How long should stainless-steel, braided brake lines last?

[thabaer]

Originally posted by Grady Clay
...
I think there should be some flex in the hydraulic brake system. As each tire rotates, the grip isn’t perfectly consistent around the perimeter. The road surface isn’t perfectly consistent. The grip of the pad on the rotor isn’t perfectly consistent.
...
Your foot is capable of perhaps 2-3 Hz max ...

That's the first time I've heard anybody mention the variations in grip as the rotor goes 'round as it relates to wanting soem hydraulic give... makes sense. I'm planning on checking the runout and re-indexing the front rotors on one of my cars because of that pulsing, and the SS lines may be why it's so noticeable.

As to the 2nd snippet above, some of us drummer-types may take umbrage at that assertion

[Grady Clay]

Originally posted by randywebb

Grady - are you saying that the rubber hoses give the "right amount" of flex for a 'moderate,' street car type braking situation? And that the steel covered plastic hoses do the same under racing conditions?
- both determined just before lock-up

Randy,

Basically yes. I would substitute your word “moderate” for “extreme.” We are talking about maximum breaking at the limit of traction and still being able to not lock up the tires.

The "right amount” is difficult to quantify. Too rigid tends to lock up tires easily. Too spongy is uncomfortable to drive.

As most know, locking up the tires feels equivalent to suddenly running on grease. The braking effectiveness is dramatically reduced and you loose all steering input. If the rears lock up, you loop it. That is the reason for ABS.

When I’m talking about race situations, envision a Cup Car race at Las Vegas. Say only 90F and the 4000’ thin air. The rotors are cherry red all the time. Porsche tries to build in as much safety margin as possible without added weight and within the rules. Anyone who has driven proper race cars knows how poor the braking is when cold. This is from three factors; cold race tires, cold pads that only work properly hot, and very rigid (SS lines) with freshly bleed hydraulics. The warm-up lap is to get the engine, transmission, tires, and brakes up to temperature. I typically run the first part of the lap with my left foot on the brake. How long and how hard depends on the ambient temperature among other.

I don’t have any scientific data or studies to back up my assertion. This is purely anecdotal based on my personal experience and talking with others. I’m sure some others who have experience braking at the limit can chime in here.

Best,
Grady

[randywebb]

That's interesting....

I used the term 'right amount' to mean: the amount that gives enough feedback to the driver to allow proper modulation of the pedal...

All science starts with anecdotal observations... the experiments come later .. and in some fields not at all...

[KobaltBlau]

I would like to know whether the factory race cars are using rubber or teflon lines under the stainless. The stainless braid is probably a good idea for cut protection on frequently maintained race cars, but most people feel that if there is a "firmer" feel from the "stainless" lines, it's because most (but not all) of them use a teflon line instead of rubber underneath the SS sheath.

FWIW, I'm using fresh OEM rubber and don't intend to change.

[Kahuna]

I can'y believe what i'm reading here, Porsche brakes are great BECAUSE they have so little compliance, less id better here.

[Wil Ferch]

Kahuna..

I think you're reading too much into this...the point Grady is making is a matter of degree....not that you would want purposefully spongy response.

Wil

[SC-targa]

I used to road race motorcycles and one of the few mods you could do on a production class racer was to substitute stainless brake lines for the oem rubber lines. Using gloved fingers for brake acutation gives finer control than using a foot in a shoe. Stainless lines were a signifcant improvement in brake feel and control.

Those things were quick, light and intense. Hard braking lofted the rear wheel and you'd have to have a pretty fierce 911 to accellerate as hard.

When I rebuilt the brake system on my 911, I used stainless lines and I'm happy with them.

Regards,

Jerry Kroeger