VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1937 Brake fluid what to use ?

Looking for someone with experience. I have read up on this but would like some input on it . All NOS parts master cylinder and wheel cylinders so it has the old rubber,read to stay away from dot 5 as that will swell up the older rubber. Dot 3 and 4 are the same but boiling point is higher on number 4, but 3 would need to be changed more often as it does not keep out moisture as good as 4. I figure I got one shot at this and don't want to screw it up .

Thanks The Honer

It is just the other way....Dot 3 has less glycol so it absorbs less moisture. Dot 4 has more glycol to raise the boiling point but neds to be changed more often. That is why European cars recommed more frequent Dot 4 changing.
For the most part Dot 3 is suficent for old cars, cars seldom driven in mountains or that o a lot of emergency high speed brakaing.
As the glycol picks up water (forthe air) the boiling point increases.
For a 1937 system Dot 3 is fine and a great improvement over the brake fluid available in 1937.

I will not go into the specific chemicals that are in the DOT 3 and DOT 4 brake fluids as 99.99% of you wouldn't know what it all meant. I worked for the largest brake fluid company when DOT 4 was developed. It was specifically aimed at disc brake vehicles with hotter caliper temperatures.

Boiling brake fluid is a BAD situation! My recommendation is to use DOT 3 in all drum brake vehicles.

So silicone fluid (DOT 5 I believe) is NOT recommended? If so, why not.

Dick

Silicone fluid will past the test of time. The others cause corrosion of aluminium parts depending where you live. Glycol based fluids are fine for vehicles that are regularly used.Cheap too.

If the parts are truly NOS, I would think the rubber would be highly suspect. I would be looking at installing kits.

There are folks here that use DOT 5 so it's not that it's not recommended. My understanding from previous threads is that DOT 5 is not compatible with DOT 3 or 4 so if you want to make the switch you'll need to meticulously clean or replace all components that saw DOT 3 before you can add DOT 5. If I misunderstood someone will correct me.

Seems that this subject comes up fairly regularly. There are a series of tests that need to be passed for any brake fluid to meet the specifications. One is rubber swell which no matter if DOT 3, DOT 4, or DOT 5 must be: does not swell or shrink brake cup rubber parts. Glycol and glycol ether based brake fluids have some tendency to adsorb water. Those blends with higher molecular weight components are more susceptible to viscosity and boiling point reduction. Those two factors are the major reason that European vehicle manufacturers have recommended replacement of brake fluid every two years (for at least the past 50 years). Silicone fluids are more prone to air entrainment. Those small air bubbles result in a "soft" pedal.

I have a quantity of silicon brake fluid but to date have not used it. The two reasons: 1. It is necessary to clean and flush all the DOT 3 or 4 fluid. 2. Silicone fluids should be replaced every 2-5 years.

Yes I understand that there are folks that have had silicone brake fluid in their vehicle for 10 or more years without any problems. There are also folks that have had conventional brake fluid in their vehicle for 10 or more years. That does not mean that it is smart to do so.

In the last 40 years I have used all of the above fluids in various cars with no problems....just take your pick.
With the 1936-1950 HUCK style brakes your wheel cylinders are less apt to stick (rust) with the Dot 5 fluid.

I agree with the various comments, especially those from Chipper and Gene. I also have used all 3 types in various vehicles over many years.

My practice for the last 15+ years is to use DOT 4 in any vehicle I own and flush the system every 2 years. I think the last time I had to rebuild or replace a wheel cylinder or caliper was just before I started that practice.

My guidance is that whatever you use flush the system every 2 years. You will be surprised at the small rubber particles you get from the seals on the master and wheel cylinders. Plus you minimize any issues with moisture or air absorption.

I replaced every part in the brake system, including wheel cylinders, master cylinder & hoses. I used the existing brake lines, but blew them out with Prepsol several times to clean them of the old brake fluid. I filled & bled the system with DOT 5 (Silicone).

The DOT 5 has been in there now for at least 15-years at an average use of 2,500 to 3,000 miles per year and have never had a brake issue, including still using the original brake light switch. No "soft" pedal, either, as I've heard from others. I check the M/C yearly and the brake fluid is still nice & clear.

The '36 I'm currently building will also have DOT 5.

I think that DOT-3 is just fine for a 37 or any Huck brake system. The only drawback to it is the sticking problem that Gene mentioned. If the car is not driven often with the brakes exercised, the the sticking can be a real nuisance.

Charlie

Thanks for all the input. They are all NOS Delco Moraine Products Div. I took them apart cleaned bores I did replace a few cups but they where also nos delco rebuild kits all rubber nice and soft,assembled with Raybestos Manhattan assembly fluid. All new stainless lines and stainless hoses. So I will say cost is not a problem when I have spent this much all ready . Thinking Dot 5 .

The Honer

That would be my choice for a number of reasons.