DOT 5

[bull]

Last I heard, DOT 5 brake fluid was catching some flack but I forget what the issue was with it. Some of its advantages are a higher boling point, resistance to moisture and (for those $20K finishes) its silicone composition that does not eat paint.

So remind me, what's bad about it again? I'm getting closer to buying brake fluid for the whole system so if it's got a downside or two I'd like to get informed so I can weigh my options.

[tan top]

i would never  use it  but   , lots do & as you say don't damage paint work  or absorb moisture ,
i forget now why i would not sounds silly i know  , but remember reading about the stuff , & thought no not going to use that gear , also one thing !  its not recomended for ABS  , think because it froths up , i await to be corrected    i could be remembering  what i read wrong  

[bobs66440]

This was taken off the Afco Racing Tech page and echos what I've read over the years. Because our systems were designed for it, I would just use dot 3 and flush it regularly. 

Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.

Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.

Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance


From what I've read, the dot 5 pretty much eliminates deterioration of the different components of the brake system because it doesn't absorb water like dot 3 or 4. Therefore, it's used often in show cars that don't get driven much. Also, I've read a lot about the spongy pedal at high altitudes. Also, if changing from dot 3 or 4 to dot 5, you need to make sure ALL of the previous fluid is flushed out.

[bull]

Some of the reading I did since starting this thread said it is "somwhat" compressible rather than "highly" compressible as it says above. Fluids in general are not considered highly compressible but I'm sure there are some that are a lot more than others.

But as you said, mixing it with the non-silicone brake fluids creates problems according to what I read, namely a weird sludge that can cause major problems. In my case I think DOT 5 might be a good thing because none of my system has been exposed to DOT 3 or 4. Almost all of it is new and the parts that aren't had DOT 5 in them. As long as the system starts out dry and you bleed it well I don't think there's much opportunity for water to get in.

[bobs66440]

As long as the system starts out dry and you bleed it well I don't think there's much opportunity for water to get in.

Right, I agree. I have read some posts on other forums and they like the dot 5. The main complaint being the spongy pedal. I think I would still flush it regularly though. Apparently, the moisture gets in there somehow even though it's a closed system. I can't hurt anyway. 

[elacruze]

DOT 5...hm. This debate has been raging since it was introduced.

DOT 5 is good if you're worried about paint. I use it in my Charger, because I don't intend to overheat the brakes.

DOT 5 sucks because it's harder to find system components that are compatible. If you use DOT 5 in systems designed only for DOT 3-4, the rubber will eventually swell and deteriorate, and you will at best have a leak and at worst lose your master cylinder. Trust me on this one, I've done it twice.

DOT 5 also sucks if you do any painting, since like everything sticky it gets everywhere and silicone is impossible to clean, and is a big no-no around paint.

DOT 5 'should' be changed yearly or two, since it does not absorb water whatever water is in your system ends up at the bottom of all your iron holes, like calipers wheel cylinders and master cylinders causing rust more quickly, especially if stored.

DOT 5 when severely overheated turns into something like Dippity-Doo in your calipers and fails completely.

[bull]

When you say "severely overheated" how hot is that?

[John_Kunkel]

Any brake fluid that carries a DOT certification must be compatible with all other DOT fluids.

The so-called "sludge" problem is usually found in systems that had already started to sludge up before the introduction of the silicon fluid.

The only legitimate downside to the use of silicon fluid is the spongy pedal and it ain't that big of a deal from my experience.

[elacruze]

When you say "severely overheated" how hot is that?

uh...VERY hot...motorcycle roadracing hot. 

[flyinlow]

I remember when it first came out it sounded great ,high boiling point, not hydroscopic and did not damage paint as easily. The down side was it did not lube the moving rubber seals as well and would cause faster wear in a daily driver. Used it in some classic Mercedes that where garage Queens. Don't remember any problems.

[Charger-Bodie]

Ive used in 25 or so cars that weve done for ourselves and others and Have never seen a problem. Only thing even remotely like a problem is that it takes a little more work to bleed the system. Works great though,IMHO

[Plumcrazy]

I have had the same DOT5 fluid in my car since 1992.  Nothing in the hydraulic system has needed to be replaced and the pedal is nice and firm. I wouldn't use anything else.

[bull]

Thanks for the good, first-hand information. I'll be using Dot 5. Since I'll be going with manual disc brakes I could probably use a little sponginess.

[resq302]

Just be sure that the stuff that you get is compatible with the DOT 5.  Last year I had my hold off valve rebuilt and it came with a warning paper saying NOT to use DOT 5, only DOT 3 or 4 and use of DOT 5 will void any warranties.

[gtx6970]

Dot 5 is all I've used in older cars the past 15 years, and never one single issue to date

[bill440rt]

I have DOT5 in my '70, which has a stock power disc system where the original components were all rebuilt. It's been in there since the late '90's (damn, has it been that long???), with periodic flushes. The pedal doesn't feel overly spongy to me, and there have been no issues.

I run Valvoline synthetic DOT3/4 in my '69 with the Wilwood's, as they specified not to use DOT5 for some reason.
I'll be running the same stuff in my '68 (formerly stock drums now Master Power front discs), as Master Power also stated DOT5 would void any warranties. I may switch back to DOT5 once the warranty period is over as long as there are no compatibility or safety issues.

I would listen to the manufacturer's recommendation of what fluid to use if you are running an aftermarket brake system.

[bull]

It doesn't make sense to me that Dot 5 would harm any brake components if what John said above is true. And I believe it has to be true or it would have been banned long ago. How can anyone legally manufacture a brake fluid that might damage brake parts and potentially cause an accident? I've never heard of any lawsuits over the issue and you'd think there would be plenty of them by now if there was a real problem.

If a manufacturer of brake parts is telling you to not use Dot 5 I have to believe they are just covering their a$$ based on assumptions and myths.

[elacruze]

It doesn't make sense to me that Dot 5 would harm any brake components if what John said above is true. And I believe it has to be true or it would have been banned long ago. How can anyone legally manufacture a brake fluid that might damage brake parts and potentially cause an accident? I've never heard of any lawsuits over the issue and you'd think there would be plenty of them by now if there was a real problem.

If a manufacturer of brake parts is telling you to not use Dot 5 I have to believe they are just covering their a$$ based on assumptions and myths.

It's the rubber (or synthetic stuff) inside; seals and cups. Some are incompatible and swell up and soften when used with DOT 5.

[bobs66440]

It doesn't make sense to me that Dot 5 would harm any brake components if what John said above is true. And I believe it has to be true or it would have been banned long ago. How can anyone legally manufacture a brake fluid that might damage brake parts and potentially cause an accident? I've never heard of any lawsuits over the issue and you'd think there would be plenty of them by now if there was a real problem.

If a manufacturer of brake parts is telling you to not use Dot 5 I have to believe they are just covering their a$$ based on assumptions and myths.

I don't think that anyone is saying it's dangerous to use, except for racing applications where it is universally not recommended because it doesn't absorb moisture and the "puddles" of water that may enter the system may boil with high heat, and in ABS systems because it tends to cavitate/aerate when pushed through small orifices because of it's viscosity or tendency to hold more air. Just that it's not compatible with dot 3 or 4 and that it may cause a spongy pedal because it tends to aerate under heavy use. I also read that it doesn't play well with some internal parts but can't confirm this. Not saying what John said is wrong, but I've read up on it quite a bit over the years and recall reading many times that it's not compatible with 3, 4, or 5.1.

Now, I also read that the dot 5.1 has all the positive characteristics of dot 5 (hi-temp, lubrication, etc.) but is compatible with dot 3 & 4 and the older brake system designs. Maybe consider that as an option. It seems like the best of both worlds.  

[John_Kunkel]

There is a lot of myth/misinformation regarding silicone brake fluid, I tend to believe what the DOT says:

"All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids)."

The actual DOT specification requires chemical compatibility, IOW the two fluids won't cause reactions if used in the same system, but they certainly won't mix, either. As a test I mixed silicone with DOT 3 in an old mayonaise jar and it's been sitting on a shelf for over thirty years...I occasionally shake up the mixture and put it back on the shelf.

[bobs66440]

Interesting 

[bull]

It doesn't make sense to me that Dot 5 would harm any brake components if what John said above is true. And I believe it has to be true or it would have been banned long ago. How can anyone legally manufacture a brake fluid that might damage brake parts and potentially cause an accident? I've never heard of any lawsuits over the issue and you'd think there would be plenty of them by now if there was a real problem.

If a manufacturer of brake parts is telling you to not use Dot 5 I have to believe they are just covering their a$$ based on assumptions and myths.

It's the rubber (or synthetic stuff) inside; seals and cups. Some are incompatible and swell up and soften when used with DOT 5.

Then I'd have to assume substandard parts and/or brake fluid was the cause of any breakdown, not just the fact that it's DOT 5 fluid. According to the rules, every fluid should work with every other fluid and every other part. DOT 5 has to pass all the same tests on the same type of components that DOT 3, 4 and 5.1 does.

http://www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrruletext.aspx?reg=571.116

[bill440rt]

I didn't use it in the two different systems for warranty reasons only. If there were a problem & the parts had to be sent back, if they found traces of DOT5 in the system the warranty would be null & void. After plunking down a considerable amount of cash (especially on the Wilwood's), I didn't want to take a chance. It would have been the equivalent of throwing it in the garbage if something had gone bad.

So far, so good.

[bull]

I run Valvoline synthetic DOT4/5 in my '69 with the Wilwood's, as they specified not to use DOT5 for some reason.
I'll be running the same stuff in my '68 (formerly stock drums now Master Power front discs), as Master Power also stated DOT5 would void any warranties. I may switch back to DOT5 once the warranty period is over as long as there are no compatibility or safety issues.

I would listen to the manufacturer's recommendation of what fluid to use if you are running an aftermarket brake system.

I was just thinking about your quote today, especially regarding Wilwood. Last I heard Wilwood says their brakes are for race application only but it's common knowledge that many people use them on classic cars out on the streets. IMO Wilwood classifies their brakes as race-only to avoid liability should they fail due to quality issues or if someone installs them wrong, etc. That way when someone plows into a tree or a minivan full of kids they can pull the "race-only" card. I understand this is just speculation on my part but if I'm right I can't help but think they're doing the same thing on the DOT 5 issue. This is one reason I probably won't be using any Wilwood products if I can help it. If they don't believe in their products it doesn't really give me much confidence in them either.

[FLG]

Curtis,

I dont think its a matter of having faith in there products, but rather having faith in the person that installs them.