My friend Ryan and I just finished upgrading the brakes on my 1960 Buick invicta and have run into some issues. Some background first. The master and booster where installed using a new 1968 LeSabre master , booster and proportioning valve that was removed from a stock 68 wildcat. After all the lines were hooked up, we bled the system using the standard start at the right rear wheel. Then we found out that according to the manual, you need to start with the left front and go the opposite direction. So we did that. The issue we are confronted with is a soft pedal when the engine is running. Sitting still without the engine on, the pedal seems perfect and right where it shoudl be with a good feel. Once the engine is turned on, the pedal softly goes to the floor. Perhaps we still have air in the brake line? It was suggested that we should bleed with the engine running to affect the booster. I've never heard of that method. Comments or suggestions would be appreciated.
I'll be glad to check the booster for leaks, but my inexperience in doing so has got the best of me. Can you advise me on the method to do so or refer me to an manual/article on the topic.
You state a new master, but are you using the 44 year old booster and prop valve? What pedal assembly are you using, and are the pedal ratios the same on the '62 and '68? Can you full stroke the open-circuit master before the pedal bottoms out? All bleeding should be done with vacuum depleted and engine off. The pedal should be hard and near the top with no boost, and will drop with the engine running, but should not go near the floor. It should not matter what wheel or axle you start to bleed on a dual system, as you're going to "circle" the brakes several times while bleeding.
We used a brand new booster. The prop valve I took off an old 68 wildcat and cleaned it up. Also, the pedal ratios were the same. The length of the rod was the same as well. I used the stock pedal.
Is your Buick drum/drum? If so, the part you took off the '68 is likely a distribution/pressure differential combination switch/valve. (drum/drum do not use proportioning vales) The problem with hydraulic parts this old is they can leak internally and/or be unreliable, and I would not use them. If drum/drum, run the lines directly out of the master to their axle tees.
With the engine off, pump all the vacuum out of the booster. The pedal should be very firm and up at the top. The pedal should hold and not sink at all, give it a minute with light to medium pressure. If it drops and you have no leak, the master could be bypassing internally. You run into it now and then when you utilize a master out another car, how new was it to the '68 donor? With your foot on the brake pedal, start the car. The pedal should drop maybe 1/2-1", but remain firm. That confirms that your booster is good. Being that the rods were the same length, I'd suspect that the master itself is bypassing. Bob
Did you bench bleed the master cylinder before installing to make sure its good ? New doesn't mean it works. Normaly when a booster is bad when you mash the pedal it sounds like air brakes on a truck everytime you pump the pedal. I have always bled brakes no matter what car or truck starting with the wheel farthest away from the master cylinder and work backwards to master. Another thing,are you getting plenty of vacumn to the booster ?
The buick is drum/drum. The 68 item is a distribution switch. I used the wrong terminoligy and called it a prop valve. It came off a drum/drum car.
Yes sir. I did bleed the master before it was installed onto the booster. I'll double check to make sure we're getting enough vacuum to the booster. Thanks
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