Brake Flush on W20

[grindstone01]

Originally Posted by twinboat

That's not true. The reservoir fluid is just that, fluid in a reservoir.

The only time any fluid returns to that reservoir, except a tiny amount, is when you manually retract the calipers. Otherwise they continually move out and hold more fluid as the pads and rotors wear down.

The ever increasing amount of fluid in the calipers will slowly get more and more moisture ladden. The moisture works its way in around the seals.

At some point, during a hard stop, the moisture will boil out of the fluid and create a steam pocket. That steam pushes the fluid back up the system, when you release the brakes. The next brake application results in a pedal to the floor.
You hope that doesn't happen when your half way down a hill.

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The calipers are pulsating open and close by applying the brakes to stop and then opening when the brakes are released and the rotating rotor pushes the caliper open. This pulsating will move the brake fluid around in the system. If you were to put a drop of red dye in the reservoir and bleed the brakes 6 months later, the brake fluid will come out red immediately.

[WeatherTodd]

if you have brake fluid in the reservoir "mixing" with fluid on the passenger rear calipers... that is incredible.

I want a system like that...lol.


I hate speed bleeders. Probably because I know how to use a vacuum pump.

A compressor powered pump with 4 quart container works great! Makes bleeding the system a 15 minute affair.

[CJ7365]

Originally Posted by grindstone01

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The calipers are pulsating open and close by applying the brakes to stop and then opening when the brakes are released and the rotating rotor pushes the caliper open. This pulsating will move the brake fluid around in the system. If you were to put a drop of red dye in the reservoir and bleed the brakes 6 months later, the brake fluid will come out red immediately.

Well I was going to stay out of the this one, but I cant.

I believe you are confusing ABS activation with regular braking.

You will only get pulsating if your ABS is activated, otherwise you brakes do NOT pulsate.

I would imagine, that only a hand full of RV have actually had the ABS activate, unless you use a Tech 2 or other device to activate the ABS

[F4Gary]

So easy even a caveman can do it...


Oemy's Web Site - Speed Bleeders

[BMGM37]

On my W16 chassis I always just remove all the old fluid in the reservoir and then just let gravity do the work. Attach a tube to the bleeder, put in a bottle, crack the bleeder and let it flow for a while. You would be surprised how fast it works and just keep the reservoir full and watch the bottle for a color change. I would do this while working on other things.

[Motor7]

Oldtimer, the Speedbleeder part number for all 4 calipers is ……SB71624

[grindstone01]

Originally Posted by CJ7365

Well I was going to stay out of the this one, but I cant.

I believe you are confusing ABS activation with regular braking.

You will only get pulsating if your ABS is activated, otherwise you brakes do NOT pulsate.

I would imagine, that only a hand full of RV have actually had the ABS activate, unless you use a Tech 2 or other device to activate the ABS

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As a retired auto engineer, I understand ABS brakes pretty well. The pulse I am referring to is when the brakes are applied, the brake cylinder gets squeezed out and when the rotor gets released the brake cylinder gets pushed back in. Every time the brakes get applied the fluid system will get 1 pulse which over a typical drive is many pulses resulting in fluid mixing.

This isn't rocket science, just a little common sense!! By all means if you can bleed the brake system, that is the best method.

[twinboat]

Here is how much the caliper actually strokes. The grafic exaggerates the movement but it shows the theory.

[BFlinn181]

Originally Posted by grindstone01

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As a retired auto engineer, I understand ABS brakes pretty well. The pulse I am referring to is when the brakes are applied, the brake cylinder gets squeezed out and when the rotor gets released the brake cylinder gets pushed back in. Every time the brakes get applied the fluid system will get 1 pulse which over a typical drive is many pulses resulting in fluid mixing.

This isn't rocket science, just a little common sense!! By all means if you can bleed the brake system, that is the best method.

Maybe not rocket science, but it is science. Set up an experimental test system with the diameter brake lines over the distance from the master cylinder to rear brake caliper. Put your brake fluid with dye in the reservoir and see how many pumps of the pedal it takes to get the full concentration of dye in the caliper. Not just a tint, the full concentration. One application of the brake might result in one backward 'pulse' just far enough to back the caliper out of contact with the disc, not anywhere near as strong as the forward pressure. Also, explain what happens to the fluid contaminated with water? Does it magically disappear with your earlier suggestion of just changing the fluid in the reservoir?

My brother was a designer and builder of automated assembly lines. He learned by experimentation and practice. He had many bad things to say about engineers, they had the 'book' learning but no practical experience. He continually won contracts to build robotic assemblies because an engineer would design the part or system and then he would show a simpler, more efficient way to do the same thing. Did it for agricultural sprinklers, medical components, penny sorters at the Denver Mint, and many other robotic assembly lines here and in Europe. His highest 'education' was motorcycle mechanic's school. Don't wave degrees in your reply trying to make it valid.'

[grindstone01]

Braking systems are mechanics not science!! A easier experiment is to remove the old (most likely yellow) brake fluid from the reservoir and replace it with new clear brake fluid. After a month or so look at the reservoir fluid and it won't be clear but rather starting to turn yellow. This is a result of brake fluid mixing in the system. By changing the reservoir fluid, some of the water will be removed from the system, isn't that better than not removing any water??
Yes, I have heard all the bad stories about engineers, but they/we are also human and not perfect, much like in any profession.

[BFlinn181]

Originally Posted by grindstone01

Braking systems are mechanics not science!! A easier experiment is to remove the old (most likely yellow) brake fluid from the reservoir and replace it with new clear brake fluid. After a month or so look at the reservoir fluid and it won't be clear but rather starting to turn yellow. This is a result of brake fluid mixing in the system. By changing the reservoir fluid, some of the water will be removed from the system, isn't that better than not removing any water??
Yes, I have heard all the bad stories about engineers, but they/we are also human and not perfect, much like in any profession.

How can you tell that the yellowed fluid in the reservoir isn't the result of it absorbing moisture? A brake flush requires all the fluid to be pushed out of the system, not just adding more to the old. Why ever change engine oil, coolant, or transmission fluid? Just keep adding new.

Reread the first 4-5 posts. The OP asked a question about which of the two reservoirs were connected to which brake calipers. I waited a few days and responded I guess he'd just have to start the job to see. I failed to say remove all the old fluid in the reservoirs, giving the OP the credit for having the knowledge to do that important first step in the brake bleeding procedure.

Then a suggestion was made that bleeding wasn't needed. On a public forum I would never advise anyone to do something that is not accepted practice or anything that could be dangerous. That's what I was questioning.

[OldTimer]

I see there is a lot of interest in brake fluid flushing. I had no idea the direction this thread would take. But I want to post an update.

There are different ways to flush the brake fluid. I was an early adopter of speed bleeders when Oemy first introduced them. But now I use the vac method. Just personal preference. What ever method is used, it is important to not allow the master cylinder to run dry and introduce air into the brake system. I acquired a refill bottle that is supposed to keep replacing fluid in the master cylinder as the fluid level drops as I suck fluid at each wheel. My W20 master cylinder has two caps, so I assumed it had two reservoirs. So if I started sucking fluid from the left rear cylinder, I wanted the refill bottle to be attached to the reservoir that supplied the left rear cylinder. Thus my original question.

I've done this job before, so I should have remembered.....there may be two caps, but the reservoirs are linked. So when I remove both caps and suck the fluid out of the passenger side reservoir, the driver side reservoir also empties. And refilling the passenger side reservoir also refilled the drivers side reservoir. So in answer to my original question, it does not matter which opening I use for the refill bottle....it refilled both sides of the master cylinder.