[Rufus68]

My 2005 Harley Sportster came with DOT 5 brake fluid. I have personal experience with DOT 5 from changing the front brakes on my bike a couple of years after buying it new. At first, the new front brake system was spongy after the install. But I did a quick touch up bleed each morning for the next 5 days which removed the micro bubbles that settled out over the night. I stopped doing the touch up bleeds when my front brake lever became rock solid. It has remained rock solid to this day. Yes, I still have that bike and I still ride it often. I can report that DOT 5 brake systems will only be spongy if there is air in the system. And once bled properly, the system will have and will keep a rock solid feel.

I also had to replace the rear master cylinder on that bike several years ago. And my rear brake pedal is also rock solid. You just have to do touch up bleeds with a DOT 5 system after working on it.

 

[105810]

Why users experince "soft pedal feel"
A.2.2.8 AIR SOLUBILITY—
It has been reported that dimethyl polysiloxane fluid, which is a major component of silicone based low water tolerant type brake fluids (SAE J1705), can typically contain dissolved air at a level of 16% ± 3% by volume at standard temperature and pressure. This compares with a typical level of 5% ± 2% by volume of dissolved air for glycol ether based SAE J1703 (DOT 3 and DOT 4) type brake fluids


A.2.2.9 COMPRESSIBILITY—
Silicone based brake fluids are more compressible than conventional brake fluids and the difference is magnified at higher temperatures (concept covered in a basic chem course).

The compressibility of SBBFs (Silicone-based brake fluid) may be calculated at any combination of temperature and pressure [see J. A. Tichy and W. O. Winer, “A Correlation of Bulk Moduli and P-V-T Data for Silicone Fluids at Pressure up to 500,000 PSIF,” ASLE Transactions 11,338 – 344 (1968).]



if it tickles your pickle

https://www.researchgate.net/public...f_Bulk_Moduli_and_P-V-T_Data_for_Silicone_Fluids_at_Pressures_up_to_500000_psig

 

[105810]

can't edit my own post, forgot to add one more thing

Once the DOT 5 fluid (PDMS) gets hot, it allows liquids or air bubbles to pass through it - the end users will continue to experience squishy peddles

 

[105810]

[...] all Dot 5 pretty much the same?

no even a simple $3 usb charger for a phone is widely different from manufacture to manufacture

 

[cougar70]

One nice thing about DOT 5 is it won't harm any finish on the car when it leaks or spills. I used DOT 5 with manual Granada brakes and it worked well. Never failed to stop the car.

A fresh flush with DOT 4 brake fluid has always resulted in improved pedal feel in my cars. A quart or two of brake fluid flushed through the system every year or two will keep the system in good shape.

The army has specified DOT 5 since the early 80s. That has kept ABS and stability control off army vehicles. Now the army needs to upgrade to modern systems. The army did a study to see what the issues of silicone brake fluid are with ABS equipment. It looks like the purple dye might have something to do with it.

https://events.esd.org/wp-content/uploads/2017/08/Silicone-Brake-Fluid-Compatibility-with-Anti-Lock-Braking-Systems-for-Identifying-Future-Military-Brake-Fluid-Requirements.pdf

 

[anbo]

I have been told that all silicon brake fluid is either manufactured in China or the USA. I know where I'd be sourcing mine from.

 

[pprince]

I have used dot 5 in my 65 Mustang for 27 years. Never a problem. Hard pedal.

Flushed it twice in those years. It's always in a heated garage. In fact, my Mustang still has its original brake hard lines.

 

[blkfrd]

I knew here was a reason I needed to buy a vacuum chamber! :nerd:

I switched to DOT5 a few years ago and it seems fine to me. Plus, like someone already said, I don't have to worry about getting it on painted surfaces...that was the biggest reason for doing it.

I flushed out my system with denatured alcohol and then used an air gun to dry it out before putting DOT5 in. Don't want any DOT3/4 in there as it won't mix.

Wilwood doesn't like DOT5:

Wilwood Disc Brakes - Brake Fluid Tech Tips

Why users experince "soft pedal feel"
A.2.2.8 AIR SOLUBILITY—
It has been reported that dimethyl polysiloxane fluid, which is a major component of silicone based low water tolerant type brake fluids (SAE J1705), can typically contain dissolved air at a level of 16% ± 3% by volume at standard temperature and pressure. This compares with a typical level of 5% ± 2% by volume of dissolved air for glycol ether based SAE J1703 (DOT 3 and DOT 4) type brake fluids


A.2.2.9 COMPRESSIBILITY—
Silicone based brake fluids are more compressible than conventional brake fluids and the difference is magnified at higher temperatures (concept covered in a basic chem course).

The compressibility of SBBFs (Silicone-based brake fluid) may be calculated at any combination of temperature and pressure [see J. A. Tichy and W. O. Winer, “A Correlation of Bulk Moduli and P-V-T Data for Silicone Fluids at Pressure up to 500,000 PSIF,” ASLE Transactions 11,338 – 344 (1968).]



if it tickles your pickle

 

[stephen_wilson]

I have used dot 5 in my 65 Mustang for 27 years. Never a problem. Hard pedal.

Flushed it twice in those years. It's always in a heated garage. In fact, my Mustang still has its original brake hard lines.

My '89 Toyota 4x4 has had DOT 3/4 for 29 NJ winters and it sits outside. Only gets flushed if I have to do service work, every 5-10 Years ? Pretty much a worst-case for brake fluid. OEM hard lines, except for the one I bashed on a log ! IMO the only reason to use DOT 5 is if you're worried about it getting on your paint. You have to be pretty clumsy for that to happen !

 

[Flade]

Interesting Wildwood says to never mix DOT types of any rating.

Any reason to replace DOT 3 with DOT 4, or DOT 5.1 when doing a brake job?

 

[rbohm]

no even a simple $3 usb charger for a phone is widely different from manufacture to manufacture

actually when it comes to brake fluid, and engine oil, they have to meet a minimum standard for the type of fluid rating put on the can. for instance ALL dot 3 brake fluids have to meet the same standard regardless of who makes it.

Interesting Wildwood says to never mix DOT types of any rating.

Any reason to replace DOT 3 with DOT 4, or DOT 5.1 when doing a brake job?

that depends, are you having issues with dot 3? if so then step up the dot 4, same if you are having issues with dot four,step up to dot 5.1.

the only issue with mixing the fluids is that it compromises the temp rating on the higher rated fluid. add dot 3 to a dot 4 system, and you lose temperature resistance of the dot 4 fluid. same with dot 5.1.

 

[105810]

I have used dot 5 in my 65 Mustang for 27 years. Never a problem. Hard pedal.

Flushed it twice in those years. It's always in a heated garage. In fact, my Mustang still has its original brake hard lines.

Formula may have changed or may have been modified (I'm assuming the later)

Sounds like the manufacture who created that did a good job

 

[105810]

I knew here was a reason I needed to buy a vacuum chamber! :nerd:

I switched to DOT5 a few years ago and it seems fine to me. Plus, like someone already said, I don't have to worry about getting it on painted surfaces...that was the biggest reason for doing it.

I flushed out my system with denatured alcohol and then used an air gun to dry it out before putting DOT5 in. Don't want any DOT3/4 in there as it won't mix.

Wilwood doesn't like DOT5:

Wilwood Disc Brakes - Brake Fluid Tech Tips

Hooray for attractive interactions between the liquid molecules - it makes ***** happen!

 

[pprince]

Formula may have changed or may have been modified (I'm assuming the later)

Sounds like the manufacture who created that did a good job

Which means what?

Ford did a great job considering many of these cars are now 54 years old.

 

[Lawnjockey]

My DOT 5. Been running this in British as well my American cars.

 

[Woodchuck]

I wouldn't hesitate buying DOT5 from any major auto parts store. That said, I'd be changing fluid (a/k/a brake flush) once every year and, if you store your vehicle for the winter months, right before you put up for storage.

 

[anbo]

That's interesting that Wilwood do not like Dot 5 fluid because they actually sell it.

"Wilwood does not recommend using DOT 5 fluid in any racing applications. DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid, and results in beads of moisture moving through the brake line, collecting in the calipers. It is not uncommon to have caliper temperatures exceed 200 degrees F, and at 212 degrees F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 fluid is highly compressible due to aeration and foaming under normal braking conditions, providing a spongy brake feel."

 

[Flade]

actually when it comes to brake fluid, and engine oil, they have to meet a minimum standard for the type of fluid rating put on the can. for instance ALL dot 3 brake fluids have to meet the same standard regardless of who makes it.



that depends, are you having issues with dot 3? if so then step up the dot 4, same if you are having issues with dot four,step up to dot 5.1.

the only issue with mixing the fluids is that it compromises the temp rating on the higher rated fluid. add dot 3 to a dot 4 system, and you lose temperature resistance of the dot 4 fluid. same with dot 5.1.

With a standard Mustang, K/H front drum rear, stock engine, I would think DOT 3 would be fine. If you are into autocross, racing, or have a high powered engine, I can see a reason to move up to the higher temp rating of DOT 4 or 5.1

 

[rbohm]

With a standard Mustang, K/H front drum rear, stock engine, I would think DOT 3 would be fine. If you are into autocross, racing, or have a high powered engine, I can see a reason to move up to the higher temp rating of DOT 4 or 5.1

i agree flade, in fact for many years dot 3 was just fine, even in most racing situations. although there were enough issues with it at the track that dot 4 was developed. and for the vast majority of people dot 3 is just fine, even us hot rodders with big engines, and heavy right feet. but there have been times when i wished for a higher rated fluid, it might have prevented my brakes from fading on a long down hill run in my old F250.