Break fuild

[e34musician]

Can I just change whatever in the break fuild reservior weekly until it's clean? I just don't want to mess with bleeding if not necessary.

Can I mix dot3 with dot4? What do you guys use? Thanks!

[DaveVoorhis]

Brake fluid doesn't circulate, so if you change the juice in the fluid reservoir you'll wind up with a clean reservoir, but all the stanky old goo will still be riding around in your calipers.

You can add DOT4 where DOT3 is being used, but it's a bad idea to add DOT3 where DOT4 is being used because you'll reduce the fluid boiling point.

[e34musician]

Thanks! I thought the fuild circulate. If not, (just curious) how come the fuild get dirty in the reservior if it doesn't circulate?

Hmmm, if that's the case, I probably need to get dirty again for this. Any suggestion if I have to do it myself without a helper?


Brake fluid doesn't circulate, so if you change the juice in the fluid reservoir you'll wind up with a clean reservoir, but all the stanky old goo will still be riding around in your calipers.

You can add DOT4 where DOT3 is being used, but it's a bad idea to add DOT3 where DOT4 is being used because you'll reduce the fluid boiling point.

[swenpro]

beer is common break fluid... I personally recommend orange juice :D

[DaveVoorhis]

The dirty appearance is mainly from absorption of airborne moisture, which occurs throughout the system. Also, a contaminant introduced at any point in a fluid will slowly disperse throughout all the fluid. Put a drop of food colouring in a perfectly still jug of water and you'll see.

You can use a one man bleeding kit (see http://www.corral.net/tech/maintenance/brakebleed.html, for example), but I regard brake bleeding and other multiple-bodies-needed jobs as a good excuse to get the bro's around for beer and BBQ, or a way to test if your girlfriend is truly worthy.

[Ross]

The dirt in the resevoir is a result of the fluid that flows back when the brakes are released. Not circulation perse. The fluid is hydrophillic, so the moisture it absorbs from the atmosphere rusts the steel parts in the system. Hence the need to refresh it.
You can gravity bleed your system yourself by removing all you can from the resevoir with a turkey baster, refilling and opening the bleeders one at a time until clear fluid flows. Be careful not to let the resevoir run dry.

[DanDombrowski]

It doesn't circulate, but enough of it goes back and forth when you pump the pedal to make the resivoir look dirty after you fill the resivoir with clear fluid.

I have a motive power bleeder (since I have 0 friends that like to work on cars), and I can bleed the brakes on an E34 in about 20 minutes. Its very easy.

I ususally run the rear of the car up on ramps to get to the back two bleeders, and I can reach the front two without lifting the car IIRC. Screw the cap on the power bleeder to the MC resivoir and pump up to 15 psi. Bleed all 4 calipers and you're done.

[Evan]

great post, dave

[zman-95-540i]

I also use a Motive bleeder. It is definitely worth the money.

[e34musician]

Heard quite a bit of good thing about "Motive Bleeder".

Where can I buy one (Motive Bleeder) from? Does AutoZone carry them?

Break Fluid is the only fluid in my car that have not been changed.

[Kibokojoe]

I can only tell you about an experience I had with a 66 austin healy sprite. I mixed dot 3 and 4 and it melted the seals in the brake system. I had to rebuild all brake cylinders and the master cylinder. Hopefully the BMW brake system is not so whimpy.

[attack eagle]

Kibo. Classic british cars use natural rubber seals, and dot 3 breaks them down... that's why you can only use dot 4 in them.

OP: if you have blackish deposits along the bottom of the reservior, it could be the seals breaking down. My DSM's clutch reservoir was like that, right before it failed.

I've never added Break fluid to any car... they tend to break down enough without inciting it...

now BRAKE fluid is another matter entirely :D

[Kibokojoe]

So if you add dot 3 to dot 4 it will break :-)

[DanDombrowski]

Yeah, pretty much.

Pretty much the only brake fluid youll find at auto parts stores these days is either STP (DOT3) or the Valvoline Syntec (dot 5.1 mabye)? These might be different in your market, but down here in the south it appears Valvoline must have paid autozone a bunch of money to kick everyone else's brand off the shelf.

Most tech articles will scream and shout not to mix DOT5 (silicone) brake fluid with DOT4, but the Valvoline Syntec is NOT silicone (even though it has a DOT5.xx rating) and is what I use in all of my cars. There was a rudimentary comparison awhile back on a Volvo board I think that showed that it had the highest boiling point/$. A lot of people even use it at the track, and its about half the price of the ATE superblue.

[Tiger]

I agree on the Syntec Brake fluid... great stuff. If I ever want to break someting, I'll throw some break fluid on it... :)

[repenttokyo]

I was given the gift of 1 litre of Castrol synthetic racing fluid for my birthday, DOT4. I have no idea what is in my car right now - is it safe to drain my entire braking system and refill it with this?

[70383roadrunner]

I just buy the BMW fluid at the parts counter. With the 20% BMW Car Club discount it costs the same as the good stuff in the store.