Home » Public Forums » GMCnet » Master cylinders, bleeding, brake fluid
| Master cylinders, bleeding, brake fluid [message #197753] |
Thu, 07 February 2013 20:55  |
Harry
Messages: 1888
Registered: October 2007
Location: Victoria, BC CANADA
Karma: 3
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Senior Member |
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Brake fluid does wear out and become contaminated.
Some people are still rejecting the notion of changing transmission fluid on a regular basis. How are we going to convince them that they should now change brake fluid regularly?
For years, many considered brake fluid to be a brake-job-to-brake-job service item. Do a brake job, and rebuild the wheel cylinders. Then, bleeding the brakes will flush the system - sort of.
Well, brake fluid always was, and continues to be hygroscopic - meaning that it absorbs moisture like a sponge. Leave a container of brake fluid open for a few hot, humid summer days, and it will likely absorb enough moisture to render it un-useable according to DOT specifications.
From a brake engineering point of view, absorbing and dispersing moisture throughout the system is good. It keeps moisture from forming in puddles within the system. Of course, these water puddles would settle into the lowest areas - such as wheel cylinders and calipers - where they can easily be boiled into steam by the heat generated by hard braking conditions and cause a loss of braking known as brake fade.
The downside of brake fluid being so hygroscopic is that the moisture dispersed throughout the system lowers the brake fluid boiling point, increases its viscosity, and promotes rust and corrosion.
• BRAKE FLUID SPECIFICATIONS
The DOT 3 specification requires a minimum boiling point of 401° Fahrenheit for "dry" brake fluid - fluid that contains no moisture whatsoever. To meet DOT 3 specs., "wet" or fully saturated fluid should reach 284° before boiling.
DOT 4 specs calls for minimum boiling points of 446° dry and 311° wet.
Most DOT 3 and DOT 4 brake fluids sold today meet or exceed the above specifications, but it is important to know the numbers.
NAPA DOT 3 brake fluids, for example, actually exceed minimum DOT 4 standards with a dry boiling point of 450°, while many of the cheaper brake fluids barely meet the minimum requirements to call themselves a DOT 3.
As with most other things there really IS a difference between a cheap brake fluid and a quality brake fluid.
DOT 5 is silicone-based brake fluid with a wet boiling point of more than 500° F.
You may ask yourself why the manufacturers do not simply switch to DOT 5 spec fluid. After all if some is good, more is better, and too much is just right. Right?
Well the DOT 5, while better under heat conditions than DOT 3 or DOT 4, does NOT absorb any moisture, so any moisture that finds its way into the system WILL puddle up somewhere causing rust, corrosion and, possibly, brake fade. You don't want slugs of water floating around any brake system.
Also, DOT 5 silicone fluid contains more absorbed air than DOT 3 or DOT 4 glycol, and it will aerate much more easily when it is pumped through small orifices such as those on an ABS system. For that reason, most manufacturers warn against using a DOT 5 fluid in cars with ABS.
DOT 5 is recommended for vehicles that sit for long periods such as antiques and classics that are stored all winter, and, of course, for racing due to its high heat tolerance. But conditions within the hydraulic system MUST be monitored.
• THE REAL WORLD
Even in sealed automotive brake systems, brake fluid will absorb one percent or more moisture every year simply from opening the reservoir to check fluid level, opening the bleeders, and through microscopic pores in the rubber hoses.
According to one trade publication we read, many two-year-old vehicles have been found to contain two to three percent water in the brake fluid. Imagine how much water must be contained in some six, seven, eight year or older vehicles that have never had their brake fluid serviced.
One percent water content can push DOT 3 fluid down to a 369° boiling point while two percent can push it down to 320°. Three percent can get it down to 293° - dangerously close to minimum DOT 3 requirements.
The rate at which this occurs depends on a lot of things such as the age of the vehicle and the type of hoses used. Better quality hoses are lined to make them less permeable to moisture. Some manufacturers chose to skip the lining in order to sell their product a little cheaper. You get what you pay for.
DOT (Department of Transportation) 3 and DOT 4 specification brake fluids are made from glycol and additives. Glycol absorbs and disperses moisture. The additive package helps to keep the moisture from attacking the internal components of the brake hydraulic system.
Another area of concern on today's automobile that was not a factor years ago is Antilock Braking Systems or ABS. There are many close tolerance components within the ABS system, and moisture can wreak havoc with them. Replacing a single ABS component is often much more expensive than a simple brake fluid service would have been.
The average car on the road today is 10 years-old. According to Brake & Front End Magazine, only half of these cars have ever had their brake fluid changed.
For the average motorist, there might not be that much risk under normal driving conditions. But, prolonged braking such as mountain driving and trailer towing might tax old brake fluid beyond its capacity.
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| Re: [GMCnet] Master cylinders, bleeding, brake fluid [message #197758 is a reply to message #197753] |
Thu, 07 February 2013 22:20  |
mickeysss
Messages: 1476
Registered: January 2012
Karma: 0
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Senior Member |
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thank you for allowing me to understand this for the first time. I have always wondered what the dot numbers mean and why a leaky brake has been
stated as an automatic brake fluid change by one of my mechanics. I think i will change it, now what do it do? How do you change it alone.
how much does it hold. I know to pump the brakes before i take off.
mickey
77 palm beach
anaheim ca.
On Feb 7, 2013, at 6:55 PM, David H. Jarvis wrote:
>
>
>
> Brake fluid does wear out and become contaminated.
> Some people are still rejecting the notion of changing transmission fluid on a regular basis. How are we going to convince them that they should now change brake fluid regularly?
>
> For years, many considered brake fluid to be a brake-job-to-brake-job service item. Do a brake job, and rebuild the wheel cylinders. Then, bleeding the brakes will flush the system - sort of.
>
> Well, brake fluid always was, and continues to be hygroscopic - meaning that it absorbs moisture like a sponge. Leave a container of brake fluid open for a few hot, humid summer days, and it will likely absorb enough moisture to render it un-useable according to DOT specifications.
>
> From a brake engineering point of view, absorbing and dispersing moisture throughout the system is good. It keeps moisture from forming in puddles within the system. Of course, these water puddles would settle into the lowest areas - such as wheel cylinders and calipers - where they can easily be boiled into steam by the heat generated by hard braking conditions and cause a loss of braking known as brake fade.
>
> The downside of brake fluid being so hygroscopic is that the moisture dispersed throughout the system lowers the brake fluid boiling point, increases its viscosity, and promotes rust and corrosion.
>
> • BRAKE FLUID SPECIFICATIONS
>
> The DOT 3 specification requires a minimum boiling point of 401° Fahrenheit for "dry" brake fluid - fluid that contains no moisture whatsoever. To meet DOT 3 specs., "wet" or fully saturated fluid should reach 284° before boiling.
>
> DOT 4 specs calls for minimum boiling points of 446° dry and 311° wet.
>
> Most DOT 3 and DOT 4 brake fluids sold today meet or exceed the above specifications, but it is important to know the numbers.
>
> NAPA DOT 3 brake fluids, for example, actually exceed minimum DOT 4 standards with a dry boiling point of 450°, while many of the cheaper brake fluids barely meet the minimum requirements to call themselves a DOT 3.
>
> As with most other things there really IS a difference between a cheap brake fluid and a quality brake fluid.
>
> DOT 5 is silicone-based brake fluid with a wet boiling point of more than 500° F.
>
> You may ask yourself why the manufacturers do not simply switch to DOT 5 spec fluid. After all if some is good, more is better, and too much is just right. Right?
>
> Well the DOT 5, while better under heat conditions than DOT 3 or DOT 4, does NOT absorb any moisture, so any moisture that finds its way into the system WILL puddle up somewhere causing rust, corrosion and, possibly, brake fade. You don't want slugs of water floating around any brake system.
>
> Also, DOT 5 silicone fluid contains more absorbed air than DOT 3 or DOT 4 glycol, and it will aerate much more easily when it is pumped through small orifices such as those on an ABS system. For that reason, most manufacturers warn against using a DOT 5 fluid in cars with ABS.
>
> DOT 5 is recommended for vehicles that sit for long periods such as antiques and classics that are stored all winter, and, of course, for racing due to its high heat tolerance. But conditions within the hydraulic system MUST be monitored.
>
> • THE REAL WORLD
>
> Even in sealed automotive brake systems, brake fluid will absorb one percent or more moisture every year simply from opening the reservoir to check fluid level, opening the bleeders, and through microscopic pores in the rubber hoses.
>
> According to one trade publication we read, many two-year-old vehicles have been found to contain two to three percent water in the brake fluid. Imagine how much water must be contained in some six, seven, eight year or older vehicles that have never had their brake fluid serviced.
>
> One percent water content can push DOT 3 fluid down to a 369° boiling point while two percent can push it down to 320°. Three percent can get it down to 293° - dangerously close to minimum DOT 3 requirements.
>
> The rate at which this occurs depends on a lot of things such as the age of the vehicle and the type of hoses used. Better quality hoses are lined to make them less permeable to moisture. Some manufacturers chose to skip the lining in order to sell their product a little cheaper. You get what you pay for.
>
> DOT (Department of Transportation) 3 and DOT 4 specification brake fluids are made from glycol and additives. Glycol absorbs and disperses moisture. The additive package helps to keep the moisture from attacking the internal components of the brake hydraulic system.
>
> Another area of concern on today's automobile that was not a factor years ago is Antilock Braking Systems or ABS. There are many close tolerance components within the ABS system, and moisture can wreak havoc with them. Replacing a single ABS component is often much more expensive than a simple brake fluid service would have been.
>
> The average car on the road today is 10 years-old. According to Brake & Front End Magazine, only half of these cars have ever had their brake fluid changed.
>
> For the average motorist, there might not be that much risk under normal driving conditions. But, prolonged braking such as mountain driving and trailer towing might tax old brake fluid beyond its capacity.
>
> --
> "I've always been crazy, but it kept me from going insane"
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Master cylinders, bleeding, brake fluid [message #197769 is a reply to message #197758] |
Fri, 08 February 2013 07:03 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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| mickeysss wrote on Thu, 07 February 2013 22:20 |
... I think i will change it, now what do it do? How do you change it alone. how much does it hold. ...
|
I built a pressure bleeder back in the 80's. DIRT SIMPLE and even cheaper today.
1 - Get a cheap hand pump garden sprayer. You can usually even find them at Dollar General. If not get a small one at the home improvement store or Wally World. The one I currently use holds about 1 1/2 quarts.
2 - At a junk yard or somewhere get a metal top for your master cylinder.
3 - At a hardware store get a hose barb fitting (I've found that a male air tool fitting works well and I usually have a bunch around) that is close in size (ID) to whatever your sprayer wand is.
4 - Drill and somehow rig the hose barb into the top of the new top. Depending on the top, you may have to move the fitting for the front and rear reservoirs.
5 - From an auto parts store, get some rubber hose that fits between the new hose barb in the top and the sprayer wand. Hose clamps to hold them on. A longer hose is more convenient because you can sit it on the ground but the closer to the level of the MC takes less pressure to push the fluid.
6 - Fill the sprayer up with NEW brake fluid no more than the max fill line.
8 - Rig a way to lock the trigger on the sprayer open.
9 - Pump some pressure into the sprayer...doesn't take much.
10 - Starting at the closest wheel and working through the furthest, slowly open the bleeder screw and leave it open until the brake fluid runs clear. Keep an eye on the fluid level in the sprayer tank. If you run out of fluid and put air in the system...start over and pay more attention. That's it.
One caution is that brake fluid is not good for paint and such so rig some way to catch any overflow.
Jim Hupy has a tool available that does this but it's not rocket science.
Back in the early 70's I had a 41 Plymouth that I could not get to bleed with the two person pump and crack the valve method. My brother-in-law worked at a Goodyear store and he put their pressure bleeder on it just like described above. A few years later I needed to do it again so I built what is described above. You can also make a flat plate drilled and tapped (it is a pipe thread btw) for a hose barb. Some sort of gasket around the master cylinder and clamp it down. It doesn't have to be super tight because you don't need much pressure. Rig something to catch any overflow and some cat litter or oil dry to absorb the spills
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: [GMCnet] Master cylinders, bleeding, brake fluid [message #197772 is a reply to message #197753] |
Fri, 08 February 2013 07:18 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Well, I learned when my first Chrysler minivan antilock system died. Fortunately for me, Chrysler warrants the pump and hydraulic system (Master cylinder) for life on the first year vans. If I remember, the tech at Hayes told me they billed Chrysler something over $3 Large for the warranty repair. Anything with antilocks I drain completely and refill every two years and while I'm doing it anyway, I do the coach and the toad. A couple gallons of fluid is about $30, while one antilock master cylinder is on the order of many hubndreds.
--johnny
'76 23' transmode norris
'76 palm beach
From: David H. Jarvis <jarvis210@shaw.ca>
To: gmclist@temp.gmcnet.org
Sent: Thursday, February 7, 2013 9:55 PM
Subject: [GMCnet] Master cylinders, bleeding, brake fluid
Brake fluid does wear out and become contaminated.
Some people are still rejecting the notion of changing transmission fluid on a regular basis. How are we going to convince them that they should now change brake fluid regularly?
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Unsubscribe or Change List Options:
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Master cylinders, bleeding, brake fluid [message #197774 is a reply to message #197753] |
Fri, 08 February 2013 07:30 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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Senior Member |
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I have long used the pressure bleeding procedure for my cars, but have also used the vacuum bleeder (using a pump that created vacuum and is attached to the bleeder screws) with good results, though I've never tried it on my GMC yet. I've also liked using Speed-Bleeders on my other cars to make things easier for a one man operation.
Using different colored ATE brake fluid helps tell you when you've removed all the old fluid. Another trick is to try to empty out the master cylinder as much as possible from the fill (vacuum bleeder helps here), then fill with new fluid before starting bleeding the lines. Makes it a much faster procedure than trying to pump the whole master cylinder's fluid through the lines.
Hope some of these hints help! It is important to keep those brakes maintained and safe.
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: Master cylinders, bleeding, brake fluid [message #197790 is a reply to message #197753] |
Fri, 08 February 2013 08:41 |
An87ttype
Messages: 157
Registered: September 2012
Karma: 0
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Senior Member |
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I've only used vacuum bleeders on my cars and GMC.. They work great. You just have to make sure to keep the master cylindar filled. just changed the MC on the GMC this Summer. Took just a few minutes to flush the whole system.
1975 Eleganza II
Hudson Valley NY
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| Re: [GMCnet] Master cylinders, bleeding, brake fluid [message #197795 is a reply to message #197758] |
Fri, 08 February 2013 09:28 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| mickeysss wrote on Thu, 07 February 2013 23:20 |
thank you for allowing me to understand this for the first time. I have always wondered what the dot numbers mean and why a leaky brake has been
stated as an automatic brake fluid change by one of my mechanics. I think i will change it, now what do it do? How do you change it alone.
how much does it hold. I know to pump the brakes before i take off.
mickey
|
Mickey,
Answers to the questions I think you are asking.
The dry system holds just a little less than 1 quart, but unless it is real clean, you should get two quarts of brake fluid. Pick any one, it should be changed again before it matters.
You can do the job alone with a pressure bleeder or a vacuum bleeder, but the vacuum requires a lot of trips back and forth to the master cylinder to check the level.
On a stock coach, you will also need to hold in the pin on the combination valve to get fluid through the front.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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