If I understand correctly, stock master brake cylinders on mid fifty ford 5-100 can not use synthetic brake fluid becasue of the brake light pressure switch on the back of the master brake cylinder. The stock swith requires 60-100 lbs of pressure to activate. Mid Fifties has a low pressure switch that activates at 20-50 lbs pressure. I installed the low pressure switch. Mid Fifty claims the low pressure switch accepts silicone fluid. I assume this is a synthetic brake fluid? If so, is there an advantage of using silicon brake fluid in these mechanical brake systems?

 

Synthetic is different than Silicone brake fluid, although silicone is a synthetic brake fluid. Lots of advertising BS there. There is no "natural" brake fluid. Classic brake fluid is glycol ester based, and is DOT-3. DOT-4 is usually synthetic or synthetic blend, basically a better glycol fluid, but is not silicone. DOT-5 is silicone. Silicone won't absorb water vapor like glycol fluids, and won't remove most paints like glycol will. Silicone also has a higher boiling point than other fluids, not likely an issue on drum systems.

I never heard that about the pressure switches, as far as compatibility. I am running Prestone DOT-3/4 synthetic in my stock '52 system with no issues.

 

I have'nt seen any silicone fluid for sale for awhile. It was great for ax racing back in the day because of the high boiling point, you wont have to worry about boilng brake fluid in normal driving situations.

 

Thanks, I like the sounds of the Prestone 3/4. Maybe will run that and see what happens. Thanks for the help guys.

 

I'm about ready to get some brake fluid for my truck and was wondering how much brake fluid I need to get for my 55 F250? I didn't see that in the manual.

Also, I saw a review on the Super Tech brake fluid that it is bad for systems with rubber in them. Is that true? I'm cheap, but I also don't want to ruin my components.

By the way, the system is all stock with drums all around and the stock master cylinder.

 

I went with a dual master cylinder and bought a 32oz bottle of fluid. It was more than enough to fill a totally dry system and have some left over.

It's an F100, but I don't think the F250 would take much more if any. Especially since I had to fill the larger MC.

 

Many of the flathead owners in San Antonio have been running DOT-5 in their restored cars for years with good results.

 

Where did you see that? There isn't a brake system made without rubber.

As far as how much to buy, it costs a little more but buying more small bottles is better than one big bottle. No matter how tightly you cap a bottle once opened, it will start absorbing moisture. Many sources recommend throwing away any opened bottles after a few months (but this is where the fluid is being used in ABS systems, too).

 

Well it was a Walmart review, but they did reference a web site about a Toyota recall because some brake fluid didn't have the polymers to keep the rubber from drying out. I would be interested to have some verification on this from you experts.

Here is the review and the link: "DO NOT USE SUPER TECH BRAKE FLUID IN OLDER VEHICLES OR IMPORTS THAT HAVE RUBBER IN THE MASTER CYLINDER.Super Tech Brake Fluid does NOT have the Polymers required to keep Rubber from drying out. Unless you want leaks. Toyota recall: Brake fluid problem affects 1.5 million vehicles - CSMonitor.com "

Good suggestion, I hadn't thought of that.

 

That's real interesting... My reaction is, if Toyotas require some polymer that isn't in one of the DOT-X fluids, they better have a REAL clear warning that ONLY Toyota fluid should be used, right on the cap. On some links I found, owners posted that the manuals just said to use DOT-3 that met SAE specs, nothing special. Most techs who posted believed the problem was a bad seal design, nothing more.

 

That makes much more sense. Thanks Ross.