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Brake fluid
#1413036 Mon Jun 07 2021 10:59 PM
Joined: Dec 2019
Posts: 177
3
37 GC Offline OP
'Bolter
In my ‘37 1/2 ton: Considering everything is new; master cylinder, slaves and lines, what are opinions of using DOT 5 silicone? Pros and cons


Larry
All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.
Re: Brake fluid
37 GC #1413038 Mon Jun 07 2021 11:41 PM
Joined: Jul 2000
Posts: 1,311
G
Insomniac
This has been discussed over the years. e.g.:
Brake Fluid Discussion

I chose DOT5. It's nice not to worry about spilling paint remover on the floor when topping up the master cylinder.

Last edited by Gord&Fran; Mon Jun 07 2021 11:43 PM.

Gord
----
1954 1/2 ton 235 4 speed
Re: Brake fluid
37 GC #1413052 Tue Jun 08 2021 01:45 AM
Joined: Dec 2019
Posts: 177
3
37 GC Offline OP
'Bolter
thanks Gord, that link was pretty informative. I wonder if opinions have changed much since those articles and threads are pretty old.


Larry
All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.
Re: Brake fluid
37 GC #1413083 Tue Jun 08 2021 12:24 PM
Joined: Feb 2011
Posts: 923
R
'Bolter
I've had Dot 5 in my 1939 for more years than I can remember. Never had a problem.

Rick

Re: Brake fluid
37 GC #1413240 Wed Jun 09 2021 02:41 AM
Joined: Dec 2019
Posts: 177
3
37 GC Offline OP
'Bolter
early posts had concerns with what the silicone did to the rubber, most others pooh pooh that, that the DOT rating says it should be safe for the seals. Pooling of moisture and the bake light switch seem to be legitimate concerns. Any experiences there? Maybe like all things mechanical, a bit of luck doesn't hurt.


Larry
All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.
Re: Brake fluid
37 GC #1413266 Wed Jun 09 2021 05:24 AM
Joined: Apr 2007
Posts: 889
L
'Bolter
My only experience with DOT 5 was helping a neighbor restore a mid-70s FMC (Food Machinery Corp.) RV, that a previous owner had converted to DOT 5. This vehicle was from Phoenix, AZ and all of the cylinders were ruined by rust, apparently resulted from water layering out as I recall beneath the silicone. How that vehicle got that much moisture in the cylinders I don't know, maybe it was stored in a lot that flooded during our summer rain? He had to replace the whole system.

From my perspective, DOT 3 or 4 is hygroscopic which means it absorbs water. This is actually good, at least to a point, so that a little water does not affect performance or cause pooling and any water can be removed by periodic bleeding. Periodic bleeding is really very simple and inexpensive, so routine maintenance will remove any moisture that gets in and you won't have rubber problems like you might with DOT 5. My 2016 Silverado uses DOT 3 so the engineers must think it is still a good choice (or was GM just trying to save a dollar or two on each truck?).

Clearly, many people have had success with DOT 5 and I would not try to convince them otherwise, especially if it was installed in a new system. A skeptic would rightfully claim my apparent fondness for DOT 3 might stem from the fact I live in a very dry area. although I would point out that my '92 Jeep Wrangler crosses creeks and washes and the brake system has been maintained in fine shape by routine bleeding of it's DOT 3 system.

Kent

Last edited by Lightholder's Dad; Wed Jun 09 2021 05:25 AM.

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix
Re: Brake fluid
37 GC #1413308 Wed Jun 09 2021 04:15 PM
Joined: Jan 2003
Posts: 323
H
'Bolter
I use DOT 4. Two major differences from DOT 3. 1) Higher dry and wet boiling points. 2) Most DOT 4 fluids contain a borate ester. The borate ester reacts out water so it is not corrosive until enough water has entered to use up the borate ester.. Look for phrases like "low moisture activity", "low water sensitivity", etc. Some product data sheets (not MSDS) list a borate ester ingredient.


Harold Wilson
41 Chevy 3/4 Ton
Re: Brake fluid
37 GC #1413493 Fri Jun 11 2021 01:43 AM
Joined: Dec 2019
Posts: 177
3
37 GC Offline OP
'Bolter
thanks Harold, I was wondering if anyone would weigh in on DOT 4 or 5.1. It seems the boiling point wet and dry points to DOT 5.1 being the best in that aspect. How is 5.1 for water absorbtion compared with dot 4? Why it not a more common upgrade?


Larry
All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.
Re: Brake fluid
37 GC #1413569 Fri Jun 11 2021 11:08 PM
Joined: Jan 2003
Posts: 323
H
'Bolter
Back when I was working DOT 5.1 was originally developed as a glycol ether based alternative to silicone based fluids. I had very little personal experience with it. The higher wet boiling point could indicate borate ester technology or the differences in ingredients and formulation. I haven't done a lot of searching for product data sheets. I doubt that many are easily available that have that information.


Harold Wilson
41 Chevy 3/4 Ton

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