Brake Fluid

[Patcon]

I am close to filling up the brake system with fluid. So I have been doing a lot of research. I have been using some synthetic Dot 3/4 stuff in all my other vehicles. What is everyone using for fluid? I have pretty much already ruled out Silicone fluid because of the poor pedal feel. I did find the Motul RBF600 which I find really interesting. Really high dry and wet temps. It is expensive, but I am not opposed to that if the benefits justify the expense.

[grannyknot]

Prestone Dot 4 works well for me and flush it every two yrs.

[Mike W]

So to add a little controversy to this discussion, I have had raging debates  with a number of my Z club members about the wisdom of using Dot 5 silicon fluid versus the more conventional Dot 3/4 fluid.  To me the benefits of using a non corrosive fluid (to paint) out weighed the negatives that I had read about Dot 5, so I gave it a try about 2 years ago when I installed a big brake kit on my car. 

I can say for certain that I do not have poor pedal feel and in fact my pedal feels a little better than with Dot 3/4.  I have not noticed any differences in stopping power, although with the big brake kit installed, my car stopped significantly better than with the stock setup. Based on my experience, I have been very happy with the Dot 5 and it also gives me some peace of mind wrt paint corrosion.  Having said that, if I were tracking my car or using it in other really high performance situations, I would probably stick with Dot 3/4 as it does have better characteristics under those conditions. 

Having said that, switching over to Dot 5 and actually using it is a little trickier than Dot 3/4.

First if you have been using Dot 3/4, you will need to completely flush your brake system as the 2 fluids are not compatible.  Second, for some reason the Dot 5 fluid tends to hold onto air bubbles and so you need to be really careful when you pour it into your reservoirs or into a pressure bleeding system.  I use a pressure bleeding system and will let the fluid sit in the container for a few hours to let the air bubbles escape.  I will also usually bleed the brakes completely, let the car sit for 12-24 hours and then bleed again.  I have found that doing it this way lets me get all of the air out of the system and results in a very good pedal feel.

Hope that helps.

Let the controversy begin!!

Mike.

[Patcon]

19 minutes ago, Mike W said:

So to add a little controversy to this discussion, I have had raging debates  with a number of my Z club members about the wisdom of using Dot 5 silicon fluid versus the more conventional Dot 3/4 fluid.  To me the benefits of using a non corrosive fluid (to paint) out weighed the negatives that I had read about Dot 5, so I gave it a try about 2 years ago when I installed a big brake kit on my car. 

I can say for certain that I do not have poor pedal feel and in fact my pedal feels a little better than with Dot 3/4.  I have not noticed any differences in stopping power, although with the big brake kit installed, my car stopped significantly better than with the stock setup. Based on my experience, I have been very happy with the Dot 5 and it also gives me some peace of mind wrt paint corrosion.  Having said that, if I were tracking my car or using it in other really high performance situations, I would probably stick with Dot 3/4 as it does have better characteristics under those conditions. 

Having said that, switching over to Dot 5 and actually using it is a little trickier than Dot 3/4.

First if you have been using Dot 3/4, you will need to completely flush your brake system as the 2 fluids are not compatible.  Second, for some reason the Dot 5 fluid tends to hold onto air bubbles and so you need to be really careful when you pour it into your reservoirs or into a pressure bleeding system.  I use a pressure bleeding system and will let the fluid sit in the container for a few hours to let the air bubbles escape.  I will also usually bleed the brakes completely, let the car sit for 12-24 hours and then bleed again.  I have found that doing it this way lets me get all of the air out of the system and results in a very good pedal feel.

Hope that helps.

Let the controversy begin!!

Mike.

Thanks Mike,

The biggest thing I saw for silicone fluid was the lack of pedal feel. As for tracking your car, from what I understand you have done plenty of high brake heat driving. I do really like the idea of no paint damage. I also like that the silicone fluid isn't hygroscopic, so there is less chance for corrosion when the system sits.

Let the debate begin...

[grannyknot]

9 hours ago, Mike W said:

I can say for certain that I do not have poor pedal feel and in fact my pedal feels a little better than with Dot 3/4.

Mike, I didn't even want to mention Dot5 but I have found the same thing, I have done 2 classic cars and 2 bikes with Dot5 and felt no difference between silicone and Dot3/4 with regards to braking. The only downside to Dot5 that I found was it sometimes dyes the white plastic of the reservior purple.

[wheee!]

Interesting information!

[Patcon]

3 hours ago, grannyknot said:

The only downside to Dot5 that I found was it sometimes dyes the white plastic of the reservior purple.

I would prefer not to do this. Is this always the case?

[Chickenman]

Motul RBF 600 is an excellent brake fluid for track days or Road racing. Probably over kill for the street.

I use WilWood 570 in my street cars. mainly because a local supplier sells it dirt cheap, and it's more than sufficient for Track days. Note that DOT  5.1 ( Synthetic ) is completely different from DOT 5.0 ( Silicone ). In fact, DOT really messed up with their naming convention. Synthetics should have been in a class all by them selves. DOT 6.0 for example. 

Silicones are good for Vintage cars or cars in storage for a long time. They are NOT good for cars used in any competition. They are more viscous than DOT 3,4 and 5.1. This causes them to form air bubbles under repeated hard applications. And the bubbles will not disperse easily.  Silicone fluids cannot be used in cars with ABS because of the thicker viscosity and the pumping action of the ABS Hydraulics will cause air bubbles to form. 

Stop Tech has a good article on Brake Fluids:

http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

And a large number of Technical White Papers on Braking systems in general. Well worth a read: 

http://stoptech.com/technical-support/technical-white-papers

Edit: Stop Tech used to have a good article on the differences between DOT 5.0 and DOT 5.1. But I can't seem to find it now. However, here is a quick reference chart:

http://www.advancepetro.com/differentbrakefluid.htm

 

 

 

Edited August 9, 2018 by Chickenman

[Chickenman]

What AP racing has to say about Silicone brake fluids.  

http://www.apracing.com/Info.aspx?InfoID=49&ProductID=3717

 

[grannyknot]

7 hours ago, Patcon said:

I would prefer not to do this. Is this always the case?

Seems to depend on the material that the reservior is made from, neither of the BMW resevrviors were affected but both of the aftermarket cups for the TR6 and the Honda CB350 were stained.  There is also one more drawback to silicone Dot5, fish eyes.   If you ever go to paint an area that has had silicone on it you have to take it down to bare metal, no amount of cleaning, sanding or solvent will eliminate the silicone. 

[Patcon]

7 hours ago, grannyknot said:

If you ever go to paint an area that has had silicone on it you have to take it down to bare metal, no amount of cleaning, sanding or solvent will eliminate the silicone. 

That's an excellent point.

I read four or five of those articles at Stoptech

Wilwood 570 looks promising