Hi! have a '48 chevy coupe that was rebuilt a long time ago. Very solid. The last owner put a 305/350 auto in and a power brake booster. The brake pedal was soft when i got it & with a pump or 2 you got a light pedal. So, I have bled and bled and re-bled the lines. No pedal. Replaced front wheel cyl's & re-bled. still nothing. At one point the pedal was decent & then lost it..... Any thoughts on this? Help..... Thanks, Mack
A couple things it could be.... The M/C piston and bore are 15/16 and need to be 1 inch.... The calipers are mounted on the wrong side so the bleeders are facing down, and they need to be facing up..... Can be simple as air stuck in a part of the line that may need more bleeding? Brakes stuck, like slides, causing spongy pedal.... The list goes on, Perhaps the brake pedal isn't returning all the way, perhaps the brake light switch needs adj. If the pedal doesn't return all the way, the M/C wont get a full stroke, not allowing it to get full pressure.....
Yes, Vacuum bleeder was not a help. With my son pushing the pedal for me we had some better although mixed results.
Wow, I replaced the front cyl's and adjusted them. The pedal ratio is off as well. It's approx 3:1 now. I am not certain how to change this? Also, the MC could be an issue as we did have a high/hard pedal at one point & then lost it.... frustration is setting in. Mack
Hi guys, Ok. Replaced MC & now booster. Replaced a brake line & bled MC. Bled lines to the point of no bubbles.... Still soft pedal... Also checked for leaks & none. Is this simply more line bleeding necessary? All components are new at this point. Any thoughts on bleeding with the car running? Posted using the Full Custom H.A.M.B. App!
I too am having brake problems. I RFI (reverse fluid injection) bled the system and was very careful to not allow any bubbles into the calipers. When I was finished I stepped on the pedal and it bottomed out.......nothing, nada. So I then called my wife and we bled them the old fashioned way and I now have a tall firm pedal. But, you should have seen the air bubbles that came out of the driver's side caliper............unbelievable! Like you I have new everything and as soon as the rain quits I'm going for a test drive. You might try a combination of RFI and manually bleeding or power bleeding. Maybe the reversing of the brake fluid in the system helps remove trapped air bubbles.
I'm glad you got it all set!! I'm looking forward to a test drive when I get this figured... Thanks! I'll try the RFI! Posted using the Full Custom H.A.M.B. App!
Not sure if I'm all set or not. I've been working (off & on) on this problem for months now. I have a manual system and I haven't had braking up front since replacing a leaking MC. Before that I had brakes that were like power brakes. I have replaced the MC three times, new calipers, new pads and a new residual valve. I even disconnected all the brake lines and fittings and blew them out. I used to laugh at guys having all these brake problems. Karma.
You should list the components that make up your system. I'm guessing that you have drums all around with the MC on firewall, but I don't know size of MC or what kind it is, or what size booster. Also how do you know it's a 3:1 pedal ratio?
just to make sure, you did bench bleedthe MC before hooking up the lines? if it has a booster i've always bled with the car running... so that's another reason to toss the booster
Be sure the caliper has the bleeder screw at the top of the caliper!!! Be sure that the rod going from the booster to the MC has the correct play...about a 1/4 inch play in the brake pedal before any resistance is felt....I have had the MC sleeve rod come out a couple of times...lucky it was in the MC box and I re-installed it before putting the rod in the booster and MC. I think I have the same problem....but its still not put together enough to street drive it....I think it is sucking in air into the system....had that problem with my vette recently....put in new rubber seals....had brakes in 30 min after spongy brakes for 2 full days.
I have dealt with many brake problems mostly on customer cars. If you have access to a set of brake pressure gauges you can check pressures. I would start at the master and work my way to the wheels dead head the master into the gauges and check what pressure is or if you have good pedal at that point first. If you don't have gauges do the dead head without them and feel the pedal it should be hard because fluid is noncompressable . If it is spongy you have air in the system, if the pedal is hard and slowly drops your master is bypassing and needs replacing. Pedal ratio should be 4:1 for power and 6:1 for manual. I have had the calipers on aftermarket kits clocked with the bleeder not quite at the top and could not get all the air out. Hope this helps Jim Ford (55willys)
Thanks Jim! What does "Dead Head" the master mean? How do I do it? I don't have access to pressure gauge either.... If you pump the pedal a couple times you get a weak pedal. Mack Posted using the Full Custom H.A.M.B. App!
Also, all stock drums, bleeders at the top all four. Headed out to try vacuum bleeder.... Mack Posted using the Full Custom H.A.M.B. App!
Kursplat, yep, bench bled the MC. Going to try vacuum bleeding now, car running... Fingers crossed! Mack Posted using the Full Custom H.A.M.B. App!
Vacuum bleeding can be tricky. I suggest you wrap plenty of teflon tape on the bleeder screws. If you don't they will suck air in through the threads and you'll see bubbles forever.
Guys Sorry to chime in but.. I'm frustrated as well. I'm having the same issues with my manual drum brakes as well on my roadster. Replaced leaking hose on front left. Replaced wheel cylinder on front left. Replaced master cylinder. Bench bled master. Dead head master cylinder, firm pedal, does not move over 1/8". Pressure bled attached to master cylinder, bled, bled, bled. Gravity bled. Pump bled. Pedal goes to floor after sitting Jacked up front end 2 ft , bled. Checked all connections. No leaks on master cylinder connections or seals. What's this about the brake switch? How much air in lines to cause this issue? Started out as a leaking front brake hose... Morphed from there. Ready to fork over $$ for the reverse Phoenix bleeder kit.
Head'n out to garage now. Going to pedal bleed again. This time. I'm not pumping the pedal fast. Just one or two slow pumps. Also checking the rear drums/ shoes (Chevy blazer) adjustment, again. Early Ford fronts are good.
Mack I raised the car and inspected all connections for leaks. I lowered the fluid in the MC. It was brim full. None. I then pedal bled the brakes again by myself using a short 2x4 and an old ottoman, placing it on the front seat wedging the board between the padded ottoman and the pedal. Works pretty good. No kids and wife at work. I also re-adjusted the rear brake shoes/ drums, maybe rubbing a little bit. Got a slightly firmer pedal. Waiting to test drive it. Trying not to create more variables. Keep throwing out ideas guys. All of us has been here one time or another.
Dave, Fingers crossed man!!! I'll report my results tomm... Mack Posted using the Full Custom H.A.M.B. App!
Mack how old are the wheel cylinders , if they are old and have cracks , you could be sucking air when they return to rest . the seals are under the boot on them and do not have to leak fluid to suck air as the fluid will expand them and make them seal . also watch the brake hoses to make sure they are not expanding as the old ones have a cloth liner that goes bad over time , you will physically see the line expand in size with the pedal application . the hose should not expand at all . it it expands any amount replace them all as one is bad all are going to be bad , some chevy trucks have had this problem and it makes the pedal soft as soon as you replace the hose the pedal is hard .
Thanks Stimpy! New wheel cyl's all the way around. Hoses appear very good cond.... Will check it out. Thank you!! Mack Posted using the Full Custom H.A.M.B. App!
since this is pieced together, are you using a residual valve or the metal cups in the wheel cylinders? could be pulling air past the seals in the wheel cylinders if not good luck
Did you try what 55Willys stated about dead heading the MC? Plug both outlets at the master cylinder. If the pedal drops, the seals or internal value are bad on the MC. If the pedal is firm and moves 1/8" or so, the MC is good Some MC manufacturers tell you to bench bleed the MC using the plugs. I performed this test and the MC pedal/rod did not move more than 1/8". I also bled the MC this way. I went ahead and replaced the seals in the MC. No leaks.
Dave29, Thank you for explaining deadheading. Ok, will try that first. Re:wheel cyl's.... I had good pedal at one point with these new cyl's.... Hmmm.... Posted using the Full Custom H.A.M.B. App!
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