1956 brake fluid non synthetic or synthetic?

[Louise-EE]

I’m rebuilding the brake booster. Got a kit from Larry’s Thunderbird Parts. When I called back, they recommended any non-synthetic brake fluid. I can’t find a nonsynthetic. My local parts house can order a silicon based DOT 5. I’ve only read on this forum that folks are using a synthetic and mostly 5….and not to mix 3 with 5. Pretty sure what is in it now is 3 so I bought a synthetic 3. But second guessing..any tips?

This page contains affiliate links for which I may be compensated. As an eBay Partner, and Amazon Associate I may be compensated if you make a purchase at no cost to you.

 

[Louise-EE]

I’m rebuilding the brake booster. Got a kit from Larry’s Thunderbird Parts. When I called back, they recommended any non-synthetic brake fluid. I can’t find a nonsynthetic. My local parts house can order a silicon based DOT 5. I’ve only read on this forum that folks are using a synthetic and mostly 5….and not to mix 3 with 5. Pretty sure what is in it now is 3 so I bought a synthetic 3. But second guessing..any tips?

Update: I found in the Midline kit a warning not to use DOT 5 Silicone brake fluid.

 

[Shawnski]

I’m rebuilding the brake booster. Got a kit from Larry’s Thunderbird Parts. When I called back, they recommended any non-synthetic brake fluid. I can’t find a nonsynthetic. My local parts house can order a silicon based DOT 5. I’ve only read on this forum that folks are using a synthetic and mostly 5….and not to mix 3 with 5. Pretty sure what is in it now is 3 so I bought a synthetic 3. But second guessing..any tips?

I did a complete brake system with new lines, wheel cylinders and new master cylinder. Use DOT 3 full synthetic and I’ve not had a single issue. I’d have to dig out my 1956 original factory manual, but I’m pretty sure it called for (back then) DOT 3…

 

[Louise-EE]

I did a complete brake system with new lines, wheel cylinders and new master cylinder. Use DOT 3 full synthetic and I’ve not had a single issue. I’d have to dig out my 1956 original factory manual, but I’m pretty sure it called for (back then) DOT 3…

Thank you. The manual I purchased is on back order. Switching to discs in the front is next.

 

[sre]

I have been restoring cars, mostly Fords but a few GM's for over 40 years. I ALWAYS use DOT 5 never had a problem. Still have a '68 Mustang F/B since 1989, never had a problem w/brake system. Silicone brake fluid is a neutral. Dot 3 will and does over time draw moisture in the brake system. Take it for what it's worth.

 

[Louise-EE]

I have been restoring cars, mostly Fords but a few GM's for over 40 years. I ALWAYS use DOT 5 never had a problem. Still have a '68 Mustang F/B since 1989, never had a problem w/brake system. Silicone brake fluid is a neutral. Dot 3 will and does over time draw moisture in the brake system. Take it for what it's worth.

Thank you. We finished the rebuild with the DOT 3 in light of the warranty “warning” . We didn’t find a huge improvement so that was disappointing but it’s one more check off of the so-to list.

 

[56Redbird]

DOT3, DOT4 and DOT5.1 are all available as synthetic and conventional.

Don't confuse the term 'synthetic' with 'silicone'. Only DOT5 is silicone based, and should not be mixed with 3,4 or 5.1.

Personally when I replaced my entire brake system with new lines, cylinders and front discs, I settled on DOT4 which has a higher boiling point than DOT3.

My look at DOT5 left me a little unsettled as not everyone seemed to support its long term benefits.

 

[Tom Alpers]

DOT3, DOT4 and DOT5.1 are all available as synthetic and conventional.

Don't confuse the term 'synthetic' with 'silicone'. Only DOT5 is silicone based, and should not be mixed with 3,4 or 5.1.

Personally when I replaced my entire brake system with new lines, cylinders and front discs, I settled on DOT4 which has a higher boiling point than DOT3.

My look at DOT5 left me a little unsettled as not everyone seemed to support its long term benefits.

I've always used DOT 3. I've had vehicles I ran for 15 to 22 years ...125,000 miles.... on the stuff and never had to replace anything except one master cylinder. Anymore I use synthetic DOT 3. If you keep the system closed there's not much way moisture can get in and if you redo and bleed brakes every 50K you flush out most of the old stuff. I know a lot of people think the dot 5 is technically better because it won't absorb moisture but one of the counter arguments I've heard to that is that that doesn't mean moisture doesn't still get into the system and what happens is instead of the fluid absorbing the moisture it all just settles to the low spots in the system and it makes the rust and corrosion at the low spots worse than you might have got with dot 3. I have no idea of the validity of that claim it's just one of the things I've read when I looked at switching between the different fluids. But I still basically fall back on I've never had a problem using dot 3 on any car so I just don't see where it's the big worry some people seem to be concerned about.

 

[lcboyer]

I’ve used DOT 4, synthetic for several years without any issues,. I like it because it doesn’t remove paint

 

[sre]

lcboyer, yes that is a big plus for silicone, it's a neutral. It doesn't remove paint and it doesn't draw moisture. Dot 3 will draw moisture. The only negative is it cost more then dot 3

 

[Tom Alpers]

Silicone has other negatives, one of which is spongier brake pedal and it can be more difficult to bleed.