The care and feeding of hydraulic systems

[redjay]

Can you mix Dot 4 synthetic and Dot 4 non synthetic ?

[almsy]

Originally Posted by RACNRAY

Most rotors on our skoots are made of a stainless steel aloy, very hard and tuff material. Minor grooving is normal on m/c rotors, when replacing pads we always sand the rotors with 80 grit to remove the glaze and smooth out normal wear.

It's always a good idea to measure rotor thickness to ensure theyr are not worn past the minimum.

RACNRAY

thanks for that info. I was also wondering about how deal with the rotors during a brake pad change

[smokey]

Originally Posted by redjay

Can you mix Dot 4 synthetic and Dot 4 non synthetic ?

apparently from the article I read, yes. I guess it is kind of like mixing dino oil with synthetic oil.

[RACNRAY]

I have a 2020 Voyager in the shop for the initial service with about 700 miles on it.
Again here is a prime example of the need to flush and bleed hydraulic systems even on new skoots, and regularly there after.
There was some air in the rear line. The fluid in the 2 front m/c's was already dark, and in the case of the clutch almost black, even what came out the slave cylinder.

RACNRAY

[redjay]

The master cylinders/calipers could have been assembled for a while (complete with hydraulic fluid) as a sub assembly before they are put on the bikes on the assembly line ? Then when the bikes are assembled how long do they sit around before they are shipped ? Then they could sit in the dealership for 6 months or longer, but you already know that.

[RACNRAY]

Originally Posted by redjay

The master cylinders/calipers could have been assembled for a while (complete with hydraulic fluid) as a sub assembly before they are put on the bikes on the assembly line ? Then when the bikes are assembled how long do they sit around before they are shipped ? Then they could sit in the dealership for 6 months or longer, but you already know that.

YES...of course I already know all of this. Those mentioned above are a moot point as explained below.

My goal is to inform the "less knowledgeable", 44 years as a m/c tech I know what most do not nor ever will and brake maintenance, or I should say "lack of" unnecessarily pays me well. This would be considered by most as a "brand new skoot" and a flush n bleed of the systems would never be a thought.

This thread, as in most of my threads are knowledge I share as a "public service announcement" and one way I give back to a community that has supported me for 44+ years.

RACNRAY

[redjay]

My reply was not directed at you but rather a reinforcement of what you said for others that read your post.

[spby52]

Originally Posted by RACNRAY

I have a 2020 Voyager in the shop for the initial service with about 700 miles on it.
Again here is a prime example of the need to flush and bleed hydraulic systems even on new skoots, and regularly there after.
There was some air in the rear line. The fluid in the 2 front m/c's was already dark, and in the case of the clutch almost black, even what came out the slave cylinder.

RACNRAY

Good stuff Ray....did mine after a year was bad....wish I had looked this up on the forum....thanks

[DragonLady58]

Put in speed bleeders and change out fluid every so often....
When brake fluid is used, every time you pull the cap off, the fluid grabs water out of the surrounding air and contaminates it. Change fluid every couple of years....
Especially in high humidity enviroments....

[Sabre-t]

Originally Posted by redjay

Can you mix Dot 4 synthetic and Dot 4 non synthetic ?

I know the above is an old post from this thread, and does not directly relate to RACNRAY's posts, but I would like to comment on it.

All DOT brake fluids are synthetic! Some say synthetic on the label and others, don't but they are all synthetic.

DOT 3, 4, and 5.1 are all polyglycol ether based. They don't have to be, but the industry has made it a defacto standard. The Federal DOT requirements do not require it, but use a standard laboratory glycol in comparison and compatibility tests.

DOT 4 and 5.1 have borates in them to raise the boiling points. These borates can swell the seals of DOT 3 based systems, so should not be used in a DOT 3 system unless all of the rubber parts have been upgraded to handle the borates.

DOT 5 is silicone based. May refer to DOT 5 as synthetic and the glycol based fluids as non synthetic. Again, they are all synthetic. DOT 5 should NEVER be mixed with the other grades. It requires special seals. It has also proven to have very poor performance. Even though it does not have the issues with absorbing water that glycol based fluids do, oxygen dissolves easily in it making it more compressible and therefore reducing braking efficiency and increasing corrosion. That is one of the reasons DOT 5.1 was developed. DOT 5.1 has higher boiling characteristics than DOT 4 but without the compressibility and rubber degradation issues of DOT 5.

The DOT standard does not require brake fluids to be compatible with each other. It does not even require that 3, 4, and 5.1 be glycol based. There are boiling point, chemical and heat stability, color, pH, and corrosion requirements.

A particular glycol based fluid must be compatible when mixed with the glycol lab standard, but this does not guarantee that every glycol based brake fluid is compatible with every other one, and, in fact, there have been issues with mixing fluids from different manufacturers (even though the same grade) gelling in some brake systems after some use. It is generally recommended that you completely flush out old brake fluid before the final fill with new brake fluid of a different brand, even if they are the same grade, to avoid the possibility of the fluids reacting badly to each other.

If your vehicle specifies DOT 3, you should use DOT 3 unless you are absolutely certain that all of the rubber parts have been upgraded to handle the borates in DOT 4 or 5.1.

If your vehicle specifies DOT 4, you can use 4 or 5.1.

If your vehicle specifies DOT 5, you have my sympathies, but you should use DOT 5.

When choosing a brake fluid of a particular grade, look at the wet and dry boiling points. Then stick with that particular brand and grade unless you plan to do a thorough flush on the next change. I use Bosch ESI6-32N that has dry/wet boiling points that are higher than the minimum DOT 5.1 standard but costs much less than DOT 5.1 fluids, even some with lower boiling points that just meet the 5.1 requirements.

Change your brake fluid every two years regardless of miles ridden/driven. Brake fluid will absorb moisture which will reduce the boiling point and cause corrosion.

If you find that you need to add brake fluid between those changes, you have a leak which needs to be addressed. You should never have to add brake fluid to a properly working brake system. Every time you open the reservoir to add fluid, you are letting moisture into the system. If you are not going to address the leak, at least make sure you add fluid from a newly opened container. Brake fluid that has been opened for more than a few weeks can have absorbed enough water to lower the boiling point considerably.

[DragonLady58]

What Sabre-T Said! If you've opened a fresh bottle of Brake Juice to top off your system after a fluid change, after a few weeks....dispose of it! Old brake fluid into a newly rebuild brake system only undoes what you've done....opens your brake system to corrosion and possibly seal/o'ring failure....
Always write the opening date on bottle. When it gets too old, I use it for paint stripper/degreaser on engines before I Gunk it. Rest, I pour into some old kitty litter, letb it sit for 3 or4 days, it evaporates. I've know folks to heat it to about 200 degrees to boil/evaporate water outta it, then reuse to FLUSH OUT systems, then discard it....

[Sabre-t]

I would not recommend boiling brake fluid to "rejuvenate" it. Moisture in the brake fluid will break down the corrosion inhibitors, pH buffers, and other additives. Since the glycol based brake fluids are, well, glycol based, they break down in the presence of water and heat into organic acids, just like glycol based coolants do. Those acids attack the metal components of the brake system. Boiling off the moisture will not replace those additives, but the acids will remain, or will form if/when any remaining corrosion inhibitors are depleted.

[smokier]

Well, THAT was a lot of good info. I have been doing those bad things for years. No more BIG BOTTLES to sit on the shelf for me. I change all fluids every other season. However, had been buying big bottles and letting them sit there for top offs and changes until a another bottle was needed. Thank you guys for the education.

This is a perfect example of exactly why I love this forum.

Ride safer,
Smokier

[andyvh1959]

DOT 3, DOT 4 and DOT 4 synthetic can all mix. DOT 5 is it's own type and cannot be used in a brake system not designed for DOT 5 (I found out the hard way decades ago). Its not that DOT 5 won't mix with the other fluids, DOT 5 ATTACKS the seals throughout a system designed for DOT 3 or DOT 4 and causes significant swelling/softening of the seals. Brake drag is the usual result and it can only be solved by a complete system tear down and all new seals throughout the system installed. DOT 5 can also attack the inner tube of the brake hose and cause it to soften/swell to the point it can act like a check valve and not allow complete pressure to bleed off and cause brake drag big time.

Speedbleeders are a great improvement service/maintenance wise. Standard OEm brake hoses, other than the teflon inner tube/stainless steel braid hoses, are generally the cheapest hose use on a bike. Other than trying to keep a bike looking stock i would never waste the money to replace OEM brake hoses with OEM brake hoses, it simply is not worth it, and aftermarket S/S braided hoses are a big improvement worth every penny.