dark brake fluid = bad? contaminated?
Should I go ahead and change it if its dark?

To change it would I just bleed the brakes completely until the reservoir and lines are dry? Then refill?

If my bike says dot 4 only can I use Dot 5?
No? bad idea?
thanks alot

 

yuppers!!

dark fluid is almost always a sign of contamination, its typically not anhydrous at this point, and can rust pistons and ferrous metals in the brake system..

the 4 and 5 rating is basicaly a boiling point number in consideration to the hydroscopic affect brake fluid has..

dot 4 is glycol based, while dot 5 is for silicone


DOT3DOT4DOT5

Dry Boiling Point 401F 446F 500F

Wet Boiling Point 284F 311F 356F


dot 5 will feel ever so slightly spongier since its actually very slightly compressible, and this will relate tobrake feel.. may not translate to much tho on a bike.

 

I wouldnt touch Dot 5 just because its notquite the same. if its anything like a car, which it is,the seals will get ruined in time, if you use Dot 5.
So go for Dot 4, its more than capable of doing the job.
As for bleeding the system, i would bleed it normally,just keep filling the reservoir as u bleed, youll know your all done once the colour of the fluid is nice and clean with no chucks of cr*p in it.
i hope i was a help. good luck

 

why the crap does my bike have 3 dot 4 reservoirs?? lol

 

2 front discs and one back? what kind of bike is it?

 

Being a hydraulic instructor for the last 4+ years and in the career field for 15 now, let me throw my hydraulic hat on for a second here.

Hydraulic fluid is not an area to generally be messed with. The DOT rating for the fluid your system requires is there for a reason. This applies to brake systems, transmissions, and anything else that runs on hydraulic fluid.

Don't get confused here, thinking that since the "5" is a bigger number than a "3" or "4" that it will perform better. There are different qualities to that fluid, i.e. viscosity and boiling points but the biggest problem here lies in the chemicals that make up the fluid. Some chemical properties of each DOT rated fluid may/won't work together, and it's not the mechanical components that will suffer -it's the seals in that particular systemthat aredesigned specifically to handle the DOT fluid that the manufacturer calls for.

Now there are a few companies out on the market that manufacture synthetic brake fluids that are a suitable substitute for your DOT-whatever fluid your bike requires. This is about as far as I'd venture off of what the label says on your reservoir cap.

Unfortunately, you'll have to look other places for performance upgrades.

 

thanks
I'm trying to bleed the breaks. I bled the front one completely and got it dry. I put my plug back in and refilled it with dot 4.

So, I apply brake pressure and leave it in. Then unscrew the plug a little to let the air and fluid out. Then screw the plug back in.
<Repeat>
Its NOT building pressure!!

What am I doing Wrong?

thanks alot

 

comp, thanks for the great info bro! i'm by far not a hydraulics expert.. lol


ez: you may have to vacuum bleed the brakes til you get some fluid into the pistons...if the fluid wont gravity feed with the bleeders opened, and you don't have a "mity-vac" you can ghetto rig a shop vac to get the fluid into the piston..

the fluid will not draw itself thru if it has nothing to pressurize itself against, and create a vacuum on the reservoir for the master cylinder.. make sure only one bleeder screw gets cracked when you're bleeding, otherwise you're just neutralizing the pressure difference you'd essentially be building.

you may get lucky with a gravity bleed with both bleeders opened... pump the master slowly a few times to promote fluid migration.. if you finally get fluid at the screws, shut em both, then focus on one side, and pump em up, then crack the 1 screw on the side you're working on. after a few goes at this, go to the other side and do the same.. it's gonna take a while...

keep us posted, and if anyone else has a better idea, please tell me!! i can always use good tips as well...

 

TODAY:
I got nothing, even with my vacuum bleeder. Even though I was Over the recommended 10 mm/Hg vacuum (which youre not supposed to go over).I mightve gottenjust a few Drops max
I guess I was being impatient and yes, I was pumping fast.

completely true... I noticed this when I was using my vacuum bleeder.
Because I had both opened I couldnt build up vacuum and I could hear the air being sucked in

reservoirs are full
I will have another go at it when I get off work
I've NEVER had a problem bleeding car brakes but I guess I'm a newb or something
MAN, it SUCKS sliding around on your worn out rear wheel!!! (or fun I cant tell which cause its kinda scary lol)
thanks for being so helpful

 

man.. i had a hell of a time once with an '89 FZR 600 that i had to service.. it was realbad.

took FOREVER to get any feel from the lever.. i think the master was shot personally..

i usually don't have any trouble with bleeding with a mityvac... thats odd you're having such a "stellar" time with your bike.. i wish i had a suggestion for ya... maybe bench-bleed the master? just to ensure the master is not air-locked, and that the seals are good.

keep us posted bro! gooooood luck on that.