brake booster/servo pipe diameter.

[RuskiWeldFab]

Hi Guys. a sort of quick question. is that pipe that goes from the manifold to the booster has to specific diameter? the reason why i am asking i because i am trying to diagnose a weird brake issue i am having on my track car. basically after about 3-4 laps pushing hard. my brakes will start to fail after long straights.. but work good everywhere else. push the pedal and nothing. but pumping few times works well.
have CL6 pads. 665 race fluid. all new lines, high carbon discs, air ducts and deflectors.. so trying to understand if the diameter of the pipe makes a difference? currently, i have a braided fuel line (had left over) connected there instead of the OEM pipe. its slightlyu large diameter. wondering if it introduces air in to the system somehow?
some people suggest i am boiling the fluid. i am struggling to see how i would boil 665 fluid in an under the 900kg car.
cheers.

 

[robzracing]

Unlikely to be related to that hose. Otherwise you’d probably have the same problem all the time.
I could be wrong but I would have thought either pad knockback or IMO more likely you need a bit more bleeding of the brakes.


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[RuskiWeldFab]

Unlikely to be related to that hose. Otherwise you’d probably have the same problem all the time.
I could be wrong but I would have thought either pad knockback or IMO more likely you need a bit more bleeding of the brakes.


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Yeah I heard someone mentioned the knock back thingy but not how to cure it. It is very strange how it starts after 3-4 laps. I bleed the Them before Rockingham today on Saturday. Run about a litre of fluid through. No bubles were coming at all. Using eBay pressure bleeder. Wondering if I am doing it wrong. Everything about a car is perfect (touch wood) even the oil temps under control (max was 106deg after 20min on track) only the brakes that I loose confidence in. Went of the track few times because of that.


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[robzracing]

I used to use a pressure bleeder and they're great to get the worst of the air out, but I've found there's no substitute for doing it the old school way with one man on the pedal and one man working around each caliper.
Although knockback is a thing it's unusual to happen on new discs and I've only ever experienced it on larger brake systems with larger diameter discs that amplify any warping or vibration. If your feeling any vibration that could cause the knockback but my money is on the bleeding.

 

[RuskiWeldFab]

No vibration whatsoever. I think I will try the old fashioned way. Thanks Rob


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