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Discussion Starter #1
Hello all,

Yesterday, I got a wild hair to replace the dirty fluid inside the rear resevoir of my '99 M750. I completely drained the system and refilled it using DOT 3 fluid. My problem comes from noticing(too late) that the cap of the rear cylinder says to use DOT 4 fluid. (The front resevoir and the cluth resevoir say DOT 3+5). I bled the brakes twice because the test ride revealed a REALLY spongy rear brake. Even after two bleedings, the brake is still spongy and soft. I am confused, why would Ducati use a different fluid for the same Brembo brakes, and I am also wondering what is the difference between these fluid. Would the use of DOT 3 instead on DOT 4 make my brakes spongy???

I plan a shopping trip today to get the DOT 4, but I am still curious about this. Anybody have a answers??
 

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DOT 4 has a higher boiling point than DOT 3. use DOT 4 or DOT 5.1. the higher the DOT #, the higher the boiling point. *caution* DOT 5 is silicone. do not use. DOT 5.1 is polyglycol (good stuff). your spongy pedal is not from the DOT 3. air got in during the bleeding process.
 

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Yeah, what howie said. Bleading the rear brake can be tricky, you may have to remove the caliper & hang it overnight.
 
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Discussion Starter #4
Thanks for the replies fellas. I was wondering if you might be able to tell me why Ducati uses two different types of fluids for the same Brembo Brakes on the same bike?

Will the DOT 3 Fluid damage my brake system in any way??
 

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just a thought.............my rear brake caliper on my 95 Duc is mounted on the underside of the rear disc. This means the bleed screw is at the bottom (Upside down), to bleed you would have to take the caliper bolts off & moove it to the top of the disc so the bleed screw is at the top of the caliper. if its not at the top the air can't get out. Do it with the pads on the disc otherwise your pistons will fully extend.

Just an observation.
 

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DOT 3 won't hurt a thing. DOT 5 will mess you up.
 

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not really adding anything significant here, but i remember reading that DOT4 is more hygroscopic (wow, 4 syllables!) meaning it it will absorb moisture more easily than DOT3. probably why you see it sold in tins rather than bottles.

moisture = bad!
 
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Discussion Starter #12
i would think to get all the air out you would have to unless you had a darn good pump. That bleeder valve really should be the high point.

A alternative to a block of wood in the caliper and tends to be easier is a nice sized deep well socket. The round shape makes it easier to get in/out. I once had a piston bite into the block of wood. Had to beat the heck out of the wood block to get it to release.
 

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whats all this crazy talk about inverting??

I think you guys just arent doing it right........ Take a little hose... clear of course, and put it in a jar of brake fluid, when you slowly pump your front brake, then release the valve, air will come out the tube, and into the jar....

Before the brake lever gets to the end, close the bleeder valve on the caliper. Repeat until no bubbles come out.....

Doesnt matter what position the caliper is in....

We can bleed complex ABS systems that have all kinds of valving inside them.... a VERY simple Monster system is no sweat.....
 

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Just got back from Holidays......the horror of work is again a reality!!

CETME,
this may be a silly question, but, if you don't invert the caliper, how do you get the air out? Air bubbles go up, right?
 

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I think you can do it without inverting the caliper but it would help to have the aid of a vac pump to force the air down and out. I just did my rear brakes and I had a hard time also. I ened up getting a MightyVac hand pump (about $30) and put the caliper on the top of the disc. This did the trick.
 
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Discussion Starter #17
i picked up a mighty-vac at Pep-Boys the other day. I figured clutch and brakes alone on the duc would be much nicer. Gotta to the car soon too. Worth its price tag for sure.
 

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first off, a mightvac brake bleeder is only like $40 and works soooo well for this kind of thing.

secondly, are you sure dot 5 will harm anything. i've converted many an old honda (1970's vintage) and old yamahas to dot 5 from dot 3. did this because of the crap that seems to grow in dot 3 fluid down here in florida. i've been running these converted bikes for 7 years now without a single problem at all. i would think that if anything would be sensitive to the change it would be those very old brake systems. i haven't converted my duc yet but i intend to when the time comes for a brake flush.
 

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Unless there is something in DOT5 that Ducatis in general do not like there should not be an issue. The issue with 5 is that if you top it off with some 3 or 4 you will have big problems (they are not compatible). So most people avoid 5 and go with the compatible 3/4/5.1 to make things more idiot proof.
 
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