Brake Fluid Off The Top: How Much Can I Remove?

jaymar

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Need to draw fluid from the reservoir to prevent overflow while changing brake pads/pushing pistons around.

How much do I need to remove, and how much CAN I remove without risking any kind of air in the system? (Or is that not even a concern?) Plan to refill with new fluid from the top, so I want to remove as much as I can. (Not looking to get into the brake-bleeding circus today...)
 
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So I can do that even if I'm NOT bleeding the brakes now, yes--basically empty the reservoir? :)
Ok well I guess I should ask which method you are going to be using to push the pads in. I prefer to open the bleeder valve when I push the pads in so I don't push the crap back up into the master cylinder, if you are going to do that maybe leave the reservoir about 1/2 full. Others are fine just taking the cap off the reservoir and then pushing the pads in, if you do that go ahead and empty the reservoir.
 

LandLocked93

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Ok well I guess I should ask which method you are going to be using to push the pads in. I prefer to open the bleeder valve when I push the pads in so I don't push the crap back up into the master cylinder, if you are going to do that maybe leave the reservoir about 1/2 full. Others are fine just taking the cap off the reservoir and then pushing the pads in, if you do that go ahead and empty the reservoir.
Good point here.
I've done both methods and still had to get a pro bleed service, even after I bled them myself with a vacuum tool.
Hard to beat 'the machine'. Plus you can also get a full flush, refill with new, and a master res bottle clean-out for little extra at the same time.
It's just miles faster and easier for the 60 some-odd dollars they charged to do it all.
 
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Maybe I'm missing something here, but in the last 30 years I have never had to remove any brake fluid from any reservoir when doing pads. Brake fluid is not consumed unless there is a leak. The level in the master will gradually fall as the pads wear. Replace the pads on a caliper, step on the brake a few times to seat them, move to the next caliper. Lather, rinse, repeat.
I bleed fluid after replacing pads or whatever I'm doing on the brake system and fill reservoir to the "full" line. Done.
Brake fluid should be water clear.
 

thatcabledude

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Maybe I'm missing something here, but in the last 30 years I have never had to remove any brake fluid from any reservoir when doing pads. Brake fluid is not consumed unless there is a leak. The level in the master will gradually fall as the pads wear. Replace the pads on a caliper, step on the brake a few times to seat them, move to the next caliper. Lather, rinse, repeat.
I bleed fluid after replacing pads or whatever I'm doing on the brake system and fill reservoir to the "full" line. Done.
Brake fluid should be water clear.
Some people keep the reservoir “topped up”. Maybe quick lube places add fluid during changes too. I don’t know. I’ve worked on plenty of vehicles that if I didn’t suck some out before doing the pads the MC would have overflowed. I learned this the hard way at about age 16 in auto shop class doing a brake job on a Toyota T100.
 
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I usually steal a hand soap pump from the house or keep a few of them around for this purpose. After emptying the soap from the pump, stick the pick up tube into the reservoir and pump out the fluid into an old bottle, can or whatever I have around. No need to remove more than half to do a brake job, and as pointed out above, shouldn’t be necessary at all if you haven’t been topping off as the pads wore down.
 
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I use a marinade injector (a buck @ Dollar Tree)

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Doesn't drip down like a turkey baster
 

Gumby

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Don't top off. If its low find out why. Usually worn linings, occasionally a leak. Either way fix it.

Opening the bleeders to compress the pistons is a great idea. Then, of course, replace the fluid that came out. Keeps the bleeder free too.
 

leonard_nemoy

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I have had the brake light come on from low brake fluid torwards the end of my brake pads life before so I have definitely topped off the master and subsequently had to remove fluid when changing pads.

Like others have said just use a syringe or turkey baster.

Maybe it is possible to go through a set of pads without ever topping off the fluid, but your fluid level would certainly be on the low end.

After boiling the brakes on my 91 I personally like to keep as much fluid as possible in my reservoir. Plus I like to remove as much fluid from the reservoir as I safely can and replace with new once a year as a poor man's brake flush. Kind of like a drain and fill on the tranny every 3rd oil change.
 

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