# Advice on Brake System Flushing



## peahrens (Jun 7, 2010)

How often should I change out the brake fluid on my goat? I don't want the lines to leak from internal corrosion. Is the Harbor Freight flushing system below a preferred item for a 1-man approach, or do you recommend another?

I'm not sure the link below will appear as one you can just click (vs. having to cut an paste into your browser).

Brake Fluid Bleeder


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## geeteeohguy (Feb 2, 2008)

For me, about once every 5 years. I just open the bleeders, take the cap off the master, and let gravity do the work. Be sure to wash off any brake fluid on the suspension parts with plain water after you're done. No need for fancy gadjets. If you want to speed it up, suck the old brake fluid out of the master with a syringe or basting bulb and start with a master cyl full of new brake fluid. Doesn't take long. When you're getting clear fluid out of the bleeders, you're done.


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## 400fitz (Jul 7, 2010)

Cool tip. I'm going to give it a try.


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## jetstang (Nov 5, 2008)

I like GTOguys advice and love a car that will self bleed, but anything with a check valve will not self bleed. Just need to act like your bleeding the brakes, but it's full of fluid. Even with good brakes if you bleed them right you will get all the air out of the system.


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## crustysack (Oct 5, 2008)

I have just used a similar device (mighty vac) to bleed my clutch and brakes, takes less than 10 minutes, no fluid all over your car and no air left in the system at all. Its worth the money just to not get brake fluid all over the place.


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## 1970 Lemans (Jul 25, 2009)

In the case of vehicles that have a metering valve or combination valve, my understanding is that their is a valve pin, underneath a rubber bulb or boot, that must be depressed during the bleeding operation. 

If you are bleeding as a one-man operation, how do you hold the pin in or what do you all use to hold the pin in?


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## peahrens (Jun 7, 2010)

Gosh...I've got a Mityvac I use to suck out my outboard motor oil! Don't know if the supplied tubing is the right size for a brake bleed but I guess I can make that happen. Sounds like a great way to do it. Thanks.


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## Koppster (Jul 27, 2008)

Mityvac rocks, I've got the model that hooks to a compressor, works great


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## geeteeohguy (Feb 2, 2008)

I never worry about the metering valve. With just gravity, I've always been able to get clean new fluid out of all 4 corners, and I'm talking new vehicles, too. No need to depress the pedal or anything else. Just evacuate the master cyl. reservoir, fill with new clean fluid, and gravity bleed the 4 corners, keeping an eye on fluid level. The idea is to flush or exhange the old fluid with new, not bleed air out of the system.


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## 1970 Lemans (Jul 25, 2009)

I thought the purpose of the metering valve, at least in the case of power front disc brakes, was to prevent flow until a certain pressure was reached ( in order to allow the rears to do their stuff slightly ahead). Thus, I thought you couldn't get flow without depressing the 'relief' pin. Is this incorrect ... that is, good flow will occur without depressing? I never tried it, so I don't know (just reading from the manual).

TIA


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## geeteeohguy (Feb 2, 2008)

I've done many, many vehicles with no pressure on the pedal at all...just crack the bleeder, take the MC cap loose, and sit back. Believe me, it will pass fluid. The car is not being driven, the brake pedal is not being depressed, therefore the metering valve or proportioning valve is not active as it is when driving the vehicle.


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## 1970 Lemans (Jul 25, 2009)

geeteeohguy said:


> I've done many, many vehicles with no pressure on the pedal at all...just crack the bleeder, take the MC cap loose, and sit back. Believe me, it will pass fluid. The car is not being driven, the brake pedal is not being depressed, therefore the metering valve or proportioning valve is not active as it is when driving the vehicle.


Thanks, that's good to know. I was/am planning on using a Mityvac to assist in this, but will try without worrying about depressing the valve. 

Actually, the reason I am interested in knowing how to bleed the line correctly is because the metering valve appears to have developed a slight leak (~1-2 drops per day) at/from the pin valve and I am going to replace it with a new one, thus ...


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## 1970 Lemans (Jul 25, 2009)

FWIW, was initially able to bleed the system as per geeteeohguy's method, ie gravity and didn't need to depress the metering/hold-off valve. 

That said, my reason for getting into this was to replace the metering valve with a new one as the old had a leak. With the new one in place, lines would not bleed until the relief pin was depressed.


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