The weather here was finally nice enough to take my 32 3 window for a spin. Everything was fine until I tried stopping at the end of the driveway. The pedal went almost to the floor got it back in the garage and checked all lines and wheels for leaks. Also checked M.C and it was full, It has disc front drums rear and power brakes. Never had this happen before, next I checked the hose from the center carb ( 3 twos ) for any worn places also checked fitting on carb for leaks. Finally disconnected hose at carb and plugged fitting this helped but pedal is still very low . Hooked every thing back up started car and again pedal to the floor ???? Can I plug the fitting at the carb and plug the hose going to the booster so I have manual brakes. Can you do this?? Thanks everyone in advance
Sounds like a blown master. Pump the pedal quite a few times and look for leaking brake fluid. If there aren’t any leaks, most likely the master. I have had drums so far out of adjustment that the pedal would hit the floor, but that usually happens slowly as the brakes wear
Possible bad master cylinder. Might verify the link between the master and booster is still in proper adjustment, that can also cause a similar symptom you're describing.
If the master cylinder is full of fluid you can’t have a leak, therefore no need to check for fluid in the booster, it’s possible the master cylinder is leaking internally, if it’s bypassing leaking between the chambers it would cause this
I have a small block Chevy with tri power and power brakes it gets its vacuum from the base of the middle carburetor also. Where do you get the vacuum for your PCV ? If it shares the same fitting with the booster that maybe your problem. But my gut says its actually sounds like a bad booster or master
It would probably be more ideal to have separate vacuum ports for each one . But if it worked for a long time without a problem I wonder why it would act up now? You could plug or crimp the pcv line and see what happens. I also installed a check valve (OEM style ) between the middle carburetor and the brake booster. I always thought the factory installed the check valve to stop oily vapours from damaging the booster- but not certain of that. It still sounds like a bad master or vacuum leak.
If the pedal goes to the floor It is not the booster Or any of the vacuum lines . If the booster fails the master cyl still works as it should but only the power assist is gone and your foot effort will need to increase.
Pump up the pedal, then hold steady pressure on the pedal, if it slowly goes away, you'll need a new master.
Sometimes people mistakenly say that their “pedal goes to the floor “ when what really might be happening is that the booster fails and the pedal goes down and gets hard and the car doesn’t stop as well. I’m not saying that’s what’s happening but the original question is POWER VS MANUAL BRAKES. But it probably is the master!
OK, the master cylinder is bad. Guys before me nailed it. Why? The booster does not lose it's mechanical connection to the master cylinder from the brake pedal unless something really bad happens. You can have a situation from leaking wheel cylinders that will cause the sealing diaphragm of the master cylinder to droop and cause the master cylinder to not be able to draw fluid in the master cylinder reservoir as the wheel cylinders gradually leak down. I know this first hand and buying time with my 3/4 ton DD to be able to tear down the rear brakes and replace 1993 parts. You can also have a brand new junk master cylinder and a just like it spare that you bought at the same time. Pick your size of hydraulic brake vehicle. Bypassing master cylinders will really get your gourd when you buy one from a purportedly good source, and the spare.
Some really good answers, I'm going to try a few this weekend and I'll let you know what I found. I appreciate everyone's response you guy's are the best !!
Don't overlook the flexible brake-lines to the front disk brakes. They do age and wear with use, and can swell under pressure -- resulting in reduced pressure to the wheel cylinders.
Adjust the rears, give all bleeders a shot to see if you have air anywhere. The acid test for a booster is, engine off, pump out all the vacuum. You should have a high pedal, at least as high as you can get it right now. Foot on the pedal, start the engine, the pedal should sink somewhat. This takes the booster out of the equation. But if you cannot get a decent pedal after bleeding, it indicates a bad master. Another good trick, put the car on jack stands. Wait until dark and look under the car with a flashlight. Fluid leaks show up better this way. Wheel cylinders, hose connections, junction blocks and so on.
Today I tried to adjust rod from master to pedal with no luck. I still have a very low pedal the car does stop but almost a white knuckle thing. I can pump the pedal up where I kinda have a pedal but when I start the car it really drops?? I might try bleeding the brakes next. Getting mildly frustrated but I guess that's part of the fun !!
Adjusted the rod? If the brakes worked well before you parked it, there are no adjustments needed. Many have suggested that if you have no external leaks, you probably have a bad master cylinder. I agree. It's likely that a rubber cup inside the master cylinder has deteriorated and blew out the first time you hit the brakes. The tiniest little tear will allow fluid through. If you're handy, you can buy a rebuild kit with new rubber cups, buy a small hone for your electric drill to freshen up the bore in the master cylinder, clean, reassemble, reinstall, and it'll work like new. Or just buy a new one. Sent from my VS835 using The H.A.M.B. mobile app
What is the proper way to adjust the rod from the booster to the pedal. I probably messed it up trying to adjust it.
There normally is not any booster control (input) adjustment, only for input rod length, to position the pedal. The pedal should have it's own return spring, and be able to move back farther than necessary, to make sure the booster input (control) rod is fully returned when the foot is off the pedal.
Could I just take the booster off and run manual brakes? The car doesn't weigh that much. It came on the car and was a M.C. booster combo.
You will likely need a different master cylinder if you remove the booster. Different bore diameter. Do you dislike power brakes? Why remove them? You havent found the source of your problem yet. Probably a bad master cylinder on your current set up, as described above.
Do you have history with the car? Was this the first ride of the season? Do you have a real lumpy cam ,,, does the engine make enough vacuum to operate booster? Does it have rear drum brakes? Does it have Residual Pressure Valves? are the rear drums adjusted correctly Maybe the rear cylinders sucked air while sitting and just need bled.
We all put in fluid in small amounts, especially with disc brakes as the pads wear the pistons on the calipers move outward. That over time will lower the fluid level in the master cylinder. You never put fluid into the booster.
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