Bleeding master cylinder in the car

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65Vart

65Vart

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I just finished a brake conversion and bench bled the master as per the instructions. It was a ***** removing and replacing in the car because of the brake pedal linkage but it’s done. Now , while bleeding the brakes, I ran the master dry, like a dumb ***. Can I bleed the master in the car this time pumping the brake pedal?
No way I want to rip this apart again.
 
I use a Mity-Vac. And do the Farthest away line 1st.
 
If you can make brake lines, just make a couple that connect to the MC and run straight back into the top.
 
I just swapped to power brake and never did the bench bleed. I would just bleed the brakes like you normally would. Worked for me.
 
I have that kit with plastic adapters and hose, it works, but makes a drippy mess.

I like to use metal lines cut to length and looped into the reservoir. Much cleaner.
 
I just went through this after a wheel cylinder leak. I had recently installed a new master cylinder and did a bench bleed. Recervoir went dry for back brakes. Refilled it and bled back brakes without bleeding the master cylinder again. All is well. Might be worth a try. If not, bleeding kits mentioned above work fine.
 
regarding getting brake fluid on your paint - I went to DOT 5 (silicone) in all my Darts and never looked back. It's expensive to buy but not as expensive as taking a bunch of stuff out to do a good job of repairing the mess when things go wrong. No need to get every little bit of DOT 3 out as the 2 fluids are compatible.
 
str12-340 said:
regarding getting brake fluid on your paint - I went to DOT 5 (silicone) in all my Darts and never looked back. It's expensive to buy but not as expensive as taking a bunch of stuff out to do a good job of repairing the mess when things go wrong. No need to get every little bit of DOT 3 out as the 2 fluids are compatible.
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Did you hear about moisture issues when using DOT 5? It's inability to absorb moisture causing corrosion and brake fade due to water puddling?
I use any DOT fluid except 5 for that reason.
 
I've been using DOT 5 since 2005 with no issues. In a properly bled and maintained system, how would any moisture get into the lines???
 
Agree 100%, when we got 67 in 2012, we made a mess with DOT 3 and it peeled firewall paint. DOT 5 went in next day and just bleed them until it pi$$ed purple. ZERO issues in 11 years. No compatibility issues here.
str12-340 said:
regarding getting brake fluid on your paint - I went to DOT 5 (silicone) in all my Darts and never looked back. It's expensive to buy but not as expensive as taking a bunch of stuff out to do a good job of repairing the mess when things go wrong. No need to get every little bit of DOT 3 out as the 2 fluids are compatible.
Click to expand...
 
When I replaced my master cylinder I was advised by a mechanic and a couple of other people to stay with the fluid originally used with the braking system. Their reasoning was the brake components were designed to work with it. I was ready to go to DOT5 as well. I was on the fence about it but decided to stick with DOT3 for my car and everything is fine. My car still has standard drum braking.

This issue is similar to the dino oil versus synthetic oil debate. There might not be a wrong answer here.
 
sireland67 said:
Condensation.
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The lines should be completely filed with fluid (along with the wheel cylinders, master and calipers) normally I would think of condensation as moisture that came out of solution from the air because of a drop in temperature. If the system is properly bled (no air bubbles in a system - a condition that would have its own issues) then there is nowhere for any moisture to be in the system at all, until something fails. I'm not a mechanical or chemical engineer, but I would hate for folks to not take an excellent remedy for an old problem if indeed there are no issues with the DOT 5. Ehrenberg, the tech editor at Mopar Action has been recommending DOT 5 for many years. I hope someone with some real qualifications can give us more info.
 
str12-340 said:
The lines should be completely filed with fluid (along with the wheel cylinders, master and calipers) normally I would think of condensation as moisture that came out of solution from the air because of a drop in temperature. If the system is properly bled (no air bubbles in a system - a condition that would have its own issues) then there is nowhere for any moisture to be in the system at all, until something fails. I'm not a mechanical or chemical engineer, but I would hate for folks to not take an excellent remedy for an old problem if indeed there are no issues with the DOT 5. Ehrenberg, the tech editor at Mopar Action has been recommending DOT 5 for many years. I hope someone with some real qualifications can give us more info.
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The system is not going to be completely full of fluid, because for brakes to work, fluid leaves the master cylinder, when the brake is pushed, filling the wheel cylinders, and calipers full of fluid, which stops the car.
When the brake petal is released, the fluid travels back to the master cylinder. The wheel cylinders, and calipers will not be full of fluid and the car moves.
A cold system, when heat is introduced, will sweat causing condensation.
Its simple physics.
Why will a good looking brake line, actually break, because it rots from the inside out.
DOT 3 or 5 will work, if you have replaced every component, at our age you will not have to worry about it.

Real qualifications, I am a degreed engineer, and have worked in industry for over 30 years designing aircraft.
 
sireland67 said:
The system is not going to be completely full of fluid, because for brakes to work, fluid leaves the master cylinder, when the brake is pushed, filling the wheel cylinders, and calipers full of fluid, which stops the car.
When the brake petal is released, the fluid travels back to the master cylinder. The wheel cylinders, and calipers will not be full of fluid and the car moves.
A cold system, when heat is introduced, will sweat causing condensation.
Its simple physics.
Why will a good looking brake line, actually break, because it rots from the inside out.
DOT 3 or 5 will work, if you have replaced every component, at our age you will not have to worry about it.

Real qualifications, I am a degreed engineer, and have worked in industry for over 30 years designing aircraft.
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I guess instead of saying "full with liquid", a better way would be "void of air",
Right?
Air can be compressed, causing a soft pedal whereas compressed liquid creates hydraulic pressure?
 
sireland67 said:
The system is not going to be completely full of fluid, because for brakes to work, fluid leaves the master cylinder, when the brake is pushed, filling the wheel cylinders, and calipers full of fluid, which stops the car.
When the brake petal is released, the fluid travels back to the master cylinder. The wheel cylinders, and calipers will not be full of fluid and the car moves.
A cold system, when heat is introduced, will sweat causing condensation.
Its simple physics.
Why will a good looking brake line, actually break, because it rots from the inside out.
DOT 3 or 5 will work, if you have replaced every component, at our age you will not have to worry about it.
Click to expand...
Sorry, but that just isn't how brake cylinders and calipers work. When you let up on the pedal, the pistons in the cylinders and calipers pull back since they aren't under pressure - no air involved, just brake fluid. I've never had a brake line "break" in 50 years of working on cars in continuous use. If a car sits for a long time and the system is no longer sealed, then moisture laden air can be introduced. If nobody replaces the lines there could be issues.

The idea that DOT 3 protects the lines by absorbing the moisture in a system, including at the surface of the reservoirs in the master cylinder, also seems suspect in that such DOT 3 would be considered to be contaminated and compromised.
 
Joey4speed said:
Did you hear about moisture issues when using DOT 5? It's inability to absorb moisture causing corrosion and brake fade due to water puddling?
I use any DOT fluid except 5 for that reason.
Click to expand...

The main issue with DOT5 is mixing it with DOT2 or 3. DOT 2 and 3 can absorb moisture. So while the different DOT fluids are compatible, what happens is the old fluid has moisture in it and the DOT 5 can’t, so it can create “bubbles” of trapped old fluid which has moisture in it. Since the fluid doesn’t move all that far it can rust out a localized section of line, if left alone long enough.

In theory, at least.

It’s why DOT5 is recommended for new systems and not as much for upgrading old systems unless you really clean the old system out.
sireland67 said:
The system is not going to be completely full of fluid, because for brakes to work, fluid leaves the master cylinder, when the brake is pushed, filling the wheel cylinders, and calipers full of fluid, which stops the car.
When the brake petal is released, the fluid travels back to the master cylinder. The wheel cylinders, and calipers will not be full of fluid and the car moves.
A cold system, when heat is introduced, will sweat causing condensation.
Its simple physics.
Why will a good looking brake line, actually break, because it rots from the inside out.
DOT 3 or 5 will work, if you have replaced every component, at our age you will not have to worry about it.

Real qualifications, I am a degreed engineer, and have worked in industry for over 30 years designing aircraft.
Click to expand...

What?

Good grief man. The calipers and wheel cylinders are always full of fluid in a properly bled brake system. The fluid displaced by pushing the pedal is moved from the MC through the lines to move the pistons in the calipers/wheel cylinders and returns when the pedal is released. The only part of the system with an air gap is the master cylinder above the level of the fluid.

The fluid is in incompressible, otherwise none of it would work. Air is compressible, which is why you have to bleed all the air out for the brakes to work. No void space is ever created in the system below the MC, the pistons move back and forth proportionally to the fluid displaced and everything below the level of fluid in the MC remains full of fluid.
 
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