Home » Public Forums » GMCnet » Brake fluid and moisture (Moisture absorbsion is good. Really)
| Brake fluid and moisture [message #155945] |
Sun, 08 January 2012 14:14  |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
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As I was reading the thread on dot 5 fluid the message seemed to say the best fluid for our units is dot 5, and therefore anything else is not best. Wait a minute!! The brake hydraulic system actually has a constantly changing fluid volume due to temperature expansion, pad and shoe wear, stretching brake hoses, and moisture. Tiny amounts of air in the system also compress. Air is the medium that makes up the differences in this volume through the changing levels in the reservoir. Mostly, air gets into and is expelled in the system through the master cylinder reservoir and even a little past seals Yes, tiny amounts of air gets into the system due to sepage past seals (not enough to make brakes unusable however, but enough that over a long period of time must be dealt with). This air will have moisture and as temperatures drop will condense in the brake system. Hense water in the system. Water causes rust, pitting in cylinders and lines, and sludge. All bad things in the system. Some of you have even experienced rusted through brake lines in our 35 year old machines. (I have)
Dot3 and dot4 fluids allow the water to chemically combine with the fluid and disperse throughout the system through the movement of fluid while using the brakes to prevent the sludge, rust, and pitting. Pretty good thing right? Once the fluid absorbs all that it can, it is known to be wet and can no longer do it's job properly. (we want to be sure we flush the system before this point). Vehicles that sit for long periods of time are worse. ( topic for another discussion).
Dot5 fluid does not absorb moisture therefore the water stays as a separate component and pools in parts of the system, allowing the water to do it's damage starting immediately. Car collectors and race drivers use these to avoid some of the breathing absorption while their vehicles sit. But must flysh regularly Dot5 actually needs more frequent flushing than dot3 or 4. The difference between 3 and 4 is the boiling point when wet. Another problem with moisture.
All types of fluids need flushing and replacement on a regular basis. The time between these is a matter of opinion I suppose, but recommendations by the manufacturers will keep you out of trouble.
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: Brake fluid and moisture [message #155953 is a reply to message #155945] |
Sun, 08 January 2012 14:34  |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| John Heslinga wrote on Sun, 08 January 2012 12:14 |
...
Dot5 fluid does not absorb moisture therefore the water stays as a separate component and pools in parts of the system, allowing the water to do it's damage starting immediately. ...
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I agree with pretty much all of your statement.
ALSO: Seems to me that if the water isn't absorbed into the fluid, it could freeze in the lines. Frozen water in the brake lines makes for brakes that are a bit hard to use. (Not that I use my GMC very much during freezing weather... but I MIGHT pass through some cold areas.)
I'll stick with the stuff it was designed to use.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: Brake fluid and moisture [message #155956 is a reply to message #155945] |
Sun, 08 January 2012 14:52 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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You bet ya. Freezing is a problem if large enough pools of water accumulate. Especially for those of us that are closer to freezing temperatures. However that is also a problem with old-old Dot 4 and 5. North of the 49th parallel we have dealt with this occasionally. Another good reason to follow suggested flush schedules.
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: Brake fluid and moisture [message #156023 is a reply to message #155945] |
Sun, 08 January 2012 22:56 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Right on John. Thanks for the Posting.
I would only use DOT 4 or something like the ATE stuff in our coaches. It all mixes with DOT 3 and the biggest difference is the wet boiling point.
The wet boiling point is important as several people have found out. You have no brakes when that WBP temperature is exceeded.
Forget the DOT 5 stuff.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Brake fluid and moisture [message #156025 is a reply to message #156023] |
Sun, 08 January 2012 23:03 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Ken Burton wrote on Sun, 08 January 2012 22:56 |
Right on John. Thanks for the Posting.
I would only use DOT 4 or something like the ATE stuff in our coaches. It all mixes with DOT 3 and the biggest difference is the wet boiling point.
The wet boiling point is important as several people have found out. You have no brakes when that WBP temperature is exceeded.
Forget the DOT 5 stuff.
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Actually I said that wrong. I should have said "you have no brakes when the boiling point is exceeded and that boiling point varies depending on how much water has been absorbed by the fluid and the type of fluid used".
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Brake fluid and moisture [message #156068 is a reply to message #155945] |
Mon, 09 January 2012 12:34 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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My Opinion is the same.
I would also like to point out some other problems with Dot 5 in our coaches and other vehicles as well. These are the things the person selling you the product will not tell you (Mostly because they do not know, and we live by the adage of “Get the good stuff and that must be the one that is most expensive”)
** With Water being heavier than the silicone base that dot 5 is made of, it has a tendency to accumulate in the lowest parts of the brake system. (It sits in the bottom of the wheel cylinders, and Disc Callipers) Regular flushing or bleeding just about never gets rid of it, unless the cylinder is just about full (That's a lot of water) It is very difficult to get enough flow in these areas during flushing or bleeding to pick up the water and force it out of the cylinders because the bleed holes are on the top of those cylinders. Bleed holes are intended to bleed air not drain water. Even regular flushing of DOT 5 may not get rid of the water. This leaves the water to do it's pitting damage, which leads to seal leaking. The water in the wheel cylinders and calipers is the worst place for the water to be. They are the places which pick up the most heat from braking. (The Callipers the hottest) Once the water boils, calliper pressure is not enough to provide adequate braking.
In order to be confidant you have gotten rid of the water you almost have to take those items apart. (sure does not sound like the maintenance regime I would like to get into)
** Dot 5 can be very tricky getting air out as well. It has a tendency to form very fine bubbles, which do not easily combine into larger ones. Bleeding and flushing needs some “Wait time” so that tiny bubbles can combine. When working with this you must be vigilant in not shaking the can and pouring the fluid into the reservoir gently.
** I am told that Dot 5 is actually a bit spongy.(I'm guessing that it is somewhat compressible) this may not be a real problem, but it's my opinion that we need every bit of pressure we can get to the pads and shoes.
**Once you put it in, It's very very difficult to change back (Preparing to install it is also very difficult)
** Dot 5 Fluid is going to increase the amount of attention you will need to give your brakes in yearly maintenance. No matter how many miles you drive (especially the hydraulic system). If you do it yourself and like doing it for the cool factor, that’s one thing. But if your are paying someone to do the work for you at $90.00+ per hour, you will quickly tire of the exercise.
** Dot 4 Fluid is an excellent product that meets the needs of our coaches and requires very little attention. That will allow you to spend more time enjoying your coach, (which is why we have them)
(Alright : I know that for some people, the project is more important than using it. And working on them is the enjoyable thing.  )
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: Brake fluid and moisture [message #156071 is a reply to message #156068] |
Mon, 09 January 2012 12:54 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
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Also the tiny puddle of water sitting on the bottom of your brake cylinders has a boiling point of 212 degrees, far lower than wet DOT3...
Boiled water means no brakes.
Silicone is for rarely driven show cars and "actresses"
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] Brake fluid and moisture [message #156072 is a reply to message #156068] |
Mon, 09 January 2012 12:56 |
UziYaH
Messages: 282
Registered: July 2007
Location: 10-O-C
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For anyone even contemplating using DOT 5 in their motor home, DON'T, for all the reasons stated by others. I did, as suggested by my 'shade tree mechanice' and it cost me greatly to correct the problem including replacing all of my brake system.
Someone, on this forum, suggested I use Motorcraft High Performance DOT 3. It has all the specifications of DOT 5 and has worked well for me.
How come some of us are too soon old and too late smart? Part of the GMC Motorhome experience, I guess. Just sharing my 2 cents worth.
Howard Nylander
Royale Class of '78'
Greeneville, Tn.
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Howard Nylander
Royale Class of "78" "Rocinate"
E-10-o-C
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| Re: Brake fluid and moisture [message #156075 is a reply to message #155945] |
Mon, 09 January 2012 13:23 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
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I would also recommend the Ford heavy duty truck brake fluid, very high boiling point. We used to use in the the race car before switching to DOT5.
I would not recommend DOT5 fluid in general, though that is what is currently in my coach ( which does still sit still 95% of the time). Time will tell if it was a good decision when mine was converted over, but DOT4, regularly bled appropriately, is probably the safest bet.
Probably the best opinions come from folks that use their coaches in mountainous areas and not from us flatlanders!
George Rudawsky
Chicago, IL
75 Palm Beach
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