Brake fluid

[Jazz]

Hi everyone ! I'm in the process of putting my series I back on the road after many moons of sitting (inside, thank goodness) - like 13 years! In any event, I'll be working on the brakes, and I had forgotten whether I had replaced the standard Girling fluid with synthetic. Is there a way to determine the difference between the two? I'd hate to top off the reservoir with the wrong stuff when I bleed the brakes.
Thanks a million for any input...

Jim

 

[Barry]

All modern brake fluid is synthetic. The last non-synthetic brake fluid was DOT 2 (castor oil + alcohol) which was replaced by DOT 3 in the late 1940's.

 

[Jazz]

Barry, thanks for the response. For some reason I was under the impression that there were two options for fluid where one was prone to absorbing moisture and the other was not, but had some other downside. So you're saying all brake fluid today is standardized and it should not be an issue. Thanks!

 

[chazza]

Jazz, I think you might mean silicone brake fluid,

Cheers Charlie

 

[Toyanvil]

I use Castrol GTLMA in my Ser II and have always used Castrol for the last 40 years. If you can't find it, I would recommend using a German made brand.

 

[Tom H]

Forum members, His key question is how can he tell what he has in the system now. Does anyone have that answer?

Jazz, the key thing you need to know is that you should not mix types, so if you cannot find out what you have, you would be best off to totally clear the old fluid out and start fresh. Probably a good idea anyway since car has been sitting for 13 years.

I use silicone fluid (DOT 5) in my Alpine since I restored it 30 years ago and have been happy with the results.

Tom

 

[65beam]

Moss Motors has a good tech article on brake fluid. pretty much explains everything.

 

[Barry]

So you're saying all brake fluid today is standardized and it should not be an issue. Thanks!

Jazz,

I am NOT saying that all brake fluid today is standardized; sorry if it came across that way.

There are currently four types of readily available brake fluid:

DOT 3 (glycol & glycol esters) has been around for 60+ years and is by far the most widely used.

DOT 4 (glycol & glycol esters + borate esters) has been available since the mid-80's and has been the standard brake fluid for U.S. made cars since about 2006. DOT 4 has higher dry / wet boiling points than DOT 3.

DOT 5.1 (glycol & glycol esters + a higher level of borate esters) has been available since about 2000. DOT 5.1 has higher dry / wet boiling points than DOT 4. It is a "niche / high performance" product.

ALL glycol based brake fluid (DOT 3 / 4 / 5.1) is hygroscopic (readily absorbs moisture) and the boiling point drops as the moisture content increases.

DOT 5 (silicone = at least 70% by weight of a diorgano polysiloxane) is hydrophobic (does not absorb water). It is not compatible with DOT 3 / 4 / 5.1 brake fluid; putting silicone brake fluid in a system that has any traces of glycol based brake fluid can result in system failure. DOT 5 has a higher viscosity, cannot be used with ABS systems, absorbs air which requires special bleeding procedures, etc.

DOT 3 should be fine unless you plan to use the brakes really hard for a prolonged period. DOT 4 and 5.1 provide higher dry / wet boiling points, but the borate esters may adversely affect SBR rubber materials (seals and brake hoses) made "back in the day". Modern (since about the mid-1980's) SBR and EPDM seals and brake hoses are compounded to resist the borate esters in DOT 4 and DOT 5.1 brake fluid.

Fresh (i.e., no moisture) brake fluid is much more important than the type of brake fluid. "Dry" DOT 3 brake fluid has a higher boiling point (401 F.) than "wet" DOT 4 (311 F.), or "wet" DOT 5 / 5.1 (356 F.).

Just my opinion based on 30+ years supplying the automotive brake industry, YMMV.

 

[Alpine 1789]

...I had forgotten whether I had replaced the standard Girling fluid with synthetic. Is there a way to determine the difference between the two?

Since no one has answered Jim's original question, I'll take a shot:

Girling fluid makes a very effective paint remover. So, just spill a little on a painted surface. If the paint softens and comes off, it is Girling. If not, it is silicone. I do, however, recommend finding a test surface other than your car.

 

[Jazz]

Thank you all for the quick responses! Charlie, you're right in suggesting I meant silicone as opposed to synthetic. Right now, I'm leaning to purging the system of whatever is in there and replacing all the (contanimated?)rubbers I can.
Purging, as I understand it, is to use alcohol to flush out the lines. Then replace the seals, reassemble, and follow up with fresh fluid. Does that sound like a sound plan?

 

[Greggers]

As Barry said, Dot 5 is not compatible with Dot 3 and Dot 4, so it's typically (if not always) a different color (typically purple or blue so you know when you've flushed out the old). Dot 3 and 4, however, are compatible with each other. So if your fluid's bluish, it's likely Dot 5. If it's honey-colored, Dot 3 or 4. If it's brown or black, flush it to hell regardless of what it is.

 

[chazza]

Right now, I'm leaning to purging the system of whatever is in there and replacing all the (contanimated?)rubbers I can.
Purging, as I understand it, is to use alcohol to flush out the lines. Then replace the seals, reassemble, and follow up with fresh fluid. Does that sound like a sound plan?

You only need to purge the system if you plan on changing to a new incompatible brake fluid.

If you decide to to stick with a Dot 4 fluid, any old fluid in the pipes will be flushed out when you bleed the brakes.

Use Alpine 1789's advice and test the fluid you have on paint. If it curdles the paint and you want to use silicone fluid, then flush with alcohol,

Cheers Charlie

 

[snamelc]

Jim:

My Series II had silicone brake fluid in it when I bought it new in 1961. DOT 5 is purple, so check your existing fluid and if it is purple, it's DOT 5 (silicone). I am using DOT 5 in both my brakes and clutch in my current Series II and have had no problems with it.

Bill

 

[Jazz]

It does appear that I do not have silicone fluid in my system which suits me just fine as I really wasn't looking forward to an alcohol purge anyway - ha! I'm slowly becoming older and wiser as this process unfolds - thank you.

For the record, I did come across an interesting comment from an outside source (he may be a Brit) with regard to determining the difference between "regular" brake fluid and the silicone variety...

"Speaking of brake fluid, let’s talk about Castrol LMA verses Silicone. These are the only fluids that this writer recommends, so don’t you dare use anything else! Most conventional brake fluids are nearly clear, while Silicone fluids are often purple or some other queer color. If you are not sure of what is in your system, add a few drops of the fluid to an ounce of water. For you metric system guys, that is about a shot glass full. The conventional fluid will disappear, while the Silicone will not mix. As you know, conventional DOT4 brake fluid is cheap and is also an excellent paint remover."

 

[Tom H]

OK, so it's not silicone, But I think you still need more info on what IS on there. If it's Castrol LMA, then I don't think, but not sure, that you can mix it with Dot 3 or Dot 4

Hopefully others will comment

Tom

 

[Greggers]

OK, so it's not silicone, But I think you still need more info on what IS on there. If it's Castrol LMA, then I don't think, but not sure, that you can mix it with Dot 3 or Dot 4

I thought Castrol LMA is Dot 4. In fact, according to the site below Castrol GT LMA has been renamed Castrol Dot 4.

https://www.pegasusautoracing.com/productselection.asp?Product=3308

 

[Barry]

Castrol GT-LMA is and always has been a DOT 3 brake fluid

Castrol Advanced Performance DOT 4 Brake Fluid is, ..... well, a DOT 4 brake fluid.

The Pegasus Racing website does NOT say or suggest that Castrol GT-LMA has been "renamed Castrol Dot 4"; what it says is that "Castrol Advanced Performance (DOT 4 brake fluid) is 100% compatible with Girling / Castrol GT-LMA. Add this fluid directly to any system with GT-LMA still in it. You do not need to drain or flush the system."

I would not mix DOT 4 or DOT 5.1 brake fluid with DOT 3 brake fluid, but FWIW, all DOT 3 / 4 / 5.1 brake fluids are compatible.

 

[65beam]

FYI, Castrol GT- LMA fluid exceeded DOT 3 and 4. that means it met the specs for DOT 4. DOT 3 and DOT 4 can be mixed and are compatable. The Castrol Advanced DOT 4 is what we now sell since we don't have the product available with the old label which read GT-LMA. The black bottle has replaced the old blue and white bottle. it now clearly says DOT 4 and still has the LMA. just read the bottle.

 

[Jay Laifman]

Definitely a shout out for labeling the masters! I got a Tiger that I didn't realize had DOT 5 in it (purple). I bled it with Castrol LMA. In two weeks time my clutch was gone. I know there are people out there who say you can bleed them from "standard" to silicone and some say you can only go the other way. Some say that what happened to me shouldn't have happened. All I know is that it happened and the clutch was working just fine before I went and bled it.

 

[Chazbeam]

I just made this costly mistake!

OK so i grabbed a bottle of dot 3 high temp synthetic off the auto store shelf without really giving it a good look over, i was in a hurry and didn't spend the time to pay attention..Also i thought dot 3 was dot 3! one would think they would DOT it a different freeking number..(yeah yeah it does not work like that)..,SO
I topped off my brake and clutch and a few days latter they are leaking like sives right into the interior of the car all over the floor and loosing fluid by the time i have drive about 30 mill.. and its both cylinders and some of the leakage looks like the color of rubber... I could not be more pissed at myself over it and being careless but i post this as a lesson to everyone that may make the mistake, DON'T!
Not all brake fluid is created equal..... what does not kill me makes me learn.. its just painful lessons...


Cheers