Q. For you techs about brake bleeding...

I've decided that since my 98 Corolla needs new brake fluid, I would just use DOT4 to replace the current DOT3 fluid. I've built a homebrew pressure tank bleeder to make it a 1 man job. You can take a look at it here:

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My question: Since I on flushing out the entire system, would it be advisable to simple flush out the entire system with air to get out ALL of the DOT3 fluid, and then refill with DOT4? Is it a good idea or bad to have an 'empty' brake system? I know DOT4 is compatible with DOT3, I just want to be sure ALL of the DOT3 fluid is replaced. Thanks.

Reply to
stevelibert
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Nope. Just use a turkey baster or small hand pump to empty the master cylinder reservoir and top it up with fresh fluid. Then just start forcing the new fluid through the system (opening one bleeder at a time). You should be able to tell if you have flushed all the old fluid out just by the change in color.

For most passenger vehicles, I've found that a 32oz bottle of fluid is sufficient for a complete flush.

Cheers, Nirav

Reply to
njmodi

Yep..that's the way i did it. Just finished. Old stuff was amber color. New DOT4 is almost clear.

Reply to
stevelibert

Is DOT4 compatible with DOT3 systems? I know DOT 5 isnt but DOT5.1 is, but earlier DOTs i cant remember.

J
Reply to
Coyoteboy

Dot4 and Dot3 are glycol based and cross compatible. Dot5 is silicone based and not compatible with Dot3 or Dot4. I don't know about Dot5.1.

The largest user of Dot5, the US military, may be phasing its use out. This may make it more difficult to find in the civilian market.

-- Mike Harris Austin, TX

Reply to
Mike Harris

Ahh so 3 and 4 are ok too - thats good. You can use DOT5.1 as a direct replacement for 4 - it has better properties again, better heat dissipation and is less susceptible to absorbtion of water apparently. I've been using it in my system for 12 months and on my mountain bike disc brakes.

J
Reply to
Coyoteboy

Isn't that complete overkill for mountain bike brakes? Certain motorcycles come with DOT 5 and it's used in road racing (auto sports in general). We'll see if the govt dropping it phases it out, or just makes it even more expensive.

For normal auto purposes, I don't mess with switching from DOT 3 to DOT

  1. If I'm using something that sees heavy brake use and a lot of heat build up, I'll use a synthetic DOT 4, which a high boiling point...
Reply to
DG

Water absorption isn't really much of a problem. Yes, glycol based fluids are hygroscopic but can only absorb ~ 1% or so, maximum. Under normal service this doesn't pose a problem. Glycol fluids also contain anticorrosives (buffer salts, I believe) which prevent internal rust but which deplete or "wear out" after about two years.

If you feel that you have to usr Dot5 in your mountain bike brakes - I'm glad that I don't have your mountains!

-- Mike Harris

Reply to
Mike Harris

Just like the others say; just flush it out with the new DOT4. They are compatible and can be mixed. You'll flush the new one out anyways so. Make sure the reservoir never runs dry or you will have air in it.

Reply to
RT

Blowing air thru your entire brake system would also add moisture to your entire brake system. My best guess would be more moisture than a typical brake system would ever see in its entire life. Now weather that is enough moisture to even matter I don't have a clue.

But brake fluid is only exposed to the moisture in the air that is trapped with it or when a cap is off. For the system or the bottle so that might be a huge amount of moisture.

If it was refrigerant lines they would be deemed "wet" and no amount of flushing would allow them to be called "dry." Only a deep vacuum for a extended period of time would be accepted to dry out refrigerant lines that have just been exposed to air.

Dan

Reply to
Danny G.

Wasnt aware of the additives, interesting info :)

Yup, i do have to use dot5.1 on my bike and no its not overkill :) In the quest for light weight parts they are made to get very hot lol. Dot5.1 is capable of shifting more heat away from the pads and with regular water-dunkings its best to have every possible protection against that. Its also a bit thinner, which makes lever feel a bit nice (makes brake pedal feel in my car feel nicer too).

As for hills - ive been on several alpine holidays where they were used to the max (blue rotors and that lovely overheating pad smell lol) but more recently i relied on the rear alone to get me home after the front seized and had to be removed. I dont know if dot4 would have handled the near-glowing rotors any less well but I like to cover all bases :D

J
Reply to
Coyoteboy

with it or when

exposed to air.

Agreed, never blow them through with air. Just flush through with your replacement fluid and it'll be fine. You're less likely to remove all the old with air anyway, the fluid is more likely to push/drag the old stuff out.

J
Reply to
Coyoteboy
[DOT5.1 brake fluid]

Aren't disc brakes in general overkill for bicycles? I always found the traditional cable-operated "squeeze" brakes to be perfectly adequate.

Geoff

Reply to
Geoff Miller

No. Maybe for the average going-to-the-shop rider, but not if you ride off-road and to any sort of performance level above the aforementioned going-to-the-shop-rider. Its much the same as cars - drums do just well if you just tootle around locally and dont really care much about performance or driving feel. On a bike V's/canti's/U brakes are suitable if you dont really use a bike to its potential but when you're navigating rocky downhill sections at 40mph you want every ounce of stopping ability, control and fade protection you can get. I was never a big disc believer until A) I rode in the Alps and melted a set of my normal pads to the rim. B) Wore *through* the rim with mud and brakes. C) Couldnt stop due to ice on the rim in winter. Then i tried 4-pot discs on my bike. Lighter, better lever feel, more modulation, i can stop from 40mph in less distance than my car without fade, un-phased by ice/snow/mud. Little maintenance needed, no cables freezing in winter, snapping, needing to be cleaned and lubed. No stretch in the cable when you pull the lever hard.

I dont run them on my trials bike, i run Magura HS33 hydraulic rim brakes on there as they provide a little more low-speed bite and less modulation (very on-off)- ideal for trials but less good for higher speed use. I have an old rigid bike built up with Vs but using it is scary - you just cant do anything as fast or as fluid as you can with better brakes.

Having said all that I have used my discs to their extreme on road too, riding to work - stupid drivers pulling out of side-roads in front of you while youre travelling at 30mph (cyclists cant go fast so obviously you dont need to look at them and judge their speed lol!) - i know for certain i couldnt have stopped in time with my Vs.

J
Reply to
Coyoteboy

Theres my babies:

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't be without them anymore. J

Reply to
Coyoteboy

Those are cool! And tiny; I didn't realize how small and light they were. Thanks for posting the link.

Did you have to buy special wheels, or did they fit onto the existing ones?

Geoff

Reply to
Geoff Miller

30 mph may not seem fast in a car, but it sure as hell does when you hit the pavement at 30...
Reply to
Scott in Florida

Question....

Do you have the same size front and back?

How do they work in 'real life'?

Are they good and progressive?

Reply to
Scott in Florida

Try getting stopped in a hurry in the rain on a bicycle with rim block brakes, and then ask again with a straight face.

They'll work - Eventually... And when they dry out it'll be sudden, you'll have to work to avoid going over the handlebars.

Been there, Done that, left the bike home in the rain after that.

-->--

Reply to
Bruce L. Bergman

Like most Americans, I spent much of my childhood and adolescence riding bicycles. I rode in the rain quite a bit, because that was how I got to school. Had to get that paper route done, too. And unless there was a torrential downpour, I wasn't about to sit at home getting bored on a rainy weekend.

I learned to compensate for the effect you're describing by anti- cipating the brakes' starting to "grab" as the rims dried, and loosening my grip. A lighter than usual touch on the front brakes also helped. It was instinctive.

With bicycles as with so many other things, I find that a lot of safety pitfalls can be circumvented with an approach that can be summarized as "paying attention and being careful."

It's interesting how so many things concerning bicycles are con- sidered to be issues nowadays, but scarcely merited a moment's thought when I was a kid in the Seventies. If someone had told me back then that in a couple of decades most people would be wearing crash helmets when they rode bicycles, and that anyone would be afraid to ride in the rain due to grabbing brakes, I'd have been incredulous.

We didn't wear helmets back then, and those of us with ten-speeds often rode no-hands because it was comfortable to sit straight up. The horror!

Geoff

Reply to
Geoff Miller

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