Bench Bleeding with Silicone Fluid
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
Bench Bleeding with Silicone Fluid
You may have already read my other post about going to DOT5, but I wanted to cover another topic related to it.
I have spent the better part of a day trying to fully bleed out the MC with the DOT 5 fluid. It just keeps blowing small bubbles! I found if it pump and release slowly, about 3-4 seconds per stroke, it clears up and doesn't produce any bubbles. However if I pump any quicker say 1-2 seconds per stroke, bubble just start appearing in the clear lines! I can actually see bubble form in the middle of the clear hose! I thought at first they might be coming from the cheap plastic hose barb fittings, but I have tightened them and even tried Teflon tape to seal it up. I really don't think it's coming from the fittings.
How can you keep air out of the lines? Should I not be stroking so fast?!
If it is because of pumping and releasing, why would it not do it under normal quick braking?
I have spent the better part of a day trying to fully bleed out the MC with the DOT 5 fluid. It just keeps blowing small bubbles! I found if it pump and release slowly, about 3-4 seconds per stroke, it clears up and doesn't produce any bubbles. However if I pump any quicker say 1-2 seconds per stroke, bubble just start appearing in the clear lines! I can actually see bubble form in the middle of the clear hose! I thought at first they might be coming from the cheap plastic hose barb fittings, but I have tightened them and even tried Teflon tape to seal it up. I really don't think it's coming from the fittings.
How can you keep air out of the lines? Should I not be stroking so fast?!
If it is because of pumping and releasing, why would it not do it under normal quick braking?
Safety Car
Joined: May 2004
Posts: 4,364
Likes: 1,588
From: los altos hills california
The implication is that any air that is in the fluid has an intrinsic vapor pressure and in a vacuum would "boil" out of the fluid. You know, like your blood would boil in space. Suggests that there is a lot of air in that container. The guy who uploaded the video is on Facebook and I suppose if somebody wanted to contact him to see exactly what he did .... I am kind of surprised there are no comments. I am not standing behind this video in any way, thought it was kind of interesting if it's really what it says it is.
I had a bad experience with Dot 5 but the last time I posted somebody told me I didn't know what I was doing so I gave up taking that path.
I had a bad experience with Dot 5 but the last time I posted somebody told me I didn't know what I was doing so I gave up taking that path.
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
I'm hoping someone much wiser then me knows their stuff about this fluid and can tell me why all my thoughts are wrong.
Instructor
Joined: Nov 2014
Posts: 161
Likes: 17
From: Georgia
I had the same exact results using dot 3/4 synthetic fluid, new MC from NAPA. Instructions said to pump very slowly, 3/4 to 1 inch strokes until pressure builds (plugs sent with MC) then slow 1/8 in. strokes. I used tubes off the MC bleeders first then the plugs. Took about 1 hr but eventually cleared up with a generous amount of tapping . When I stroked too quickly I saw tiny pools of foam being released . I agree that's not real world function. Don't know how its going to work out yet, I still have to bleed the system. .
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Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
At this point I have dumped the DOT 5 out of the MC and washed it all up and dried it. I'm leaning heavily back towards DOT 3/4 to see if it bleeds better and doesn't create bubbles. I was really hoping DOT 5 would be the answer to not having to completely rebuild the brakes every 10-15 years.
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
Okay, now I'm asking. What were your experiences?
At this point I have dumped the DOT 5 out of the MC and washed it all up and dried it. I'm leaning heavily back towards DOT 3/4 to see if it bleeds better and doesn't create bubbles. I was really hoping DOT 5 would be the answer to not having to completely rebuild the brakes every 10-15 years.
At this point I have dumped the DOT 5 out of the MC and washed it all up and dried it. I'm leaning heavily back towards DOT 3/4 to see if it bleeds better and doesn't create bubbles. I was really hoping DOT 5 would be the answer to not having to completely rebuild the brakes every 10-15 years.
I have the OEM master cylinder in my 78 along with 4 SS calipers installed in 1985...change the brakes fluid every 3-4 years with DOT 3/4 and have zero issues....30 years and counting. Change the brake fluid periodically on these cars and you will be much happier than most concerning C3 brake issues. You cannot have brake fluid in these cars for 10-12+ years and not change it which is what I suspect many C3 owners do.
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
I have the OEM master cylinder in my 78 along with 4 SS calipers installed in 1985...change the brakes fluid every 3-4 years with DOT 3/4 and have zero issues....30 years and counting. Change the brake fluid periodically on these cars and you will be much happier than most concerning C3 brake issues. You cannot have brake fluid in these cars for 10-12+ years and not change it which is what I suspect many C3 owners do.
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
This is the point that I'm trying to make. It seemed to be when the fluid it under extreme vacuum, it would form air bubbles in the fluid. So if one were to press hard on the brake pedal and then quickly release it such as sliding your foot off the pedal and allowing it to snap back, this would cause a very short, strong vacuum in the MC and down the brake lines and develop bubbles in the lines. At the rate that I was stroking it, it wouldn't even have to be that quick of a release. I just can't see how bubbles will not form in the lines under normal use.
I'm hoping someone much wiser then me knows their stuff about this fluid and can tell me why all my thoughts are wrong.
I'm hoping someone much wiser then me knows their stuff about this fluid and can tell me why all my thoughts are wrong.
Okay, have you ever watched the prop of a boat start spinning and creating bubbles. When fluid is suddenly put under a low pressure it boils which creates the bubbles. Boiling does NOT mean it reaches 212 degrees but rather indicates its changing from a liquid to a gas. Under a sudden low pressure ANY fluid will create bubbles but then those bubbles are almost instantly absorbed back into the fluid.
Here's another way to look at it. When you see bubbles form in liquid brake fluid you aren't looking at air but rather the absence of that brake fluid.
Thread Starter
Racer
Joined: Jan 2014
Posts: 425
Likes: 3
From: Jefferson City Missouri
Okay, have you ever watched the prop of a boat start spinning and creating bubbles. When fluid is suddenly put under a low pressure it boils which creates the bubbles. Boiling does NOT mean it reaches 212 degrees but rather indicates its changing from a liquid to a gas. Under a sudden low pressure ANY fluid will create bubbles but then those bubbles are almost instantly absorbed back into the fluid.
Here's another way to look at it. When you see bubbles form in liquid brake fluid you aren't looking at air but rather the absence of that brake fluid.
Here's another way to look at it. When you see bubbles form in liquid brake fluid you aren't looking at air but rather the absence of that brake fluid.
I totally understand what you are saying. I'm just trying to wrap my head around this whole thing. And it one of those things that you get one chance of the entire system being completely clean. I don't want to have to take everything back off and apart to clean out fluid to change it back over. Just trying to make the right decision the first time.
Melting Slicks
Joined: Aug 2005
Posts: 2,683
Likes: 34
From: Working on the car NY
You still have to bleed on a regular schedule using Silicone brake fluid. If not it will still cause calipers to leak and gunk up. I couldnt believe the crap that was there when i replaced seals on leaking calipers after using SBF. Water (condensation ) will "puddle" using Silicone BF instead of mixing with it using Dot 3/4. I flushed the Dot 5 and went back to 3/4. Needless to say it was a lot cheaper. The only good thing about Dot 5 is that it won't lift paint if split but you shouldn't get ANY brake fluid on fiberglass. Ideally bleed every 2 years. Just my experience.
Last edited by TWINRAY; Aug 16, 2015 at 08:27 PM.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
When I switched over to DOT 5 I took the calipers and master cylinder off and pulled them apart. Then I blew 150 psi of compressed air at them to remove as much of the old DOT as possible. I also blew the lines out to purge them too. After the thorough cleaning I put the new DOT 5 fluid in and bled the brakes as usual. That was about 3 years ago and so far all is well as far as I know. I don't think the DOT 5 will cause crud to form but rather will create crud when mixed with DOT 3 and I don't think that crud would be harmful at all other than looking bad.
But DOT 5 does require the new J-1401 hoses because it'll swell the OEM hoses completely shut within 3 months.
But DOT 5 does require the new J-1401 hoses because it'll swell the OEM hoses completely shut within 3 months.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
This is the point that I'm trying to make. It seemed to be when the fluid it under extreme vacuum, it would form air bubbles in the fluid. So if one were to press hard on the brake pedal and then quickly release it such as sliding your foot off the pedal and allowing it to snap back, this would cause a very short, strong vacuum in the MC and down the brake lines and develop bubbles in the lines. At the rate that I was stroking it, it wouldn't even have to be that quick of a release. I just can't see how bubbles will not form in the lines under normal use.
I'm hoping someone much wiser then me knows their stuff about this fluid and can tell me why all my thoughts are wrong.
I'm hoping someone much wiser then me knows their stuff about this fluid and can tell me why all my thoughts are wrong.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
The only problem with that logic is that it is a sealed system. there is no vacuum. if you release the brake pedal, the pressure releases. no way for a vacuum to form. if there was, the pistons would retract. letting off the pedal only allows the pressure to equalize, not create vacuum...we use a hydraulic system for brakes for a reason, if it formed bubbles, it completely defeats the purpose of a closed hydraulic system. that is why bleeding is important, to remove any air which compresses. and changing fluid is important, so as to not have moisture absorbed, which would not happen anyway under normal circumstances, as the M/C is closed and sealed at all times. you are not supposed to leave the cap off for this very reason. if you do, it's advised to suck out the fluid in the M/C and re-fill...
When the brake pedal is suddenly released and retracts behind the tiny fill hole a small vacuum is momentarily formed between the master cylinder piston and the brake fluid. Just a little one and that tiny vacuum creates fizzies of brake fluid VAPOR.................not air. Then the fizzies get absorbed back into the brake fluid.
Last edited by toobroketoretire; Aug 18, 2015 at 08:56 AM.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
I highly doubt the spring in the master creates such a high vacuum it can boil the fluid. Especially when the master has cup seals that will just let fluid flow around them when forced to go backwards in the bore.You still have to bleed on a regular schedule using Silicone brake fluid. If not it will still cause calipers to leak and gunk up. I couldnt believe the crap that was there when i replaced seals on leaking calipers after using SBF. Water (condensation ) will "puddle" using Silicone BF instead of mixing with it using Dot 3/4. I flushed the Dot 5 and went back to 3/4. Needless to say it was a lot cheaper. The only good thing about Dot 5 is that it won't lift paint if split but you shouldn't get ANY brake fluid on fiberglass. Ideally bleed every 2 years. Just my experience.
I found it seemed I never got rid of the air either. I'm supposed to tap all over the brake system with a little hammer and pressure bleed and go exxxxttttrrrrrreeeemmmmllllyyyyy ssssllloooowwwwlllllyyyy with that crap. No, I'd rather just use DOT4 and easily bleed the brakes without wasting time.
Last edited by lionelhutz; Aug 18, 2015 at 09:48 PM.