Bleeding brakes question. How do you know when it's flushed?

You hook up a hose to the bleeder valve, and direct it into some bottle.
Then you pump the brake pedal while topping off the master cyl. (This requires 2 people)
But, how do you know when you’ve pushed out all the old fluid?
Does it start to look different once the new fluid is being pumped out?

When it looks the same coming out as it does going in, you are done…

What will the old fluid look like? I assume it’s the same color, so what if what’s going in looks exactly like what’s already in there?

Also, you need 3 people, right?

  1. Pump the brake
  2. Top off the fluid
  3. Checking the exit flow to check when you’re done.

I stopped when I had gone through a quart of fluid. It looked the same starting as ending.

The old brake fluid will look darker, almost black if it’s really old

The new fluid should be almost clear

If you had to replace a hydraulic then more than likely the fluid will be dirty and dark in color. You know all old fluid is out when clear fluid bleeds through.

Thank you. I have a feeling my car has original 10 year old brake fluid. I might as well bleed it and learn something. I bet almost every car on the road is on the original brake fluid. I have never bled a car in my life in fact. Never had a problem. Always drove old beaters too.

If that’s the case then be very careful, brakes are one of the most important systems on a car. Your not only playing with your life but others as well.
Brake fluid absorbs moisture and overtime rusts metal lines, flush the fluid periodically.

Its better to have a car that wont start then a car that wont stop.

“I bet almost every car on the road is on the original brake fluid.”

Maybe the leased ones that get no maintenance. :slight_smile:

Many manufacturers recommend replacing brake fluid every 30,000 miles. I recommend brake fluid flush at 30,000 mile intervals and/or when a major brake service is done. I think the only older cars with original brake fluid are ones where the driver either doesn’t know to do maintenance or ignores suggestions to do so.

I have started doing gravity flushes. The color of the fluid is a good indication. I believe they sell blue brake fluid for those who have a severe case of OCD (mine is mild).
I have started paying more attention to the color of the fluid and every 2 years is just enough. I had to rotate the tires on my Camry this weekend and flushed the brake fluid too. It was probably 18 months old, but the color was getting darker and a $6 bottle of DOT 3 fluid doesn’t make me more broke.

What’s a good kit to do bleeds with? What kind of hose do you need?

I’ve used vacuum bleed kits to make it a one man job but I don’t find they work that great. I usually use gravity bleed but you need to be very patient to do that. The best way I’ve found to change fluid is to use the vacuum kit to suck out all but the last bit of fluid from the reservoir and pour in clean. Then the bleed-down is with fresh fluid. To speed up the process, pump the brake pedal, with one helper on the pedal and the other opening and closing the bleeder. The reservoir is big enough to do one corner at a time before refilling. The best method, though, is to get a spare reservoir cap, add a fitting so you can hook it to a very low pressure air source (5 psi or so) and bleed each corner with the pressure pushing the fluid through. Remove and refill the fluid between each wheel bleed.

I guess everyone has their own method for bleeding brakes. Mechanics almost universally say the power bleed using compressed air and a special adapter gadget on the master cyl is what works best. I’m not sure what “gravity bleed” means. Does that mean you just open the bleeder screws at the wheels, fill the master, and wait for it to drip out? I can see that might work and be effective at driving the air bubbles out.

Me, I’ve had pretty good success using those special “quick bleeder” fittings to replace the normal one at each wheel cylinder (or caliper). They have the one-way valve in them already. I don’t bother with the hose. I just let it bleed at each wheel to the ground, then clean up later with a rag. A helper pushes the pedal (gently, slowly, with his hand only) in time w/me opening and closing the fitting, starting at the longest line and working to the shortest. I used to use the method where the helper presses the pedal hard with his foot to drive the air to the end of the line, but I found I had air staying in the system that way. My current method is what works best for me. I do usually have to repeat the process at least one more time after a few days of driving.

You can google brake bleeding and you will get a lot of videos on how to do it. Obviously many methods. I believe if you have a good helper the 2 person method is the better one. In my case, I am having my doubts about my wife or daughter holding the pedal still when I am closing the bleeder. I have had better results with gravity bleeding and yes it is time consuming. You can buy clear tubing from the parts store.

I know there is one poster here that just drains and refills the master cylinder. I want to know what the consensus on that is? Is the brake fluid in a linear fashion and does not mix in the system at all (hence changing the master cylinder reservoir part being useless), or mixing does happen? Also, if there is mixing, shouldn’t small bubbles of air be removed with time without bleeding?

Just a note, there is a sequence to bleeding, not longest to shortest. I’d have to check the book but I believe it is LF, RR, RF, then LR. I don’t know why, and at my age I don’t care to know why, I just follow the book.

Another good way to get an indicator of when you’re done exchanging brake fluid is to buy ATE brand. It comes in two colors. There’s no difference between the two except for the color. So, put one color in one time, and the next time put the other color in. When the brake fluid coming out is the same color as what you put in, you’re done.

This comes in handy if for whatever reason you have to bleed the system before the fluid has time to get dirty.

You don’t have to have a kit. You could let it run out the bleeder into a pan or the floor and no air will suck back into it.

spray brake cleaner and kitty litter will help with clean up.

All brake fluid is basically the same. I just need "brake fluid"
It seems the easiest is to just pump the brake pedal.
How does this work.

Open Bleeder valve

Press brake pedal.
Open master cylinder cap and top off.
Close master cylinder cap

Press brake pedal.
Open master cylinder cap and top off.
Close master cylinder cap

Press brake pedal.
Open master cylinder cap and top off.
Close master cylinder cap

Close Bleeder valve

Is that right?

EconoboxBMW … Many owner’s manuals specify to use “dot 3” brake fluid – “dot 3” is a standard which will be printed on the can, not a brand name – but some cars may require a fluid meeting a more stringent or different standard. Owners manual will say if dot 3 is the one to use or not.

You bleed on wheel at a time. In this sequence. Open bleeder, press pedal down almost to floor, close bleeder. Take foot off of brake pedal and let it rise. Repeat. Move on to next wheel.

You have to check the master cylinder frequently to make sure it stays topped off. If it goes empty, it’s not a disaster, but you have to start over again at the first wheel.

The biggest problems I’ve had w/brake bleeding is that the bleeder valves are rusted shut. It can take several days of spraying thread penetrant to get them to loosen up. Sometime they just won’t ever loosen and round off from repeated attempts, then you usually have to replace the entire wheel cylinder or caliper. I just bought two new wheel cylinders for my Ford truck for this very reason.

As per above; and you don’t open and close the master cylinder cap. Open it first, empty with turkey baster or syringe, fill with fresh fluid and keep it topped off until you are done with 4 wheels and then close the master cylinder cap.