Too much front brake- need different pads front and rear?

[Jims5543]

Originally posted by Craig911
Sounds like you'll have to do track events..... rather than autocross!

I stopped Autocrossing 2 years ago, but, what I have learned Autocrossing has proven to be so helpful on the road course.

I was getting bored with Autocrossing so I moved on the DE's for now and possibly NASA racing in about a year or so when I feel I have learned enough not to be a rolling chicane in a race.

[ted]

Couple questions.

My 911 has 930 brakes.
The 23 MC gave me brake feel and eliminated the 21 MC 2+ inches of brake pedal travel.
The factory front brake bias made the car nose dive during threshold braking.
I had Pagid oranges all around.

I kept the oranges in front and went to blacks in the back.
That did move the bias to the back, car no longer nose dived.
I am considering a dual master cylinder set up and then returning to Pagid oranges all around.

Fyi my car has 275 and 335/17 710s.
Camber f and r 2.8/2.5
The way the car warms up I think the wide rear tires and 20 quarts of oil take longer to heat up than the brakes.

The graphs are interesting.
With my current set up should I be concerned that during my warm up lap(s) that either the front or rear brakes will heat up first creating a temporary brake imbalance?

Are my cold car handling concerns more critical due to the black rear (higher friction) brakes warming quickly and the wide 335 tires warming slower?
In a similar situation street driving what tendency's would my brakes/car have if a sudden stop were required after the brakes had been cooled for a half hour on the freeway. Lockup in the rear first?

2 more cents, rear brake bias is preferred in rain racing to avoid any front lock up, though too much rear brake bias can make a car push at turn in.

[Bill Verburg]

Originally posted by ted
Couple questions.


The graphs are interesting.
With my current set up should I be concerned that during my warm up lap(s) that either the front or rear brakes will heat up first creating a temporary brake imbalance?

Are my cold car handling concerns more critical due to the black rear (higher friction) brakes warming quickly and the wide 335 tires warming slower?
In a similar situation street driving what tendency's would my brakes/car have if a sudden stop were required after the brakes had been cooled for a half hour on the freeway. Lockup in the rear first?

2 more cents, rear brake bias is preferred in rain racing to avoid any front lock up, though too much rear brake bias can make a car push at turn in.

That's why you want parallelism in the friction graphs as much as possible, if you use the same pads f/r that is guaranteed to a point(the fronts will always be a little ahead of the rears). If you use different pads f/r then at least try to get the curves as close to parallel as possible for the sake of consistancy.

To much rear under any condition will make the back want to turn more than the front, I don't believe that is called push, but I am not 100% up on NASCAR talk.

In street driving the dynamics are so slow compared to on a track that it won't usually make a difference, I suppose you can come up w/ all sorts of possible scenarios where there would be an issue but the likely hood of all of them is low.

I have used Both RS4-4 and RS 19 on street in crisp conditions(unexpected snow), no problem

[rnln]

Bill Verburg,
What is a p/v Bill? Power Valve?

[Bill Verburg]

p/v - proportioning valve aka pressure limiting valve. It limits line pressure seen at the rear wheels.

[rnln]

ahh, thanks Bill

[80911]

Everything I have seen on this thread relates to premature front lock-up. I have the opposite problem on my '80 - 911SC in that the rears lock early in D/E situations. I am running all stock brakes and M/C with 205/225 tires. The only suspension modification is adjustable Koni's in the front. Anybody have any ideas? I am about to replace the M/C in an effort to rectify.

[Bill Verburg]

Originally posted by 80911
Everything I have seen on this thread relates to premature front lock-up. I have the opposite problem on my '80 - 911SC in that the rears lock early in D/E situations. I am running all stock brakes and M/C with 205/225 tires. The only suspension modification is adjustable Koni's in the front. Anybody have any ideas? I am about to replace the M/C in an effort to rectify.

The m/c has nothing to do w/ bias. Normally functioning SC brakes will lock the front just slightly before the rears.

Check to be sure that the fronts are functioing @100%. It's easy for the pads to become glazed or oil soaked, or the rubber lines to swell internally. All of these things reduce the effectiveness of the afflicted units.

If you still have issues after that the do the opposite orf the above use more agressive pads in front than in back.

[80911]

Thanks. I'll check the pads for oil. I have replaced the original lines w/SS so they should be good . . . .but I'll check them anyway. So, if the M/C doesn't bias F/R, and there is no biasing valve, how do they balance the system?

[Craig 930 RS]

Usually piston size, but Bill knows the specifics better than I -

[DanielDudley]

It is always a good idea to get the brakes working hard on cars that have been parked a lot or driven casually. Pads can glaze, and rotors can surface harden, leading to the need to turn or replace them. The rear brakes on my SC were a touch grabby this spring, but an hour of fun sorted that out quite nicely.

Medium braking, working up to hard braking can do wonders deccelerating from 60 to 25 or so. A couple or three in a row, then drive for about 1/2 mile and repeat for few cycles. Drive a few miles before parking, and don't forget to check your mirror frequently. YMMV

[Bill Verburg]

Originally posted by 80911
Thanks. I'll check the pads for oil. I have replaced the original lines w/SS so they should be good . . . .but I'll check them anyway. So, if the M/C doesn't bias F/R, and there is no biasing valve, how do they balance the system?

As Craig mentioned, caliper pistons, specifically the ratio of the area of the front caliper pistons to the area of the rear caliper pistons and rotor diameters

[80911]

Seems like a rather crude solution, but I guess they know what they are doing! I will look at the rotors for glazing, they are original although not a lot of miles (70k) but they have seen multiple DE's and a lot of elapsed time. If I replace the rotors, any thoughts on stock style v. cross-drilled?

[Bill Verburg]

No, it's basic engineering.

the pads glaze from over heating not the rotors.

also look at the pads for signs of contamination.