brake fluid (DOT 5)

Kevin Lang · 07-11-2009, 07:23 AM

Just finishing brake system on my stocker build and wondering if anyone has used DOT 5 silicone brake fluid before. It has a boiling point of 550 deg. and does not harm painted surfaces so I am told. Hurst lineloc instructions call for DOT 3 or DOT 4 fluid. Standard DOT 3 has boiling point of 287 deg. Thanks for any help!!!!!.............. ps. Leave on the last yellow or get a pillow and blanket!

rallye bob · 07-11-2009, 08:07 AM

DOT5 brake fluid is also known as "silicone" brake fluid.

Advantages:

DOT5 doesn't eat paint.
DOT5 does not absorb water and may be useful where water absorption is a problem.
DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.)

Disadvantages:

DOT5 does NOT mix with DOT3, DOT4 or DOT5.1. Most reported problems with DOT5 are probably due to some
degree of mixing with other fluid types. The best way to convert to DOT5 is to totally rebuild the hydraulic
system.
Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5
formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent
formulations.
Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can
cause localized corrosion in the hydraulics.
Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form
large bubbles over time. It may be necessary to do a series of bleeds.
DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4.
DOT5 is about twice as expensive as DOT4 fluid.

Mark Ruset · 07-11-2009, 11:14 AM

Kevin from my own personnel experience I would not use DOT 5 . Like Ralley Bob stated it doesn't like Dot 3 and most brake components when assembled use DOT 3 from the manufacturer. You will most likely end up with premature failure of your master cylinder.

Chris DeGidio · 07-12-2009, 01:12 PM

We use DOT 5 in many postal vehicle with no problems.A lot of myth's about DOT 5 are just that.I could go on about those,but I've got better things to do.It's very good stuff to use,and won't harm paint.It is expensive.

As a alternative,Valvoline's SynPower brake fluid is excellent fluid to use and has a high boiling point.I use it in my race car as Wilwood said not to use the DOT 5.I do use DOT5 in my Road Runner(OE drum brakes) with excellent results.

07-11-2009, 07:23 AM	#1
Kevin Lang Junior Member Join Date: Apr 2003 Location: southern connecticut Posts: 38 Likes: 10 Liked 0 Times in 0 Posts	brake fluid (DOT 5) Just finishing brake system on my stocker build and wondering if anyone has used DOT 5 silicone brake fluid before. It has a boiling point of 550 deg. and does not harm painted surfaces so I am told. Hurst lineloc instructions call for DOT 3 or DOT 4 fluid. Standard DOT 3 has boiling point of 287 deg. Thanks for any help!!!!!.............. ps. Leave on the last yellow or get a pillow and blanket!

07-11-2009, 08:07 AM	#2
rallye bob Member Join Date: Sep 2006 Location: Genoa, Illinois Posts: 488 Likes: 9 Liked 6 Times in 4 Posts	Re: brake fluid (DOT 5) DOT5 brake fluid is also known as "silicone" brake fluid. Advantages: DOT5 doesn't eat paint. DOT5 does not absorb water and may be useful where water absorption is a problem. DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.) Disadvantages: DOT5 does NOT mix with DOT3, DOT4 or DOT5.1. Most reported problems with DOT5 are probably due to some degree of mixing with other fluid types. The best way to convert to DOT5 is to totally rebuild the hydraulic system. Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5 formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent formulations. Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics. Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form large bubbles over time. It may be necessary to do a series of bleeds. DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4. DOT5 is about twice as expensive as DOT4 fluid.

07-11-2009, 11:14 AM	#3
Mark Ruset Member Join Date: May 2006 Location: Southwest Florida Posts: 263 Likes: 35 Liked 43 Times in 29 Posts	Re: brake fluid (DOT 5) Kevin from my own personnel experience I would not use DOT 5 . Like Ralley Bob stated it doesn't like Dot 3 and most brake components when assembled use DOT 3 from the manufacturer. You will most likely end up with premature failure of your master cylinder. __________________ Mark Ruset 2048 STK

07-12-2009, 01:12 PM	#4
Chris DeGidio Member Join Date: Jun 2007 Posts: 364 Likes: 8 Liked 2 Times in 2 Posts	Re: brake fluid (DOT 5) We use DOT 5 in many postal vehicle with no problems.A lot of myth's about DOT 5 are just that.I could go on about those,but I've got better things to do.It's very good stuff to use,and won't harm paint.It is expensive. As a alternative,Valvoline's SynPower brake fluid is excellent fluid to use and has a high boiling point.I use it in my race car as Wilwood said not to use the DOT 5.I do use DOT5 in my Road Runner(OE drum brakes) with excellent results. __________________ Nautilus Racing