Bleeding brake help. hissing noise

[GTP]

Not to hijack but is this a dedicated track car? My understanding is that SRF is not hygroscopic at all, meaning any moisture that will get into the system will not be absorbed by the fluid and could create air bubbles, leading to issues.

My understanding is SRF is recommended track only because of this. There are really good street fluids that will absorb moisture and provide good performance (ATE, RBF etc...).

I know this doesn't solve your issue but thought I'd mention. Somebody with more knowledge can clarify this...?

I'm pretty sure that only silicone brake fluid does not absorb any water but all others do.

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[DrZed]

I'm pretty sure that only silicone brake fluid does not absorb any water but all others do.

hmmmm not sure. That would be risky for a manufacturer to do that (my Harley is silicon based). Somebody solve this! Sorry OP.

 

[GTP]

hmmmm not sure. That would be risky for a manufacturer to do that (my Harley is silicon based). Somebody solve this! Sorry OP.

Silicone brake fluid is Dot 5 and not recommended for our cars.

 

[NightmareMoon]

This is a guess, but take the cap off the brake fluid reservoir, do it, and see if it still hisses.

I think that cap should be off when you're bleeding fluid. If the piston is pushing significant fluid out, something has to go in to replace the missing volume in the resevoir. Its possible either the piston/booster is doing something to compensate or air is being sucked into the reservoir past the cap or the line to the clutch.

 

[NightmareMoon]

Not to hijack but is this a dedicated track car? My understanding is that SRF is not hygroscopic at all, meaning any moisture that will get into the system will not be absorbed by the fluid and could create air bubbles, leading to issues.

My understanding is SRF is recommended track only because of this. There are really good street fluids that will absorb moisture and provide good performance (ATE, RBF etc...).

I know this doesn't solve your issue but thought I'd mention. Somebody with more knowledge can clarify this...?

SRF isn't as hydroscopic, meaning it doesn't actively absorb in water just from contact with air. If you just somehow put water directly into the brake fluid, and that water-infused fluid makes it to the calipers, then yeah it would vaporize easily, but not more so than in any other brake fluid for the same amount of water content. Not being hydroscopic means it won't take up very much water from contact with humid air (water has no way in other than by contact with air, mostly at the reservoir I guess, which can't be entirely pressure sealed or the reservoir would crack as the brake pads wear and the fluid moves from the reservoir down to the increasingly extended pistons. Soo.... SRF is not more dangerous, far from it.. However there are rumors it might not be good for the clutch system, which the brake reservoir also feeds.

 

[5550snotamerc]

It's interesting that the order is the "classic." I have another car where the order is not intuitive, I think it's based on distance from the ABS module.

 

[Spyshot]

This is a guess, but take the cap off the brake fluid reservoir, do it, and see if it still hisses.

I think that cap should be off when you're bleeding fluid. If the piston is pushing significant fluid out, something has to go in to replace the missing volume in the resevoir. Its possible either the piston/booster is doing something to compensate or air is being sucked into the reservoir past the cap or the line to the clutch.

the cap was just sitting on, not screwed down.

 

[NightmareMoon]

the cap was just sitting on, not screwed down.

Still, might be worth a try, its a longshot but if its loose but still making a seal... idk.

Otherwise you just gotta get your ear down there and figure out what part is doing it.

 

[cerbomark]

the cap was just sitting on, not screwed down.

so you should be good to got then after tightening the cap. You said you have a nice firm pedal.

 

[sk47]

Hello; two things come to mind. Is the engine is running during the bleeding procedure? I have never done a brake bleed with the engine running.
Second thing is the power brake system gets the "power" from engine vacuum. There is a fairly large vacuum canister attached to or near the brake master cylinder. If the engine is running that vacuum canister can maybe hiss during a bleeding attempt. Even with the engine off the first brake pedal push will allow some air to rush into the canister. Could this be the source of the hiss?

As I mentioned I have not tried this with a running engine so cannot say about the possibility.

Note; I use to think the brake pedal needed to be pumped up hard to do a bleed. I do not find that needed. Just a firm enough push so that when the bleeder is opened the pedal goes to the floor. Then the pedal is held to the floor while the second person closes the bleeder valve.

Second note; There is a bit of noise as the pedal goes down and the fluid is moving thru the lines. maybe that is the "hiss"???

 

[Buldawg76]

If the SRF fluid stand for silicone racing fluid then it is not the same as DOT3,4,5.1 fluids that absorb water in normal use. Silicone fluid like is used in most bikes DOT 5 I.E Harleys is silicone based and absorbs air not water and is used in bike because it does not eat paint like the 3,4,5.1 fluid will damage paint or cause corrosion of internal brake hard parts.. But being that it absorbs air it is easy to get large amount of air trapped in the fluid itself in the system if bleeding incorrectly.

1. never pick up the bottle and shake it up like is common for automotive brake fluids, doing so just introduces air into the fluid that can take up to 48 hours to dissipate back out of fluid. 2. never use a pressure bleeder on silicone fluid since it will just force air into the fluid while bleeding. 3. using a vacuum bleeder is fine as long as you don't have your compressor set above 40 psi to keep the vacuum signal low enough to draw the fluid thru the lines but not agitate the fluid in the process.

Bleeding by pumping will also work fine as long as you pump the pedal up with bleeder screw closed at each wheel and then have person pump brake pedal hold constant pressure on pedal and follow the pedal all the way to the floor and hold it there until you close the bleeder screw before they release the pedal and then repeat until no air is seen coming out of bleeder. Also attach a hose to the bleeder with free end submerged in container of fluid with end of hose below fluid level so it can only suck fluid back in hose not air. Go slow with the pumping up of the pedal and take your time since the idea is to not overly agitate the fluid which introduce air into the fluid.

Personally I would not use silicone fluid in an automotive application for any reason. If the silicone fluid ever reaches it boiling point you just created air in the fluid that will instantly give you zero pedal at all since air does compress. When doing high speed brake testing at Harley in research and development here in bama on the Talladega superspeedway our rider would quickly boil the fliud and end up with no brakes and have to return to the shop to have the fluid completely changed out after complete cooling of the caliper and rotors. Even then it was difficult to get all the air out of the system without several hours of allowing the bike to sit stationary.

BD

 

[WItoTX]

If the SRF fluid stand for silicone racing fluid then it is not the same as DOT3,4,5.1 fluids that absorb water in normal use. Silicone fluid like is used in most bikes DOT 5 I.E Harleys is silicone based and absorbs air not water and is used in bike because it does not eat paint like the 3,4,5.1 fluid will damage paint or cause corrosion of internal brake hard parts.. But being that it absorbs air it is easy to get large amount of air trapped in the fluid itself in the system if bleeding incorrectly.

1. never pick up the bottle and shake it up like is common for automotive brake fluids, doing so just introduces air into the fluid that can take up to 48 hours to dissipate back out of fluid. 2. never use a pressure bleeder on silicone fluid since it will just force air into the fluid while bleeding. 3. using a vacuum bleeder is fine as long as you don't have your compressor set above 40 psi to keep the vacuum signal low enough to draw the fluid thru the lines but not agitate the fluid in the process.

Bleeding by pumping will also work fine as long as you pump the pedal up with bleeder screw closed at each wheel and then have person pump brake pedal hold constant pressure on pedal and follow the pedal all the way to the floor and hold it there until you close the bleeder screw before they release the pedal and then repeat until no air is seen coming out of bleeder. Also attach a hose to the bleeder with free end submerged in container of fluid with end of hose below fluid level so it can only suck fluid back in hose not air. Go slow with the pumping up of the pedal and take your time since the idea is to not overly agitate the fluid which introduce air into the fluid.

Personally I would not use silicone fluid in an automotive application for any reason. If the silicone fluid ever reaches it boiling point you just created air in the fluid that will instantly give you zero pedal at all since air does not compress. When doing high speed brake testing at Harley in research and development here in bama on the Talladega superspeedway our rider would quickly boil the fliud and end up with no brakes and have to return to the shop to have the fluid completely changed out after complete cooling of the caliper and rotors. Even then it was difficult to get all the air out of the system without several hours of allowing the bike to sit stationary.

BD

SRF isn't silicon based.

 

[sk47]

fluid ever reaches it boiling point you just created air in the fluid that will instantly give you zero pedal at all since air does not compress.

Hello; Overall good post. Figure the above is a typo. Air is bad in brake fluid because it does compress.

 

[Buldawg76]

SRF isn't silicon based.

Ok then my above post is not relevant.

BD

 

[Buldawg76]

Hello; Overall good post. Figure the above is a typo. Air is bad in brake fluid because it does compress.

Yep, it was indeed a typo, and has been corrected, Thanks.

BD

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