Brake fluids are notorious. When I started in this industry, DOT 3 brake fluids were used everywhere, but they had a terrible reputation for damaging paint. For custom guys that was the kiss of death. Just the mention of bleeding brakes would raise eyebrows and cause skin to crawl.
Then suddenly we were saved. Somebody developed DOT 5 a silicon based brake fluid. You could pour it over your new custom paint job without a problem. We thought we were saved.
Then it started to get confusing. Another chemical engineer developed DOT 4 supposedly for high temp applications. What the hell?
Suddenly I didn’t know what to use where. Of course most manufacturers put their recommended fluid on the caps of all master cylinders, but that doesn’t work for some custom applications.
I’ve wanted to create a reminder sheet for brothers to follow for safe application of the various DOTs. I spoke to Eric Bennett at Bennett’s performance recently for a shop perspective.
“DOT 4 is bad for paint but it handles heat,” Eric said. “But DOT 3 is even worse on paint. You can’t mix DOT 4 with DOT 5. It will cause calipers to lock up. Stick with what it says on the master cylinder, if you can read it. All European makes use DOT 4 now.”
I spoke to John Dunne the Spectro Oils tech expert and he cleared up lots of issues.
I will list all of the Spectro scientific data, but here’s the drill.
DOT 3, DOT 4, DOT 5.1 and even DOT 600 are a different compound from the silicone based DOT 5.
Harley and military applications use DOT 5 because of the more flexible silicon based compound, which gives the rider a softer feel and won’t mess with paint.
DOT 3, 4, 5.1 and 6 are made up of a chemical compound that can handle more heat and give the rider a more immediate response. It’s meant for tougher application and most European makes use DOT 4 now. The higher the number the more pure the mixture, but there’s a catch. You can’t leave a DOT 3, 4, 5.1 or 6 open. It will collect moisture, which will cause corrosion and affect the boiling point.
Perhaps mixing DOT 5, Silicone based material with any of the others would be like adding water. That’s not the case. DOT 5 will not mix with the other DOTS.
If the water or DOT5 causes the material to expand, it could lock up your brakes. Don’t co-mingle fluids,” said John Dunne.
I spoke to Rick over at Performance Machine. He mentioned a couple of helpful items. Harley recently switched from the softer DOT 5 to the more performance oriented higher heat tolerant DOT 4. “DOT 4 won’t compress,” said Rick. We confirmed the years at the factory with H-D:
These models all use DOT 4: ’06-later VRSC™, ’07-later XL, ’06-later Dyna and Softail, and ’05-later Touring models.
Starting in 2005 with certain touring models, Harley-Davidson began to spec DOT 4 brake fluid by 2007 all models were using DOT 4.–Jenn
Rick also pointed out that DOT 3 and 4 can mix. They are basically the same chemical make-up but DOT 4 is more pure. Mixing will harm the purity but won’t cause major issues.
If you open a master cylinder and don’t know what resides there both DOT 3 and 4 will mix with water, but DOT 5 will not and separate from the water.
Eric mentioned a caliper that locked up with DOT 4 mixed with DOT 5. Rick explained, “The mixture will cause the fluid to coagulate and block the tiny master cylinder return hole which will cause the caliper not to release.
Here are the Spectro Specs:
Designed to surpass all DOT 5 specifications and requirements, Heavy Duty DOT 5 is the ideal brake fluid for all Harley motorcycles specifying a DOT 5 fluid but it’s better, because this fluid beats specs in every way. Check the master cylinder caps and note the models and years above.
It meets full OEM requirements, and should be used according to manufacturers’ instructions. Do not use when a DOT 5.1 or DOT 4 fluid is specified! Non-hygroscopic, it will not absorb water; it will not harm painted surfaces, and it is formulated specifically for Harley and Big Twin applications. Dyed purple. It exceeds all known OEM and Harley-Davidson warranty requirements.
Golden Semi-Synthetic Supreme DOT 4 Brake Fluid Used in all late model Harley models
Designed to meet the most demanding high performance conditions in today’s braking systems. Suitable for ABS systems, this moisture resistant synthetic fluid has a dry boiling point of 271º C (520º F). Golden Supreme DOT 4 surpasses DOT 4 specifications and meets European DOT 5.1 specifications.
This borate ester polyalkyglycoalkylether fluid is formulated to provide the highest possible resistance to fluid boiling and degradation in high performance and racing conditions, Spectro® DOT 4 Racing Brake Fluid “600” is your best defense against “lost” lever pressure caused by progressive heat buildup. Spectro DOT 4 surpasses DOT 4 specifications — with a 312° C. dry boiling point, it solves virtually any fluid boiling problems hard riding can create. Excellent for both on and off-road applications.
Spectro Oils Contact info:
P: 203-775-1291 x108 C: 646-302-3484
A: 993 Federal Rd. Brookfield, CT. 06804
Sources:
Spectro Oils
Biker’s Choice
Bennett’s Performance
Performance Machine
