Black brake fluid

[Shugalou]

I'm in the process of refinishing my booster and master cylinder so last night I take the turkey baster and I'm pulling off the brake fluid. The top layer has a nice golden hue...everything looks fine, when i get down to the bottom it has darkened right up and is looking black.

I am new to the truck but judging by the colour I'm guess that the fluid is old and broken down and was topped up more for appearances.

I plan to flush with new dot 5 and put some isopropyl alcohol before the new fluid to help clean the lines.

Just wondering if you guys have any input or suggestions?

Thanks

[BMERDOC]

It may be a blanket statement but most brake systems never get flushed on a routine basis. They only get topped off. I wouldn't be suprised by dirty fluid. Go ahead and flush it. If its bad enough you may want to do it again in another month or so. Never heard of running alcohol through it. Why do you feel you need DOT 5?

[Shugalou]

Thanks for the respsonse BMERDOC (is that BMW Doctor?)

I was a little worried seeing it so black that I'm hoping nothing is corroding from the inside out.

Alcohol to clean the lines - I read about it in a chevy truck restoration book that I am reading, guessing it just helps to clean them out more?

Dot 5 cause it's non corrosive to paint and doesn't absorb water, also read this in the chevy truck restoration book.

[BMERDOC]

Yup. BMW Doctor (almost 18 years now). I would shy away from using alcohol or DOT 5 in an older system. Flushing with DOT 4, flush again in a month and then flush once every two years will be sufficient. Trying to add some magic to an older system is only asking for trouble.

[Shugalou]

Thanks for the advice Doc. I wouldn't have considered it if this book wasn't so well detailed, however you have made me think twice about the plan of attack.

I have a 98 540 6 speed, so far working on this truck is so much easier (and cheaper).

[BMERDOC]

I wouldn't mind DOT 5 on a lightly used car (race car, museum piece) with new parts but I get the shakes when I think about ti being used in a DD.

Nice car you have! 5-series of that model (E39) is the best car BMW built. That engine and transmission was meant for that car!

[79Betty]

I jus redid mine new everything but lines n prop valve (replaced last year). To make sure i get all the air out, could one put a dye in the brake fluid to make sure there is no air left in the lines when bleeding? I'm turning 44's on a DD so brakes are important!

[Shugalou]

To make sure all the air is out, bleed until there are no bubble.

Pump brake pedal for pressure, keep it held down, than crack the bleeder screw to let bubbles out, tighten and build pressure again and repeat.

BMW doc, yeah I think it's one of the best they made, the drivetrain does have it's shortfalls. The shifts are longer than I like and the gearing could be shorter. I was planning on addressing these things but would rather keep it stock (other than removing the annoying CDV) and mod the truck instead. On the HWY the car really performs well.

[BMERDOC]

You shouldn't have any bubbles in the system unless you opened it to replace a component. Most times people would tell you to start bleeding the system at the furthest bleed screw but this instance is different. Empty the M/C out with your turkey baster and wipe out the resevoir with a clean rag. Refill it and start your bleeding procedure at the LF caliper, move to the RF then LR and finish off with the RR. You can do whats know as Gravity Bleeding. All you have to do is crack the bleed screw and let it drain. It can take some time but is thorough. Keep the lid off the M/C and don't let it run dry! I'd use a clear tube that fits snugly over the bleed screw. The reason I want you to start with the left front is to evacuate that mess out of the M/C bore and proportioning valve as quickly as possible. If you crack a bleed screw and fluid doesn't come out remove the screw and clean it out with a paper clip. Use the same clip to poke in the caliper hole for the screw.

[hatzie]

DOT3 & DOT4 can be mixed so any DOT3 left in the system will not cause problems. I wouldn't use DOT5 on anything other than an exotic.

Alcohol could cause problems with the seals depending on which alcohol you use. I'd stay away from flushing with anything other than DOT3 or DOT4 brake fluid.

The black is probably one of the many Iron Oxide varieties. Wipe it out of the Master Cylinder then fill with DOT4 and flush the system. I flush brakes every 2 years or so. Pressure bleeders (you can build one from a garden sprayer) are real nice for this procedure just keep the pot around 15 PSI and no higher than 20.

You can flush it again in a couple months if it makes you feel better but most of the loose crud should rinse through the lines and out the bleeders.

[willett]

If your that worried about Just bleed the dark fluid out. Why would you want to run a fluid that is not brake fluid through your system? You need to use dot 5.1 not dot 5. If memory served me right dot 5 is only for silicone seals and it will eat the rubber seals in your master and calipers. At the end of the day you won't notice any difference at all though. Higher dot rating = higher boiling point. These trucks were designed for dot 3 and they don't boil with dot 3.


Just my .02

[Shugalou]

Thanks a lot for the info guys, I figured dot 5 because it was silicone based and no need to worry about paint or absorbing moisture, but if it's designed for higher end applications then I'm sure that will come at a higher price.

I'll stick to Dot 3 or 4

[Tx Firefighter]

I always poo poo on the rhetoric that Dot 5 is only for seldom used collector cars or exotics or whatever.

For years I worked for the United States Postal Service maintaining over 800 mail trucks in the Fort Worth area. Every single one of them had Dot 5 in them. We used no special seals or components, just generic parts. And I guarantee you this, the mail man is hard on brakes on his truck. We virtually never had brake hydraulic issues on any of the trucks. Dot 5 is good stuff.

[BMERDOC]

Originally Posted by Tx Firefighter

I always poo poo on the rhetoric that Dot 5 is only for seldom used collector cars or exotics or whatever.

For years I worked for the United States Postal Service maintaining over 800 mail trucks in the Fort Worth area. Every single one of them had Dot 5 in them. We used no special seals or components, just generic parts. And I guarantee you this, the mail man is hard on brakes on his truck. We virtually never had brake hydraulic issues on any of the trucks. Dot 5 is good stuff.

Not being a Smart A... You have experience with it and the OP wanted to know. Mail trucks are properly maintained fleet vehicles. Did they come new with Dot 5? If they were retrofitted was there any changes made? What was the interval for flushes? I'm sure I should have more q's but I can't think of them.

[Tx Firefighter]

We converted them to Dot 5 after taking delivery. They came with Dot 3/4 from GM. I do not know what chemical was used to flush the system during the conversion process. There were no hard parts changed though. The hard parts are the same as you'd buy for an S10 pickup at any parts store. At times when the parts channel failed, we would order normal AC Delco parts from the local wholesaler until we could get our normal channels working again.

There are no flush intervals.

[hatzie]

DOT brake fluid specs are minimum boiling points and viscosity.
Look up the individual fluid manufacturers specs because some have higher wet and dry boiling points.
Pentosin Super DOT4 has Wet boiling point 329F (165C); Dry boiling point 509F (265C)
ATE SL-6 Super DOT4 has Wet boiling point - 347F (175C); Dry boiling point - 509F (265C)

[franken]

Flushing brake fluid periodically is recommended (or demanded), particularly for the hygroscopic (absorb water) fluids. I think DOT5 doesn't absorb water, but the bad part is water settles in spots and creates rot.

DOT3/4 vs DOT5 is like arguing dino vs synthetic. You still have to change (flush) the oil. And brake fluid is just another oil.

Much like detergent vs not oils, do you want the water (or in the case of oil, crap) suspended in the fluid, or allowed to accumulate in some spot.

It depends on the design of the system.

Either way, flushing the brakes and changing the oil are a good idea.

[Shugalou]

Good discussion guys, I'm going to have to think about this a little more, I could care less about boiling points because this isn't going to beat on like I was at a track or anything, I just want to put something I won't have to worry about but like everyone is stating it doesn't really matter as long as the system is maintained.

I've never worked with Dot 5 and I don't need to deal with any unexepected surprises.

[BMERDOC]

Originally Posted by Shugalou

Good discussion guys, I'm going to have to think about this a little more, I could care less about boiling points because this isn't going to beat on like I was at a track or anything, I just want to put something I won't have to worry about but like everyone is stating it doesn't really matter as long as the system is maintained.

I've never worked with Dot 5 and I don't need to deal with any unexepected surprises.

Couldn't have said it better. I'm no pro with DOT 5 but I feel retrofitting to an old system still may be asking for problems you don't need. DOT 4 is good enough and if a problem arises you can be sure it was from an old part and not a clue to complete system contamination.

[Tx Firefighter]

Keep in mind, with the discussion above about my experience with Dot 5, I still run generic Dot 4 in my trucks. But, I religiously flush them every year or so. I just use a turkey blaster to remove the old fluid from the master cylinder and refill with fresh stuff. Then open each bleeder valve individually and allow it to flow a while until I'm confident that the fresh fluid has drained completely through. Keep in mind that you must be diligent to keep the level in the master cylinder topped up as you're allowing it to drain.

[Rich84]

My brake fluid is black too. Never changed it. Last brake job 1998 (15,000 miles) ..LOL
So do you guys change Power Steering fluid too??

[Tx Firefighter]

I do. Along with coolant system flushes and rear differential oil too.

[hatzie]

I usually go 30-40K on power steering and diffs. I also have a Rare Earth magnet on the inside of the reservoir, the bottom of the diffs, in the transmission pans or on the side covers, and magnetic drain plugs in the NP208s. Prolly overkill. It gives me warm fuzzies...

GM and VW recommended brake flushes at 2 years on the new cars I've bought in the last decade. In 2 years it'll get dark enough that I can tell through a clear hose when it goes from the old fluid to new clean stuff.

"Wet" is defined by FMVSS as 3.5% water. That ain't much. Mine run 4-5% in 2 years. Borrow or buy a hygrometer and test it. If you've been 15 years I bet it's 7% or more. Brake flushes are preventive maintenance. You got away with it. That doesn't mean its a good idea to neglect it. Rust eventually makes calipers and combination valves stick especially on lightly used vehicles where it can settle to the bottom of the components. Iron oxide is a mildly aggressive abrasive too. I have never worn out a master cylinder or locked up a caliper or combination valve on a car I bought or maintained from new and some of em had/have over 300k in my possession. I've never had brake fluid boil but I don't want to find out how it feels either.

I posted two examples of DOT4 fluids that I actually had specs for and then the chart of FMVSS DOT minimum standards to avoid a religious war over "what's the best brake fluid". There ain't one. Do some research or just get some DOT4 or DOT5.1 in a metal can and be well.