Brown brake fluid

[B.barket]

hey guys. Just took a a look at my brake fluid in my 84’ jimmy for the 1st time and it’s brown. How much is ok to siphon out of the master cylinder?. Don’t want to introduce air into the system by pulling to much out. The fluid has got to be pretty old to be as brown as it is so assume I probably have dot 3 in there and should top off with that?.

 

[Bent77]

Dot 3 is fine

If you don’t actuate the brake pedal, the level on the pressure side of the cylinder won’t change. Though replacing it may not do much, you can siphon it out and replace with new

 

[sweetk30]

such as much as you can .
clean paper towel and whipe out the resivor .
refill with dot 3 or 4 only .
best at this point to blead the system starting at r.r. to l.r. to r.f to l.f. and keep a eye on the level and fill as needed . keep going on each wheel until new color fluid is coming out .

do NOT push the pedal to the floor doing this on a older master it has been known to cause problems and take out the master from all the junk built up over the years . just go 2/3 to 3/4 max travel and you only need light pressure for a fluid swap out .

the old nasty fluid swap will also prob get you a better pedal feal when done as old fluid brakes down and also holds moisture and don't work as good as old .

years ago i had my atv that sat for years and i got it going . the brakes felt like crap even with a new set of pads . i just swapped the fluid as i said how above and i got perfect pedal back after this .

 

[eric67camino]

Best thing to do is a full flush. It's generally recommended to flush the brake fluid every couple years (not that I keep up with thay myself).

Also, don't mix fluid types. They don't play well with each other.

 

[sweetk30]

dot 5 is the odd ball out of the group for the most part . it will make a semi solid mix of fluid and swell up every piece of rubber to leak and be trash . unless the system is set up for dot 5 to begin with .

 

[B.barket]

Thanks fella's.. I guess I'd better get on this asap. I figure the brown fluid is due to moisture in the system which probably means rust in the system correct?. Off to find a pop bottle and some clear hose for the one man DIY bleeding method. If it is moisture/rust that's responsible for the brown fluid. I'm cringing at the thought of seized bleeder screws!.

 

[diesel4me]

If the bleeder screws had a rubber cap over the end of them,that will increase your chances of success getting them to unscrew without breaking off..
If they didn't have a cap over them,I'd use a tiny drill bit to ream out any rust and dirt from the bleeder hole and squirt some penetrating oil in there with the spray nozzle straw,and heat up the caliper or wheel cylinder with a torch briefly around the screw ,if your lucky they will come loose without breaking..then you may have to finish cleaning the bleed hole out or replace them (best option) so the brakes can be bled..

Some brake fluid turns dark as it ages too,so it may not be moisture,but chances are its due for a flushing anyways,if its been in there more than 3 years..up here brake lines rot and pop about that often,so most vehicles have relatively "fresh" fluid in them..

 

[yblow]

best at this point to blead the system starting at r.r. to l.r. to r.f to l.f. and keep a eye on the level and fill as needed . keep going on each wheel until new color

^^^that's what I do. I just add dot4 synthetic and bleed out the old crap till it flows clear.

 

[B.barket]

hey guys. I picked up 2 liters of dot 3 and some 3/8" clear hose.. I was just guessing at the hose diameter needed. Would you say 3/8 is the correct size to get a decent seal on the bleeder screws?. I'm hitting the bleeder screws with PB blaster all week this week so I can see about taking a run at this on the weekend.

 

[Wes Harden]

more like 1/4 or 3/16th 3/8 may work if you push over the hex but you would need to remove to use a wrench on the bleeder

 

[kallisti5]

The M1009's Military K5's come with DOT 5.
When I replaced the master brake cylinder + rubber lines ~ 2 years ago (because 30+ years old and filled with a lovely sludge of dot 3 + dot 5 an unknowing mechanic added for the previous owner) i switched to dot 3 and flushed well with clean dot 3.

Converting from dot 5 -> dot 3 isn't the boogie man it seems, The calipers have had both, and seem to be ok still (knock on wood)

I also put "speed bleeders" on my K5, they're magic and a lot easier than the two-man bleed.

A picture is worth a thousand words:

 

[sweetk30]

how did it even work before ? @kallisti5

 

[diesel4me]

Who peuked in the master cylinder ?...

I've seen some grungy ones in vehicles that sat in the junkyard for years,but maybe not THAT bad!....