mixed brake fluid

[84CUCV]

working on my friends suburban. its a 89 3/4 ton. in the master cylinder there is dark fluid on the bottom and light color fluid on top. truck stops fine.

must be two different fluids right? should we flush it out? a 89 burban would be dot 3? thanks

 

[dremu]

The military apparently used DOT5 -- the synthetic stuff -- on the CUCV's, but by the time I got mine it had been flushed and switched back to the regular stuff.

Otherwise, yep, all of our trucks use the regular stuff. (IIRC, DOT4 and 3 can be mised, but you rarely see 4.)

-- A

 

[4X4HIGH]

The dark stuff at the bottom is probably nothing more than old dirty fluid. Like Aaron said, you can mix DOT3 and DOT4 but not DOT5 as that is synthetic.

 

[nvrenuf]

I'd suggest pulling the m/c lid and try wiping the side of the resevoir with something to see if it's just a dirty film. Over time as pieces in the system break down a dark film can develop that you can see thru the plastic tank.

I'd probably flush it either way.

 

[84CUCV]

going to flush it. how should i go about doing it? thanks

 

[dremu]

going to flush it. how should i go about doing it? thanks

Turkey baster to get out most of what's in the reservoir, refill with clean fluid. Get the crud at the bottom out with a paper towel.

Then just bleed the system as usual. My choice is the garden sprayer pressure set up.

-- A

 

[kevin400ex]

brake fluid (dot 3.4) turns black when its contaminated with moisture. flush the system with new fluid and your good.

 

[84CUCV]

thinking about using air to blow out the lines too

 

[badmix]

thinking about using air to blow out the lines too

Thatll never happen.

To properly flush the system, go to the back right (furthest from the master cyclinder) and you can go about it a few ways:

1) get a vacuum pump designed to PULL fluids and attach that to the bleed valve

2) Gravity bleed the system, open up the bleed valve and let it drip out, but you have to keep putting fluid in the master cyclinder so you dont run it dry, get air bubbles or air in the line.

3) get myty vac. this is what I use, its basically a one man bleeding contraption that works well.

 

[84CUCV]

3 sounds good. where did you get it? price? im about to go to advanced auto. see if they have it

 

[YZEATER]

sears has them for sure, just seen one last nite.

 

[dremu]

I've never had success with vacuum bleeding, and I'm too impatient for gravity bleeds.

Pressure bleeding, option #4 in that list of three, is far superior IMO

http://www.bmw-m.net/TechProc/bleeder.htm

Rather than a cap for the master, I use a piece of 1/4" plate with rubber on the bottom. I welded a hose fitting onto it, and with a coupla pieces of scrap steel, some J-hooks and chain ... voila:

The other half is pretty simple...

Then a piece of tubing on the far end into a jar collects the crap. I tell ya, when you see the old fluid come out you'll go ... it looks like iced tea if you're lucky, and Coke if you're not

-- A

 

[84CUCV]

thanks #4 it is.