[Camfab]

[QUOTE=Msquared;11415250]

Originally Posted by Camfab

Something to consider. The tanks like the Motiv set up are actually introducing air into your precious fluid. This is especially a problem in high humidity areas. Remember brake fluid absorbs moisture./QUOTE]
Unless you overfill the reservoir, your brake fluid is always exposed to air in the same location as when you use a Motive pressure bleeder. The only concern about air in a brake system is if it gets into the lines, but that's not an issue with a pressure bleeder (unless you let the fluid level get too low in the reservoir).

I don’t agree. Your reservoir is sealed for a reason. The motiv set up exposes a large area of brake fluid to pressurized air, which particularly in a humid environment will contaminate your fluid. A real pressure bleeder as shown above, never exposes the fluid to pressurized air. Engineers developed this system. The motiv solution was a backyard manipulation of a garden sprayer, do as you please.

[Msquared]

There is literally air above your brake fluid in the reservoir at all times, as there is when you open the bottle and pour the new fluid in to whatever you pour it into. Therefore, there's no "introducing air" into the fluid with a pressure bleeder - they've known each other since the fluid was manufactured! Brake fluid doesn't absorb air anyway. That's just not a thing.

Finally, I don't think these reservoirs are as tightly sealed as you believe they are. If they were, then the fluid level inside them could never drop because no air could get in to replace the lost fluid; which would obviate the entire purpose of the reservoir. They are sealed enough to keep large amounts of moisture out, but that's about it. But no matter what method you use to bleed your brakes, the fluid is going to be exposed to air with moisture in it for most of the duration of the process. There's probably a good argument that the pressure bleeder is actually keeping more moisture away from the fluid during a bleed/flush process, since it forms a semi-sealed system with the fluid instead of just leaving the reservoir open.

[MT-SS1LE]

I have the Motive bleeder with all the adapters that I bought years ago. Tried it on several vehicles and never was completely satisfied with it. Extremely finicky as far as getting a tight seal on the reservoir. I never could get it to seal 100% for a complete brake flush on three different vehicles. And if you fill it with fluid you run the risk of it leaking and getting brake fluid everywhere.

I gave up on it and bought a Mityvac vacuum bleeder that requires attachment to an air compressor. Works 10X better and doesn't require any adapters, no risk of leaks, and it's faster. If you have access to an air compressor, it's the way to go.

[The Maverick]

Originally Posted by Camfab

I don’t agree. Your reservoir is sealed for a reason. The motiv set up exposes a large area of brake fluid to pressurized air, which particularly in a humid environment will contaminate your fluid. A real pressure bleeder as shown above, never exposes the fluid to pressurized air.

It's an interesting theory, but a little web searching didn't uncover any technical articles to show that this presents a practical problem as opposed to a theoretical concern. Motive pressure bleeders aren't brand new to the market. If there was a statistically significant amount of moisture being introduced by the Motive bleeder, I'd expect there would be a good number of examples out there in the way of customer complaints. While there is nothing wrong with being extra cautious about moisture contamination of brake fluid, the diaphragm bleeder may not have a clear advantage over the Motive when it comes to the likelihood of introducing moisture into brake fluid - particularly for occasional DIY use.

[Badmojo]

Just add the stainless steel speed bleeders. They are less likely to shear off than the weak factory bleeder material and you don't have to have any special tooling if you need to bleed them at the track without a helper.

[Camfab]

Originally Posted by The Maverick

It's an interesting theory, but a little web searching didn't uncover any technical articles to show that this presents a practical problem as opposed to a theoretical concern. Motive pressure bleeders aren't brand new to the market. If there was a statistically significant amount of moisture being introduced by the Motive bleeder, I'd expect there would be a good number of examples out there in the way of customer complaints. While there is nothing wrong with being extra cautious about moisture contamination of brake fluid, the diaphragm bleeder may not have a clear advantage over the Motive when it comes to the likelihood of introducing moisture into brake fluid - particularly for occasional DIY use.

I’d agree on a daily driver, if you’re spending huge money for the absolute best on race car it’s just science. I do believe that the speed bleeder is a far better solution. I am going to purchase them and give them a try on my other cars. Correct me if I’m wrong here. The speed bleeders have a sealant on the threads which prevents air or liquid from backing up into the caliper when loosened. Does that mean you need replace them at certain intervals?

[Camfab]

Originally Posted by Msquared

There is literally air above your brake fluid in the reservoir at all times, as there is when you open the bottle and pour the new fluid in to whatever you pour it into. Therefore, there's no "introducing air" into the fluid with a pressure bleeder - they've known each other since the fluid was manufactured! Brake fluid doesn't absorb air anyway. That's just not a thing.

Finally, I don't think these reservoirs are as tightly sealed as you believe they are. If they were, then the fluid level inside them could never drop because no air could get in to replace the lost fluid; which would obviate the entire purpose of the reservoir. They are sealed enough to keep large amounts of moisture out, but that's about it. But no matter what method you use to bleed your brakes, the fluid is going to be exposed to air with moisture in it for most of the duration of the process. There's probably a good argument that the pressure bleeder is actually keeping more moisture away from the fluid during a bleed/flush process, since it forms a semi-sealed system with the fluid instead of just leaving the reservoir open.

Matt every vented cap I’ve ever encountered has had a rubber bladder below it. The vent allows the bladder to move, allowing the movement of fluid. It’s not about air being dissolved into the fluid, though at a high enough pressure it would. It’s about relative humidity and the hygroscopic nature of brake fluid. Think of it this way, when you use your compressor you are just compressing outside air. What happens, you end up with a ton of water. Now that’s an exaggerated example because you’re moving a large volume of air. At 75% humidity at Atmospheric pressure the air above the brake fluid contains 75% of the water that a given volume of air can hold before it precipitates into water drops. Now taking that same air and pressurizing it increase the likelihood that the moisture will go from a gas to a liquid. Knowing that brake fluid loves water you can guess what happens next. It’s something to consider when you are looking for the absolute best performance from your brakes. This is why the best and admittedly biggest hassle pressure bleeders isolate the fluid from air with a diaphragm.

[Msquared]

Originally Posted by Camfab

It’s not about air being dissolved into the fluid, though at a high enough pressure it would.

I understand that, but that's what I though meant when you wrote: "The tanks like the Motiv set up are actually introducing air into your precious fluid." My reply was that they aren't introducing any more air than is already being introduced during the bleed/flush process anyway.

It’s about relative humidity and the hygroscopic nature of brake fluid. Think of it this way, when you use your compressor you are just compressing outside air. What happens, you end up with a ton of water. Now that’s an exaggerated example because you’re moving a large volume of air. At 75% humidity at Atmospheric pressure the air above the brake fluid contains 75% of the water that a given volume of air can hold before it precipitates into water drops. Now taking that same air and pressurizing it increase the likelihood that the moisture will go from a gas to a liquid. Knowing that brake fluid loves water you can guess what happens next. It’s something to consider when you are looking for the absolute best performance from your brakes. This is why the best and admittedly biggest hassle pressure bleeders isolate the fluid from air with a diaphragm.

The humidity of air is about how much water the air can hold. It doesn't mean that water is going to somehow transfer into your brake fluid: it's already absorbed into the air! The only way this is going to hurt anything is if the water condenses and falls out of the air and into the brake fluid (consdensation). This is determined by the relative volume of the air at ambient vs a compressed state. But a Motiv bleeder doesn't operate at high enough pressures (15psi) to cause condensation. If it did, you'd literally see condensation droplets all over the inside walls of the jug, and that doesn't happen. OTOH, an air compressor that usually operates at over 100psi can cause condensation, and one only has to drain one's compressor tank to see that. That's why those professional systems need a bladder.

[Camfab]

Originally Posted by Msquared

I understand that, but that's what I though meant when you wrote: "The tanks like the Motiv set up are actually introducing air into your precious fluid." My reply was that they aren't introducing any more air than is already being introduced during the bleed/flush process anyway.


The humidity of air is about how much water the air can hold. It doesn't mean that water is going to somehow transfer into your brake fluid: it's already absorbed into the air! The only way this is going to hurt anything is if the water condenses and falls out of the air and into the brake fluid (consdensation). This is determined by the relative volume of the air at ambient vs a compressed state. But a Motiv bleeder doesn't operate at high enough pressures (15psi) to cause condensation. If it did, you'd literally see condensation droplets all over the inside walls of the jug, and that doesn't happen. OTOH, an air compressor that usually operates at over 100psi can cause condensation, and one only has to drain one's compressor tank to see that. That's why those professional systems need a bladder.

Matt a hygroscopic material is a substance that absorbs moisture from the air. It really doesn’t matter, just keep flushing your fluid regularly and you should be ok. I’m out.

[Msquared]

Originally Posted by Camfab

Matt a hygroscopic material is a substance that absorbs moisture from the air. It really doesn’t matter, just keep flushing your fluid regularly and you should be ok. I’m out.

Of course it is, and the air that that is in contact with the brake fluid as you bleed/flush or just add new fluid is the same whether you use a Motive style tool or any other method.

[Badmojo]

They sell replacement "sealant," but I haven't had to reseal them yet. I use Castrol SRF and only bleed them twice a season.

Originally Posted by Camfab

I’d agree on a daily driver, if you’re spending huge money for the absolute best on race car it’s just science. I do believe that the speed bleeder is a far better solution. I am going to purchase them and give them a try on my other cars. Correct me if I’m wrong here. The speed bleeders have a sealant on the threads which prevents air or liquid from backing up into the caliper when loosened. Does that mean you need replace them at certain intervals?

[Camfab]

Originally Posted by Badmojo

They sell replacement "sealant," but I haven't had to reseal them yet. I use Castrol SRF and only bleed them twice a season.

Thank you

[N Camarolina]

This whole discussion about forced air and moisture is kind of academic considering most of us who track use Castrol SRF, specifically because we know that the wet boiling temp of SRF is better than the dry boiling temp of most other Dot4 fluids.

Now if I was using Motul, I'd have significant concerns about moisture. My track buddy insists on using Motul despite the fact that it turns much darker after only 1 or 2 track weekends and seems to need to be bled or flushed several times a season. Don't know why he bothers given that he could just use SRF and flush once a year at most, with no bleeding required in between.