'72 lt1 brake question
09-23-2018, 08:39 PM
#1
Intermediate
Thread Starter
Member Since: Apr 2013
Posts: 37
Likes: 0
Received 0 Likes
on
0 Posts
'72 lt1 brake question
I have a '72 LT1 Coupe with J56 calipers all around and front J56 brackets. I installed the calipers early this year and have consistently gotten air in the system after driving the car for one to two weeks. I have checked the rotor run-out several times, and all calipers have no run-out or are within two thousandths. Does anyone know if the J56 calipers and/or pistons are prone to leaking or letting air into the system. None of the calipers leak any fluid. By the way, after bleeding the calipers the brake performance is awesome (significantly better than my stock calipers).
I would appreciate any advice.
Thanks!
I would appreciate any advice.
Thanks!
09-24-2018, 09:43 AM
#2
Race Director
Are ALL of the calipers sucking in air??? Or just one or two.
Are you sure all of your wheel bearings are well within tolerances???
The calipers design in regards to the pistons and seals are the same regardless of what type of caliper the car came with. Meaning that a seal is installed on the piston and it seals against the bore of the caliper and the piston moves. So that dynamic is the same.
DUB
Are you sure all of your wheel bearings are well within tolerances???
The calipers design in regards to the pistons and seals are the same regardless of what type of caliper the car came with. Meaning that a seal is installed on the piston and it seals against the bore of the caliper and the piston moves. So that dynamic is the same.
DUB
09-24-2018, 09:53 AM
#3
DId you use stainless steel lines? I have found the stainless lines need to be burnished/lapped into their fittings because the stainless is harder than mild steel lines the double flares are not concentric... I usually snug them then spin the line in the fitting to burnish the surfaces/lap them together.
10-03-2018, 06:11 AM
#4
so I have been fighting a similar issue on my '73. I found a couple fittings that weren't properly tightened and even though they were not leaking fluid they were leaking air in on the release of the brake pedal. I do not know what your fittings look like at the ends of all your lines but if any of them are chewed up I would replace it. and if you have stainless line and want to make it look good you will probably need a hydraulic flare tool or just by a pre-formed line. flaring stainless steel line manually sucks bad.
10-03-2018, 09:49 AM
#5
Race Director
I can not believe by any stretch of the imagination that a lose brake line fitting will allow air to come into the system but not allow fluid to escape. Especially when roughly 800+psi of fluid pressure is put on the system when you press the brake pedal and yet NO fluid leaks out. That make absolutely no sense at all.
What can happen and I have seen it and dealt with it is that the bearing run-out along with the rotor run-out is excessive and YES...the piston will allow air to be sucked into the system ...and yet...when you press on the pedal it does not leak due to the deign of the seals in the caliper bores.. THAT I can believe
Because if air is being drawn into the system at this lose fitting and it is being drawn into the system due to bearing and rotor run-out not being correct....because the piston is a bellows...so-to-speak. The due to the fitting being loose and it is not a one way check valve. Fluid must be able to leave when put under much higher pressure at the fitting due to how the air is getting in this slightly loose fitting that can not be measured due to being so minute....which is why it makes no sense. When a brake pedal is lifted after being pressed down...the system is not drawing back at the 800psi
DUB
What can happen and I have seen it and dealt with it is that the bearing run-out along with the rotor run-out is excessive and YES...the piston will allow air to be sucked into the system ...and yet...when you press on the pedal it does not leak due to the deign of the seals in the caliper bores.. THAT I can believe
Because if air is being drawn into the system at this lose fitting and it is being drawn into the system due to bearing and rotor run-out not being correct....because the piston is a bellows...so-to-speak. The due to the fitting being loose and it is not a one way check valve. Fluid must be able to leave when put under much higher pressure at the fitting due to how the air is getting in this slightly loose fitting that can not be measured due to being so minute....which is why it makes no sense. When a brake pedal is lifted after being pressed down...the system is not drawing back at the 800psi
DUB
10-03-2018, 09:54 AM
#6
I can not believe by any stretch of the imagination that a lose brake line fitting will allow air to come into the system but not allow fluid to escape. Especially when roughly 800+psi of fluid pressure is put on the system when you press the brake pedal and yet NO fluid leaks out. That make absolutely no sense at all.
What can happen and I have seen it and dealt with it is that the bearing run-out along with the rotor run-out is excessive and YES...the piston will allow air to be sucked into the system ...and yet...when you press on the pedal it does not leak due to the deign of the seals in the caliper bores.. THAT I can believe
Because if air is being drawn into the system at this lose fitting and it is being drawn into the system due to bearing and rotor run-out not being correct....because the piston is a bellows...so-to-speak. The due to the fitting being loose and it is not a one way check valve. Fluid must be able to leave when put under much higher pressure at the fitting due to how the air is getting in this slightly loose fitting that can not be measured due to being so minute....which is why it makes no sense. When a brake pedal is lifted after being pressed down...the system is not drawing back at the 800psi
DUB
What can happen and I have seen it and dealt with it is that the bearing run-out along with the rotor run-out is excessive and YES...the piston will allow air to be sucked into the system ...and yet...when you press on the pedal it does not leak due to the deign of the seals in the caliper bores.. THAT I can believe
Because if air is being drawn into the system at this lose fitting and it is being drawn into the system due to bearing and rotor run-out not being correct....because the piston is a bellows...so-to-speak. The due to the fitting being loose and it is not a one way check valve. Fluid must be able to leave when put under much higher pressure at the fitting due to how the air is getting in this slightly loose fitting that can not be measured due to being so minute....which is why it makes no sense. When a brake pedal is lifted after being pressed down...the system is not drawing back at the 800psi
DUB
10-03-2018, 10:22 AM
#7
Race Director
Simply because when I pressure bleed brakes I use a pressure bleeder that I can set the pressure to 22 psi and IF any of my brake line fittings are even lightly loose I can see fluid leaking and that is at 22psi. When I test the system after I have bled it and the pressure is at 1500psi and 800psi and the fittings do not leak I KNOW that is no way in heck air can get into them.
I am not going to argue with you on this. If air can get into a loose fitting... then fluid under pressure has to be able to weak out to some degree.
DUB
10-03-2018, 10:42 AM
#8
If you stand behind what you wrote...all well and good. And I am glad your brakes work as designed for you. Well...then this is a first ....and it goes against the physics of how this system works. Obviously physics do not apply in this case. .
Simply because when I pressure bleed brakes I use a pressure bleeder that I can set the pressure to 22 psi and IF any of my brake line fittings are even lightly loose I can see fluid leaking and that is at 22psi. When I test the system after I have bled it and the pressure is at 1500psi and 800psi and the fittings do not leak I KNOW that is no way in heck air can get into them.
I am not going to argue with you on this. If air can get into a loose fitting... then fluid under pressure has to be able to weak out to some degree.
DUB
Simply because when I pressure bleed brakes I use a pressure bleeder that I can set the pressure to 22 psi and IF any of my brake line fittings are even lightly loose I can see fluid leaking and that is at 22psi. When I test the system after I have bled it and the pressure is at 1500psi and 800psi and the fittings do not leak I KNOW that is no way in heck air can get into them.
I am not going to argue with you on this. If air can get into a loose fitting... then fluid under pressure has to be able to weak out to some degree.
DUB
I had a fitting on my right passenger side that was not leaking brake fluid visibly. I had air in the system. I bled the brakes with a power bleeder everyday for a week. I changed the chewed up fitting (vice grips from previous owner chewed up the fitting) and the brakes work amazing. Never had a sign of brake fluid.
Last edited by sobervette88; 10-03-2018 at 10:58 AM.
10-05-2018, 09:28 AM
#10
Race Director
No confusion on my end here. I am not confused about this at all.
Not knowing if you are aware of this or not but.....bearing run out and rotor run out are critical and need to be correctly indexed with a dial indicator or brake caliper issues can begin. Even simply installing new brake pads on the original brake calipers or replaced calipers that had brake pads on them... can cause for issues due the brake caliper design and lack of brake fluid maintenance. Also...simply installing new rotors DOES NOT make them right in regards to rotor run out. EVEN IF the bearings are correct. I generally have to make custom shims to correct this rotor run out issue.
DUB
Not knowing if you are aware of this or not but.....bearing run out and rotor run out are critical and need to be correctly indexed with a dial indicator or brake caliper issues can begin. Even simply installing new brake pads on the original brake calipers or replaced calipers that had brake pads on them... can cause for issues due the brake caliper design and lack of brake fluid maintenance. Also...simply installing new rotors DOES NOT make them right in regards to rotor run out. EVEN IF the bearings are correct. I generally have to make custom shims to correct this rotor run out issue.
DUB