TR2/3/3A Is there a Silicon safe Master Cylinder for TR3?

[martx-5]

Hopefully it never had DOT3 in it as DOT4 is for the British rubber seals and cups.

Actually, the only real significance between DOT3 and DOT4 fluids is the dry and wet boiling points, with the DOT4 having higher boiling points. It is not just for old British brake seals.

What you're thinking of is the days when there were different fluids for different British brake manufacturers. I seem to remember such designations as "Crimson" and "Amber" and "Green". Below is a quote from Moss about this very topic, followed by a link to the whole article which has a lot of good technical info in it.

"
Traditional Concerns for British Car Owners

In the good old days, dire warnings of problems caused by using the wrong brake fluid in a British car were common. Anyone reading a warning like "as the cups in the master cylinder are pure [natural] rubber; it is imperative to use only the recommended fluid. Any other fluid may be dangerous" would probably take it seriously. Such strong concerns were very valid in the 1950s, but much less so now, even for 1950's vintage cars. There are several reasons why we can be less worried about our hydraulic systems "turning to goo" if the wrong fluid is used:

1) Pure natural rubber hydraulic seals are no longer made for our cars
2) More than likely, the original natural rubber seals have been replaced.
3) Brake fluids meeting current standards are compatible with the virtually every type of seal available, including natural rubber
4) Brake fluids meeting current standards are safe to mix (although mixing them is not recommended)
​

And this brings us to the subject of this article – brake fluid.
Classification of Brake Fluids

Brake fluids are classified by their physical properties. The standards in the US come from the Department of Transportation, which is where the “DOT” in the brake fluid classification DOT 3, DOT4, DOT 5 and DOT 5.1 comes from. The standards are set forth in the Federal Motor Vehicle Safety Standards 116 (FMVSS 116). [26] The Society of Automotive Engineers (SAE) also has standards that apply. SAE Standard J1703 (DOT 3 Brake Fluids), J1704 (DOT 4 Borate Ester Brake Fluids), and J1705 (Low Water Tolerance Brake Fluids, or DOT 5 Silicone Based Fluids) are frequently cited in publications on brake fluid, along with the International Organization for Standardization (ISO) 4925 specification for “non-petroleum based brake fluids for hydraulic systems”. The DOT 3, 4, 5 and 5.1 brake fluids we will be discussing are all non-petroleum based brake fluids."


https://www.mossmotors.com/SiteGraphics/Pages/Brake_Fluid/brake_fluid_long.html

 

[LarryK]

Art:

I know the generalization of the brake fluids as I have to know what to use at different tracks in racing. But, I also know most people on the forum have to do their own work. Years ago fluid was put in the owners manuals to what that manufacturer needed for that specific model or brakes. Today it is pretty much whatever you want in the new cars. I will only suggest what the manufacturer wants as if I am doing that persons car. Liabilities are just to high to make an off the cuff suggestion. If a person comes to me with a specific fluid, I'll show him/her how to put it in, so as not to take the penalties of general fluid use. I agree the new parts can take different fluids, but if DOT 3 is a certain price, I will always go to DOT4 for the higher degree of temp just in case the owner does track days or even go to the Ford fluid for trucks for even higher temps and faster track periods. Even my parts are always an upgrade as the cost is nil in the long run. I once put brake lines on a TR3 and the owner scrimped on getting them pre crimped and I had to make one by hand. I told him it might not work, he did not believe me, and as he went for a test drive down a hill, the brakes did not work. Guess who he wanted to blame? Never worked on his car again.