timothypaul

#48
Today 05:17 PM by timothypaul
Brake Failure
Hello Olds enthusiasts

Today I lost my breaks and drove through my garage door. Not too much fun.

I have had to fill the small chamber of the master cylinder often but the larger chamber is always fine. I'm am wondering what may have happened. I've checked the wheel cylinders and can not find a leak. As well as the proportioning valve. I have no clue where the leak is. But if the larger chamber has fluid why would I lose the brakes?

Ty. Tim. :-(
Edit Reply

MDchanic

Okay, not to break your chops (any more than your garage door...), but

Are you saying that you kept driving a car that was losing brake fluid, without fixing, or even diagnosing the problem?

One side of the M/C reservoir going down, while the other side either goes up, or stays the same, with no leaks, equals a bad master cylinder.

The small reservoir at the back of the M/C is for the rear brakes, and the large reservoir at the front is for the front (disc) brakes.
If the rearmost reservoir is losing fluid, the fluid is going out the back of the M/C and either down the front of, or into, the booster (in manual brake cars, it sometimes is absorbed into the sound padding and carpet under the driver's feet).
If the front reservoir is losing fluid, it usually goes into the rear reservoir.

In your case, your master cylinder was in the process of failing, and, in fact, the rear circuit did fail, leaving you with front brakes only, which you didn't notice, and then, when the front half of the failing master cylinder finally gave up, there weren't no more brakes left to be had.

Did your BRAKE warning light go on at any time?

Hope your car's not too dented up.

- Eric

rustyroger

What has happened is an expensive lesson in not heeding warnings.

Why didn't you investigate why you were losing brake fluid?. If you couldn't figure out what was happening you should have got someone who could before you drove that car again.
Be thankful your brakes failed at home, not on a busy highway or a stop light. If I don't come across as sympathetic it's because I'm not.

But, as Eric says, it seems you have a bad master cylinder. Don't just put on a new one, go through the whole of the braking system and check everything out, fix anything that isn't right. You got lucky this time, next time might be your (or more importantly some innocent third party's) unlucky day.

Roger.

FMB42

Never ever continue to drive a vehicle with a known brake problem. Not sure if your car has a power brake booster. But if it does, you'll want to make sure that the master cylinder isn't leaking into it (which can sometimes hide a fluid leak). Master cylinders can also occasionally leak through the firewall and thus hide a fluid leak is rare tho). Carefully check for even the slightest sign of brake fluid in and around the area where the master cylinder mounts to the booster or fire wall and work your way out from there. A loss of fluid and/or line pressure in one chamber and/or hydraulic line/section can cause total brake loss. Most dual reservoir master cylinders are, unfortunately, not the same as a completely independent (front and rear) brake system.

MDchanic

I'm not sure about "most" systems, but all of the systems I have ever seen are, at least until the master cylinder seals fail and allow fluid from one side to transfer to the other.

- Eric

rustyroger

When that happens you will get an unmistakable warning that something is drastically wrong, as in the brake pedal going almost to the floor. The only car I came across with two master cylinders was a Rolls Royce.

Roger.

MDchanic

Yes, whenever I have had one side fail, whichever one it is, the pedal has always gotten noticeably lower, even when the rear side has failed, leaving me with almost-normal-feeling front brakes.

But, aside from the master cylinder piston, and the frame of the car to which the tubing is bolted, there is nothing connecting one side to the other.

- Eric

FMB42

Yep, and some Rolls Royce vehicles have a back-up brake booster that will give you power braking for several stops when the engine isn't running. Anyway, it is not at all uncommon for a brake pedal to go all the way to the floor when a line fails or while bleeding the brake system. And yes, some braking may still exist on the non-fail end, but it isn't always enough to stop the vehicle.

timothypaul

Well. Not feeling to bright at the moment. Yes, I was driving the car under all those conditions.

Because the vacuum is so low, I just presumed that's why the brakes were bad. The Master cylinder never even crossed my mind. I looked all around the wheel cylinders and could never find anything. And while the pedal didn't feel great the car has always stopped ok.

After your post, I checked and there is fluid going down the power booster.

I put a new master cylinder on this morning. I bench bled it. It seems to still be leaking there also. Could something be wrong with the power booster? Or should I assume I got a defective MC.

Of course I snapped a brake line while doing this, just to give me something else to play with.



:-(. TP
Edit Reply

timothypaul

Hmm. And while I'm learning. What does the proportioning valve do?

boese1978

It proportions the amount of brake pressure between the front and rear brake systems.

timothypaul

Right. So if both lines from the MC are going into the proportioning valve do they stay isolated? Not to sound stupid, but until I read Eric's post, I always thought the small chamber on the MC was a backup (reserve).

I figured if the proportioning valve was regulating the flow to all four wheels, that as long as the larger chamber had fluid there was fluid getting into the valve.

MDchanic

The proportioning valve is divided into two parts that never mix.

Not sure about your year, but I believe '71 and later also serve as the differential switch, which makes the BRAKE warning light come on if you lose pressure on one side of the system.

- Eric

D. Yaros

I recently lost the brakes on my '62. No signs of leaks anywhere. It was in fact a defective vacuum assist booster. The seal went south allowing all the fluid in the MC to be sucked into the booster.

timothypaul

Question about bench bleeding.

Do you seal the ports where the brake lines go? Or should the fluid drip out of them?

Also - wouldn't this be easier to do with the Master Cylinder installed on the car but without the brake lines connected?

Thanks...TP

timothypaul

I answered my own question.

Nice video on bench bleeding

Professur

You can do it on the car if the MC is level. A jack and stands is usually enough to make it work .. but if you're replacing the MC anyhow, all it takes is a bench vise while out of the car. If you flub up something after installing it( New-in-box defective?), it's more work the other way.

timothypaul

I took the MC off and see that the powerbooster has brake fluid inside of it.

1. Is it supposed to (common sense tells me no).
2. Can I just drain it, if neccesary?

Thanks again....TP

Junkman

You need to replace the brake booster, since the brake fluid will eventually deteriorate the rubber inside the brake booster. If you want to keep the car all original, send the booster to "Booster Dewey" in Oregon. He does excellent work. If you don't care about originality, then buy a rebuilt replacement from one of the local auto stores. Since A1Cardone, is the brand that almost all auto parts stores carry today, look for the least expensive one, and you can also buy it with a rebuilt master cylinder attached. Not all stores carry the combo units, and will want to sell you the master separately. The combo unit is the least expensive way to buy this part.
While you are doing the job, consider rebuilding the front and rear brake cylinders also, and change all the rubber hoses. If your car has disk brakes, if the calipers are not leaking, then I suggest that you just change the fluid in them.
The government mandated dual master cylinders in the late 1960's because people neglected the braking systems, and brake failures were a common event. It was thought that having a dual system would alleviate this concern on neglect. As you have experienced, neglect continues, and so does brake failures. Dual systems, when they fail suffer from the same problem as the single master cylinders do when they fail. The loss of braking power leads to accidents. Doesn't matter which system your car has, you have to do periodic maintenance on the braking system, if you want it to be trouble free.

timothypaul

Ugh. Ugh.

So looking up power boosters I see sizes from 9 - 11 inch that say they are for A bodies. Which size is correct?

MDchanic

Your original booster was 11".

- Eric

Junkman

From Rockauto dot com...


A-1 CARDONE Part # 501106 Reman. Vacuum Power Brake Booster w/Master Cylinder
Front Disc Brakes; Rear Drum Brakes = $133 less $30 core = $103 plus shipping.








A-1 CARDONE Part # 5471106
Reman. Vacuum Power Brake Booster w/o Master Cylinder = $110.79 less $21 core = $89.79


Use this code, and get a 5% discount.. 58706B0C3F9D33

timothypaul

Oh my. Are the bolts for the power booster against the firewall and not by the brake pedal. How in the world does one get to those. :-(

Lady72nRob71

Against the firewall. Use box end wrenches. Removing the wiper motor and inner fender helps, too. It will take a while to do this.
If the nuts are tight, use long handled wrenches for more torque, or hook two wrenches together for a longer handle.
Have patience. If you round one off, it will be heck getting it off after then (dremel and carbide cutter). Been there done that...
https://classicoldsmobile.com/forums...tml#post298896

timothypaul

What does the adjusting nut on the power booster that connects to the brake pedal do? Is that just there for brake pedal height?

Sampson

(Quote). The government mandated dual master cylinders in the late 1960's because people neglected the braking systems, and brake failures were a common event. It was thought that having a dual system would alleviate this concern on neglect. As you have experienced, neglect continues, and so does brake failures. Dual systems, when they fail suffer from the same problem as the single master cylinders do when they fail. The loss of braking power leads to accidents. Doesn't matter which system your car has, you have to do periodic maintenance on the braking system, if you want it to be trouble free.[/QUOTE]

This is sorta right, but not exactly. Dual master cylinders divide the brakes into 2 independant systems, front and rear. Should any component such as a wheel cylinder or brake line past the master cylinder fail, the brakes will still function on the set of brakes on the unaffected wheels. IE: if the brake line blows on the front wheel, the rear brakes on the car will still function and vice versa. This takes care of 90% of the components that can fail in the brake system and is exponentially safer than the old single master cylinder systems. Now to your point about neglect and the remaining 10% of potential problems. If the master cylinder leaks either internally or externally all bets are off. Also the reason for the large reservoir for disc brakes relates to the travel of the piston in the caliper as the brakes wear. As the pads wear the caliper piston travels further an requires more fluid.

timothypaul

Was really hoping I could get the answer about the adjusting nut on the power booster. I think we covered the other stuff in December. :-(

MDchanic

The adjusting nut sets the gap between the pushrod and the booster.

There is a specification for this setting in the CSM, if I recall.

If it's too small, there will always be a tiny amount of pressure on the booster, and the brakes will frag.

If it's too wide, the pedal will sit low, and you will have incomplete braking.

- Eric

Fun71

Well that sounds extremely frightening.

Unless you meant drag.

If so, then not quite as dramatic.

MDchanic

Ha ha. Yes, "drag."

Frag would be far more dramatic than I intended, though far more interesting than most of the problems we see posted.

- Eric

timothypaul

I kind of figured that out. :-)

I read the FSM and it says a tad over an inch. Not sure how I'm supposed to figure that out now that it's in the car. So I'm kind of just playing with it to see how the brakes feel.

The thing I'm noticing is that the brakes feel like a rock. The car stops but to me there is zero vacuum assist. I'm wondering if there is something wrong with the check valve. When I got the power booster there was a tag on it saying the warrentee was void if the valve was removed so I didn't touch it...

Junkman

At present, I don't own the same model as you have, so my instructions in this post are going to be generic.
If you look at the brake pedal, where the power brake booster rod comes through the firewall, you will find that it is pinned to the brake pedal through a clevis and pin, and that the pin has a clip on one end of it. You need to remove this clip, and then pull the pin out of the brake pedal. This will allow you to pull the brake pedal toward the rear of the car. Once you do this, you will see if the activation rod and clevis that connects the booster to the brake pedal needs to be lengthened or shortened. The clevis that goes through the should enter the brake pedal hole in a neutral position, not pushing on the booster. After you have the push rod clevis properly aligned, then you might have to adjust the brake light switch to activate the brake lights, when you push on the pedal. I usually set this so if you have a little play in the pedal before the brake lights come on.
Now that I have covered the way that the General did it on most of the cars, I will also say that I have seen some, where the brake activation rod, has to be adjusted also, on the other side of the booster also. This adjustment sets the distance of the diaphragm in the power brake booster to the master cylinder piston. If this adjustment is not set properly, then you will also have constant pressure pushing on the piston in the master cylinder. Setting this without the factory tool, can be a little tricky. The tool looks just like the tool for setting the drop on carburetor floats, but just like the floats, it can be done by careful measurement with a steel ruler. This setting, if required, will be shown in the factory service manual.
The following pictures are of both Delco Moraine and Bendix power brake booster, and are from a 1968 Pontiac FSM, that I happen to have handy while typing this reply, but they should be very similar to what is on an Oldsmobile. The first two pictures are the Bendix system, and the last two are of a Delco Moraine system.

Junkman

A vacuum assist booster will not suck the brake fluid out of the master cylinder, if the seals in the piston were not worn. You had a defect in the master cylinder that allowed the brake fluid to be sucked into the vacuum assist booster, which in turn, damaged the booster itself. The diaphragms in the boosters are attacked by the brake fluid, and will deteriorate quickly. When this happens, it means that both parts will need to be either rebuilt or replaced.

timothypaul

I think before I even get that correct I need to figure out a way to test the vacuum assist / power booster. I didn't understand what the FSM saying.

When I pulled off the check valve yesterday a lot of built up vacuum escaped. I done remember my old one ever doing it.

Junkman

The new booster if functioning properly, and the old one didn't hold the vacuum, because the diaphragm in the booster was leaking as a result of a crack in the rubber. It is clearly obvious that you don't understand the principles of how a power brake booster works, and that is what is leading to your problems. It is very difficult to repair a system if you don't understand the principles of how it works, and at this point, I suggest that you get assistance from someone with more experience, or do a Google search for "how a power brake booster works", and learn the basics, before proceeding. I am not trying to be harsh, but if you mess up, the results could be disastrous for both you, your passengers, and your car.

MDchanic

Yeah, after reviewing this thread from the beginning, I'm done, too.

I never say this, but have it towed to a shop. Somebody could get hurt.

- Eric

DLaz70OLDS98

Don't forget the poor SOB in front of him.......

D. Yaros

And, both were in fact rebuilt.

Junkman

Rebuilt is a very vague term today, because, unless you did the rebuild yourself, many times, you have no idea of the condition of the core that was "rebuilt", or the quality of the work that was performed. When it comes to brake booster, there are only 2 firms that I trust to do it correctly every time. One is Booster Dewey in Oregon http://boosterdeweyexchange.com/ , and the other is Karps Power Brake Service in California. http://www.karpspowerbrake.com/


When it comes to master cylinders, I only trust my own work, since I can carefully examine the bore, and determine if it is suitable for rebuilding. If the bore is honed oversize, that increases the likelihood that the pistons are going to leak. In these cases, I send them for sleeved in brass to Apple Hydraulics in New York. http://www.applehydraulics.com/ Karps also does sleeving, but I have never used them for that service, and have no recommendations, although, based on the quality of the work that I have received from them, I have no doubts that that service would be first class also.

D. Yaros

If I was so inclined, I might assume that you are calling me "less than smart" and are being more than condescending towards me.

FIRST you imply that I do not know what I am talking about when you state in response to one of my posts that "A vacuum assist booster will not suck the brake fluid out of the master cylinder." Then you immediately add an exception.

I can tell you that on inspection by me a) the MC was dry, b) there were no visible signs of leakage, and c) when I disassembled the booster I found the missing fluid.

SECOND you state with authority that there are only 2 firms in the world that have the capability to do a proper rebuild. I won't even bother to comment on that remark.

Since I do not know you, I shall give you the benefit of the doubt (which is far more than you gave me) and assume you are trying to be helpful with your remarks and I shall try to not take offense to them.