I think I'll try to vacuum out the dirty fluid, refill it, and watch to see if the new fluid turns black.

If it does, I guess I'll be doing a rebuild of the master cylinder.

Henry

if you are getting that much black murk from your seals I would start to wonder if maybe they aren't getting ready for a rebuild?

You can remove some of the master cylinder fluid with a turkey baster. Try not to let the level get below the cylinder pickup level or you'll get air in the system. If your still getting dark fluid out, just keep pouring in new fluid until it stops.

Good luck,

Kelley

"If you can afford the car, you can afford the manual..."

I tried to bleed out the brakes last weekend but did not seem to be getting the result I wanted.

I went through a 16oz bottle of fluid and I hardly made a difference in the black stuff that was in the master cylinder.

I wonder if I should try to vacuum out the black stuff in the master cylinder reservoir and start again?

The fluid that did come out at the wheels was dark and murky.

Any ideas?

Henry

I would bleed and change standard fluid every 3 years in these cars that are not used regularly.  Probably not a bad idea with silicone either although I don't typically do it unless there is a problem.

Bill's comment about silicone being fit for trailer queens is baloney.  I have it in all my old cars, they are used regularly and I don't own a trailer.

I'd get the big one (quart?).  It's not about how much the system holds, but if you're bleeding to replace fluid or to get out an air bubble, it's not a one for one replacement.  There's going to be waste involved.  I've always tried used a large bottle whenever I broke a line or decided to do a flush.  I think once it came down to using the last drop to top off the MC.

willy

TTT anyone?

Even an approximate capacity?

Does anyone know the fluid capacity of the Mini brake system?

I'm not sure how large a container of DOT4 I should buy.

Henry

the black is tiny particles of rubber that are dislodged by working on the system, and a good fluid flush is what it needs.

Those brake hose clamps always seemed to me like a dicey thing to use, since they crush a hose that you depend on for holding pressure to do its job (kinks = crack starting points). An old timer showed me how to instead put a sheet of saran wrap under the master cylinder cap (to block the breather hole) to prevent the fluid from leaking out (by using atmospheric pressure). I also put a cap the end of the open brake line, but with the saran wrap very little drips out by this method.

Even silicone fluid wants to be bled periodically since the water that is in the system (and water will be in every brake system due to heat/cool cycles "breathing" atmospheric moisture into the fluid) will collect at the lowest point: at the wheel cylinders, which will rust if you leave the water in there.

3 years is a decent interval for brake fluid flushing. For a classic car that sits a lot, 2 years is better (less driving = less heat generated from use to "boil off" some moisture out of the fluid).

Maybe in the case of silicone, only bleeding is needed, compared to flushing in the case of dinosaur oil, but fluid is cheap and brakes are important, so I would flush regardless of fluid used.

Norm

I took a closer look into my Master Cylinder and found more black gunk.

I still have to bleed the old fluid out and I hope doing so will get rid of the mess in the master cylinder.

Henry

Two to three years.

If those I maintain cars for would have me bleed their brakes every 3 years I'd lose a lot of money on the brake jobs I wouldn't have to do!

Thanks for the good info guys!

What would you say a 'regular' interval would be to do a bleed/flush?

I put around 2000 miles a year on the car.

Henry

DOT 5.1 is not typically marked that way any longer... it generally says "DOT 3/4 compatible fully synthetic" and  has more of the positives of DOT 3/4 (including wet and dry boiling temps greater than or equal to DOT 5) and less of the negatives (less paint damage, less hydroscopic).

I use only Castrol GT/LMA (DOT 4) or one of the 5.1 fluids (Valvoline Synthetic at the low end, various racing fluids at the higher end) and have experienced no issues even with natural rubber seals.

If the car is mainly a trailer queen, DOT 5 is a reasonable option (with a complete rebuild of all soft parts in the system), but for drivers I prefer on-silicone based fluids.

I would regularly bleed/flush any of these fluids, even DOT 5.

Bill

Minis are supposed to use DOT 4. The DOT 5 is only usable if you drain and completely bleed all the old brake fluid out. Flush the old out with alcohol or similar. The DOT 5 is not for use with any other brake fluids. So you must get all the old out if you are gonna use the 5.  Put the 4 in and keep bleeding it until it is clear.

My Mini's are un-officially sponsored by Coor's brewing company.

Now that you mention the rubber thing Mark, I used clamps on the hoses while I had the system apart.

When I removed the clamps from the hoses, they came back to shape but they were still stiffish as I think they should be (?).

Maybe the fact that I clamped the hoses caused them to stain the fluid.

It did go clear after a few pumps so I think it was just from the hose.

Maybe I will do a purge of the system once I get some more fluid.

Henry

Whichever fluid you choose to use it should be replaced periodically as you described.  I don't know that this is carved in stone anywhere but I think the rule of thumb for DOT-3 fluid is to bleed the system every three years to flush out all the old fluid.  DOT-4 is probably similar.  People tend to leave DOT-5 in place longer but as Speedpilot said there are two opposing camps regarding the use of DOT-5 anyway.  DOT-5.1 is one of the newest fluids (not to be confused with DOT-5).  I believe it also needs to be bled/flushed periodically.   If DOT-3 is working for you now, there's no reason I can think of to switch.  Just remember to flush the system periodically.

Doug L.

Unless the fluid has been in for mega years, all you have to do is to bleed it off until it is clear again. 

I did at one time use Castrol LMA which is a dot 4 but have switched to a Motul which is also a dot 4. Good stuff.

The only 'black' thing in the brake system is rubber. Rubber seal to make pressure at the head, rubber seals to accept the pressure at the end. If you have black in your lines, you most likely have rotting rubber. The only other thing I could think of would be water in with the fluid, breaking down the insides of your lines. Either way you look at it, get it out! I heard Dot 3 breaks down the older seals. I filled my lines with Dot 3 when I got my car going after 24 years, and within a week my brake light switch died. Coicidence? I don't think so.

Mark Looman, Ada Michigan 1967 Austin Cooper S

I use dot 5 (silicone) but there are compatability issues so it is best to do at the time of a major brake rebuild. Do a search and you may find a thread with the pros and cons, some people like it some don't.  I was glad I didn't have to worry about it bubbling off the paint today when I bled my brakes.  I used the e-z bleed today and it took about 20 minutes and most of that was me looking for wrenches and moving the drop light when I changed corners.  LR RR LF RF 

Like the title says, I was bleeding my brakes after the double trailing arm rebuild and the initial flow of fluid was very dark.  Like coffee, Ummm!

It did clear up after a few more pumps but it got me thinking about replacing the fluid.

I imagine it would be a nasty job.  I think you would do it as you would after replacing a master cylinder.  Go to all wheels individually and keep pumping till you have a good amount of fluid in your container.

Also would it be a good idea to change to better fluid.  Currently using DOT3.  If I do a fluid type change, would it be done the same way or are there some compatibility issues that would cause me to pull everything apart/rebuild?

Henry