The Stovebolt Site Forums The Shop Area Driveline Synthetic Dot 5 Brake Fluid Poll

I will start this off with I am replacing all my
brake components with new rubber,Stainless steel lines and changing to Dot 5 Brake fluid in my 1959 1/2ton stepside just wondering what the pros and cons are and how many are using this type fluid???

I changed my 1981 Honda 900F Motorcycle over to DOT 5 in 1982. I have had zero problems with it.

My 1951 1/2T has all new system with DOT 5 in it. It is not on the road yet but I expect no problems.

Paul

You know there's 5.1 also available which is glycol based and not silicone? Glycol is far more forgiving than silicone based fluids. It's also easier to tell if a glycol based fluid has been contaminated than a synthetic one. In fact DOT5 is widely stated to be more corrosive because of this fact and unless frequent fluid changes are done it's in fact worse for the system. About the only advantage I see of DOT5 is the fact it's paint-friendly.

Dot 5 will eat through rubber parts pretty quickly unless you find freindly replacement parts to use in the master cyl and wheel cylinders, etc. Thats why they say dot 3 only. Ive heard of people using it for a few years before all the rubbers gone and the brake parts all fail.

In my experience most motorcycles are meant to run on dot 5. If you can find a source for dot 5 rubber parts, please let us know where.

Jeff

I tried it. Seemed ok, until the master cylinder and front wheel cyliders started leaking. Fortunatly, I caught it before the failed, as I noticed an odd wet spot on the floor that wasn't oil. Called Wagner, they say no dot5 in their stuff, exept fpr some European cars that use it as OE. They did say that it makes a good brake assembly lube, though.

Another downside to DOT 5 is that if you ever get a significant amount of moisture in the system you can get severe brake fade if that part of the system gets above 212 deg F. That's because the moisture is not soluble in DOT 5 so that little drop of moisture will boil at 212 deg F. For the glycol based fluids the moisture is soluble and the boiling point will be somewhere between 212 and the boiling point of the dry fluid. That's another reason DOT 5 fluids need to be changed regularly.

Dont use dot 5 fluid, thats my advice. When servicing customer vehicles doing brake flushes we use dot 4 as a replacement. But thats only when doing a complete flush. Stick with dot 3 or 4,
Dot 5 will eat the seals in your system.

When I was going through my brakes several years ago, I was persuaded to go to Dot 5 by my friend at the local Carpart Store. His reasoning was this: that dot 3 fluid absorbs moisture, these old brake systems are open vented systems, and that especially when these trucks are not being driven daily the brake fluid absorbs too much moisture and the workings will rust. He had gone to dot 5 fluid on all his old vehicles.
I am not a specialist in these questions, but if this line of reasoning is a pile of bovine excrement I would like to know, so I can prepare for another round fixing my brakes - which have been running for 2 years now on dot 5 fluid without problems.

DOT5 is fine in systems designed for it, or have ALL of the rubber conponents changed over to parts compatible with it. However, most companies do not make parts for DOT5 compatability as it is not the OEM reccomended fluid. The only company I know of for sure that did make all of their rubber parts DOT5 compatable was EIS, and they're out of business. Also, the OEMs do not suggest DOT5 in any vehicle using ABS, as it will cavitate in the module.
Like I said, though, I did try it, based on suggestions from severaly publications concerning older vehicles with open systems. The braking action was exellent, good pedal and such. But when I noticed that spot on the floor, an tracked it to the M/C, well, I got worried. I had just read an article in Brake & Front End about DOT5, which discussed problems with it, including how it damages the rubber if not 100% compatable. This convinced me to contact Wagner. They say not to use it. Raybestos says the same.
Oh, and one more thing. Yes, DOT5 will not attack the paint, but if you get it on anything that you plan to paint later, it'll cause the same problems as silicone wax products!
I'll stick with good ol' DOT3/4.

Dot 3 brake fluid does have the ability to absorb moisture which is why I will be using it in my 51 gmc. If any moisture gets in the system it will be absorbed by the fluid and will protect the internal parts. If you have any moisture in your system without a hydroscopic fluid, the moisture will settle at the low spots and start to corrode the internals. Have a look at this page to help aid in your decision.

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

The best mositure protection is the DOT 4 fluids formulated with borate esters. The borate ester reacts with the water to produce boric acid and a glycol ether neither of which will lower the boiling point. Boric acid is a very weak acid and does not increase the corrosivity. So until the borate ester is used up, water will not significantly decrease the boiling point.

Thanks Guys I am rebulding the master cylinder again this time with dot3 fluided and replacing all the wheel cylinders with new ones
I think it will be the safest bet

very good call on the dot3. kudos to robin 58 on the 5.1. the silicone fluid is very very over rated for a system not designed for it! motorcylces should use it but its an over priced mess for these old trucks. (sorry to act like i know it all, but we just got trained on this topic for work. (i am a service dept. whipping boy)) take care

I have used synthetic brake fluid for over 15 years in my 1960 mga and have had no problems. ron

I have been running Dot 5 in my system since 1980 up until last year when I went to an open drive line. Totally reworked the system and went to a dual master cylinder and been doing good since then. My brake man claims it's the best thing they have ever come up with for brakes and he has been working on brakes since the late 60's.

Joe

I have used DOT 5 in my suburban, but only for about 4 years. All parts in the brake system were new, so there was no concern about contamination. I did contact vendors to screen wheel and master cylinders to confirm they were DOT 5 compatible (not all vendors would confirm compatibility).

The only problem I had was a bad new master cylinder from Jim Carter. I guess that I should have first taken it apart and cleaned it. It had oil or grease in it and this did not allow the piston to return (after driving it for about 500 miles).

Tim

I have only seen bad results with old brake systems and DOT 5

Grigg

I changed my '57 Belair wagon to DOT5 in the mid 80s. I rebuilt the wheel cyclinders with the standard kit from the parts store. I didn't rebuild the master cyclinder. I have driven it for 20 years with no problems. Maybe I got lucky.

I do have a problem with my '56 with DOT3. After not driving it for a year the brakes grab really bad. I haven't checked it out but I'm guessing it is rusted up wheel cyclinders.

Maybe one reason Wagner doesn't reccomend DOT5 is because they don't make it. Ford Motor Co. doesn't reccomend driving Chevys either.

Here is a great commentary on the DOT3/4 vs. DOT5 debate.

http://www.xs11.com/tips/maintenance/maint1.shtml

Here's another

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

I've run DOT5 in my 55 Belair for almost 20 years with no problem. Ditto for my 74 E100, which had been sitting for 15 years with DOT3 and had (mostly) unrecognizable brake components from the rust..

Dot 3 was O.E. in my '54 GMC when I replaced everything new in the system I used Dot 3 again, now the brakes work fine. I use Dot 5 in my Harley but the rubber components are compatable so I have had no problems in the 17 years I have owned the Harley.

OK after reading all the post now I am completely confused, very easily done, I have new MC,lines, rubber lines and wheel cylinders. What type fluid do I use? Thanks prior
Dan

It seems to me that DOT 5 compliant rubber kits are marked with colored dots that indicate that compliancy. It seems they are yellow and white, but I would have to check into that to say for sure. You might want to chack with the vendor to find out if your components are DOT 5 compliant. I personally have no problems with DOT 3 unless my vehicles sit for too long without use.

Here is something I found:

This article is from the Ducatis Motorcycles FAQ, by Duke Robillard duke@io.com with numerous contributions by others.


5. "Should I use DOT 3, 4 or 5 brake fluid when replacing?"
(Thanks to Michael Ragsdale, from the race list, for some of this info.)

DOT 3 and DOT 4 are functionally very similar. 4 has a higher boiling
point, but motorcycle brake systems don't generate the kind of pressure and
temperatures that need it on the street, in general, although it certainly
won't hurt your system to put it in.

DOT 5 is very different--it's silicone based, doesn't absorb water, isn't
corrosive, is bad for some seals, is hard to bleed, and is not miscible
with 3 or 4. Stay away from it--it needs a system designed for it.

DOT 5.1 is compatible with DOT 3 & DOT 4 (If I ever get hold of the
bonehead who named DOT 5.1...)

Here's more detail than you really want:

DOT3 is an aliphatic polyether.
DOT4 is borate ester based.
DOT5 is polydimethylsiloxane (silicone based).
DOT5.1 is borate ester based, thus its compatibility with DOT3 and
DOT4.

More information can be obtained from the following standards documents:

DOT3: SAE J1703
DOT4: FMVSS 116; proposed SAE standard J1704
DOT5: SAE J1705
DOT5.1: No SAE spec

If you are interested in obtaining copies of these standards documents, you
may order them directly from SAE at
http://www.sae.org/PRODSERV/STANDARD/gv/179.htm

According to DOT Federal Motor Vehicle Safety Standards specification
49CFR571.116 (which refers to SAE documents J1703, J1704, J1705), the
minimum equilibrium reflux boiling point requirement in deg C for each is:

DOT 3 205
DOT 4 230
DOT 5 260
DOT 5.1 260

This shows that, all else remaining the same, DOT 5.1 has a significant
advantage in heat capacity over DOT 4. Note that these specifications are
for completely dry (no H2O content) brake fluid.

Of course, all else does not remain the same and other than boiling points
and H2O content (which is very detailed in itself), most other properties
were beyond the scope of testing/interest of my friend. Any other
information should be gained from SAE, DOT or other authority.


and this:

Can DOT 5 Brake Fluid Be Used Instead of DOT 3 or 4?

Always refer to vehicle owner's manual for what the manufacturer recommends or warns against. As a rule, vehicles equipped with antilock brakes (ABS) should not use DOT 5 brake fluid.

DOT 5 brake fluid is silicone based. DOT 3 (standard) and DOT 4 (heavy-duty) are glycol-based. It can be distinguished from conventional brake fluids by its purple color (which comes from a dye).

Silicone does not absorb moisture. DOT 5 brake fluid does not become contaminated with moisture over time as conventional DOT 3 and 4 brake fluids do. Silicone is also chemically inert, nontoxic and won't damage paint like conventional brake fluid. It also has a higher boiling point.

Because of this, it is often marketed as a premium "lifetime" brake fluid. It is often used to preserve brake systems in antique vehicles and those that sit for long periods of time between use.

DOT 5 silicone brake fluid is also very expensive (costing four to five times as much as ordinary brake fluid), and it won't mix with glyco- based brake fluid (creating concern over sludging if all old fluid isn't removed when a system is refilled with silicone).

Silicone also has slightly different physical properties and compressibility, making it unsuitable for ABS systems calibrated to work with DOT 3 or 4 brake fluid.