Switch to silicon brake fluid?

[Joe777]

I have a 46 Ford 1.5 ton dump truck. I’m getting tired of dealing with corrosion in the brake wheel cylinders with DOT 4 brake fluid. I would like any opinions from those that have switched to DOT 5 silicon fluid. Are you happy with the conversion? How did you flush the old fluid out? I live in the northeast so the truck is stored for 5 months of the year. Thanks for any advice on the conversion.

[tubman]

If you are having that many problems with corrosion in your brake system, there must be some other problem. I have found that the typical life of DOT-3(4) brake fluid to be 9-15 years. How many "beaters" are out there with 20+ year old brake fluid that are still functioning? A bunch. In my opinion, you have ongoing contamination in your system which needs to be flushed out and eliminated.

I would advise against using DOT-5 for a number of reasons. The most important of these is that, since it is incompatible with ABS systems, it will get harder to get and much more expensive in the future. I do have experience with it and do not recommend it. I put DOT-5 in a '68 Corvette in the late nineties. It was a bitch to get bled properly. It had to be heated to drive out the air and I had to close the bleeder after each pump of the pedal (this almost cost me the relationship with my late girlfriend). After I finally got it in with a firm pedal, it was great. However, it was such a problem that I swore off it after then.

These days, I use DOT-4 in all of my cars. I have an electronic doohickey I got from Amazon that tests the moisture content of the brake fluid. I have found that collector cars stored under good conditions will go 9-15 years before the moisture content gets high enough to become a potential problem. I test my cars every couple of years, and if the moisture content starts getting to be a problem, I grab a fresh bottle of DOT-4 and run it through the system. It has been mentioned that I am a believer in "Speed-Bleeders". That is true, and allows me to cycle the fluid with a minimal expenditure of time and effort all by myself.

I use DOT-4 instead of DOT-3 because it's a little better and costs about the same. Bleeding is the same as DOT-3. If you have the extra money, a lot of time, and a cooperative companion, DOT-5 is OK, but I'm short on all of those these days.

[Joe777]

Thanks for relating your experience tubman. I’ve heard the conversion to dot 5 can be a challenge. How did you heat it?

[Ken/Alabama]

I’ve been using Dot 5 in my three 40s for the latest 30 years. Yes it can sometimes be a challenge to get them bled but the upside is that Dot 5 doesn’t absorb moisture and eat paint like Dot 3.

[hotcoupe]

I use Dot 5 in my '32 and my '37 1/2 ton, if you decide to change your current brake fluid to Dot5, you will have to completely disassemble all of the hydraulic components and clean them with denatured alcohol. Another thing that I learned, the way that you handle Dot5 is important, when filling the reservoir, avoid creating turbulence, instead of pouring Dot5, insert a rubber hose to the bottom of the reservoir and a small funnel and slowly add the Dot 5. Just the act of pouring Dot5 5 will introduce micro bubbles and make it harder to get a firm pedal.
Tom

[tubman]

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When I did my Corvette, the instructions that came with the DOT-5 said to heat it to about 200 degrees. Strangely, when I have looked for this in the past, I have not been able to find it anywhere else. Anyway, I bought a cheap aluminum teapot at the dollar store for that purpose and just heated it on my garage heater. I was also careful when refilling the master reservoir to minimize any agitation of the heated fluid (as above). The problem with DOT-5 is that it absorbs air, not water.

[signsup]

No ersonal experience, but I have replaced entire brake systems on vintage military vehicles and have asked the owners if they wanted to go DOT 5 as this would be the time to do it. Not one has gone that route. DOT 3 or 4. Their decision after research, not mine. You will read that 5 is not compatable with 3 or 4 and I would certainly bleed down the system and perhaps run some mineral spriits through the system and then bleed dry. But someone told me that if you read the labels on DOT 5 you will not see any warnings about mixing with other bluids. Interesting.

[Drbrown]

I'm with Tubman. I have stayed with DOT 4. One has to be very careful about converting.
For about $40 labor and material my mechanic flushes the systems about every 5 years. Exception: My modern VW which uses DOT 5 says flush about as often.

[flathead4rd]

I have DOT-5 in my 50. Disc in front drum in rear. Been there going on 10 years now. Here is the problem I see with DOT-5. You cannot bleed the brakes using the old method. It is important when bleeding to pump the brakes up very slowly. you cannot use the rapid pump up method. Why? Because rapid pumping puts air into DOT-5 fluid and you will never get it out. Results: Spongy brake pedal. Might as well drain the whole system and start over.

[signsup]

One method of flushing old fluid that I have read about is every one or two years, bleed the brakes and add about 1/3 the capacity of the master cylinder with fresh fluid 3 or 4. Then, in theory, every 3 to 6 years, you've replaced all your fluid without a major flush. I don't know enough about how the fluid circulates in a closed loop to know if you only need to open up the furthest away bleeder and would get fresh fluid in the entire system.

[Kube]

Originally Posted by tubman

If you are having that many problems with corrosion in your brake system, there must be some other problem. I have found that the typical life of DOT-3(4) brake fluid to be 9-15 years. How many "beaters" are out there with 20+ year old brake fluid that are still functioning? A bunch. In my opinion, you have ongoing contamination in your system which needs to be flushed out and eliminated.

I would advise against using DOT-5 for a number of reasons. The most important of these is that, since it is incompatible with ABS systems, it will get harder to get and much more expensive in the future. I do have experience with it and do not recommend it. I put DOT-5 in a '68 Corvette in the late nineties. It was a bitch to get bled properly. It had to be heated to drive out the air and I had to close the bleeder after each pump of the pedal (this almost cost me the relationship with my late girlfriend). After I finally got it in with a firm pedal, it was great. However, it was such a problem that I swore off it after then.

These days, I use DOT-4 in all of my cars. I have an electronic doohickey I got from Amazon that tests the moisture content of the brake fluid. I have found that collector cars stored under good conditions will go 9-15 years before the moisture content gets high enough to become a potential problem. I test my cars every couple of years, and if the moisture content starts getting to be a problem, I grab a fresh bottle of DOT-4 and run it through the system. It has been mentioned that I am a believer in "Speed-Bleeders". That is true, and allows me to cycle the fluid with a minimal expenditure of time and effort all by myself.

I use DOT-4 instead of DOT-3 because it's a little better and costs about the same. Bleeding is the same as DOT-3. If you have the extra money, a lot of time, and a cooperative companion, DOT-5 is OK, but I'm short on all of those these days.

What you said...

[34fordy]

I sure love the mechanical brakes on my old puttster. LOL

[GB SISSON]

"The safety of steel from pedal to wheel." :1st Henry, chapter '38

[deuce_roadster]

I didn't see any mention of the stock stop light switches failing due to the silicone getting into the switch, a very common problem. Many change to a mechanical switch or a Harley switch that is made to withstand the silicone. I personally only had 1 miserable experience with the Dot 5 but that was enough.

[Joe777]

Thank you all for your words of wisdom as it is very much appreciated. I think I’ll stick with the dot 4 fluid and bleed the system more often. On a related note, my replacement wheel cylinders (china) have steel pucks in them instead of aluminum like the originals had. Any downside?

[Farmall_1937]

We considered DOT 5 for a '66 Mustang, but decided to stick with DOT 3. The manufacturer of the disk brake recommended we didn't use DOT 5, but didn't give much reasoning. Might not hurt to check with the wheel cylinder and master cylinder vendors before switching in the future. My grandfather's '39 Buick is running DOT 5 and has been working well. As others have said, bleeding it can be a pain.

[1948F-1Pickup]

Never used it. I wouldn’t retrofit it. Girling doesn’t seem to be too fond of it-

[PeteVS]

One thing to consider is the master cylinder gasket. My '63 Chevy has a flat, thick rubber gasket. There's a small hole in it that allows air to go into the chamber each time the brakes are applied or if there's a loss of fluid from a leak in the system. Each time a bit of fresh air comes into the reservoir, it brings a bit of moisture along with it. I'm not sure when it happened but shortly after '63, that flat gasket with a hole was replaced with a convoluted molded gasket, kind of like a bellows which would flex when the brakes were applied without the introduction of moist air to the the fluid itself eliminating the build up of water in the system, eliminating water collecting in the bottoms of master and wheel cylinders. When I redid the '63, I opted for silicone fluid instead of switching to a later master cylinder design.

[petehoovie]

Originally Posted by 1948F-1Pickup

Never used it. I wouldn’t retrofit it. Girling doesn’t seem to be too fond of it-

[Mart]

Dabbled with dot 5 on my t-bird 30 plus years ago but switched back to dot 4 and have dot 4 in all my vehicles. Dot 4 is better than dot 3 in my opinion.