Bleeding Brakes
Thread Starter
Pro
Joined: Jan 2001
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From: Mt. Laurel NJ
Bleeding Brakes
The brakes on my 67 were starting to feel a little soft. So I decided it was a good time to replace the master cylinder and clean things up a little. Got everything back in and bled each caliper. All except the left front bled as expected. The left front just kept bleeding air. I must have run a half quart of brake fluid through it. No leaks, just lots of air bubbles. Now I can lock up all wheels except the left front. And the "brake" light comes on. Normally when this type of thing happens there is a leak somewhere, but I don't see one. Any thoughts on what might be wrong?
CUL Jim
CUL Jim
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Joined: May 2000
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Re: Bleeding Brakes (Jim_C)
From the anecdotal evidence of many other brake problem posts, it seems a lot of one wheel problems have been traced to bad hoses - internal flaws that cannot be seen with an exterior visual inspection.
At least by knowing it is just the LF corner, you've limited the scope of the investigation. I'd suggest removing the hose and blowing through it see if it is clear, and maybe just replacing it. The other thing to check is the steel line from the D-block to the left front for any damage like a kink or rock ding. This is the shortest steel brake line on the car, so it should be easy to inspect. Also check the connections.
If it still won't bleed, the the caliper should probably be removed and disassembled for a careful inspection.
Duke
At least by knowing it is just the LF corner, you've limited the scope of the investigation. I'd suggest removing the hose and blowing through it see if it is clear, and maybe just replacing it. The other thing to check is the steel line from the D-block to the left front for any damage like a kink or rock ding. This is the shortest steel brake line on the car, so it should be easy to inspect. Also check the connections.
If it still won't bleed, the the caliper should probably be removed and disassembled for a careful inspection.
Duke
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Joined: Jan 2001
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From: Mt. Laurel NJ
Re: Bleeding Brakes (SWCDuke)
SWCDuke
Thanks for the reply!!! The front end is a recent restoration so the flex line to the caliper and all the hard brake lines are new, as is the caliper. Probably only a thousand or so miles on them. Certainly doesn't mean there isn't a bad component somewhere. I just can't figure where all the air is comming from. You would think that a leak would show itself by fluid leaking when braking, but there are no leaks.
Would pressure bleeding, or using one of those vacuum bleeders be more effective removing the air?
CUL Jim
Thanks for the reply!!! The front end is a recent restoration so the flex line to the caliper and all the hard brake lines are new, as is the caliper. Probably only a thousand or so miles on them. Certainly doesn't mean there isn't a bad component somewhere. I just can't figure where all the air is comming from. You would think that a leak would show itself by fluid leaking when braking, but there are no leaks.
Would pressure bleeding, or using one of those vacuum bleeders be more effective removing the air?
CUL Jim
Melting Slicks
Joined: Apr 2002
Posts: 2,620
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From: 20 forward gears to shift through in MD
Re: Bleeding Brakes (Jim_C)
Jim, I have seen where the bleed valve fitting (when loosened) on the caliper will allow air to enter from around the threads and just "suck air". You could try turning the bleed valve less when opening it or try either a pressurized bleed system on the master cylinder or one of those Mighty Vac types of bleeders. Best of luck, soft brakes definitely suck in a fast sports car...
Melting Slicks
Joined: Oct 2001
Posts: 3,025
Likes: 12
From: Pleasant Grove AL
Re: Bleeding Brakes (Denney)
I have had absolutely no success trying to use a MityVac for brake bleeding, even with teflon tape around the bleeder screws. Pressure bleeding might be the trick. Since the one caliper seems to be the problem, try tapping on the caliper with a plastic hammer in between bleedings. Sometimes air can get trapped . If that doesn't do it, I'd consider rebuilding or replacing the caliper-even though it's "new".
Melting Slicks
Joined: Aug 2000
Posts: 3,077
Likes: 2
From: The Garden Spot of the Garden State
Re: Bleeding Brakes (62fuelie)
....i've also had the problems with the loose bleeder screw but i would go back to duke's advice first and change one thing at a time - changing the hose is cheap insurance unless you are CERTAIN that the hose is OK....i'm not sure the bleeder screw "leak by" would allow enuf air back in to make a difference - do you notice any fluid leaks around the pistons?
....if you have to rebuild the calipers (i would do both fronts, sorry), it is a very simple procedure but requires great care and removing absolutely all dirt (assuming the piston cylinders are OK)
....if you have to rebuild the calipers (i would do both fronts, sorry), it is a very simple procedure but requires great care and removing absolutely all dirt (assuming the piston cylinders are OK)
Drifting
Joined: Aug 2000
Posts: 1,805
Likes: 36
From: Annapolis MD
Re: Bleeding Brakes (Kid_Again)
Just got done bleeding the brakes on Julie's '70 when she finished the rear suspension rebuild using a vacum pump / bottle setup and it worked great. Since the cross-over line was new it took quite a few pumps initially to get things going. Once the fluid starts filling the lines it's easy. Couple of pumps to get 20" vacum and then just let it bleed a little. We pulled enough fluid through to get fresh fluid through the whole system.
It's easy to see with this setup if you have a leak at the hose/bleeder fitting as you will see a continuous stream of very small bubbles. Push down hard on the bleeder/hose and they stop. Also, you don't need to open the bleeder much, 1/3 to 1/4 turn at most, 1/8 will actually do.
With the high vacum in the system ANY small leak will bring in lots of air, so would likely also be a good diagnostic for your problem.
-Greg
It's easy to see with this setup if you have a leak at the hose/bleeder fitting as you will see a continuous stream of very small bubbles. Push down hard on the bleeder/hose and they stop. Also, you don't need to open the bleeder much, 1/3 to 1/4 turn at most, 1/8 will actually do.
With the high vacum in the system ANY small leak will bring in lots of air, so would likely also be a good diagnostic for your problem.
-Greg
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From: Mt. Laurel NJ
Re: Bleeding Brakes (GregP)
Thanks for all the help!!! I can't find any sign of a leak. No fluid anywhere. I've been carefull to keep the master cylinder resevoir full, so I just can't imagine where the air is coming from. Even if the line was completely dry, I pumped enough fluid through to fill ten sets of brake lines.
I did notice that if I open the bleed valve a quarter turn it is quite loose. It does let air in to the fluid discharge. If I open it about an eighth turn and press it in toward the caliper, the amount of air decreases. That is how I finished the job.
I have a friend that has a vacuum pump he is bring to work tomorrow. I'll give that a try and let you all know how I make out.
Thanks again for all the help!!!!
CUL Jim
I did notice that if I open the bleed valve a quarter turn it is quite loose. It does let air in to the fluid discharge. If I open it about an eighth turn and press it in toward the caliper, the amount of air decreases. That is how I finished the job.
I have a friend that has a vacuum pump he is bring to work tomorrow. I'll give that a try and let you all know how I make out.
Thanks again for all the help!!!!
CUL Jim
Last edited by Jim_C; Nov 12, 2016 at 06:07 AM.
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