Brake Fluid

[triker mike]

Can you mix synthetic(sp) & regular Brake fluid? Same dot # 4

[N2PPN]

As a "generalized" rule NO.

The two major type of brake fluids are silicone based Hi-Temp (DOT5) and Glycol based (originally DOT3)brake fluid, which has undergone advances in it's own DOT3 technology to increase it's temperature rating (boiling point) for higher temp (racing) use. There IS a GLYCOL based "DOT 5" rated brake fluid which has a DOT 5.1 temperature rating, but it is EXTREMELY hard to find and rather expensive.

As a generalization you should not mix different DOT classes of the SAME BASED BRAKE FLUID together as you have now changed the characteristics of the fluid in your bike and they really won't mix together if you were to add the different type to the master cylinder as a "top off"... if you are doing a complete replacement (bleeding) of the entire brake system on your bike, as long as you keep the same fluid base, you can go from say a DOT3 to a DOT4 fluid providing you flush as much of the remaining older DOT3 fluid out as you can, as you replenish the entire system with the DOT4 fluid.

While brake fluid change is one of the required maintenance items on our bikes, unless you are an oval track rider or are especially hard on your brakes, the DOT rating of the OEM fluid in your bike will suffice and provide adequate protection.

The main advantages of synthetic brake fluids are added corrosion resistance and reduced water absorption. These two things are the dreaded enemies of all brake systems. The moisture from the air will be absorbed into the brake fluid and will eventually corrode the internal parts of the brake system if not changed at the specified intervals. The glycol based DOT fluids take the absorbed water and disperse it throughout the entire volume of fluid , this is why the brake fluid starts off kinda clear and starts to turn brownish as it ages and absorbs water... this is an indicator that it's time to change your fluid.

Silicone based brake fluids (remember the DOT5 stuff?) while having superior abilities to prevent boiling and other heat related fluid failures, DO NOT ABSORB WATER, they simply displace it.... the silicone fluid is LIGHTER than water and any water absorbed into the brake system (rain, high humidity, etc.) "falls" to the lowest point of the brake system (remember water is heavier than the silicone fluid?) and will corrode the calipers on the bike (usually the lowest point of the bike's brake system) as they will eventually be filled with water and not brake fluid.... also silicone fluid DOES NOT CHANGE COLOR AS IT AGES, AND HAS MOISTURE INTRODUCED INTO IT, so there is no indication that it is time to change your brake fluid until one spring you go to take the first ride of the season and your brakes lock up or give you trouble...

Read the label on the synthetic brake fluid bottle, if it is glycol based fluid and you bike has glycol based fluid in it, you can use it if you are doing a system bleed, but if you are just adding a little to top off your master, get the OEM fluid (or what ever is the same as what is in the bike now) and use that until it's time to bleed out the old stuff...


Rich

Just my $0.02 worth....

[triker mike]

I am not trying to mix dot classes i am mixing synthetic with regular both are dot4

As a "generalized" rule NO.

The two major type of brake fluids are silicone based Hi-Temp (DOT5) and Glycol based (originally DOT3)brake fluid, which has undergone advances in it's own DOT3 technology to increase it's temperature rating (boiling point) for higher temp (racing) use. There IS a GLYCOL based "DOT 5" rated brake fluid which has a DOT 5.1 temperature rating, but it is EXTREMELY hard to find and rather expensive.

As a generalization you should not mix different DOT classes of the SAME BASED BRAKE FLUID together as you have now changed the characteristics of the fluid in your bike and they really won't mix together if you were to add the different type to the master cylinder as a "top off"... if you are doing a complete replacement (bleeding) of the entire brake system on your bike, as long as you keep the same fluid base, you can go from say a DOT3 to a DOT4 fluid providing you flush as much of the remaining older DOT3 fluid out as you can, as you replenish the entire system with the DOT4 fluid.

While brake fluid change is one of the required maintenance items on our bikes, unless you are an oval track rider or are especially hard on your brakes, the DOT rating of the OEM fluid in your bike will suffice and provide adequate protection.

The main advantages of synthetic brake fluids are added corrosion resistance and reduced water absorption. These two things are the dreaded enemies of all brake systems. The moisture from the air will be absorbed into the brake fluid and will eventually corrode the internal parts of the brake system if not changed at the specified intervals. The glycol based DOT fluids take the absorbed water and disperse it throughout the entire volume of fluid , this is why the brake fluid starts off kinda clear and starts to turn brownish as it ages and absorbs water... this is an indicator that it's time to change your fluid.

Silicone based brake fluids (remember the DOT5 stuff?) while having superior abilities to prevent boiling and other heat related fluid failures, DO NOT ABSORB WATER, they simply displace it.... the silicone fluid is LIGHTER than water and any water absorbed into the brake system (rain, high humidity, etc.) "falls" to the lowest point of the brake system (remember water is heavier than the silicone fluid?) and will corrode the calipers on the bike (usually the lowest point of the bike's brake system) as they will eventually be filled with water and not brake fluid.... also silicone fluid DOES NOT CHANGE COLOR AS IT AGES, AND HAS MOISTURE INTRODUCED INTO IT, so there is no indication that it is time to change your brake fluid until one spring you go to take the first ride of the season and your brakes lock up or give you trouble...

Read the label on the synthetic brake fluid bottle, if it is glycol based fluid and you bike has glycol based fluid in it, you can use it if you are doing a system bleed, but if you are just adding a little to top off your master, get the OEM fluid (or what ever is the same as what is in the bike now) and use that until it's time to bleed out the old stuff...


Rich

Just my $0.02 worth....

[N2PPN]

Are both DOT4 fluids the same base (either Glycol or Silicone)??

Are you mixing them because you are bleeding the brakes and don't have enough of one or the other to complete the entire bleed?

As long as the bases are the same, you should be OK to mix them.

Personally, I would take a trip to Walmart or Pep Boys auto supply and get another bottle of whichever one I had more of... I personally don't like mixing brake fluids, and I always avoid using brake fluid from an open container,it is not good practice, as the fluid has already started to absorb moisture in it and could hasten the necessity of a bleeding job before much time has elapsed....

Either way, good luck and enjoy the day.... riding weather is on the horizon...

Rich

[thrasherg]

As mentioned, DOT4 products are made from 2 different base minerals(Glycol or Silicon), as long as you are mixing products from the same base mineral (You cannot mix the 2 different base minerals together) you should be fine, but it would be wiser to just purchase more of one product and use just that product for your entire brake system.
Some Glycol DOT4 fluids claim they can be mixed with normal mineral brake fluid (check the can), but silicon brake fluids CANNOT be mixed with mineral brake fluids..
Again, it would be best to just flush your entire brake line with a new dot4 fluid and only use that fluid, not mixing different fluids together, brakes can be handy things to have occasionally!!

Gary