Advice needed: weird vibration + long brake pedal travel only when hot on track...
#16
Nordschleife Master
Thread Starter
Hello,
In reference only to your brake fade/soft pedal issue. As others have stated once the brake fluid reaches its boiling point, the liquid turns into a gas/vapor, gas/vapor is compressible, a liquid is not. That is why you're potentially getting a soft pedal. This problem will persist since the gas/vapor will remain in the lines until you bleed the braking system. You can further avoid this by stepping up to our RBF 660 which has a higher boiling point than the SRF.
Below is an excerpt from conversations we've had here on Rennlist in the past about Motul RBF products vs the SRF that you may find useful in track applications:
If you flush your brake system often, RBF 600 or RBF 660 will out perform the SRF:
RBF 600: Dry Boiling Point: 594 F
RBF 660: Dry Boiling Point: 617 F
Castrol SRF: Dry Boiling Point: 590 F
If you're looking for an extended drain product with a longer service interval versus higher short term performance, the SRF is a better choice as it has better moisture stability when water is present in the brake system. Brake fluid is very hygroscopic which is prone to absorbing water. Water lowers the performance level of brake fluid when present in the system.
Our position is in most racing applications, water is a non factor since brake fluid is drained regularly so we put more stock in dry brake fluid performance vs wet. And as you can see, the RBF 660 has a 27 F advantage vs the SRF.
All wet boiling point tests measure brake fluid at 3% water concentration- this would be considered a long drain service specification and again, not really a factor in short drain race applications.
If you have any questions, feel free to drop a line here.-Nick
In reference only to your brake fade/soft pedal issue. As others have stated once the brake fluid reaches its boiling point, the liquid turns into a gas/vapor, gas/vapor is compressible, a liquid is not. That is why you're potentially getting a soft pedal. This problem will persist since the gas/vapor will remain in the lines until you bleed the braking system. You can further avoid this by stepping up to our RBF 660 which has a higher boiling point than the SRF.
Below is an excerpt from conversations we've had here on Rennlist in the past about Motul RBF products vs the SRF that you may find useful in track applications:
If you flush your brake system often, RBF 600 or RBF 660 will out perform the SRF:
RBF 600: Dry Boiling Point: 594 F
RBF 660: Dry Boiling Point: 617 F
Castrol SRF: Dry Boiling Point: 590 F
If you're looking for an extended drain product with a longer service interval versus higher short term performance, the SRF is a better choice as it has better moisture stability when water is present in the brake system. Brake fluid is very hygroscopic which is prone to absorbing water. Water lowers the performance level of brake fluid when present in the system.
Our position is in most racing applications, water is a non factor since brake fluid is drained regularly so we put more stock in dry brake fluid performance vs wet. And as you can see, the RBF 660 has a 27 F advantage vs the SRF.
All wet boiling point tests measure brake fluid at 3% water concentration- this would be considered a long drain service specification and again, not really a factor in short drain race applications.
If you have any questions, feel free to drop a line here.-Nick
#17
Former Vendor
Thanks Nick! Most folks on here that track their cars do so in an occasional weekend "DE" fashion, say once a month or two. And each of those days is maybe (5) 15-20 minutes sessions on track that is definitely not at race level stresses. What would you consider a recommended bleed / flush interval for usage like that? Thanks.
#18
Race Director
Mech33...what did you end up finding was the issue for the vibration while braking? thanks
#19
Rennlist Member
Join Date: Jan 2013
Location: West Vancouver and San Francisco
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4) As I keep pushing it and drive them hotter still, then the vibration gets noticeable all the time, even when not touching the brakes! And here's the kicker: once I hit this step (4) where the vibration becomes noticeable all the time, the brake pedal travel starts to ~double but only if I don't touch the pedal for a while (e.g., after a long straightaway). (!!) The feeling is extended travel, but then the pedal becomes firm at the end of that travel once I take up the pedal distance in that single stroke.
If heat is not a 100% factor, it adds the possibility of any suspension play contributing. But that would have an effect right away, not after multiple laps.
#20
Nordschleife Master
Thread Starter
I never found the exact culprit, unfortunately. I took the braking system back to 100% stock rotors and pads, and the issue has been gone ever since. I suspect it was an unlucky rotor issue that developed an axial run-out (either via physical warpage or actual play) only when very hot (hence the pad knock-back), but that's just my hairbrained theory.
#21
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I never found the exact culprit, unfortunately. I took the braking system back to 100% stock rotors and pads, and the issue has been gone ever since. I suspect it was an unlucky rotor issue that developed an axial run-out (either via physical warpage or actual play) only when very hot (hence the pad knock-back), but that's just my hairbrained theory.
#22
Race Director
I never found the exact culprit, unfortunately. I took the braking system back to 100% stock rotors and pads, and the issue has been gone ever since. I suspect it was an unlucky rotor issue that developed an axial run-out (either via physical warpage or actual play) only when very hot (hence the pad knock-back), but that's just my hairbrained theory.