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  #16  
Old 10-10-2004, 07:59 PM
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Yes, I know that brake fluid should be replaced periodically. For some reason, I have trouble keeping to a schedule on that and have ley my cars go far beyond that ISTS. A viable option, and one that I will do on my MB when I go through the brakes and replace some other compionents is silicone brake fluid. Silicone brake fluid is non-hydroscopic, so it doesn't need to be replaced. It also has a higher boiling point and as you might expect is more expensive.
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  #17  
Old 10-10-2004, 08:13 PM
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Quote:
Originally Posted by brewtoo
I wonder about this. If there are any air bubbles in the system, won't they just keep floating up as the fluid drains? I can't imagaine that air bubbles would just wash downward in that slow-moving stream of draining fluid.
I, humbly, think you are right. After finishing the job and taking it for a drive, I could swear that there is still some air in the calipers. The pedal travels more than it should and it is softer than it was before the calipers were replaced.

I had attached the Easibleed and used it as well, but, the flow rate is still fairly slow and no air was apparent. Might have to up the pressure or, return to the "two man" method.
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  #18  
Old 10-10-2004, 08:45 PM
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Gravity

You can open all 4 corners and let it gravity drain the system...just filling the reservoir when it is low does not help fight moisture in the lines. Let it gravity drain and then refill the master cylinder and then you can either bleed the lines with 2 people or by yourself you can gravity bleed the system....Jim
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  #19  
Old 10-10-2004, 08:55 PM
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Brake fluid is cheap, I do mine every spring.

Now while were on the topic how many people out their have changed their soft brake lines? I did mine last spring and they were starting to crack; now since my car is an 87 their are a lot of cars on this forum that are older then mine. So if you have never changed those lines and have no record of it being done change them!! Their about $10 each don't cheap out, I think they should be replaced every 10 years or 100k miles.
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  #20  
Old 10-10-2004, 09:08 PM
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bad a severe brake grabbing problem on my 80 chevy truck. A friend told me he had the same experience and someone convinced him to change the hoses and problem went away. I was like "yeah sure" -the hoses seemed OK, but I was out of ideas so i finally changed them. Now I believe, I BELIEVE< I BELIEVE
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  #21  
Old 10-10-2004, 11:49 PM
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Hoses collapse internally. When you apply the brake, you can push a couple thousand psi through the lines, but the return pressure is not enough to push it back through. What you get is sticking brakes.
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  #22  
Old 10-11-2004, 12:39 AM
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When the hoses fail internally the pressure you apply works it's way between the hose lining and the rubber outer. Now when you apply the brakes the pressure effectively collapses the inner hose preventing the fluid from reaching the calipers. You won't be able to see any sign of failure from the outside in many cases.

Silicone fluid is bad, bad news for daily drivers - I would not use it. It is not compatible with ABS systems, must be handled very carefully to avoid air bubbles, and the moisture which makes its way into the system will bead as droplets and collect at the low points of the system which then corrode. It also doesn't mix with regular fluid. It's typically used in track applications where the systems are regularly serviced and the high boiling point is important.

There's no need for anything fancy or tricky where brakes are concerned, just use any DOT 3 or 4 fluid and replace it every 12 to 24 months.

Kevin
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  #23  
Old 10-11-2004, 08:30 AM
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Quote:
Originally Posted by phantoms
When you apply the brake, you can push a couple thousand psi through the lines
I have heard different figures for brake system hydraulic operating pressure. Did you get this figure from a reliable source or is it an estimation?

I don't remember exactly what I read about silicone brake fluid but the gist was to use it only where recommended. I don't know what MB says about it.

This is an excellent thread that whunter recently posted a link to, I think it worth repeating.
Quote:
Originally Posted by whunter
Read these two threads...

Power Bleeder or what?
Power Bleeder or what?

126 Brakes
126 Brakes
Both are excellent threads but it was the 126 brake thread that I was thinking of.
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  #24  
Old 10-11-2004, 08:34 AM
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Quote:
Originally Posted by brewtoo
In bleeding the brakes on my airplane the other day, we back-flushed from the caliper up to the master cylinder. It worked great.
This is the way I always bled motorcycle brakes, it is the only way I have had reliable performance from the Mityvac bleeder.
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  #25  
Old 10-11-2004, 11:08 AM
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Thumbs down Bad idea...

Quote:
Originally Posted by Pete Burton
A viable option, and one that I will do on my MB when I go through the brakes and replace some other components is silicone brake fluid. Silicone brake fluid is non-hydroscopic, so it doesn't need to be replaced. It also has a higher boiling point and as you might expect is more expensive.
Danger!!!
Never use silicone = DOT5 fluid in any ABS system that does not call for itů

Silicone brake fluid can be bad in any system not made for it.

A friend changed his MGA to silicone, went to Europe for five years, returned home, dropped fuel and a new battery in the car, and drove off to visit a friend.
The seventh time on the brakes there was a hard kick from the brake pedal, then no brakes at 70 MPH in expressway traffic, coming up on a construction zone.
He hit the ditch and wrecked the car in trees.
The insurance investigator proved that while the silicone did not absorb any moisture, the system still accumulates moisture, under the wrong conditions = long storage no driving.
The system gets hot; moisture flashes to steam and explodes the weakest point in the system.
In his case the flex hoses burst.

This is a safety system.
You do not want to explain to a judge why you changed the specification of fluid for a safety system.
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Last edited by whunter; 10-11-2004 at 11:13 AM.
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  #26  
Old 10-11-2004, 01:47 PM
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Quote:
Originally Posted by whunter
Danger!!!
Never use silicone = DOT5 fluid in any ABS system that does not call for itů

Silicone brake fluid can be bad in any system not made for it.

A friend changed his MGA to silicone, went to Europe for five years, returned home, dropped fuel and a new battery in the car, and drove off to visit a friend.
The seventh time on the brakes there was a hard kick from the brake pedal, then no brakes at 70 MPH in expressway traffic, coming up on a construction zone.
He hit the ditch and wrecked the car in trees.
The insurance investigator proved that while the silicone did not absorb any moisture, the system still accumulates moisture, under the wrong conditions = long storage no driving.
The system gets hot; moisture flashes to steam and explodes the weakest point in the system.
In his case the flex hoses burst.

This is a safety system.
You do not want to explain to a judge why you changed the specification of fluid for a safety system.

VERY, VERY true. Only use the type of brake fluid recomended by your manufacturer. And NEVER, EVER mix types.
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  #27  
Old 10-11-2004, 02:45 PM
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OK, 1. I know silicone is not recommended in ABS systems, I assumed that was commonly known and shouldn't have 2. Switching to silicone makes sense IMHO only if the whole system is being adressed at once, because the old brake fluid needs to be thoroughly flushed out of everything. I've done it twice and that was when EVERYTHING was replaced:new metal lines, new hoses, new or rebuilt wheel cylinders - probably not practical for most MB owners with the cost of parts today 3. Simply draining the system and refilling with silicone is NG, that's probably what the guy did with the MBA. If he left moisture in the system when he drained it, it was still there. He wouldn't have been safe if it was filled with DOT3 either. So I retract my recommendation of silicone fluid to everyone except those few who would remove all of the old fluid
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  #28  
Old 10-11-2004, 09:22 PM
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Quote:
Originally Posted by TwitchKitty
I have heard different figures for brake system hydraulic operating pressure. Did you get this figure from a reliable source or is it an estimation?
Twitch, it's just a generalization. It really depends on the brake system. 2000psi in a brake system is quite common. On some systems, it can be less and on some it can be much more.

There is a good article (with a test) on the complete brake system at http://www.abbysenior.com/mechanics/brakes.htm for those that want to know the inner workings and the "why" of the brake system.
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  #29  
Old 10-11-2004, 10:35 PM
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Quote:
Originally Posted by Pete Burton
Yes, I know that brake fluid should be replaced periodically. For some reason, I have trouble keeping to a schedule on that and have ley my cars go far beyond that ISTS. A viable option, and one that I will do on my MB when I go through the brakes and replace some other compionents is silicone brake fluid. Silicone brake fluid is non-hydroscopic, so it doesn't need to be replaced. It also has a higher boiling point and as you might expect is more expensive.
Silicon fluid is bad for this reason.....then moisture that does manage to condense in the M/C will eventually pool up at the lowest point usually the brake callipers and cause the expected problems of water in caliper. Thats what makes it a poor choice on the street. Race cars will not go a year or more without systems being dissassembled and flushed.
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  #30  
Old 10-12-2004, 09:49 AM
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from somebody who just replaced all the soft brake lines and rebuilt a sticking caliper, changing the fluid is just the easiest and best thing to do. im definetly on the 2 year change interval from now on! especially compared to the PITA of cleaning up a corroded caliper, or the cost of replacing when rebuilidng is no longer an option!
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