How to change brake fluid?

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JamesLond

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When I've done it, I started by sucking out as much of the fluid from the reservoir as possible, using a turkey baster. Then I refill the reservoir with fresh fluid and bleed the brakes. Be sure to keep the reservoir topped off as you go, so you don't suck air into the lines. This gets everything except the ABS pump.

If you have access to a Tech2 scanner, there's a process for bleeding that, too. But I've never done it. I guess you could go on a drive and intentionally panic-stop to activate the pump. This would mix the fluid and hopefully get most of the crud out of the pump. But to get it all, you'd have to re-bleed the whole system a second time.
Does the bleed order matter?
 

rockola1971

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Never heard of this. After thinking, I suppose it could be possible on models with StabiliTrak. Is that what you were referring to?
The Tech 2 has an automatic brake bleed function. It uses the ABS Pump to "pump" the brake system instead of someone manually having to pump the brakes. Which is usually a necessary procedure because of the solenoids with the ABS manifold and those can trap air which is why the system cant be bled old school or usually even gravity bled.
 

mattbta

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The Tech 2 has an automatic brake bleed function. It uses the ABS Pump to "pump" the brake system instead of someone manually having to pump the brakes. Which is usually a necessary procedure because of the solenoids with the ABS manifold and those can trap air which is why the system cant be bled old school or usually even gravity bled.
Everything I'm reading in GM SI says perform a bleed (manual or pressure) of the entire system first and finish with the ABS bleed via scan tool. Attached is Document ID# 874224 which describes the process for JL4.
 

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rockola1971

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Everything I'm reading in GM SI says perform a bleed (manual or pressure) of the entire system first and finish with the ABS bleed via scan tool. Attached is Document ID# 874224 which describes the process for JL4.
All 3 of my K chassis (2) 2003 Tahoe LT (1) 2005 GMC Yukon Denali have been bled with my tech 2 and brakes are great. Old school bleeding on them does not work if you open the system up and drain fluid past the ABS solenoids. It traps air that you will almost never get out gravity or old school pump and hold the brake pedal.
 
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JamesLond

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I've always just done it by performing a standard bleeding process (clear hose in bottle), but staying at the right rear caliper (farthest away) until the fluid coming out is all new fluid. I'll go a couple more cycles after that to ensure. I don't have a Tech2 or any bi-directional scan tools to hold the solenoids open. When I bleed the brakes, I do a few standard pedal pumps then I'll turn the key to the "on" position just as I'm beginning another pump. The ABS solenoids are activated during a self-check when powered up. I'll do this a few times during the pumping of each corner. Also, don't push the pedal to the floor. Try to keep it within its normal range of travel. Maybe lay a 2x4 or something on the floor behind the pedal to give yourself a stop.
I've heard the part about the pedal to the floor during some research. Do you know why it's bad to do that?
 

MassHoe04

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Maybe I got lucky...
I did front two, then back two a few months later. I topped off the reservoir and never let the fluid empty out. I did not have a Tech 2 at that time and never did any ABS auto-bleed. I just bled out the lines at the calipers until fluid was clear and no bubbles coming from the new calipers. Maybe I did get lucky, but brakes have been great. ABS works great. No complaints.
 
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We went through 6 quarts of brake fluid bleeding the brakes until the fluid came out clean, both the regular way and then with the Tech-2.
It surprises me how much fluid it takes, especially since the brake lines are rather small diameter and the reservoir doesn't hold a lot. The ABS modual and MC/Booster must have large passages or something.
 

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