I just put all new brake lines and a rebuilt master cylinder on my 1971 LS5 as preventive maintenance, but now I can not for the life of me get all the air bubbles out. My buddy and I have pumped over a gallon of brake fluid through the lines but still no brakes. There must be air trapped some place but where? The only thing I can think is the rebuilt master cylinder didn't have bleeders on it (the old one did). I checked for obvious leaks, and even bought a vacuum bleeder, but nothing. I am just about to give up. Anyone have any ideas of what to do next?
-
-
Re: 71 Brake Bleeding
Tom------
For some reason that I've never been able to understand, 1965-82 Corvette brake systems are a BEAR to get bled properly. I've been down the same path as you in years past-----running gallons of brake fluid through the system and not getting a firm pedal. So far, the best method that I've come up with is gravity bleeding. This does take awhile since you have to leave the system sit for several hours, at least. Applying a little over-pressure to the master cylinder resevoirs will get the process started quicker, though. I use a special m/c cap that I've made up with fittings on each dome to apply just a very small amount of overpressure.
Also, even though your master cylinder does not have bleeder valves, there's no reason why you cannot bench bleed it. Bench bleeding using kits available from most auto parts stores does not involve use of the bleeder valves. The kits allow you to pump the fluid from the outlet ports back into the resevoirs as you bleed the cylinder.
I'm VERY interested in other folks' proven bleeding methods on this one. I'll be doing it myself in a week or two and I am DREADING it more than any other operation that I've ever performed on the car. In fact, it might even be the reason that I've procrastinated so long on everything else; it prolonged the day that I had to do the bleeing operation. Based on previous experience, I just know that immense frustration lies ahead.In Appreciation of John Hinckley -
Re: 71 Brake Bleeding
Tom------
For some reason that I've never been able to understand, 1965-82 Corvette brake systems are a BEAR to get bled properly. I've been down the same path as you in years past-----running gallons of brake fluid through the system and not getting a firm pedal. So far, the best method that I've come up with is gravity bleeding. This does take awhile since you have to leave the system sit for several hours, at least. Applying a little over-pressure to the master cylinder resevoirs will get the process started quicker, though. I use a special m/c cap that I've made up with fittings on each dome to apply just a very small amount of overpressure.
Also, even though your master cylinder does not have bleeder valves, there's no reason why you cannot bench bleed it. Bench bleeding using kits available from most auto parts stores does not involve use of the bleeder valves. The kits allow you to pump the fluid from the outlet ports back into the resevoirs as you bleed the cylinder.
I'm VERY interested in other folks' proven bleeding methods on this one. I'll be doing it myself in a week or two and I am DREADING it more than any other operation that I've ever performed on the car. In fact, it might even be the reason that I've procrastinated so long on everything else; it prolonged the day that I had to do the bleeing operation. Based on previous experience, I just know that immense frustration lies ahead.In Appreciation of John HinckleyComment
-
Re: 71 Brake Bleeding
Are you bleeding both sides on both rears? This is an easy mistake if you are new to the hobby.Also did you replace the hoses?Lyle
Comment
-
Re: 71 Brake Bleeding
Are you bleeding both sides on both rears? This is an easy mistake if you are new to the hobby.Also did you replace the hoses?Lyle
Comment
-
Re: 71 Brake Bleeding
Hello, i have replaced the brakes on my 72 ls5 ( master cylinder,all 4 calipers,rotors pads,hoses)and i just bleed one wheel at a time, having someone do the old 3 pump and hold the brake pedal with the master cylinder cap on. It worked but i had to adjust the rod on the master cylinder a few times to get a brake pedal. I don't know if you did this but this was the fix on mine. I just replaced the calipers on my iroc-z and i had to bled the brakes with the master cylinder cap off to get the air out. Thanks EricComment
-
Re: 71 Brake Bleeding
Hello, i have replaced the brakes on my 72 ls5 ( master cylinder,all 4 calipers,rotors pads,hoses)and i just bleed one wheel at a time, having someone do the old 3 pump and hold the brake pedal with the master cylinder cap on. It worked but i had to adjust the rod on the master cylinder a few times to get a brake pedal. I don't know if you did this but this was the fix on mine. I just replaced the calipers on my iroc-z and i had to bled the brakes with the master cylinder cap off to get the air out. Thanks EricComment
-
Re: 71 Brake Bleeding
I've experienced the EXACT same problems bleeding my complete system on my '70.
All I can recommend to you is KEEP PUMPING and KEEP POURING!
It will eventually come up.
Yes,frustrating,indeed!
Jim
P.S...what did you do with your original master cyl?Comment
-
Re: 71 Brake Bleeding
I've experienced the EXACT same problems bleeding my complete system on my '70.
All I can recommend to you is KEEP PUMPING and KEEP POURING!
It will eventually come up.
Yes,frustrating,indeed!
Jim
P.S...what did you do with your original master cyl?Comment
-
Re: 71 Brake Bleeding
About 99% (not a scientifically proveable statistic ;-) of the problems with not being able to get a firm pedal on C3 brake systems is in the master cylinder. I can't explain why but it seems to defy convention -nothing that has worked on any other car's brake system I've ever worked on applies to a C3. I went through the spongy pedal syndrome and tried every bleeding method known to man (pump and hold, gravity, vacuum, I even have a real pressure bleeder)...all to no avail. I ran gallons of brake fluid through the system over the years, but it didn't improve the pedal feel. I had the cleanest brake system in town. I finally bought a professional master cylinder bleeder kit (although I'm sure that even the parts store plastic jobs will do just fine, it's just that the pro jobs have a one-way check valve that prohibits reverse flow back into the cylinder), removed the lines off the cylinder, attached the bleeder, pumped the cylinder for about a minute, hooked the lines back to the cylinder, did no further downstream bleeding of the system and you know what? My pedal is and has stayed rock-hard. Go figure. After all these years of trying to throw money at the problem hoping it would go away (including O-ring calipers, stainless braded lines, different brake pads, and four master cylinders) it came down to a very fussy master cylinder bleeding operation. My car has standard brakes, so some pedal problems can be attributed to the vacuum booster, but before throwing money at it, bleed that master cylinder.Comment
-
Re: 71 Brake Bleeding
About 99% (not a scientifically proveable statistic ;-) of the problems with not being able to get a firm pedal on C3 brake systems is in the master cylinder. I can't explain why but it seems to defy convention -nothing that has worked on any other car's brake system I've ever worked on applies to a C3. I went through the spongy pedal syndrome and tried every bleeding method known to man (pump and hold, gravity, vacuum, I even have a real pressure bleeder)...all to no avail. I ran gallons of brake fluid through the system over the years, but it didn't improve the pedal feel. I had the cleanest brake system in town. I finally bought a professional master cylinder bleeder kit (although I'm sure that even the parts store plastic jobs will do just fine, it's just that the pro jobs have a one-way check valve that prohibits reverse flow back into the cylinder), removed the lines off the cylinder, attached the bleeder, pumped the cylinder for about a minute, hooked the lines back to the cylinder, did no further downstream bleeding of the system and you know what? My pedal is and has stayed rock-hard. Go figure. After all these years of trying to throw money at the problem hoping it would go away (including O-ring calipers, stainless braded lines, different brake pads, and four master cylinders) it came down to a very fussy master cylinder bleeding operation. My car has standard brakes, so some pedal problems can be attributed to the vacuum booster, but before throwing money at it, bleed that master cylinder.Comment
-
Re: 71 Brake Bleeding
Thanks for the feedback, so much for a "quick-fix"! I did not bench bleed my master cylinder, which is what I will do as soon as I get home. If that dosen't work I am going to try Joe's advice and try the gravity bleeding method. I think I can modify my old cylinder cap with a 1/4" npt fitting to generate some downward pressure on the cylinder, this should speed some things up, but it sounds like it's just going to take some time.
By the way, I kept my old cylinder and I am thinking about just rebuilding it so I can use the bleeders. The only reason I didn't do that in the first place was that the rebuild kit was more expensive than a "professionally" rebuilt one so I bought the rebuilt and just kept my core.
Thanks again for the good information it's nice to know it is not just me.Comment
-
Re: 71 Brake Bleeding
Thanks for the feedback, so much for a "quick-fix"! I did not bench bleed my master cylinder, which is what I will do as soon as I get home. If that dosen't work I am going to try Joe's advice and try the gravity bleeding method. I think I can modify my old cylinder cap with a 1/4" npt fitting to generate some downward pressure on the cylinder, this should speed some things up, but it sounds like it's just going to take some time.
By the way, I kept my old cylinder and I am thinking about just rebuilding it so I can use the bleeders. The only reason I didn't do that in the first place was that the rebuild kit was more expensive than a "professionally" rebuilt one so I bought the rebuilt and just kept my core.
Thanks again for the good information it's nice to know it is not just me.Comment
-
Re: 71 Brake Bleeding
Gravity bleeding seems to be the preferred method of many folks here. However, just be aware that you need the patience of Job to make this work. Patience is something I sorely lack. In fact, I used to pray: "give me patience, and give it to me now!"
I rebuilt the MC on my 72 and had a soft pedal. I had bench bled the MC after the new seals were put in, but I obviously didn't do an adequate job. One more bleeding of the MC on the car solved the problem.
GaryComment
-
Re: 71 Brake Bleeding
Gravity bleeding seems to be the preferred method of many folks here. However, just be aware that you need the patience of Job to make this work. Patience is something I sorely lack. In fact, I used to pray: "give me patience, and give it to me now!"
I rebuilt the MC on my 72 and had a soft pedal. I had bench bled the MC after the new seals were put in, but I obviously didn't do an adequate job. One more bleeding of the MC on the car solved the problem.
GaryComment
Comment