1970 Brake Problems
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From: Oglesby Illinois
1970 Brake Problems
I have a 1970 LS5 manual brake car. This year the brakes have had little extra travel and last week I went to make an aggressive break and the pedal went almost to the floor and the light came on. The last time this happened it was the master cylinder. I have no fluid leaks anywhere so I got a new MC from Napa. Bench bled it and installed it on the car and the pedal goes to the floor with absolutely no resistance. After some bleeding at the calipers I went and got another new MC from Napa. Same result so now I am perplexed. The Napa part is M1922. I understand their might be some air in the lines but I have no resistance and barely any flow at the calipers. Is there something else that could be wrong? On the bench I did take one of the MC, as I still have both new ones, closed off both ports and tried pressing on the plunger. It is solid and I cant push it in at all, not sure what that really means though.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
on my 69 there was an adjustable push rod between the MC and the brake pedal.....it has to be set so you have about 1/16 of free play between the MC and the pushrod when the pedal is at rest...
the rest is bleeding and making sure the proportioning valve is centered.
some times gravity bleeding is your friend especially before you put the effort into bleed them manually.
when you push on the MC and its solid that means the piston inside has a good seal.....I don't think you are getting the piston travel y9ou need. do you have the old MC still? measure the depth of the where the pushrod goes between the two from the mounting surface they should be the same.
bottom line that resistance you feel on the bench you need to feel at the pedal (although leverage will make it easier) but it has to be there or the plunger is depressing
the rest is bleeding and making sure the proportioning valve is centered.
some times gravity bleeding is your friend especially before you put the effort into bleed them manually.
when you push on the MC and its solid that means the piston inside has a good seal.....I don't think you are getting the piston travel y9ou need. do you have the old MC still? measure the depth of the where the pushrod goes between the two from the mounting surface they should be the same.
bottom line that resistance you feel on the bench you need to feel at the pedal (although leverage will make it easier) but it has to be there or the plunger is depressing
Last edited by bobs77vet; Jun 2, 2018 at 10:35 AM.
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From: Oglesby Illinois
I did check the depth of the old MC compared to the new MC and they are the same. I don't see that my rod is adjustable so i dont think that is the issue. I bled out almost 2 containers of fluid. The fluid in all 4 calipers is now clear so it has gone from the MC to the caliper so i would assume that any air in the line is gone. Even if there was air shouldn't I get decent flow?
Last edited by bill69; Jun 3, 2018 at 08:42 AM.
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Having no clue on how you are bleeding the brakes. And when you are doing this...you are trying at all costs to keep the master cylinder LEVEL.
I cannot say if the 'flow' you have is good or not. When I pressure bleed out the brakes. I can tell if one of the brake hoses is going bad due to how weak the stream of fluid coming out of the caliper bleed fitting is.
AS for the rod. It is adjustable. So...depending on how much 'free pedal' travel you have before you feel the rod contact the piston in the master cylinder. No one knows but you. The clevis can be removed off the brake pedal and the rod can be adjusted...or it can be done from under the steering column if you can get to it.
DUB
I cannot say if the 'flow' you have is good or not. When I pressure bleed out the brakes. I can tell if one of the brake hoses is going bad due to how weak the stream of fluid coming out of the caliper bleed fitting is.
AS for the rod. It is adjustable. So...depending on how much 'free pedal' travel you have before you feel the rod contact the piston in the master cylinder. No one knows but you. The clevis can be removed off the brake pedal and the rod can be adjusted...or it can be done from under the steering column if you can get to it.
DUB
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We've just about all been through this. Mine also had ZERO pedal effort for the longest time throughout the bleeding. Couldn't even get the bleeder to "squirt". But after a LONG time the pedal will finally get better. Catch the new fluid with hoses and jars, so it doesn't make a ridiculous mess and so you don't have to buy 2 gallons haha
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
bleeding C3s is a PITA.....
I think gravity is your friend with c3s
so bench bleed, gravity bleed and then pump or use motive power bleeder. mity vacs don't work they just pull air in from around the lip seal
I think gravity is your friend with c3s
so bench bleed, gravity bleed and then pump or use motive power bleeder. mity vacs don't work they just pull air in from around the lip seal
Melting Slicks
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1. make sure the rod is adjusted correctly. (you can check this on the car with 2 people) Open 1 bleeder and have someone press the brakes slowly and see how much pedal travel you need before fluid starts to flow. (Should be immediate with no pedal travel)
2. Then bleed the MC on the car like this.
https://www.corvetteforum.com/forums...-cylinder.html
3. Then bleed the calipers again. When bleeding the calipers use vise grips to hold the brake pads against the calipers pushing the piston in as far as the brake pads allow.
4. I bleed using pressure at the MC end like this.
You need to be careful not to empty the MC. If you do then go back to step 1.
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I agree with use a pressure bleeder attachment like what is shown above. Mine is similar.
But in 30+ years. I have never had to get the brake pads to pull up against the caliper. I leave them as they are when pressure bleeding....or any other method I of bleeding I use for that specific purpose. And they are not pulled against the caliper when preforming any other type of bleeding procedure that has been written. Just saying. I feel this is an unwarranted step.
DUB
But in 30+ years. I have never had to get the brake pads to pull up against the caliper. I leave them as they are when pressure bleeding....or any other method I of bleeding I use for that specific purpose. And they are not pulled against the caliper when preforming any other type of bleeding procedure that has been written. Just saying. I feel this is an unwarranted step.
DUB
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
I have never done step number 3 but I suppose the smaller the piston area the less air up at the top....that you have to worry about.
I suppose you could bleed the caliper with it not being mounted so the bleeder valve could be straight up
I suppose you could bleed the caliper with it not being mounted so the bleeder valve could be straight up
Melting Slicks
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I agree with use a pressure bleeder attachment like what is shown above. Mine is similar.
But in 30+ years. I have never had to get the brake pads to pull up against the caliper. I leave them as they are when pressure bleeding....or any other method I of bleeding I use for that specific purpose. And they are not pulled against the caliper when preforming any other type of bleeding procedure that has been written. Just saying. I feel this is an unwarranted step.
DUB
But in 30+ years. I have never had to get the brake pads to pull up against the caliper. I leave them as they are when pressure bleeding....or any other method I of bleeding I use for that specific purpose. And they are not pulled against the caliper when preforming any other type of bleeding procedure that has been written. Just saying. I feel this is an unwarranted step.
DUB
I don't do this if just flushing fluid.
Last edited by cagotzmann; Jun 3, 2018 at 01:44 PM.
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But it makes no sense to me at all. I just cannot make sense of it----sorry. The air that is in the system is just that. There is but so much air that can be in the system. And the object is to get all of the air out as you know...so thus...you cannot get 'more air out'. And pushing the the pads back against the calipers I cannot see any benefit in that at all. That is where I can not make sense of your method.
I have bled so many brake systems that were DRY. New master cylinder, lines and everything. I do not even bench bleed out the master cylinder. Because when I bleed out the system with my pressure bleeder. All I do is pump the brake pedal several times while the fluid is flowing out and tap on the frame and calipers to shock the systems so ANY air bubbles that may be stuck to the inside of the lines or calipers...brake loose and flow out in the stream of the fluid.
Others can bleed out their brakes as they see fit...and I guess I will stick with the method(s) I use due to it also works.
And bottom line...having good brakes is what it is all about.
DUB
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
If you find clamping the brake pads to the caliper....then I guess that works for you.
But it makes no sense to me at all. I just cannot make sense of it----sorry. The air that is in the system is just that. There is but so much air that can be in the system. And the object is to get all of the air out as you know...so thus...you cannot get 'more air out'. And pushing the the pads back against the calipers I cannot see any benefit in that at all. That is where I can not make sense of your method.
DUB
But it makes no sense to me at all. I just cannot make sense of it----sorry. The air that is in the system is just that. There is but so much air that can be in the system. And the object is to get all of the air out as you know...so thus...you cannot get 'more air out'. And pushing the the pads back against the calipers I cannot see any benefit in that at all. That is where I can not make sense of your method.
DUB
Melting Slicks
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I don't have a diagram of the caliper chambers to see were air could get trapped, but its seems its there at times. We are not talking about a large amount of air. Even 1 bubble is enough for me. Using the car for track days requires me to be extra fussy when it comes to brakes.
Last edited by cagotzmann; Jun 3, 2018 at 06:30 PM.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
heres a good example of how air can get trapped....note the bleed holes on the two different slave cylinders
the top one bleeds normally the bottom one doesn't you have to demount it to bleed it
compressing the piston in reduce the volume
the top one bleeds normally the bottom one doesn't you have to demount it to bleed it
compressing the piston in reduce the volume
Last edited by bobs77vet; Jun 3, 2018 at 06:39 PM.
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Comparing an aftermarket set of calipers to GM original designed calipers is like apples to oranges.
This thread is not dealing with slave cylinders. Although it can be helpful...the slave cylinder is not designed like the brake caliper. But I do know that I have to remove the slave cylinder on some C4's to bleed it correctly.
And how we got to pressing in on a slave cylinder when it was not mentioned until now is beyond me.
GM brake calipers are designed to be able to be bled as they are normally mounted on the car and do not require them to be removed.
DUB
This thread is not dealing with slave cylinders. Although it can be helpful...the slave cylinder is not designed like the brake caliper. But I do know that I have to remove the slave cylinder on some C4's to bleed it correctly.
And how we got to pressing in on a slave cylinder when it was not mentioned until now is beyond me.
GM brake calipers are designed to be able to be bled as they are normally mounted on the car and do not require them to be removed.
DUB
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I'm not sure if that is the intended design (front to rear bias?), or problems in manufacturing with location the location of the seals on the piston, or the position where the compensation port is drilled in the master cylinder.
It would be nice if someone with a Wilwood master could look at theirs and see if the "push back" of fluid into the reservoir is even or staggered.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
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IF bubbles came out of the line or tube that you had going to the rear port...so when you bench bleed it you are bleeding out the rear port. Then it is working fine.
I do know the front may actually squirt fluid up like a geyser...but the rear will NOT be as evident....and have a very slight turbulence to it. It has everything to do with IF you get flow out of the rear port back into the rear reservoir when bench bleeding it. If any of this made sense.
DO NOT plunge the piston in MORE than 1 inch.
And when I do actually decide to bench bleed one. When I am doing it...I push in the the piston of the master cylinder a little bit at a time and carefully watch the valve
move though the holes in the bottom of the master cylinder reservoir and I can stop and in a few seconds I can see bubbles that will begin to come out and then stop.
Then I push in on the piston some more and watch for them. Bench bleeding master cylinder can take a good half hour of not more to try to get those pesky bubbles to stop popping up through the holes in the reservoir.
DUB
I do know the front may actually squirt fluid up like a geyser...but the rear will NOT be as evident....and have a very slight turbulence to it. It has everything to do with IF you get flow out of the rear port back into the rear reservoir when bench bleeding it. If any of this made sense.
DO NOT plunge the piston in MORE than 1 inch.
And when I do actually decide to bench bleed one. When I am doing it...I push in the the piston of the master cylinder a little bit at a time and carefully watch the valve
move though the holes in the bottom of the master cylinder reservoir and I can stop and in a few seconds I can see bubbles that will begin to come out and then stop.
Then I push in on the piston some more and watch for them. Bench bleeding master cylinder can take a good half hour of not more to try to get those pesky bubbles to stop popping up through the holes in the reservoir.
DUB