Hey everyone heres the backstory:

upon taking my 99gt our of winter storage, I gave it the once over to prepare for the thousands upon thousand of miles i was going to rack up this summer. I changed the oil, checked all the fluids/filters/plugs ect and everything seemed to have held up very well. The car ran like new
From there i drove the car around all day and there were no issues whatsoever (even after several light thrashings on a twisty road in my area). The following day I was coming back from my friends house and my clutch pedal stuck to the floor. uh oh there goes my slave cylinder, or so i thought. It ended up being my clutch master. I changed both. I also bled the whole system about 4 times thoughout the the whole troubleshooting process. In the end the celi swapped gears effortlessly again

on to my question:

the fluid i filled the system with was DOT III CLEAR fluid (as stated on the master cyl cap). now however, this clear fluid has turned a fantastic shade of brown


compare this with my brake master cylinder where i used the same brand around the same time i did my clutch ( i was on a roll)



nice and clear

so why would the fluid in my clutch system turn brown, while the fluid in my brakes stayed looking like new?
at first i thought that it may have been some gunk inside the lines that has since broken up, but that doesnt make sense since i bled the system FOUR times. should be as clean as it gets in there

could it possibly be that the master and slave cylinders are wearing in, thus dirtying up the fluid a bit?

input and opinions are appreciated

-Luke

bump

is it possible that i've stumped the 6gc community?

that is odd, how bad black was the old fluid? it is possible that the other cylinder is on its way out and thats just some sediment stirred up from inside of it, inside the lines, and inside the reservoir.

Take out some of that "dirty" fluid and put it in a small white Dixie cup. Then take out some of the brake fluid and put in another Dixie cup to the same height. Now compare.

Brake reservoir is shallow. Clutch reservoir is quite deep, so you are seeing a tall column of fluid, which will look darker.

Just like a full cup of tea will look darker than just a little bit of tea on the bottom of a white cup.


If equal quantity still looks dirty, then you need to keep flushing until all dirt is gone.

It's definitely dirty, it shouldn't look like that.

Is the master cylinder new, used, re-manufactured, Toyota or aftermarket??

There is a chance the brake fluid is breaking down the seals in the new master cylinder. Also check the condition of the rubber clutch line, maybe the fluid is breaking down that line from the inside.

both the master and the slave have been replaced with new autozone units. I tried getting toyota parts but they could only get the master and that would take over a week (i needed the car rlly badly). also, keep in mind that i flushed the hell out of the system to clean it out because it was dark before as well.

the idea that one column of fluid is darker than the other due to the depth of the reservoir is a good idea but does not apply in this case. were talking about an inch or two of difference, not the several hundred feet that it would probably take to make such a dramatic effect. you cant tell in the picture but the fluid gets its color from tiny microscopic specs of...black.

what rubber line? theres a rubber line? what you're saying makes alot of sense hurley, care to eloborate?

This post has been edited by enderswift: Jul 26, 2009 - 2:39 PM

found the rubber hose. obviously its purpose is the allow the engine to move without sending the shock to the hard lines. I checked it out and it looks great. no hard spots, no spongy spots. all around clean.

what else could it be??

The black specs can only be bits of the rubber from the clutch hydraulic system (unless something from outside got in the system of course). There really isn't much else it could be besides the seals in the master cylinder or the rubber on the inside of the rubber line. The clutch hydraulic system is very simple and there isn't much to it, I'm sure you are well aware having replaced both the master and slave cylinders, but it goes master cylinder-->hard line-->rubber line-->hard line-->slave cylinder... that's it. Most likely its the cheap seals inside the autozone master cylinder. The only other thing it could be is the brake fluid you used is more corrosive to the rubber things in the system than what was in it last, which will also cause problems later, but as you said you used the same fluid in the brake system and that's just fine.

This post has been edited by hurley97: Jul 26, 2009 - 5:02 PM

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haha seriously, there is only so much that can go wrong in a system like this. well, I decided to bleed the whole thing all over again and you would not believe the gunk that came out, imagine the look of fine steel shavings in a blown engines oil, only black. If thats the result of piston seal deterioration then i want my money back; cuz that is not gonna last more than a few months at this rate. Cant wait to lose control of my clutch making a left turn in a busy intersection . You know I was suspicious of the fluid too, but going with the non toyota parts made me spring for the highest grade DOT III valvoline has to offer. Id imagine any defective/overagressive fluid would cause enough havoc for me to hear about it on the news by now. My new theory takes into account my original suspicions and what people have suggested thus far; its that the autozone parts have to go through a break-in period where the pistons wear themselves into the cylinder to ensure a perfect seal. maybe they make em a tad too big for this exact reason. I was otherwise very impressed with the build quality, from the casting of the metal to the quality of all the plastic bits. Either way, there is fresh fluid in there now, and im going to keep a close eye on things and post the results. Maybe someone will run into the same issue one day.

moral of the story: always, always buy OEM parts.

thanks to everyone who chimed in and offered their opinion. this is why 6gc rocks.

-Luke

This post has been edited by enderswift: Jul 26, 2009 - 7:04 PM

my cars the same way the master cylinder got really dirty when my clutch went out, and its been black since then, my dad is a MDT for toyota and he said its nothing to worry about

update:

its been less than a week since i flushed out the the old nasty fluid with some fresh dot III.

guess what. its turning dark again! what is going on???

Hey everyone, I'm bringing this thread back because I still have the same issue and have been doing research on what could possibly be the cause

1: It seems this occurs across all makes of cars and bikes too.

2: Some people assert that the brake fluid reacts with low quality aluminum to produce a dark color (has anyone heard something like this?)

3: Fluid turns black when exposed to moisture.. (i poured water into a glass of fluid and watched it over 3 days. nothing happened to it)

4: Heat from the engine causes the fluid to coke (Id imagine this would be a problem for motorcycles more than cars...)

5: cheap seals within master and slave cylinders are wearing away. (definitely possible, but wouldn't that cause and internal leak? and my clutch works great!)

anyone care to troubleshoot again??

Wish I could offer some help, but I honestly don't know about this problem.

I am curious though, how much were the master and slave cylinders? Did you install them yourself? How long did it take/how much of a pain was it?

My slave is going out something fierce (pedal stuck down, have to kick it repeatedly to get it to pop back up) and I'm trying to figure out if I should do the work myself, or just pay a local shop.

Hope you find the issue,
-TC

if i remember a new master was $50 and a new slave was ~$25. I installed both of these parts myself and it is a really simple affair. Both parts are fitted with only two bolts. Still, the slave is annoying to get to especially when the engine is hot. the master on the other hand requires you to contort under your dash. Easy but annoying is the best way to put it. Id say it can be all done in an afternoon if you have to to run to get fluid/take a break/ wait for engine to cool down. make sure you have a friend to help you bleeding! and save your reciepts in case the fluid starts to turn cloudy all the time.

This post has been edited by enderswift: Oct 12, 2009 - 4:01 PM

flush some more fluid through, it will turn clear. remember, it only takes a very little bit of black gunk to turn the fluid dark.

sir i believe the flush count is up to 7 now.

maybe its the clutch fluid you are using is too agressive and eating way at your seals.

Have you tried a different clutch fluid? prestone or OEM toyota fluid?

take the lines off and flush them out with brake cleaner, new slave, new master, new reservoir, bleed with clean fluid, i bet it stays clean.

The lines have been flushed, the master and slave are new.

I was thinking that the fluid is too agressive too.. but how could it be THIS agrressive? i've never heard of brake fluid destroying parts that are meant to withstand it!

how did you flush the line? you need to really get crazy on it, a can of brake cleaner and 100psi shop air, spray and blow multiple times or just replace it. replace everything and you'll have crystal clear brake fluid, replace the car too. a new one will have clear clutch/brake fluid.

srsly, you're freaking out about nothing dude. does the clutch work correctly? yes? stop worrying. dot3 is all you need, you can get brake fluid test strips that will tell you the water content and acidity of the fluid. does it test as OK? yes? stop worrying.

replace the whole car.. hurr hurr. No need to be condescending Bitter. My clutch does not work properly. After the car sits for a while the clutch feels as though there is no fluid in the lines at all.. I have to pump it to build up pressure, which i shouldn't have to do with new parts! This is why i want to know if the color is related to my problem. guess what? it is. observe:

Over the last week my clutch has been getting progressively worse and worse until driving home got really annoying. I decided to tackle the clutch and figure everything out once and for all.

First thing i did was have my brother help me drain all of the black fluid out of the lines and wow did that stuff look nasty. I made sure to check the rubber hose that connects the hard lines for softness and it felt fine. So that ruled out the possibility that the hose was disintegration from the inside. So, i turned my attention to the 3 month old autozone slave cylinder. Heres what i found



see that grey grease-like stuff? thats not supposed to be there, and it is obviously the cause of the dark fluid.

I decided to try something out and cleaned both the piston and the cylinder





Once they were both clean i put them back together and compressed the piston repeatedly for about a minute. Guess what i found when i took it apart again??



more of that metallic paste!! these parts are clearly out of round or just really crappy metal and are causing metal shavings to contaminate the fluid.
I compared the piston on the 'new' slave to my old one and it was night and day. The old piston (with 70k) looked brand new, while my 'new' piston was scored and scratched. Go autozone

After this, I put the original slave back in its place



Now it was time to turn my attention to my 'new' master cylinder to see if that thing was as big a piece of crap as the slave was.
Well i removed it from the firewall and took it apart to check the seals on the inside.



Surprisingly they looked pretty good

I was happy those shavings didn't damage anything. But then i thought to myself, what if its just a matter of time before this thing craps out too?

solution: take piston from the questionable master cylinder, and use it to rebuild the oem toyota unit.

thats exactly what i did and everything fit together very nicely.

just for reference this is what you should look for when inspecting the seals on a master cylinder:



That line is the result of wear, it lets fluid pass and was the cause of my original clutch problems over the summer.

Anyway. Its been several days since I've done all this and the fluid has stayed crystal clear



In the past it would almost immediately turn dark.

I guess the moral of the story is ALWAYS buy from the dealer and dont just ignore something strange as trivial. It WILL come back to bite you.

Im just SOO happy i managed to get the fluid to stay clear without replacing my whole car!!!1!!

on a serious note, I hope this helps someone else who has the same issue.

This post has been edited by enderswift: Oct 17, 2009 - 5:04 PM

Sorry to ask such a question; but could you take a picture of where the master cylinder sits so I know what to look for when I check to see if its failed?

Thank you;

This post has been edited by KAOS: Oct 20, 2009 - 7:32 PM

it's in the last pic just above your post, beneath the clutch fluid reservoir.

>

Perfect - thank you.

glad you got it fixed, you made it out to sound like the only nagging problem was the dirty fluid. new parts can be bad, actually its really common for cheap parts store masters and slaves to be bad, even brake masters and wheel cylinders. my suggestion is to get rebuild kit for the original one from the dealer, should cost a fraction of the cost of the slave and that being a cast iron body it should be fine inside.

the metal paste is there because the new cylinder was not properly finished. whether they're all like that or whether that one just skipped a step who knows. the inside of the cylinder should have a smooth finish, not a rough hone like that.