Dirty Brake Fluid

[gerviswaddell]

Hey there,

The last time I bled the brakes, (due to insufficient braking power) All units bled out clean and relatively bubble free except the drivers side rear. The fluid was dark (very dark at times) but was only this way for the first couple of pumps, then it ran clean again...So i was thinking that the dirty fluid was only inside the brake cylinder itself, which makes me also think that there is some kind of leak in there allowing debris or water or whatever, to get inside and spoil the fluid within.

Any thoughts? I am willing to replace this part, but would like to know if I should look out for any other issues down the lines (literally).

Thanks,

-GW

[Petros]

brake fluid has a "shelf" life, it brakes down over time and should be fully flushed every 2 to 4 years (depending who you listen to). Likely this is from oxidation, which allows corrosion inside the cyl and line. Unless it is really bad (causing the wheel cyl. to leak), simply bleeding until you get fresh fluid should be fine.

If you want to make sure, pull off the drum and peel back the wheel cyl. boot, if it is dry you are good. If there is any brake fluid, either rebuild the cyl or replace it.

I have seen brake fluid so far gone it formed crystals like brown sugar, I doubt yours is anywhere near that state.

[danzo]

All units bled out clean and relatively bubble free except the drivers side rear. The fluid was dark (very dark at times) but was only this way for the first couple of pumps, then it ran clean again...So i was thinking

Most likely the brakes simply weren't previously bled properly or someone just forgot to bleed that wheel. I would think a leak would tend to let fluid out (remember lots of pressure builds up inside the lines) rather than let dirt in.

brake fluid has a "shelf" life, it brakes down over time and should be fully flushed every 2 to 4 years (depending who you listen to).

Very good idea. Some manufacturers recommend replacing fluid annually, and it's common practice for mechanics to replace the fluid every time they do a brake job. Interestly, in the "track day" rules I've encountered, the tech inspector wants proof that the fluid was changed within six months.

Old brake fluid that has absorbed a lot of moisture can boil, which is very scary. When I autocrossed my old Triumph the "gawd knows how old" fluid boiled at the end of a lap. Hydraulic braking was immediately gone, the pedal simply went all the way to the floor, and the only thing to do was pull the aptly named emergency brake. Years later when I was in New Mexico driving my motorhome down a mountain, the only thing I could think of was that boiled fluid moment. Absolutely the scariest time I've ever had behind the wheel, and I've done some crazy/stupid stuff while driving. Back when I was young and spritely of course.

My next and first brake job on my T4wd will include replacing all the soft lines, wheel cylinders, drum hardware and of course the pads, rotors and fluid . Cheeep insurance that may save someone's life.

[ARCHINSTL]

Interesting - I just bled Goldie's brakes (in conjunction with removing the backing plates while doing the rear axles).
I had replaced all brake parts (save MC and hard lines) back in '06.
I got very dirty fluid out of the two rear cylinders. I had to remove the two bleed screws on the fronts, as their little holes at their base in the calipers were clogged with crud and nothing could be sucked out, even with the Mityvac at maximum vac. One even had a bit of rust on the point.
I was surprised, as when I did the job 4 years ago I ran over two quarts of fluid through the system - and the only espresso in the system at the time was in the hard lines and part of the MC. Additionally, the cap of the MC was only off a couple of times for less than a minute each to check the fluid level - and it never needed any fluid replenishment.
It made a believer of me to flush annually.
Tom M.

[takza]

I'd guess that when you let up on the brake pedal the rear rubber cups allow a certain amount of air or moisture into the wheel cylinders? Under compression they seal well...when you let up on the brake...less seal? Or maybe just substandard parts?

[Petros]

it is likely just the oxidation of the fluid. ONce it comes in contact with moisture, it eventally works its way into all of it, and cause oxidation of all the parts it comes in contact with. That is why it should be flushed out regularly, it is not only safer for the fluid, but also makes all the parts last longer.

[splatterdog]

Don't forget rubber caps for the bleeder screws. Keeps the crud out and helps prevent seizure.

[ARCHINSTL]

I've been doing the cap thing for - uhhh - many years on bleeders and Zerk* fittings. Ever since my '52 Singer had 34 (!) grease points.
The rear brakes were mechanical, with a clever system so that if the front hydraulics failed, the rears would still work - and vice-versa, too! Talk about linkages! And keeping them working during the Winter was a challenge, and not just from salt - several times the rears did not work because of being frozen from ice!
Ahh, those English...
Tom M.

* OT, but - when I got my first Morris, my Grandfather asked me if it had good old Alemite fittings or those new-fangled Zerk fittings. Huh? Zerk was all I had ever heard of - they were patented in 1929. Gpaw was born in 1885 and always worked on his cars, as did most men back in the teens-'20s-'30s. He was surprised that I had to grease the fittings "only" every 1K miles...
He also worked at the very first "gas station," right here in STL, back in 1907.

[gerviswaddell]

Thanks for all of the replies, The funny thing about this is that I have done all of the bleeding, and the system has been flushed fairly recently, (six months ago) and I have seen this dirty fluid (only like a shot glass full) each time I bleed it. Wondering If I should do those rear flex hoses...and the brake cylinder. Im going to upgrade to newer tercel brakes soon anyhow...

thanks again!

GW

[Petros]

There is only one rear flex hose, if it looks questionable change it, it is not too expensive. The rear wheel cyl. are relatively inexpensive too, if there is any moisture under the cups, or corrosion, change them too.

[4wdchico]

There is only one rear flex hose, if it looks questionable change it, it is not too expensive. The rear wheel cyl. are relatively inexpensive too, if there is any moisture under the cups, or corrosion, change them too.

My '85 t4wd has two rear brake hoses.

[takza]

I've been doing the cap thing for - uhhh - many years on bleeders and Zerk* fittings. Ever since my '52 Singer had 34 (!) grease points.
The rear brakes were mechanical, with a clever system so that if the front hydraulics failed, the rears would still work - and vice-versa, too! Talk about linkages! And keeping them working during the Winter was a challenge, and not just from salt - several times the rears did not work because of being frozen from ice!
Ahh, those English...
Tom M.

* OT, but - when I got my first Morris, my Grandfather asked me if it had good old Alemite fittings or those new-fangled Zerk fittings. Huh? Zerk was all I had ever heard of - they were patented in 1929. Gpaw was born in 1885 and always worked on his cars, as did most men back in the teens-'20s-'30s. He was surprised that I had to grease the fittings "only" every 1K miles...
He also worked at the very first "gas station," right here in STL, back in 1907.

I actually use some moly grease on the threads and ends of any bleeder valves I remove and put back in...I figure there will be positive pressure to keep the grease away from the brake fluid as they are bleed.

And...I think I can remember the tail end of when the guys at a gas station wore uniforms and several of them "serviced" your car when you pulled in for gas.