Thoughts on pressure brake bleeders

So I am changing my rotors, pads, shoes and flushing the brake fluid out soon.

The most miserable part of brake work is when I have to have someone pushing the pedal as I open the bleeder. They always act like its the most terrible thing in the world to pump a brake pedal for a few minutes.I just really can’t stand it.

I bought one of those hand squeeze vacuum guns last time I did this but it was junk, thing actually fell apart in my hands the first wheel.

Im looking at the motive power bleeder, where you attach it to the reservoir in engine bay and pump it to pressurize then just open the bleeder at the wheels and clutch slave cylinder.

Do these work well? Seems easier than a vacuum type as you dont have to keep filling the reservoir.

If anyone has a better self bleeder or trick to bleed brakes solo please let me know

I’d like to hear some answers to this also. I personally use a vacuum pump and always do a manual bleed afterwards just for safe measure.

Yes, pressure bleeders are the best way to bleed brakes solo!

Although with the right car and patience, some cars can be gravity bled. Open the bleed screw attached to the catch bottle and wait. Maybe go to lunch!

You can make your own with an extra brake reservoir cap with a air quick connect if you have a compressor you can regulate down to 5 psi. If not, the commercial pressure bleed systems work well.

Vacuum pumps suck… literally and figuratively. Even good quality hand pumps don’t bleed brakes very well.

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I vacuum bleed some of my cars, but I use a vacuum bleeder that hooks up to my air compressor. No stressed parts in the bleeder, and no moving parts that come into contact with the liquid you’re pumping, so it won’t fall apart on me halfway through the jobs like the junky hand pumps do. If you have an air compressor, this is a good solution. Just don’t crank the regulator all the way up like you would for an impact gun.

Others, I installed speed bleeders on. These little things are great. They replace the bleeder nipple. When they’re closed, they act just like a regular bleeder nipple. When you crack them open, there’s a ball valve in the stem which keeps brake fluid from coming out unless you’re pressing on the pedal. When you let up on the pedal, the ball valve snaps closed and prevents air from getting into the system.

One man brake-pump bleeding without having to fill a bottle halfway with brake fluid and mess with trying not to knock it over.

The problem with the brake bleeder you’re referring to is, it allows air and moisture to come in contact with brake fluid when it’s pressurized.

The moisture will contaminate the brake fluid.

Where this brake bleeder doesn’t allow that.

That’s because there’s a diaphragm inside that isolates the brake fluid from the air/moisture when it’s pressurized.


I had a pressure bleeder and a box full of adapters and while doing 80 to 100 brake jobs a month I rarely used the machine because it was a time wasting PITA.

Did you use the assistant at the brake pedal method?

But isn’t there air, with its moisture, above the reservoir of brake fluid all the time anyway? I don’t see how briefly adding some air pressure above the pool of fluid would change its moisture content to any meaningful degree.

That’s under normal atmospheric pressure.

Now add air/moisture at 80% relative humidity under pressure inside a container that contains brake fluid, and where do you think that moisture is going to go?


No assistant needed. Just attach a snug fitting 6" length of rubber hose to the bleeders in the normal bleeding order and crack them open enough to allow flow while giving enough restriction to build slight pressure in the system. When liquid leaks from the bleeder move to the next. Throw a little oil dry on the brake fluid and it’s all done.

Matching and connecting the proper adapter to the master cylinder and often engineering adapters and seals for master cylinders and cleaning up the mess under the hood and often on the fender of the car is a very frustrating, time consuming ordeal. And while peculiar problems sometimes brought me to use vacuum bleeders they caused more spillage and took more time than my normal method.

And FWIW, when gravity bleeding the bleeder can be totally removed from the caliper/wheel cylinder allowing quick bleeding if you can be certain to keep the reservoir from going dry. Air will not-CANNOT- enter the brake system from the bleeder port unless the pedal is pumped and if there is even a short piece of hose on the bleeder air CANNOT be drawn in when the pedal is pumped.

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Almost all will stay in the air space above the brake fluid. Even if you were injecting the air into the brake fluid, almost all would bubble up to the surface, into the air space.

A half hour every few years of air pressure in the top of the master cylinder will have no practical effect. A few years of normal air and humidity in the top of the master cylinder - that’s how a problematic amount of moisture can get into the brake fluid in the reservoir.

It’s not the top of the master cylinder that’s the concern. It’s that you’re sticking the entire volume of brake fluid that will soon be in the car into a vessel, and then stuffing in air. Anyone who’s ever opened the petcock on a charged air compressor knows that water gets squeezed out of the air when you compress it, because when you open the petcock the first thing that shoots out the drain is a whole bunch of water.

That tells you three things: Air is wet, compressed air sheds water, and that water drops to the bottom of the vessel.

So if you put brake fluid in a vessel and then stuff in compressed air on top of it, that water is going to precipitate out of the air and head straight for the brake fluid, and you are now exposing all of the brake fluid to the water, not just the small surface area that you find on top of a MC reservoir.

Worse yet, if you vacuum bleed or do the old standard brake pump bleed, you’re exposing the top of the brake fluid in the MC to the water that is in the air directly above the master cylinder, which isn’t all that much even if you live in a very humid area.

If you pressure bleed in a non-separated vessel, you are exposing all of the brake fluid to the water that is normally in a vastly larger volume of air, because that’s what air compression is - you’re taking a big volume of air and stuffing it into the space normally occupied by a small volume of air.

You therefore have lots more water interacting with the brake fluid than you do with normal air.

How much water will condense at 15 PSI? Is that significant?

Most of the vehicles that I work on have vented master cylinder reservoir caps so the fluid is ways exposed to the air, it is good for about 3 years.

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I guarantee people are pressurizing higher than 15psi, despite instructions to the contrary.

The vent is on the backside of the bellows and only serves to allow the bellows to expand down into the reservoir as the pads wear and more fluid is pulled from the master to fill the cylinder/caliper. The rubber bellows has no hole and seals the fluid from atmospheric gases.

No bellows, just a multi piece rubber cap.
This is a typical Toyota/Lexus brake reservoir cap;

My Plymouth has bellows in the master cylinder cap.

lol … I’ve had that same exact experience. No kidding. I have no idea why pushing on the brake pedal for 5-15 minutes to help get the job done, why they feel that job is such a burden, but apparently it feels that way to them. I’ve been on the receiving end of that complaint even when I’m volunteering to help bleed the brakes on that owner’s car. It’s a mystery to me. There must be a frustration factor involved is my only theory.

The pressure bleeder with a diaphragm method seems like it is the best way. I’ve heard good reports for the vacuum method that uses an air compressor to make the vacuum, and the gravity bleed.

My solution I adopted many years ago is to just do it myself, without help. Here’s how I’ve always done it, has consistently worked well on my Corolla, Ford truck, and old VW Rabbit.

(Assumes no-ABS issues and the master cylinder is air-free & isn’t an issue)

  1. connect clear hose to bleeder & run other end into a catch-container, open bleeder
  2. push on brake pedal gently, with one hand (not foot)
  3. avoid pushing all the way to the floor, maybe 3/4 of the way max (use block of wood spacer under pedal if necessary)
  4. prop pedal down with stick against seat
  5. close bleeder
  6. release pedal using hand, again very gently, don’t let it spring up by itself
  7. repeat until there’s no air pockets in the clear hose, move on to the next wheel, etc.

This seems like it would take forever, but – maybe b/c nobody’s complaining – but it doesn’t seem like it takes long at all. I’d say 1/2 hour max, with coffee breaks. I’ve always had really good results using this method on all three of my vehicles. The key to success is to press on the pedal with your hand only, slowly and gently, and the same when releasing the pedal, slowly and gently. I call it “gravity bleed for somebody in a hurry”. Works for bleeding the Corolla’s hydraulic clutch fluidics too.

After you posted those pics, I remembered a similar discussion some time back. You’re right of course, they do have both types of caps in production. I did a bit of searching to find out why. Seems with the advent of plastic reservoirs, some manufacturers chose to do the vented cap since it was supposedly “easier to service” than the bellows designed cap. I call BS on that. I think it is just cheaper to do a slit than to pay for a diaphragm design. Most manufacturers recommend 3 year intervals for fluid changes. Having the cap vented to atmosphere, especially in humid climates, almost guarantees that is necessary. Glad none of my vehicles have this design…

It is possible that the caps that are vented to outside air are for systems that use DOT 5 fluid. It doesn’t absorb water like DOT3 or 4. Just speculation.

You would think but that does not appear to be the case.