I ask, because my recently aquired 914 has DOT 5 brake fluid, but I don't know what, if any provisions have been made to the car to use it. I know a rear caliper was recently replaced with an off the shelf used caliper with stock seals.

I'd like to go back to using Super Blue. Is a flush in order, or would I be looking at a complete brake system overhaul?

Thanks!

Which DOT-5 fluid? Silicone fluid, or the "DOT 5.2" (or whatever comes after the decimal) which is still glycol-based?

If you're using regular brake fluid stuff (the 5.2), just put it in and go. If you want to use silicone fluid, umm... The short version is "don't". The long version is that you will need to replace all of the rubber in the system, including all seals inside the calipers and MC, that have touched regular brake fluid. And you'll need to change them all again once you decide that silicone fluid sucks and you want to go back to regular stuff.

For ATE Blue or Typ 200, just pour it in like regular fluid.

--DD

It's 5.1, not 5.2. DOT5 is silicone-based fluid. DOT5.1 is not.

I pretty much agree with Dave. Any silicone fluid in the system will react badly with non-silicone fluid, making this whitish goo that likes to ball up and block passages.

You might try draining a sample from the system into a cup, and add some of your favorite fluid, to see what happens.

Sorry, I should have been clearer. I've been told that the car has silicone fluid in it now. I'd like to ditch that and go with ATE's 5.1 (right?) as I have two full, unopened containers sitting on my garage's floor.

I'll see how the two react, good suggestion. So what do I do if they react poorly? Power flush?

Thank a lot!

If they react poorly, I'd probably just buy some silicone fluid and live with it until you decide to do a complete brake system rebuild. Be fairly careful pouring in new fluid, as one of the problems with silicone fluid is that it's great for trapping small air bubbles that are very difficult to bleed out.

Boo!!!

OK. Lame. I'd hate to have to open a fresh can of ATE to find out they're not compatible. I guess I could just bleed my gf's car at that point and use some of it there. Oh well.

Thanks again!

Nuthin' wrong with the purple DOT5, got it in my '81 Goldwing and '72 VW, narry an issue!

Don't mix DOT's, I know that. VW faq on DOT 5:
http://www.icbm.org/erkson/ttt/silicone.txt

My feelings on DOT5 are skewed. Back in my evil bike days, DOT5 was considered horrible. My only experience with it at the time was in a Ducati (OEM use), which had brakes that, while very powerful, always felt mushy no matter how carefully I bled it. Most bike racers wouldn't touch the stuff.

More recently, I was surprised at how vehemently British car guys will defend it. They LOVE the stuff, mostly because it won't damage their paint when a master cylinder leaks, and doesn't soak up water to rust their cast iron brake parts even if the cars aren't used more than a few times a year.

I personally won't use it, but not for any "scientific" reasons. I also don't know of many compelling reasons to use it.

I do find it interesting that even makers of very expensive cars don't use it OEM (thus nullifying the extra expense angle). There are plenty of good, and often very expensive, non-silicone brake fluids with very high boiling points (way above the DOT4 levels). There are also non-silicone fluids that are much less hydroscopic than plain DOT4 (Castrol LMA, for example).

I had a 89 Fiat X1/9 and switched to DOT 5 Silicone fluid. The brakes lost the immediate, firm, and communicative feel. Always felt like some air in the line, no matter how many times I bled the system. My vote - Don't go with it.

I'm not going with it. I already have it due to a misguided previous owner. Trying to figure out how to get rid of it. There have been some good test suggestions, and I'll give those a try when I have the chance.

Well, here's what happens when I mix the current brake fluid with ATE (the blue stuff on the bottom):







Some pictures of the two fluids after mixing (by swirling the jar for 15 seconds)





The two fluids seperate again after a minute or two.

So what would you do? Do you think flushing out the old stuff for ATE would be a safe bet? I'm pretty sure the old stuff is silicone based.

I would probably take the risk myself, however, I also wonder if heat and/or pressure is required to start a reaction. I'd be careful for the first week, and plan on a total brake rebuild.

I think you should pump out all the super blue and fill it with Silicone DOT 5.





Just kidding. Gone crazy yet Randy.


I don't have any advice (only jokes), brakes are a scary thing to mess with, but a full brake rebuild is $$$$$.

Send it off to get analyzed. Tell 'em you want to know what kind of brake fluid it is.

Try this:
Pour some of the brake fluid in a glass container. Place an equal amount of water into the container as well. Stir. If the water separates from the brake fluid, it's DOT-5. If it combines with the brake fluid then it's DOT-4 or less.

Tell you what, I got DOT-4 and -5 in the garage, I'll go mix up a batch, take pictures, and get back to ya

Way to go Toby!

I broke out two of my measuring shot glasses...of course my g/f comes walking into the kitchen at the same time, looking a little puzzled

"Yer gonna pour me something, too, right?"

"No sweetie, I'm just doing some measuring in the garage." She doesn't ask any questions, just turns around and heads back into the bedroom. Whew!

So, here's the materials in question. The DOT-4 goes in my Jetta, the DOT-5 in my Goldwing and Squareback (I haven't had to touch the 914 but judging from the looks of the fluid, it's DOT-3).

Water, 1/2 ounce of DOT-5 and 1/2 ounce of DOT-4
Click to view attachment

How they look after adding some water:
Click to view attachment

Notice the swirly effect of the water in the DOT-4 (right shot glass). The water in the DOT-5 just sinks to the bottom (left shot glass).

Note: Due to the florescent lighting in the garage, the DOT-5 looks blue; it's really a dark, pretty purple. Welcome to the world of color photography (digital or print!).

Pouring more water into the DOT-5:
Click to view attachment

Pouring more water into the DOT-4:
Click to view attachment

Cool! I'll repeat this test tomorrow with what's in the car and see what happens.

Thanks!

How the brake fluids look after pouring water into them after a few seconds:
Click to view attachment

Do you mind seeing what happens when you mix the two brake fluids together?

How they look from above, florescent lighting:
Click to view attachment

How they look with a flash (true color):
Click to view attachment
Now do you believe it's purple?

Quite posting and let me finish...I haven't gotten to those pictures yet!

Burn on you Randy!

Haha! You got it!

Hush... let the man work! :

Here's what the DOT-5 and DOT-4 look like when I pour the DOT-5 into the DOT-4. Notice the separation? And the water from the DOT-5 that spilled past is mixing in with the DOT-4 (the swirling is the water/DOT-4 mixing):
Click to view attachment

Here's the DOT-4 shot glass after a minute of sitting from when the DOT-5 was added:
Click to view attachment

Definite separation between the two. And FYI, the two fluids will NEVER combine! A listee on the Type 3 email list has a jar on his work bench that's over 15 years old that has DOT-5 on top of some DOT-3. Every once in a while he'll shake the jar but they separate and stay that way. Unlike synthetic oil and conventional oil, the two brake fluids cannot combine.



Okay, I'm done!

Sounds like you're silicone free Randy. Congrats!!!

No, I think I do have silicone now. Take a look at my photos again. My brake fluid combination results are the same at Tobys (thank you Toby!!!!). The two fluids won't combine. What's in the car now is silicone, so I need to decide if I should try flushing out what's in there with the ATE superblue.

The colors are probably confusing you. My Dot5 is a different brand and is clear, while my Dot4 fluid is blue. What came out of my car is the clear stuff.

And as a followup test, I just added water to the jar with the two fluids and the water was instantly absorbed by the ATE Dot4 fluid, while the silicone fluid that I drained from the 914 is happily sitting on top.

Arg. Maybe I'll just get the silicone stuff for now and worry about flushing when I'm ready to rebuild and replace most of the brake system (as suggested).

Thanks again Toby!

Ooops.

Yes, forgot to mention, the coloring in brake fluids generally will fade. DOT-5 is supposed to be purple when fresh (so you know what you've got if you can't read the label I guess ) but will fade over time.

Tip for flushing - flush with the cheap $2/can stuff and then do the final flush with Super Blue.

Great tip!

I may have missed something about the flushing earlier in the thread, but changing from DOT 5 to conventional brake fluid requires a dedicated flushing solution, replacement of EVERY rubber part in the brake system, then installation of the new fluid. Simply running the conventional fluid through a few times won't do it. The Cap'n

This was actually one of my original questions. Can you tell my why replacement of the rubber bits is essential? What happens to the rubber when you switch back and forth?

Looks like I'm off to buy some more silicon fluid for the time being.

I too would like to know why. Some brake systems actually specify silicone grease for pre-lubing the seals.

Those nice test photos are an indication of why silicone is not the prefered fluid for street appilications; it will not mix with water. This results in pockets of water that of course will boil in the caliper area at low temperatures. Silicone fluid can withstand very high temperatures which makes it suitable for race applications where regular bleeding of the system is the normal procedure.

My suggestion (to ROADGLUE) would be to perform regular bleeding of your system if you elect to stay with the DOT5 fluid. Oh, and don't spill it on anything; it's nearly impossible to clean off. BTW, silicone fluid will not hurt the rubber seals.

Andys

But water needs to get in the system first! The lower DOTs (3 & 4) are hygroscopic, meaning they ATTRACT water -- DOT-5 does not attract moisture. And iffin' enough water gets into the system, it's likely going to stay in the lowest point in the system, which is easily bled out with a couple peddle strokes.

I take it y'all didn't read the FAQ I posted above...

I would guess that the silicone grease is a very different (and smaller) chemical makeup. I would think even if it's not, the amount that mixes with brake fluid is negligable.

My understanding is also that silicone fluid contributes to spongy pedal feel becuase it is actually more compressible than regular brake fluid.

Matt

[/quote]

My understanding is also that silicone fluid contributes to spongy pedal feel becuase it is actually more compressible than regular brake fluid.

Matt
[/quote]

Matt,

That is quite correct. Some people are surprised at the slightly softer pedal with the use of silicone fluid. It is also a little more difficult to purge all the air out.

Andys

Google gives us an article by the deservedly famous Caroll Smith, racing car guru of the first order:

http://www.stoptech.com/tech_info/wp_brakefluid_1a.shtml

In the section by James Walker, farther down the page, is this interesting statement:

"We won’t even discuss DOT 5 fluids as they are completely unacceptable to the high-performance enthusiast, but we’ll include them in the following table for completeness."

Here's another article, this one not so harsh:

http://www.xs11.com/tips/maintenance/maint1.shtml

And another


http://www.se-r.net/brakes/fluid.html

Want more? Goggle "DOT 5 Brake fluid", as I did.

The Cap'n