DOT 4 Vs. DOT 5 Brake Fluid

[KARRDICK]

I've done a few reading on this subject. But I'm hoping those of you who knows will shed some light on this in a simplier fashion without all the scientific confusion on how the molecular level is.

What's the difference between DOT 3, DOT 4, and DOT 5 Brake Fluid? And there's a DOT 5.1?

I'm running DOT 5 in the front now and it feels different from when I had DOT 4. I don't know if it's because it's DOT 5 brake fluid or it's a combination of the fluid and the galfer brake lines and the race brake pads. My lever comes in a little further more now after the switch over versus when it was still stock. I wouldn't say it's soft or mussy. Oh, the brakes bites. They grab very well if I lock them up.

The rear is still DOT 4.


Glycol Brake Fluids
Silicone Brake Fluids


Thanks for answering this shop question.

[kidmoua]

I just use whatever is on sale.. I'ma cheap bastid

[hippylong]

I'm not sure
I believe their a no mix item.
I own nothing with dot5.
(not a statement) I just don't know

[speedjunkie]

if you mixed dot 4 and dot 5 your in a load of trouble.

they are not mixable.

EVERYTHING must be flushed, cleaned, cleaned, then cleaned, then flushed, then cleaned to swithch to dot 5. will mess up a lot of things.

dot 5 has a higher boiling point but is a different type of fluid and attracts water more then dot 4. must be bleed often to maintain top performance.
its a racing only application basically for full size cars and some race bikes.

motul rbf600 or equivlant is dot 4 and just fine. just keep fresh fluid in it.

[KARRDICK]

if you mixed dot 4 and dot 5 your in a load of trouble.

they are not mixable.

EVERYTHING must be flushed, cleaned, cleaned, then cleaned, then flushed, then cleaned to swithch to dot 5. will mess up a lot of things.

dot 5 has a higher boiling point but is a different type of fluid and attracts water more then dot 4. must be bleed often to maintain top performance.
its a racing only application basically for full size cars and some race bikes.

motul rbf600 or equivlant is dot 4 and just fine. just keep fresh fluid in it.

I haven't mixed them. My rear is Dot 4 because I didn't change out the brakes. But when I changed out the front, I went with DOT 5.

[KARRDICK]

dot 5 has a higher boiling point but is a different type of fluid and attracts water more then dot 4. must be bleed often to maintain top performance.
its a racing only application basically for full size cars and some race bikes.

motul rbf600 or equivlant is dot 4 and just fine. just keep fresh fluid in it.

I'm sure I'll be fine with DOT 4. I just had a bottle of DOT 5 when installing the new brake lines. I'll go back to DOT 4 when it's time to flush out the DOT 5 that's in the reservoir for the front.

Perhaps Ray or Matt would know of the difference between the two in regards to pros and benefits.

[Wile_E_Coyote]

Dan, just focus on having a well prepared bike. Don't get caught up in these minor details. Just use the fluids that are recommended for your bike and you'll be good to go.

[speedjunkie]

the master cylinder, lines, and calipers have to be disassembled and cleaned. if this was not done the system is compramised. they are two seperate chemicals that dont mix. might even need to replace the piston seals in the calipers. for street use i wouldnt say anything but for track use it needs to be done properly.

[speedjunkie]

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

http://www.afcoracing.com/tech_pages/fluid.shtml

[Scarman]

the master cylinder, lines, and calipers have to be disassembled and cleaned. if this was not done the system is compramised. they are two seperate chemicals that dont mix. might even need to replace the piston seals in the calipers. for street use i wouldnt say anything but for track use it needs to be done properly.

Agreed! In fact never use DOT5 unless your bike specifically requires it. DOT5 is silicon base and is not compatible with DOT3 or DOT4 fluids, which are polyglycol based. Using DOT5 on a system that requires DOT3 or DOT4 could cause problems with rubber seals.

[KARRDICK]

crap... I may have to clean out the whole system.

[speedjunkie]

crap... I really should clean out the whole system.

fixed

i have rebuilt the brakes on my bike. not to hard.

[KARRDICK]

fixed

i have rebuilt the brakes on my bike. not to hard.

It's just going to be a pain in the butt and time consuming. Gotta open everything back up and then spray brake cleaner to flush the lines out if possible.

I'll just sit on it for now. Ran them last time at BW and was fine. Will run them again I guess. Will just have to keep a watch out for fading.

[speedjunkie]

thats cool. just my suggestion. dont have to.
just dont get brake cleaner on the caliper piston seals....

[wildbear]

Well, I don't know what all the fuss is about. I run DOT-DOT-DOT-DASH-DOT-DOT-DASH in mine. lol Sorry guys, I just could resist. :rolleyes:

[speedjunkie]

umm isnt that the SOS signal?? hhahaahaha jk

[sivad87]

Im a bit rusty on this subject as its been a few years.

DOT3/4/5.1 are glycol based, and attract water well. Basically the higher the number the higher the "DRY" boiling point and the "WET" boiling point (3% water approx i believe). 3 is basically street use, 4 performance use, 5.1 race use.

DOT5 is a full silicon based fluid and is NOT compatible with glycol based systems. reserved for race application due to the extra heat added to the system and the heat capacity of the fluid needs to be higher.

Typically just use what the system calls for and one of the best things you can do is KEEP WATER OUT OF THE FLUID!!! thats what causes issues because water lowers the boiling point and once the fluid boils its DONE! needs to be flushed. Gylcol is such a great attractor of water that is can leach the water out of the AIR and even through the rubber brake lines. Once a bottle of brake fluid has been opened you cannot store it, must be used or discarded.

Best thing to do is do a FULL flush with brand new fluid (not that old bottle you had left from last time ;)) and get a decent set of pads in there and you should be just fine.

You should never need DOT 5/5.1 unless you are running a porche/ferrari style brakes (carbon/carbon pads and rotors, ceramics, kevlar or the like) i dont know of any motorcycles that use these kind of brakes because its of no use on something the size weight and traction of a motorcycle. :word:

[Scarman]

Good information Ryan. Especially regarding not using old fluid and completely flushing the system with fresh stuff.

Gylcol is such a great attractor of water that is can leach the water out of the AIR and even through the rubber brake lines.


Although it does attract moisture, it doesn't leach moisture through the brake lines. Glycol brake fluid is designed to absorb moisture. The air in the braking system contains some amount of moisture (that space above the fluid in your reservoir) as well as the fluid itself. Thus to some degree all braking systems have moisture in them. If that moisture is allowed to separate from the brake fluid and collect around certain components (like caliper pistons) it will start corrosion. The other problem with moisture is it doesn't compress very well. Too much moisture in a concentrated area of the braking system will give you spongy brakes. Brake fluid is designed to absorb moisture and neutralize it's effect on your braking system by dispersing and suspending the moisture throughout the fluid. The fluid is also designed to change color in relation to it's moisture content so you have a visual reference as to when you need to change the fluid. Although... I just bought some DOT 4 fluid that said it does not change color with the moisture content. Not sure why, but no big deal for me as I bleed the brakes & clutch every year.

You should never need DOT 5/5.1 unless you are running a porche/ferrari style brakes (carbon/carbon pads and rotors, ceramics, kevlar or the like) i dont know of any motorcycles that use these kind of brakes because its of no use on something the size weight and traction of a motorcycle. :word:

I believe some Harleys require DOT 5. The big deal with DOT 5 is it doesn't absorb or disperse moisture and it doesn't lube like glycol. This makes your braking system more prone to corrosion and gives you spongy brakes so you need to change it frequently. Without the lubricating properties of glycol fluids, it's very bad for anti lock braking systems. DOT 5 is for very specific applications and should not be used unless your system specifically states "DOT5".

[sivad87]

Good information Ryan. Especially regarding not using old fluid and completely flushing the system with fresh stuff.



Although it does attract moisture, it doesn't leach moisture through the brake lines. Glycol brake fluid is designed to absorb moisture. The air in the braking system contains some amount of moisture (that space above the fluid in your reservoir) as well as the fluid itself. Thus to some degree all braking systems have moisture in them. If that moisture is allowed to separate from the brake fluid and collect around certain components (like caliper pistons) it will start corrosion. The other problem with moisture is it doesn't compress very well. Too much moisture in a concentrated area of the braking system will give you spongy brakes. Brake fluid is designed to absorb moisture and neutralize it's effect on your braking system by dispersing and suspending the moisture throughout the fluid. The fluid is also designed to change color in relation to it's moisture content so you have a visual reference as to when you need to change the fluid. Although... I just bought some DOT 4 fluid that said it does not change color with the moisture content. Not sure why, but no big deal for me as I bleed the brakes & clutch every year.



I believe some Harleys require DOT 5. The big deal with DOT 5 is it doesn't absorb or disperse moisture and it doesn't lube like glycol. This makes your braking system more prone to corrosion and gives you spongy brakes so you need to change it frequently. Without the lubricating properties of glycol fluids, it's very bad for anti lock braking systems. DOT 5 is for very specific applications and should not be used unless your system specifically states "DOT5".

Like i said its been a few years, i knew someone else would know :D Its true thats when you get you ass in trouble when you get water pockets in your lines, water boils and then oops faded!

see i cant think of one single reason a Harley would need to have DOT 5 except to make more money on their maintenance :word:

[MR1 Zig]

The big reason that DOT 5 was developed was that it had a higher boiling point. It was used for racing almost exclusively (cars). It works like DOT 3/4 but needs lots of flushing before being put in. The draw backs are that (as said before)it doesn't absorb water, so any water in the system will cause rust in a hurry. this isn't a problem for racers as they are constantly changing their brake fluid. Water that collects in the caliper will boil without much provocation and then you will get MAJOR fade.

If i'm not mistaken mixing of Dot 5 with 3/4 will get you goo that will block the various ports in the master cylinder and caliper.

If you are getting a bunch of fade with your stock setup AND you have recently refreshed your fluid AND your brakes are otherwise acting normally AND you are changing your fluid every 3 months then it might be ok to use DOT 5. Otherwise I'd recommend Castrol GT/LMA. It meets DOT3 and 4 standards, has a high boiling point, and seems compatable with all the seal materials outthere (i use it in my funny old cars Alfa, MG etc and on my Aprilia)

hth,