• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Brake Fluid

Share this page

healeyboz

healeyboz

Jedi Knight
Offline
What was the brand and type of synthetic brake fluid that can be used to replace the old stuff?/mix with it? Everything is rebuilt and I used the recommended stuff. Even with be as careful as possible, it has eaten the paint of the master. I don't want that to happen to the calipers.
 
I think all Brake Fluid eats paint.

All you can do is after filling and bleeding, clean it off the outside and repaint.

Hopefully, once you've filled and bled, you shouldn't be seeing anymore brake fluid on the painted surfaces.
 
healeyboz said:
What was the brand and type of synthetic brake fluid that can be used to replace the old stuff?/mix with it? Everything is rebuilt and I used the recommended stuff. Even with be as careful as possible, it has eaten the paint of the master. I don't want that to happen to the calipers.
Click to expand...
I believe Purolator makes a synthetic that they claim those properties for!

Oops! As noted below, I was thinking of the Valvoline Syntech product /bcforum/images/%%GRAEMLIN_URL%%/blush.gif
 
Silicon DOT5 is the only brake fluid that I know of that doesn't eat paint. But it is not compatible with any other Brake fluid that I know of.
 
I thought that the synthetic stuff was not supposed to eat paint?? The problem is that after everything has been cleaned, and I was VERY careful not to get any fluid on the paint, the master has "seepage" through the threads of the cap. I know this sounds strange as the cap is tight.
 
Remove one screw at a time and put a bit of sealer on it.
 
Trevor Jessie said:
Silicon DOT5 is the only brake fluid that I know of that doesn't eat paint. But it is not compatible with any other Brake fluid that I know of.
Click to expand...

X2 Don't confuse synthetic with silicone
 
Really, all brake fluid is synthetic; the Valvoline Synpower label is more of a marketing gimmick. Also, all DOT 3 and DOT 4 fluids will take paint off quickly. Mine had blistered paint under the master cylinder, probably from the phenomenon you described. Since I didn't want more paint loss, and since the old brake fluid was rusty from all the moisture it accumulated, I went with DOT 5 silicone (not silicon!).

Now DOT 3 and DOT 4 will mix OK, but DOT 5 will not, so if you want to use it you would need to start with a bone dry system. I replaced the master cylinder with a new one, replaced all the lines and hoses, and cleaned out the PDWA and wheel cylinders.

Some folks don't like DOT 5 because it is slightly more compressible than DOT 3 or 4. It's not noticeable unless you get the brakes really hot.
 
Dot 3 and 4 do not rot clearcoat.
 
OK... as an aside does the difference in spelling indicate anything? ( "e" vs no "e")

And I think there are some non-silicon fluids that are DOT5 that will mix with other non-silicon fluids.
 
Jack, they will rot clearcoat, just not as fast as enamel.
 
Trevor Jessie said:
OK... as an aside does the difference in spelling indicate anything? ( "e" vs no "e")

And I think there are some non-silicon fluids that are DOT5 that will mix with other non-silicon fluids.
Click to expand...

You may be thinking of DOT 5.1, this is more like DOT 3 or 4 in that it is non-silicone but has an even higher boiling point. All DOT 5 fluids are silicone.

Silicone contains silicon atoms, but the two are very different in properties, hence the reason we have silicone and not silicon brake fluid. Silicone makes good lubricants, and silicon makes good abrasives and semiconductors.
 
Ehhh... OK, I think. So siliconE is a generic name for a class of compounds based on silicon atoms.
 
Correct. It seems to me the technical name for silicones are polydimethyl siloxanes, but I guess polydimethyl siloxane breast implants might scare some folks :D.
 
Organic chemistry was never my thing. It never occurred to me that the "E" spelling was an actual class of compounds. I thought it was just a different spelling. I knew that it was based on Si instead of C, but I had never given it more thought.
 
Good article:

https://en.wikipedia.org/wiki/Silicone

Interesting point about the need to keep silicones far outside automobile paint facilities. This may have some relevance to those of you who are planning to do some serious painting.

As for me, I'm stickin' with DOT3. We have a saying in the aerospace industry, " 'Better' is the enemy of 'good enough'."
 
Sarastro said:
As for me, I'm stickin' with DOT3. We have a saying in the aerospace industry, " 'Better' is the enemy of 'good enough'."
Click to expand...

Just have to love that quote.

No telling how many times I have screwed something up that was good enough.
 
Trevor Jessie said:
Jack, they will rot clearcoat, just not as fast as enamel.
Click to expand...

I have experimented with Castrol LMA (Dot 4 I think) and cured PPG Acrylic Urethane paint. After 3 days no visible effect of the brake fluid on the paint. This was by no means an exhaustive test but after seeing Dot 3 and 4 remove other paints and hearing all sorts of horror stories thought it was interesting info.

Here's the thread where this was discussed.
brake fluid experiment

Cheers,
John
 
I believe brake caliper paint typically says "brake fluid proof" on the can.

It has something in it to battle brake fluid.

I had DOT3 leaking out of my 54 ford onto the wheel, effectively stripping it off just like paint remover.

When I first got my Sprite, I was trying to figure out what was right to run in it, and settled on DOT4 fluid (eats paint.) I couldn't find Catrol LMA anywhere locally, but Napa's DOT4 fluid is called "low moisture activity"

The reason (as far as I could gather) that you'd want the LMA version of DOT4 in your british car is that most people only drive these cars occasionally and service them as rarely as possible. The LMA fluid takes on less water than the original DOT4 stuff apparently.

Long story short, I just pay the 8 bucks for the DOT4 from NAPA since it's a couple blocks from my house. The leaky master cylinder should be fixed. If it's leaking out, it is also leaking moisture in probably. Moisture isn't a huge deal, but it lowers your effective stopping power when it saturates the brake fluid and dramatically reduces brake fluid boiling points.

DOT5 silicone fluid doesn't take on moisture, but moisture can still get into brakelines, creating a total water pocket, which can cause more problems than moisture laden DOT3 and DOT4, such as rusting the brake lines from the inside out supposedly. DOT5 also compresses more, and offers up less stopping power than DOT4 or DOT3.

I'm no book of knowledge though and am just spitting out what I've rounded up elsewhere.
 
Luke_Healey said:
DOT5 silicone fluid doesn't take on moisture, but moisture can still get into brakelines, creating a total water pocket, which can cause more problems than moisture laden DOT3 and DOT4, such as rusting the brake lines from the inside out supposedly. DOT5 also compresses more, and offers up less stopping power than DOT4 or DOT3.
Click to expand...

True, silicone fluid and water don't mix, but unlike DOT 3 and 4, it doesn't absorb moisture from the air or through the brake lines. I suppose if you had some condensation under the master cylinder cap you could conceivably get water in it, but tests by General Electric (one of the early developers of silicone brake fluid) show that it doesn't get any water in the lines, despite soaking brake hoses in water and exposing it to air. Also, the "stopping power" is exactly the same as DOT 3 and 4; the compressiblity difference translates into slightly more pedal travel than the other types, but the force applied is the same (further, not harder).

There was a good article I found once that sorted out some of the DOT 5 myths and facts, and from the calculations the author figured in for compressibility of DOT 5 vs. DOT 3 arrived at a whopping difference of about 1/4" of pedal travel when it was at the boiling point (pretty darn hot, 500 degrees F). He calculated this for a TR6 based on the geometries of the master and slave cylinder bores, and the leverage of the brake pedal arm. So, unless you are racing and getting the brakes extremely hot, the difference in pedal feel is pretty small. The man's name is Nelson Riedel, but I wasn't able to find his article again. I believe it was on the Buckeye Triumphs site when I found it last.

Just trying to dispel some of the myths floating around and presenting some facts. Not saying DOT 5 is the ideal brake fluid or that everyone should use it (don't use it in an ABS system), but the military had it developed for use in their vehicles so they wouldn't have problems with moisture accumulating while their vehicles were in storage. I can say that since I switched over about 3 years ago, the fluid is still crystal clear, the cylinders have zero rust, the wheel cylinders move freely, no leaks, and it wasn't any harder to bleed than the regular stuff. If I do lots of hard braking I notice a slightly mushy feeling in the pedal, but nowhere near the limit of the travel.

My $0.02.
 
Back
Top