So I went for a nice drive yesterday. Drove the car all day and it behaved very well. When I was almost home and used the brakes, the pedal almost went completely to the floor and I had very little brake action. Scary. I parked on the side of the road, pumped the pedal, and it came back up. I slowly drove home with a hand on the emergency brake just in case. I got home safely. I did a few checks. With the car off, sit for a minute or two, if I push on the brake pedal it goes to the floor. Then I can pump it twice, it comes back. I checked to see if it would keep pressure or that it would slowly sink down. While having my foot on the pedal I keep constant pressure on it, and the pedal does not sink.
If I let it sit again (car not running) it does the same thing.
My first thought is the Master brake cylinder is giving up on me. I replaced all broke hoses and cylinders last fall, so I guess chances are small that one of those is the culprit.
My plan is:
Check brake fluid level first
Check all the wheel cylinders, hoses and lines for leaks
If that checks out, remove the master cylinder (and replace or have it rebuild).
Any other suggestions are more than welcome.
Luckily it happened at the end of the day and not at the beginning so I have enjoyed the car for the whole day :).
Let us know what you find. Curious on the fluid level.
I would hold pressure on the system for a few minutes with a board or something wedged in to hold it.
After a few minutes, check for leaks.
Let us know what you find.
Which brake system is on a 54? Wasn't this the period where Cadillac was trying everything?
System should be the same as the 55. Sounds like you have a bad wheel cylinder or line somewhere.
The 54 brake system has a remote power servo, separate to the master cylinder, it has got to be a leak somewhere.
So this is the hydra boost where there are more or less 2 masters? One the pedal is hooked to and the other that is in the booster which is the one that is acting on the wheels? Seems like the troubleshooting for this would be different than many other systems. 56 was the year Cad tried the treadle vac?
Air in the lines or master cylinder can cause your symptoms.
Since you replaced master cylinder and wheel cylinders last fall it might be one of those new components were defective and leaking.
If after finding no leaks at m/c and wheel cylinders and assuming the m/c was bench bled before installing, then the hydrovac is likely the culprit. Because, as TJ notes, the '54/'55 power booster contains the equivalent of a second master cylinder this unit has to be bled at two separate bleeder valves on the booster itself as part of a complete brake bleed. If that wasn't done, i.e. just the m/c and wheel cylinders were bled), air in the hydrovac unit could have worked its way back to the m/c which would require it to be bled again.
I've bled the m/c while on the car on my '55 by connecting a clear tube from the lower bleeding valve on the end cap of the booster (where the brake line comes out to the wheels) into the brake fluid reservoir and bleed as you would a wheel cylinder (pressing brake pedal) until no air bubbles are seen in that tube. (Bleeder Fitting #1 in pic)
Then bleed to a bottle from that same bleeder valve to bottle until no air bubbles. (keep reservoir full)
Then bleed the 2nd bleed valve (#2 fitting in pic) on the top of the hydrovac booster,
Then bleed the wheel cylinders in the normal order (furthest wheel to closest)
Now all your air should be gone. If symptoms persist or return the hydrovac unit may be defective.
'54 and '55 are similar hydrovac systems however '54 has the check valve in the master cylinder while '55 moved it into the hydrovac booster unit. As such you need to make sure your recently installed m/c is not for a '55 which would have no check valve but contains the check valve as required in the m/c in '54.
54-55HydrovacBleederValves.jpg
Hello Julien, To my opinion the ball check valve in the drawing that tluke posted is the culprit. The ball check prevents fluid from draining back to the reservoir when brakes are not applied. Starting in 1956 and similar to 1957/58, Cadillac changed the ball check to a separate rubber check valve and spring witch then was mounted on the side or front of the master cylinder depending if you had a Delco or a Bendix system. Just a month ago i had a 1958 in my shop with the same problem as you described. It turned out that the rubber check valve was swollen and could not hold the fluid from draining back into the reservoir. The fluid level was okay and clear and there were no external leaks. After renewing the valve and bleed the master cylinder everything worked fine again as it should. In your case i should suck the brake fluid out of the reservoir with a vacuum pump or syringe, clean the reservoir with brake cleaner and bleed the whole system again. If your are lucky the ball check will seat properly again with the removal of contaminated fluid. Otherwise you have to take the power brake booster apart to acces the master cylinder parts and clean and check the loose parts. Btw, in Dutch we call the check valve "bodemklep" I have several brake booster units in stock if you need one.
Hope this helps ;)
This happened to me years ago on the highway when I was using a 1956 Fleetwood as a daily driver. I don't know what caused it as I turned the car over (on a Sunday) to a service station guy I had used before we moved out of Indy. But it was sure scary. I picked the car up well in time for our trip home to Lafayette. This was back in the day when a gas station was still a SERVICE station.
Matern has some good advice. If you find no leaks and have bled your M/C and Hydrovac (which is often overlooked in bleeding on the 54-55 Cads) and wheel cylinders and no success I would do what he suggests. However, the 'ball check' in the '54 Hydrovac in the picture is NOT the check valve, rather is is a ball check that allows brake fluid to flow through the piston in the unit to the wheels when the engine is not running (no vacuum) or the hydrovac unit is defective (eg. leaking vacuum). That allows the brakes to still work. That design allows the brakes to still work pretty well without vacuum (better than the TreadleVac system in '56). The reserve check valve was moved to the hydrovac unit in '55 but in '54 it was still located in the M/C on both power brake and manual brake cars (Power brakes were optional that year). That's why I suggested to check you have the right M/C since some parts suppliers get this mixed up. A manual brake M/C is the same for 54 & 55 but different for power brakes only for '55. When you release the brake pedal, the springs at the wheels push the wheel cylinders back in to return the brake fluid back to the M/C. The check valve closes when the line is reduced to 9 pounds of pressure so some pressure remains in the brake lines for the next use. Either air in the M/C or a defective check valve in the M/C could cause your syptoms.
Thank you for all the suggestions. The master cylinder has not been been replaced by me so it is likely to be original. Because of a differential oil leak i did replace the rear brake shoes and front and rear wheel cylinders (including the rubber hoses) because i didn't know how long they had been on there. I did not find the time to start investigating yet, but hopefully this weekend i can spend a few hours.
Helle Julien, After my reply on your post it kept me thinking if was right with my answer. Well, yes and no.
Since you did not not replace the master cylinder i would start investigating there before you touch the booster. The master cylinder has also a fluid check valve to keep "rest pressure" on the hydraulic system when the brakes are not applied. This valve witch is part of a rebuild kit can go bad over the years and loss of "rest pressure" will happen. After pumping the brake pedal a few times you will have normal pressure again for the moment. Also when you have an old master cylinder the bottom of the cylinder bore will go bad because of rust and pitting with loss of pressure as a result or leaking fluid from the rear end of the pump bore.
A new Chinese made :-\ master cylinder will solve the problem, better is to re-sleeve the original cylinder with stainless ;) . This will last forever, i have done this many times with a good result. Please see the attached exploded view from the MPB, the check valve is part # 4657 on the drawing.
Update:
Yesterday I started my investigation. Before I did anything, i checked pedal feel with the engine off. Pressure was normal and stayed firm while keeping pressure on the brake pedal. Drove the car out of the garage and had normal brake action. I started with checking the brake fluid.
The fluid im the master reservoir had dropped about a 1/2 inch. So i topped that off first. Re-bled the booster in the order that was suggested above. No air bubbles appeared. Then checked the brake lines and hoses for leaks. I did not find any leaks. Then remove the wheels to check for a leaky wheel cylinder, but they were all dry as well.
What I did find was burned brake shoes at the rear right brake and lots of brake shoe dust. So using brake cleaner I cleaned that and sanded the brake shoes and drum. Also adjusted that brake a bit looser (4 clicks). Took the car for a test drive and brakes acted completely normal again. Also bled the rear brakes again.
When I came to a parking lot I literally did a panic stop (while only going a few mph) because a guy was backing up and apparently did not check his mirrors. Then I found out that all wheels did seem to lock up (and the car ofcourse came to an abrupt stop). And those Cadillac horns are pretty loud ;).
So my theory is that the rear right brake simply got so hot that part of the brake fluid boiled away. In combination with brake fade. The manual also states this as one of the possible causes of a low brake pedal.
Ofcourse I will keep an eye on it and keep it in the back of my mind while driving (start braking earlier and keep (even) more distance to the car in front of me. Always a good idea as these cars simply do not come to a halt as easily as for example a new VW Polo weighing about half as much and having anti lock disc brakes all around.
Julien, please adjust all your shoes as shown in the manual - with a feeler gauge through the slots in the drums. If you can't adjust them to spec like that then do the major brake adjustment as shown in the manual. You won't regret it, these brakes are good when set up properly.
Also you didn't mention if the power assist is working?
Phil
Thank you for keeping us updated.
When we found our 55 and woke it up, my son did not yet have his license. We did all the work together and he went on many test drives with me where I pounded leaving distance in his head. He got his license of course but still leaves good braking distance.
That old girl was a good teacher.