Please talk me into or out of DOT 5 in my C1 *NM*

[Dave Suesz]

[Duke W.]

Re: Please talk me into or out of DOT 5 in my C1

Like motor oil, this subject has been beat to death.

Might I suggest that you do some searching in the archives? The basic arguments haven't changed for 30 years and the details have been posted many times.

Duke

[John O.]

Re: Please talk me into or out of DOT 5 in my C1

They didn'y use it back then.Why use it now. If you use Dot 5 and then down the road need brake fluid and you forget Dot 5 is in there and you use any other. You will have problems and be sorry.Thats the reason I won't use it.

John

[mike cobine]

Re: Please talk me into or out of DOT 5 in my C1

I just pulled my '68 out of 10 year storage. I popped the master cylinder cover off to see how bad the damage was and I found a pair of bowls that are bright and shiny, nearly new looking, although empty. There is a little brown residue in the corners, but it looks like junk that was in the fluid that was left, not rust. DOT 5 was in it.

My '63 master cylinder, on the other hand, had regular DOT 3, I'm sure, because that was 30+ years ago. When I found that car in a barn, the fluid was all gone and the bowl was a caked up, rusty mess.

Now there are performance issues and you can find pros and cons in the archives, but from strictly a maintenance issue on restoration parts, I don't think the DOT 5 will disappoint you.

The DOT 3 will do as well if you remember to flush it for periodic maintenance.

[Joe C.]

Re: Please talk me into or out of DOT 5 in my C1

Dave:

One primary consideration is whether or not your system is completely new and dry. If you have the slightest trace of DOT 3/4/5.1 present, then you should stay with the 3/4/5.1 because these glycol based fluids are NOT compatible with DOT 5, and conversion for use of the silicone based stuff will require a meticulous flush/cleaning job.
Systems filled with DOT 5 will still attract moisture, albeit to a much lesser extent; however, the difference here is that any trapped moisture will settle out of suspension, and not form an emulsion as with the DOT 3/4/5.1. Thus, if water enters your system, you will develop localized corrosion. Best bet is to periodically change your brake fluid, in any case.

Personally, I like DOT 4 which has a higher BP than DOT 3. You can also opt for DOT 5.1, which is also compatible with DOT 3/4, but not with 5. Unless you race your car, then use DOT 4, which is a good all around choice. For race applications, or severe duty, then use 5, or 5.1.

Joe

[mike cobine]

DON'T use DOT 5 for racing

DON'T use DOT 5 for racing. This was discovered over 25 years ago by several Corvette racers.

Because it traps air more, it becomes compressible. It also becomes expandable. So the brakes heat, fluid expands, and backs into the MC. If the brake cooling is efficient, then the brakes cool, localized fluid contracts, sucks air past the piston seals, and no brakes in the next corner.

For racing, use the racing DOT 3 or racing DOT 4 fluids. There is a reason they cost more. They work.

[Clem Z.]

here is my 2 cents worth

my 1988 silverado has the orignal factory brake fluid and the only thing that has been done to the brakes in 130,000+ miles is new pads and shoes. i have not added or subtracted any fluid and also have never opened the M/C cap to let in moisture because if you stll have pedal you still have fluid. it also has a plastic M/C resevoir so i can see the level thru the walls JMHO

[John H.]

Re: DON'T use DOT 5 for racing

Most of the Viper guys who regularly run track events use synthetic race fluid like Motul 600, and change it after every track day; the next step down in wet/dry boiling point is the Ford Heavy-Duty DOT4 in the blue can, then all the rest of the regular DOT4 fluid is well below that. DOT3 is factory fill in every new production car on the planet, except the Viper; I changed it to DOT4 when I was the Plant Manager at the request of the owners (after almost a year of certification testing by Engineering before they'd sign off on its release). DOT5 is NOT high-performance or race brake fluid, by any stretch of the imagination, and it can't be used with ABS brake systems due to its tendency to form microscopic bubbles of entrained air when agitated.

[paul bowers]

Re: Please talk me into or out of DOT 5 in my C1

is there any way a person can tell by looking, smelling what ever is see which (DOT) is in the system
paul

[mike cobine]

Re: DON'T use DOT 5 for racing

I still have a can and a bottle of Motul 300 C which always worked great for me. I'm sure that they have improved more in the 8 years since I last turned a wheel.

Wilwood used to be great with its 560, but they brought out a higher temperature 700, I believe, that was like putting water in your lines. After that, I never heard much of anything with Wilwood fluid.

The Ford HD DOT 4 goes a long way back. The Mercedes fluid (DOT 4 I think) was also used by a lot of autocrosses and SOLO I guys.

The problem is not the dry temperature, but the wet temperature, as no one has dry fluid unless they fill it in Death Valley.

DOT 5 just had the lack of water collection and the very high temperature rating and most assumed temperature was the big factor. They were wrong.

[mike cobine]

Re: Please talk me into or out of DOT 5 in my C1

It tastes like chicken.

(just kidding, don't taste it!)

[Joe C.]

Add On

The ratings for brake fluids are enough to confuse most people today, and ever more complicated. I agree, that DOT 5 fluid, which as rated by the Dep't O' Trans. are currently silicone based, have all the characteristics that you describe, and yes, not best for racing duty. My error for including it.
The DOT ratings are based on wet/dry BP measurements of the working fluids, with higher values assigned to the higher DOT numbers. Nowadays, the olde fashioned glycol/mineral oil based (DOT 2-3) fluids are now converted to synthetic based DOT 3-4-5.1 fluids, which are all miscible. (i.e glycol/mineral oil based are compatible with synthetics, which is NOT the same as silicone). I believe that the "Racing" fluids mentioned above are all derived from synthetic based versions of old DOT 3 and 4 formulas. In this vein, then, DOT 5.1 would be the best of the bunch, with higher wet and dry BP's. Although this is an advantage, the higher BP can lead to a dangerous condition with significant water absorption. So, the higher the Dry BP of the fluid, the more important it is for frequent changes.

Joe

[Clem Z.]

the big problem for race car brakes is

they leave the system open without fluid when they build the car and it then picks up moisture.. when we built a new car or changed brake systems we used alcohol and dry nitrogen to flush the systems and the filled them with brake fluid. never had a brake problem as far a getting a good hard pedal. DOT 5 when you pour it you get air bubbles.

[Wayne K.]

An easy test is to add some fluid to...

water in a jar and shake it. If the fluid mixes with the water it is not DOT-5 (silicone).

[Joe L.]

Re: Please talk me into or out of DOT 5 in my C1

Duke and Dave-----

Yup, I agree. If there's anything else to be said about DOT 5 other than what's already been said here, I can't imagine what it could be. I think we could have an entire archives volume devoted to this subject all by itself.