like you may have a proportioning/combination valve issue. Does the brake light come on when you push down on the pedal? What we've done before in the shop is open all the bleeders(will make a mess)then press down on the pedal, close all the bleeders, release the pedal, fill the M/C and then bleed the system as normally done.

Yep, brake idiot light comes on each time you press down on the pedal. In fact, last night they stayed on after shutting the engine off, and I had to disconnect the battery to avoid draining the power.

Ok, do what I suggested above, just one pump though and it should center the combo valve/switch. Report back.

Will do. Jeff, give me a call if you think of anything else to try. John, 931-378-2060

watch all the rubber hoses for any kind of expansion as somone pumps the pedal. Some even new hoses fail.

Do the same, just remember Cali time

916-613-8386

Its not a vacuum problem.

RW, I mentioned the vacuum again because, with the engine running and the booster vacuum line capped, I have at least some minor braking ability. As soon as I connect the vacuum to the intake manifold (again, with the engine running), the pedal goes limp and is completely bottomed out.

Since there is no way for the Booster to "leak" air into the M/C or brake lines, I figure there must be some connection....maybe not.

Is this a 4 wl drum car? If so make sure you have all 4 wheels adjusted to slightly drag. Either way be sure all the drums are dragging on the pads. Look very closely at the hoses all 3 while there is pressure on the pedal. I have seen them blow up when you apply the brakes. This will cause your condition, and no leaks. Pull the drums again and look closely around the wheel cylinders for wet.

Do you lose any fluid? When you bleed the lines can you see the air coming out (attach hose to bib and put into container with fluid to see ifit bubbles)?

If your losing fluid can you see where it's leaking?

Seems to me when I installed the rear brake kit I was having this prob too. I think I pulled the MC off 3 or 4 times to bench bleed. What finally did the trick was how I ended up bleeding the lines. Since my wife always gives so much flak about sitting in the car and pushing the pedal(tough job) I decided to give it a go by myself.
I opened the farthest away bleeder first and with a hose in a bottle of fluid set higher than the screw I pushed fluid through with a couple of slow strokes and a couple of quick short pumps(not all the way down) and a couple more slow till the MC was almost out. Don't let the fluid run out. Did one at a time till they were all done. Worked like a charm. I figure I probably changed out all the fluid in the system with new by the time I was done and didn't have to put up with all that ""are we done yet" BS.

The booster gives you power assit. Nothing else.

Exactly, it should not have anything to do with it going to the floor, unless the actuating rod you put in was too short? Does the car still have some braking ability when it hits the floor....it probably does, just the booster makes it easier to floor it...

Be interested in what would happen with a longer actuating rod in it to give you more throw...

That's what I was thinking. John, did your new master/booster come with a new acuator rod? If so, did you use it and was it the same length or different.

The rod is adjustable.