58´ Power Brake Fail

Century1958

Member
Hello, I own a '58 Buick Century with power brakes (Delco). I had problems with missing power brakes all the time. I used silicone brake fluid.
In the garage the whole brake system was overhauled and changed to normal brake fluid. New hoses, new brake cylinders. The master brake cylinder and the brake booster were overhauled with new gasket sets. Now it brakes much better, but it loses the brake power support from time to time. The booster tank was checked with pressure and smoke for leakage. Nothing to find.
After 2 times braking or when I drive with lightly applied brakes the support is gone and I have to brake "normally".
The windshield wiper hangs on the vacuum line. There seems to be something wrong, because when the engine is running it "bubbles" in the water glass. Can this be the Problem? But According to the manual there must be a check valve somewhere. Where exactly? Is it the T-piece on Picture 2888?Does anybody else have an idea for troubleshooting? Modifications are not an option because of originality.

Regards Andre

IMG_2878.JPGIMG_2892 (Andere).JPGIMG_2890 (Andere).JPGIMG_2888 (Andere).JPGIMG_2886 (Andere).JPGIMG_2885 (Andere).JPGIMG_2882 (Andere).JPGIMG_2881 (Andere).JPG
 

firstofeight

Active Member
You have vacuum troubles, man. Obtain a vacuum hose diagram for your car and replace AII the vacuum hoses. Picture 1888 is the windshield washer pump/container. That short hose hanging off the bottom of the wiper , I bet, should be connected to the pump on top of the jar in picture 2888.

Ben
 

Century1958

Member
Hello Ben,
Where can i get a vacuum diagramm? I have all manuals but there is no diagramm inside. AACA Forum sides i can not open from germany .
Is this in the picture the check valve or is it only a T-Fitting?
9549D54C-026E-4FB7-A7C3-6320EC6F2A71.jpeg
 
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I believe the check valve is in the hard line going to the driver side from the tee you circled in the photo above. The item you circle is simply a brass tee threaded directly into the intake manifold. BTW don't make the mistake I did of putting very much stress at all on the brass tee; it is quite delicate and difficult to repair, as I found out. Always support it with a good wide wrench if detaching the hard lines.

On a 59 at least, the hard line (the larger one) coming off to the driver side is a dedicated vacuum for the brake booster. On the 59 at least the hard line is about 10 inches long and will have a device at the very end. I believe this is the check valve. The other (smaller) vacuum line going to the passenger side I believe is for your dash controls.

Can you try adding a check valve temporarily in the soft line and see if it fixes the issue; then you would know it is the check valve failed?
 
The Buick Master Parts list shows the brake vacuum check valve (GM no 5455970) comes with a pipe attached. This part no was used on late '55 thru '58 Buicks with power brakes. The '56 Buick Product School Manual confirms the brake vacuum check valve is in the vacuum line between the manifold and power brake unit. Photo 2892 shows a silver disc in the vacuum line near the oil filler/breather cap. This should be the brake vacuum check valve.

Photo 2888 shows the tee at the manifold vacuum source. The small painted pipe going off to the right side of the car should feed the vacuum advance unit on the distributor. The large pipe going off to the left side of the car feeds the brakes and wiper/washer.

Photo 2885 and 2886 show the vacuum source attachments (the 2 large hoses) at the wiper motor. The '57-58 Buicks have a rotary vacuum pump attached to the oil pump. This vacuum pump keeps the wipers supplied when the engine is heavily loaded and manifold vacuum is weak. According to the attached pages from the '57 Product School Manual, the right hose should go to the vacuum pump and the left hose to manifold vacuum. The '58 system is the same except the washer assembly is relocated from the right fender to the left cowl.

These hoses are attached to a check valve assembly on the wiper motor. This wiper vacuum check valve assembly allows only the stronger vacuum source to run the wipers/washer. The check valve assembly can be disassembled for service. Something has been modified here with the left port connected only to a stub hose. The manifold vacuum hose can be disconnected here and plugged temporarily to see if a leak in the wiper system is affecting the brakes.

The tests for brake system vacuum leaks in the shop manual will determine if the brake problem is upstream or downstream of the brake vacuum check valve. These tests are done with the engine off and indicate if vacuum reserve is sufficient.

Use of a vacuum gauge can confirm the vacuum tank is being pulled down adequately to provide enough powered pedal operations.

In addition to cracked hoses or a wiper system problem, a defective vacuum advance could cause weak manifold vacuum.

There is a '55 Dealer Service Bulletin indicating reserve braking capacity can be lost from riding the brake pedal. The same condition can be caused by a brake pedal that is not fully returning upon release.
 

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Century1958

Member
I've run some tests now.
First, I checked the check-valve. Seems to be working, because there's no passage when i blow to the brake booster.
Then I checked the tank with a brake bleeder vacuum pump.
Although only with -7,3PSI (0,5bar) - thought the value on the scale was -15 "bar", but it was "inHG" - so much less vacuum - but the vacuum remained stable.
Then, as Todd writes, I disconnected the line to the wiper and sealed it. Immediately I had it in my hand, because the pipe at the wiper motor had come loose from the pressing.
With the second check I had to find out that the hoses could be pulled off the pipes very easily. Partly even if they had a clamp. Thought already that is the error and replaced all hoses. Unfortunately the brake performance did not improve.
Next Time I have to do the "Testing Power Brake Unit" from the manual again.Had the feeling that during test "1st Vacuum Assist", I did not feel any brake support. Probably hadn't pumped with the pedal often enough to empty the system.
Test 3 "Vacuum Leak" I can probably save myself, because I can only brake assisted 2 times, sometimes not at all. So there must be a leak somewhere.
How much vacuum does the motor have to provide? I think I will do some new tests and put the pressure gauge after the valve. On the one hand to see if vacuum is built up, how much and if the valve is really tight.
I also had the manometer in the pipe to the tank - instead of the tank. Strangely enough, the vacuum was not stable there and dropped again and again - that's why I changed the surface. I have to take a more structured approach and work through the lines point by point.
Can it actually work without the tank?
In the attachment you can see a picture of how the lines run in my case.
I'll keep you informed.
Unbenannt.png
 
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Century1958

Member
Found it myself in the Manual, the Engine must have 22inHG on 1600RPM
22inHG = 10PSI = 0,7bar
 
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Century1958

Member
I'm a little confused. I read a bit on the internet and found out that Buick from 57-58 used an oil pump with a flanged vacuum pump. I assume that this pump is responsible for the vacuum for the wiper and the brake. Now an "expert" told me that this vacuum pump is only for the wiper and has nothing to do with the brake. Why then are both things connected there and pictures in the internet of 58er engine compartments show the same picture? The manual is somehow not very helpful
 
Found it myself in the Manual, the Engine must have 22inHG on 1600RPM
22inHG = 10PSI = 0,7bar
Note this data (from Chassis Service Manual pg. 2-2) only applies to the vacuum pump source.

Engine manifold vacuum is shown as 14 in. Hg (Minimum) at idle on pg. 2-1.

The Chassis Service Manual on pg. 9-23 indicates the power brake assembly utilizes the difference between intake manifold vacuum and atmospheric pressure to reduce brake pedal effort. Note it does not indicate the vacuum pump is used by the brake system.
 
I'm a little confused. I read a bit on the internet and found out that Buick from 57-58 used an oil pump with a flanged vacuum pump. I assume that this pump is responsible for the vacuum for the wiper and the brake. Now an "expert" told me that this vacuum pump is only for the wiper and has nothing to do with the brake. Why then are both things connected there and pictures in the internet of 58er engine compartments show the same picture? The manual is somehow not very helpful
Andre, per pg. 70 of the Buick Product School Manual shown above, the vacuum pump attaches to the check valve assembly on the wiper motor. Manifold vacuum connects to the other large pipe of the check valve assembly. Based on the description of operation on pg. 69, the vacuum pump source does not act upon the brake system, only the wiper system.

It is not clear where the vacuum pump source is connected on your car. It should be connected only at the wiper motor as shown on pg. 70.

As a further reference as to the purpose of the vacuum pump, it was discontinued on the '59 Buicks. This was the same year vacuum wipers were discontinued.
 
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I've run some tests now.
First, I checked the check-valve. Seems to be working, because there's no passage when i blow to the brake booster.
Then I checked the tank with a brake bleeder vacuum pump.
Although only with -7,3PSI (0,5bar) - thought the value on the scale was -15 "bar", but it was "inHG" - so much less vacuum - but the vacuum remained stable.
Then, as Todd writes, I disconnected the line to the wiper and sealed it. Immediately I had it in my hand, because the pipe at the wiper motor had come loose from the pressing.
With the second check I had to find out that the hoses could be pulled off the pipes very easily. Partly even if they had a clamp. Thought already that is the error and replaced all hoses. Unfortunately the brake performance did not improve.
Next Time I have to do the "Testing Power Brake Unit" from the manual again.Had the feeling that during test "1st Vacuum Assist", I did not feel any brake support. Probably hadn't pumped with the pedal often enough to empty the system.
Test 3 "Vacuum Leak" I can probably save myself, because I can only brake assisted 2 times, sometimes not at all. So there must be a leak somewhere.
How much vacuum does the motor have to provide? I think I will do some new tests and put the pressure gauge after the valve. On the one hand to see if vacuum is built up, how much and if the valve is really tight.
I also had the manometer in the pipe to the tank - instead of the tank. Strangely enough, the vacuum was not stable there and dropped again and again - that's why I changed the surface. I have to take a more structured approach and work through the lines point by point.
Can it actually work without the tank?
In the attachment you can see a picture of how the lines run in my case.
I'll keep you informed.
View attachment 10243
The manifold vacuum from the engine should provide at least 14 in Hg at the vacuum tank. Chassis Service Manual pg. 9-24 indicates the tank should build up vacuum within a minute with engine at idle. Tank should provide 5 slow pedal operations. Tank should hold vacuum for 12 hours.

The vacuum level at the tank will drop with each pedal operation. Vacuum should not continue to drop with the pedal held down. With the engine running, the vacuum at the tank should build back up. If a vacuum line is clogged or partially collapsed, build up time may be excessive. A vacuum leak could also increase build up time.

The tank is a vital part of the brake system and cannot be removed. The power brake cylinder is "air-suspended". This means no vacuum is present in the power cylinder when the pedal is at rest. So stored vacuum in the tank assures adequate reserve for power assisted operation. Later Buicks from '64 on used a "vacuum-suspended" power cylinder which stores vacuum in the brake unit. The vacuum storage tank was discontinued beginning in '64.
 

Century1958

Member
Thanks Todd
New test, now I have installed the pressure gauge with a T-piece in the line after the check valve and before the brake power booster/tank. When the car is started it has a negative pressure of -14 and builds it up quickly. When I step on the brake the pressure drops to -10 and rises again to -15 after releasing. Engine off, brake once and I have 0 bar. That is not good!
I will upload a YT video later.
If I have understood this correctly, one line of the wiper motor goes to the T-piece of the manifold and the other line, where I have the rubber hose stub on it, should go to the vacuum pump. But where is the vacuum pump or connection located?
 
Thanks Todd
New test, now I have installed the pressure gauge with a T-piece in the line after the check valve and before the brake power booster/tank. When the car is started it has a negative pressure of -14 and builds it up quickly. When I step on the brake the pressure drops to -10 and rises again to -15 after releasing. Engine off, brake once and I have 0 bar. That is not good!
I will upload a YT video later.
If I have understood this correctly, one line of the wiper motor goes to the T-piece of the manifold and the other line, where I have the rubber hose stub on it, should go to the vacuum pump. But where is the vacuum pump or connection located?
The vacuum pump is located inside the oil pan (fig. 2-10 in Chassis Service Manual). The vacuum pump line exits the block just to the rear of the oil filter (fig. 2-11).

The hose going from the vacuum pump line to the wiper motor should be 20.5 in long. The vacuum pump hose should connect to the wiper motor at the line which has a hose on it now.

Manifold vacuum should connect at the wiper motor line which has the stub hose on it now. From your diagram above, manifold vacuum for the wiper is fed from a tee in the manifold line. This should work.
 

Century1958

Member
Part 1
Part 2
Here i have two videos with discription in german/englisch
As I understand it, when the brake is applied, the pressure should be higher when the engine is running and should not drop to -10. Tank is connected and should compensate for this.
In the second video you can see how the pressure immediately goes to 0 at the slightest pedal touch. This should never happen and in my opinion, it should be possible to build up a vacuum even when the pedal is depressed, right? Otherwise the additional tank would empty itself immediately and it would not be possible to brake 5 times without an engine.
The "Pedal Test" for the Brake Booster doesn´t work , too. The Pedal is allways hard and does not move by Engine Start.
 
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