Dot 4 to Dot 5 fluid pit falls? Or just plain old air in the line.

[Slide Panda]

Ok, late last year my clutch slave was giving up on me.  I hadn't set to track down the problem by the time I had it into reputable local shop for it's 24k service.  They noticed that the slave was indeed leaking and swapped both my clutch and front brake systems to DOT 5 (silicone) fluid.  Everything's been fine since then until yesterday

Fast forward...  yesterday I set about to give the front brakes a solid inspection since it's been a while.  I had the calipers off, cleaned the pads etc and as part of the process pushed all the pistons back into the caliper body to make getting them back on easier. 

Pushing the pistons in did cause an over flow out of my reservoir. 

The remounted the calipers and gave the lever a bunch of pulls.  The pistons worked their way out, and the fluid level went down (not below the min line though) and I do have some brake force, but nor nearly what I had before I got to mucking about.  In pushing the bike down a slight grade I couldn't even get the front wheel to lock.  The lever feels super spongy.

My guts say that I just managed to dislodge some pocket of air from a caliper and move it into the line where it's compressing... and so I just need to bleed. 

But since the advice here is free - I thought I'd double check that there were no freak dot 4 - dot5 issues that I might have suddenly stirred up and now need to totally disassemble my brakes...

 

[ducpainter]

air in the system compresses regardless where it hides.

I'd try bleeding first and go from there.

[Slide Panda]

True... and I've though about that.  I'm just wondering if there wasn't a bubble that was stuck some place like the face of a piston where it's compressibility would not effect the whole system as much - vs. the same pocket of air getting pushed up into the line where it's now being compressed by the full pressure of the system vs just the distributed pressure going to 1 bore of 1 caliper... or do I need to go back to engineering classes and read up on my fluid mechanics?

[He Man]

silicone tends to swell o rings so maybe you can check all your rings.


Why did you convert to Dot 5 though?

[Slide Panda]

Well... I didn't per se.  The shop did it... I understand the reasoning why they did it on the clutch side since the slave was leaking.  So if it was going to keep leaking, at least DOT 5 wouldn't eat my paint.  But the brake side was fine... so no real reason it.

Not long after that I went back to DOT 4 on the clutch side since I needed a new slave.  I drained the res and pumped a lot of DOT 4 through there to clear out the DOT 5 - but never messed with the brake side since things were fine.

It's been on DOT 5 in the brakes for the better part of a year with no issues until I got to messing about.  And from the feel of things it really feels like air.  It's just odd to me how suddenly it manifested.  I had been riding in the morning and everything was normal.  Got to working in the afternoon and bam... mushy mush mush at the lever

[He Man]

you cant flush DOT5 out with DOT4. The two are like oil and water. Both compress at different rates, thats where you may be getting the air in line sensation. Im sure theres probably a bunch of DOT 5 all over the inside of your line, you just cant flush it out with straight DOT4. Ever try washing a deep fryer with just water?


This is just speculation since ive never actually dealt with dot 5 in my lines before. But you get what i mean right?

[Slide Panda]

you cant flush DOT5 out with DOT4. The two are like oil and water. Both compress at different rates, thats where you may be getting the air in line sensation. Im sure theres probably a bunch of DOT 5 all over the inside of your line, you just cant flush it out with straight DOT4. Ever try washing a deep fryer with just water?

This is just speculation since ive never actually dealt with dot 5 in my lines before. But you get what i mean right?

Well you're a little off the topic.  I'm not talking about the clutch work.  And I'm not looking at flushing the brake lines, do don't worry about that either.

But yes you are correct that DOT 4 and 5 don't mix.  The oil and water analogy is pretty accurate.

My issue's that after having my calipers off, and as part of that, pushing the pistons fully into the caliper bodies, I've got very mushy brakes that I did not have before I did that.    And it's not just a little mush... it's I should not ride the bike, since it won't stop w/o a runway mush

I will be bleeding them, and continuing with DOT5.  I'm not thrilled that the shop changed out the fluid spec on me.. but I've got to work with it.  Hopefully it's just some air making troubles...

[Howie]

I'm not sure what went wrong, but one of the disadvantages of silicone brake fluid is it is very difficult to bleed.  The air bubbles like to break up inti much smaller bubbles if the job is rushed.  First you might try letting the bike sit overnight and bleed very slowly and carefully.  I know you don't want to hear this, but if that doesn't work you may want to consider totally disassembling the brakes, clean, and reassemble with new seals as needed (assuming you can find them).  A problem with the silicone and the DOT4 not mixing is if the fluid gets hot enough the DOT 4 can actually cook on the silicone and the resulting mess can hurt seals when pushed over the DOT4, like when you push the pistons back to change pads.  Anyway, if this is the case, you should be able to see fluid leaking past the seals if you pull the dust boots back.  Yes, it is unlikely you got your brake fluid hot enough to cause this, but it is possible.

<snip>Both compress at different rates<snip> 

HuH?  Liquids do not compress if they are free of gas.

[Slide Panda]

Yeah, I'm not thrilled that I'm dealing with DOT 5 - though it did save me some damaged paint when some fluid mamaged to make it out of the res and onto my take from the wind.  So I guess I should be thankful for that.

Well the bike'll sit for a few days regardless, since I don't have the time to tackle it for a few days. 

I've considered that this might mean a tear down... I'm not thrilled at that prospect.  Especially since I've got not compressor to pop the pistons out with. 

This my street ride (well my only ride) and it's probably never gotten hot enough to cook anything.  I don't ride that hard by a long shot. 

- dust boots?  Are you talking about up at the master?

BTW - these are 999 type calipers and master if that makes any diff.

[Howie]

No, the calipers.  No compressor, you might get away with using the bike's hydraulics.  Remove brake pads.  Remove calipers from rotors.  Press brake lever slowly.  If there is any pressure at all, the pistons should come out.  999 huh? Even less likely parts are available., I would call Fred at  http://www.yoyodyneti.com   or someone who is up to date on new Brembo stuff before disassembling anything.  Try bleeding first, cheaper and easier.  It would take some serious brake work to boil the fluid.

[Slide Panda]

No, the calipers.  No compressor, you might get away with using the bike's hydraulics.  Remove brake pads.  Remove calipers from rotors.  Press brake lever slowly.  If there is any pressure at all, the pistons should come out.  999 huh? Even less likely parts are available., I would call Fred at  http://www.yoyodyneti.com   or someone who is up to date on new Brembo stuff before disassembling anything.  Try bleeding first, cheaper and easier.  It would take some serious brake work to boil the fluid.

There's pressure, I do get some brake effect when I pull the lever - it's just very mushy and not at all what it should be.  Yeah I could do that... that's just the super messy way, since I'd have a caliper full of fluid that I'm about to unseal...

So I should be looking for leaks from the pistons?  That what you mean Howie? 

Yeah, Fred's the 1st person I'd talk to.  Ungh.. man I hope bleeding will be the cure.  I'm not feeling so great about this now... I really hope my brakes and just crapped.

[He Man]

HuH?  Liquids do not compress if they are free of gas.

Everything compresses (compress solid carbon with heat and you get diamonds) but in this case, i didnt think all the way through, its neligable since you only apply as much force as you apply on the lever.

What I meant was, if you have both DOT 3 and DOT 5 in the same line, when you pull on the lever, your applying a force on both fluids, DOT5 require x amount of force to move the pads y millimeters, while DOT4 requires z amount of force to move  the pads the same y millimeters. If you have a mix of both, you wont be able to apply the proper pressure on the pads. You'd also waste alot of the energy into forcing the DOT5 and DOT4 to become a homogeneous mixture instead of globs of dot 5 and globs of dot 4.

and yuu, the thing with brake fluid and paint..... ive yet to see it happen. Ive spilled a whole bottle of that stuff over my tank. no problems. just wiped it off and water the tank down. hell, i had a thread about these nasty stains on my stock S2R wheels. I figured whats the worst that can happen, my paint job is already make the beast with two backsed up. Soaked a rag of DOT4 and tried to clean my wheel with it. after 5 mins of rubbing, i didnt even get a bit of it off. Ended up using a engine degreaser that worked great and my clear coat wasnt marred on the spot i used it on.

I think todays clearcoats are strong enough to withstand brake fluid.

[Howie]

There's pressure, I do get some brake effect when I pull the lever - it's just very mushy and not at all what it should be.  Yeah I could do that... that's just the super messy way, since I'd have a caliper full of fluid that I'm about to unseal...  A nice bucket will contain the mess.

So I should be looking for leaks from the pistons?  That what you mean Howie?  Yes.  Sorry I wasn't clear.

Yeah, Fred's the 1st person I'd talk to.  Ungh.. man I hope bleeding will be the cure.  I'm not feeling so great about this now... I really hope my brakes and just crapped.

[Howie]

Everything compresses (compress solid carbon with heat and you get diamonds) but in this case, i didnt think all the way through, its neligable since you only apply as much force as you apply on the lever.

What I meant was, if you have both DOT 3 and DOT 5 in the same line, when you pull on the lever, your applying a force on both fluids, DOT5 require x amount of force to move the pads y millimeters, while DOT4 requires z amount of force to move  the pads the same y millimeters. If you have a mix of both, you wont be able to apply the proper pressure on the pads. You'd also waste alot of the energy into forcing the DOT5 and DOT4 to become a homogeneous mixture instead of globs of dot 5 and globs of dot 4.

and yuu, the thing with brake fluid and paint..... ive yet to see it happen. Ive spilled a whole bottle of that stuff over my tank. no problems. just wiped it off and water the tank down. hell, i had a thread about these nasty stains on my stock S2R wheels. I figured whats the worst that can happen, my paint job is already make the beast with two backsed up. Soaked a rag of DOT4 and tried to clean my wheel with it. after 5 mins of rubbing, i didnt even get a bit of it off. Ended up using a engine degreaser that worked great and my clear coat wasnt marred on the spot i used it on.

I think todays clearcoats are strong enough to withstand brake fluid.

Yes, everything compresses, and, actually silicone compresses twice as much as polyglycol ether.  In a system as small as a motorcycle it is negligable. 

[Slide Panda]

and yuu, the thing with brake fluid and paint..... ive yet to see it happen. Ive spilled a whole bottle of that stuff over my tank. no problems. just wiped it off and water the tank down. hell, i had a thread about these nasty stains on my stock S2R wheels. I figured whats the worst that can happen, my paint job is already make the beast with two backsed up. Soaked a rag of DOT4 and tried to clean my wheel with it. after 5 mins of rubbing, i didnt even get a bit of it off. Ended up using a engine degreaser that worked great and my clear coat wasnt marred on the spot i used it on.

I think todays clearcoats are strong enough to withstand brake fluid.

I'm a little leary of it still though.  I got a drop on the speedo lens on my 620 and a single drop did some damage.  And the leak out of the clutch slave did eat the paint off my sprocket cover - but that wasn't anything better than rattle can.

I did a cursory check this evening and there's no obvious leaks.  I.e fluid that had run down the body of the calipers.  So there's some hope yet.  It'll still have to wait a few days for some more spare time to bleed things out.  Hopefully a slow purposeful bleed will sort it.

Howie, using the hydro power to push out the pistons is an option... but it's extra hassle filled for me since I'm working in a condo parking lot... not lucky enough to have a garage or even a drive way of my own.