DOT5

[Mike M.]

Does anyone have DOT5 brake fluid in their 62, I'm in the process of getting an original master cylinder and now I'm reading that DOT3 may be the fluid to use, I've had DOT5 fluid in the brake system for several years with no problem if it should be changed I'll change it I do not want to damage the new master cylinder, I would appreciate any advice you have.
Thanks in advance

[Stephen L.]

Re: DOT5

DOT 5 brake fluid is silicone based. It is, for all practical purposes, "inert". Your brake system won't corrode with DOT5.
You've been using it with no problem for several years. It won't harm your new master cylinder... so why change now????

[Gary Bishop]

Re: DOT5

I have been using DOT 5 in my `62 since `95. Just after the Steamboat Springs National. Up to then any all reports I read said I could flush the DOT 3 well and put in DOT 5.
I did, and also changed the rubber hoses. After a year I flushed the DOT 5 with more DOT 5. I let the sediment settle for a week or two and there was a separation. Black DOT 3 on the bottom. DOT 5 on the top.
Since then I have flushed the system with DOT 5 a couple of times and get very little separation.
I guess I have been fortunate but have not had any problems with the brakes or leaks.

[Denny J.]

Re: DOT 5 or 3 ?

Guy's
Just asking.
Does Brake fluid last for years?
Dot 3 or 5
How often do you need to flush the total brake system?
I think they ask 1 time per year? I need to check my owners book.
If that is done no water/rust/sediment will be in the lines.Denny72

[John Chesher]

Re: DOT5

I'm sure he'll chime in, but I believe Duke has previously posted that the problem w/ DOT5 is that it does not "absorb" moisture, so the any moisture entering the system remains there as tiny water droplets, which DO corrode iron/steel parts. I believe he felt this was more of a problem than DOT3, PROVIDED that you flush/change the DOT3 fluid every year or two, so that any "absorbed" moisture does not build up. Just the opposite of how it is often thought. I believe he feels DOT5 is only appropriate for racing or other very high temp conditions.

I may have gotten something wrong there, so I suggest you search the archives. I know it's been discussed many times.

[Donald T.]

Re: DOT 5 or 3 ?

I think they recommend flushing the system every 1 - 2 years for DOT 3. It is hygroscopic so it will absorb moisture which can cause corrosion in your brake system. If the brake fluid appears dark and cloudy then it's time to flush the system.

[Duke W.]

Re: DOT 5 or 3 ?

Conventional polyglycol brake fluid - DOT 3 and 4 is hygroscopic - it absorbs water, which leads to several internal corrosion mechanisims.

European OEMs have long recommended periodic brake fluid changes - typically every two years, but the domestic OEMs never have.

If you buy a new car and trade it within 6 years, lack of brake fluid changes will probably not effect you - just subsequent owners when corrosion takes out master and wheel cylinders. If you buy a "keeper", periodic brake fluid changes will likely prevent problems downstream.

Due to the lack of miscibility between DOT 5 (silicone) and DOT 3/4, I highly recommend AGAINST attempting to change from one to the other by "flushing" because the lack of miscibility will prevent all the old fluid from being expelled.

A good time to change to DOT 5 is during a complete brake system overhaul, but all pipes must be thoroughly flushed with denatured alcohol and dried, new hosed should be similarly cleaned and all hydraulic components assembled with DOT 5. You don't want one molecule of conventional fluid left in the system.

This subject has been discussed numerous times, so brousing the archives is a good idea.

Duke

[Christopher R.]

Re: DOT5

I've had DOT5 in my '62 for 20+ years. Works great. Does need to be flushed periodically. But not as often as DOT3 and 4. If you wish to change from one to the other, you should replace everything. If you don't wish to do that, stick with the existing fluid.

[Duke W.]

Re: DOT5

Corvette disk brakes are known to "pump air" into the system at the caliper due to rotor runnout. This can also "pump water" if the car is driven in wet conditions. But drum brakes are immune from this particular anamoly. Conventional brake fluid will absorb moisture out of the air even if you remove the M/C cover to inspect the level. As long as there is no entry point for liquid water in a DOT 5 system, it will stay dry and there will be no corrosion.

As I previously stated, a complete brake system overhaul is a good time to convert to silicone, and I recommend it for restorations if you follow the recommended precautions. DOT 5 reduces the need for future flushes. It should still be done if DOT 5 is installed, but the frequency of changes can be at least doubled.

Flush intervals should be based on climate and driving conditions. If you live in a typical damp US climate and get caught in the rain once in a while, flushing conventional fluid every couple of years is a good idea. If you live in the dry southwest and the car never sees rain, you can probably double the interval.

Brake systems generate debris - like mold release and wear from rubber components. Periodic flushing helps remove this debris to maintain peak system performance.

In 1968 the M/C of my SWC went out after only five years of service. In 1981 during a front brake upgrade on my 1976 Cosworth Vega I inspected the rear wheel cylinders and found corrosion. I replaced them and at that point placed all but the SWC (which has silicone) on a two year flush schedule. Since that time, over 25 years ago, I have NOT had to repair a hydraulic component on any car including '88 and '91 models that I own, which have received bienniel flushes since new.

Duke

[Mike M.]

Re: DOT5

I would like to thank everyone for their help, I will stay with the DOT 5 fluid. If anyone is interested their is a short article: Battle of the DOTS at this address:

http://www.xs11.com/tips/maintenance/maint/.shtm

it is writtem by Steve Wall
Again thanks

[Mike M.]

Re: DOT5

Sorry the correct address is:

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

[Wayne K.]

Re: DOT5

Michael,

If you are replacing the master cylinder make sure the replacement master cylinder is assembled using DOT 5 if that is what you decide to stay with.

Wayne

[Duke W.]

Re: DOT5

Absolutely! Unless you arrange with a specialist vendor to assembly a rebuilt hydraulic component with DOT 5, you much disassemble it, clean everything in denatured alcohol, and reassemble with DOT 5.

Duke

[Grant M.]

Re: DOT5

Duke,

I've probably been "lucky", but I converted to DOT 5 in 1987 when assembling my car (new MC, hoses and front steel lines, with flushing of the remaining lines), and have had no problems whatsoever; but your posting reminds me I should change the fluid SOON!

Thanks,

Grant

[Frank C.]

Re: DOT5

Michael....I switched over to DOT 5 some 20yrs ago (11 cars) and never looked back. No problems with any of them and have to plead guilty to not changing the fluid every couple of years. The m/c's look very very clean. But as Duke explains make sure the system is completely devoid of DOT 3....Regards Frank